# It Doesn't matters, It's not the bike/kit you have...



## itaa (25 Dec 2017)

https://www.gribble.org/cycling/power_v_speed.html
Probably the best cycling app there is to see how weight/dynamics affects your performance,spend 30minutes comparing different things there and you will come to revelation...

In short, save your pennies it's all damn marketing hype/tricks..You can't really re-invent a bicycle (unless its an e-bike  )

-Want to go fast? 
Get in a good aero position to achieve the least surface contact area,
after you go past 15km/h it's all about aero (Mostly Aero OF YOU (~80%) , not the bike(~20%) 
Under 15km/h it's all about the tyres you have, so the only thing you should invest in is a good set of tyres with good rolling resistance,
you can find info about most of the tyres here with all data: https://www.bicyclerollingresistance.com

-Wear good fitting clothes( don't need any special stuff) , loose some weight of yourself( less aero drag), and you will be just as fast on a cheap $50 Used 15kg mtb with NICE tyres ( Yes,just the tyres not some expensive Rims) than someone on a 7kg $5k bike wearing ridiculous outfit - as long as you have the same Aero Drag and aren't going up-hills.

-Going up-hills? Again a heavy MTB with GOOD tyres + Taking a poop before you set off will give almost the same results (2-3% difference) The weight of your bike/kit ONLY matters when you go up a hill (barely), in straights- almost 0 difference.

-Still Getting anxious about the weight of your bike/kit? It's not actually the weight of the bike.. It's The Weight of YOU+ the Bike, count those 2 together and you will realise that Just taking a poop or eating 2 less Doughnuts before you get on a bike is a much better strategy than spending money to reduce the weight of the bike.

*Does not applies to Pro-Racers which you see on TV (maybe 0.001% of all cyclists? ), the kit actually gives an edge over others (2-5% gain ,perhaps in most cases?)
So Unless you are one of those, Just Play around with your Data and see for yourself that it's all pointless.
Just go out and Enjoy cycling.


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## biggs682 (25 Dec 2017)

Here here


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## screenman (25 Dec 2017)

Going so well until you used the word " ridiculous " just seem to spoil it all for me.

Some people enjoy spending.


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## bpsmith (25 Dec 2017)

This cracked me up. Not the fact that the gains are marketing hype, but the comparison and your suggestion.

You compare a 15kg mountain bike and a 7kg road bike and suggest that “a poop” before riding cancels the difference out. Now, we are all different, but if you’re taking an 8kg “poop” then the type of bike you have is the least of your worries!


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## raleighnut (26 Dec 2017)

bpsmith said:


> This cracked me up. Not the fact that the gains are marketing hype, but the comparison and your suggestion.
> 
> You compare a 15kg mountain bike and a 7kg road bike and suggest that “a poop” before riding cancels the difference out. Now, we are all different, but if you’re taking an 8kg “poop” then the type of bike you have is the least of your worries!


Oh I dunno but after a Friday night out involving 8/9 pints of Guinness and a 'Mixed Kebab' I've certainly felt about a stone lighter after the 'Saturday Morning at Work' crap.


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## DRM (26 Dec 2017)

i know the feeling after xmas day's excesses


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## derrick (26 Dec 2017)

Should be on the joke thread that's the best one iv'e heard all week.


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## Fab Foodie (26 Dec 2017)

itaa said:


> https://www.gribble.org/cycling/power_v_speed.html
> Probably the best cycling app there is to see how weight/dynamics affects your performance,spend 30minutes comparing different things there and you will come to revelation...
> 
> In short, save your pennies it's all damn marketing hype/tricks..You can't really re-invent a bicycle (unless its an e-bike  )
> ...


Are you sure you know what you are talking about?


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## FishFright (26 Dec 2017)

Is it April already ?


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## Julia9054 (26 Dec 2017)

So . . . most cycling performance issues can be solved by having a massive poo.


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## Fab Foodie (26 Dec 2017)

Julia9054 said:


> So . . . most cycling performance issues can be solved by having a massive poo.


....under steady state conditions....


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## Gravity Aided (26 Dec 2017)

Fab Foodie said:


> ....under steady state conditions....


I'm afraid my state would not be very steady after such a poo.


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## User269 (26 Dec 2017)

I refer the honourable gentlemen to the reply I made to this house in 2015.


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## Tin Pot (26 Dec 2017)

Julia9054 said:


> So . . . most cycling performance issues can be solved by having a massive poo.



Indeed, all those constipated cyclists storing everything up until after their ride...what fools they are, if only they knew this secret! Mwa hahaha...


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## Ming the Merciless (26 Dec 2017)

A man has a poo then accelerates like shoot off a shovel


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## cyberknight (26 Dec 2017)

bpsmith said:


> This cracked me up. Not the fact that the gains are marketing hype, but the comparison and your suggestion.
> 
> You compare a 15kg mountain bike and a 7kg road bike and suggest that “a poop” before riding cancels the difference out. Now, we are all different, but if you’re taking an 8kg “poop” then the type of bike you have is the least of your worries!


+1
my slicked mtb gotta weigh close to 20 kg with panniers etc, i have drop bars on it and can get a good aero tuck but theres no way i would take it on a club run , its a beast to keep over 18 mph and on the hills you just die if you want to keep any semblance of speed.Caught a guy on a road bike the other day on the flat and gave him a draft , soon as we hit an incline he left me for dead.


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## DaveReading (26 Dec 2017)

itaa said:


> The weight of your bike/kit ONLY matters when you go up a hill (barely), in straights- almost 0 difference.



Provided you never have to slow down and accelerate again. If you do, Newton's Second Law applies.


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## derrick (26 Dec 2017)

This has to be the best thread of the year,


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## SkipdiverJohn (26 Dec 2017)

I think people are focusing too much on the poo aspect and are losing sight of the original point; which is that the majority of power is absorbed overcoming aerodynamic drag which is not weight-dependent, and that for a typical rider, losing quite a bit of weight off their bike is still only going to make a few percent reduction in the combined running weight of bike and rider.
In my clothes I weigh 90kg give or take, and I have a choice of Raleigh Pioneer that weighs 14kg, and an old-school Raleigh MTB that weighs 16 kg. Choosing the lighter bike of the two is going to save a whopping 2% on my total rolling weight. At low speed, power required is going to be roughly a 50/50 split between aero drag and rolling drag, therefore saving 2% on my rolling weight by saving 2kg on bike weight, but nothing on aero drag, is going to result in around a 1% reduction in propulsion power required for a given speed (assuming similar rolling resistance tyres are used).. And for fast riders on road bikes, the aerodynamic loss is going to be much greater than for a plodder like me, so the effect of reducing bike weight is going to be even less in terms of power required. 
It seems to me that if people are going to worry about weight reduction, their body fat should be the first thing on the agenda, not the weight of their bike (and no financial cost either), and they should only start obsessing about silly stuff like lightweight wheelsets once they cannot get any further reduction in body fat.


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## bpsmith (26 Dec 2017)

I think that you need to factor in that you don’t ride at a constant speed on the flat for your whole ride very often. Let’s have the stats for the difference in time it takes for your 16kg MTB to get to 20mph, compared to a 7kg road bike? Let’s also have the stats for the same bikes travelling up an 8% average climb?

EDIT: Forgot to ask why losing body weight and losing bike weight are mutually exclusive?


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## screenman (26 Dec 2017)

SkipdiverJohn said:


> I think people are focusing too much on the poo aspect and are losing sight of the original point; which is that the majority of power is absorbed overcoming aerodynamic drag which is not weight-dependent, and that for a typical rider, losing quite a bit of weight off their bike is still only going to make a few percent reduction in the combined running weight of bike and rider.
> In my clothes I weigh 90kg give or take, and I have a choice of Raleigh Pioneer that weighs 14kg, and an old-school Raleigh MTB that weighs 16 kg. Choosing the lighter bike of the two is going to save a whopping 2% on my total rolling weight. At low speed, power required is going to be roughly a 50/50 split between aero drag and rolling drag, therefore saving 2% on my rolling weight by saving 2kg on bike weight, but nothing on aero drag, is going to result in around a 1% reduction in propulsion power required for a given speed (assuming similar rolling resistance tyres are used).. And for fast riders on road bikes, the aerodynamic loss is going to be much greater than for a plodder like me, so the effect of reducing bike weight is going to be even less in terms of power required.
> It seems to me that if people are going to worry about weight reduction, their body fat should be the first thing on the agenda, not the weight of their bike (and no financial cost either), and they should only start obsessing about silly stuff like lightweight wheelsets once they cannot get any further reduction in body fat.



Why silly, it is my disposable, this sort of topic often seems to show up a green eyes monster.

What do you do with your disposable each week that is sensible.


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## bpsmith (26 Dec 2017)

screenman said:


> Why silly, it is my disposable, this sort of topic often seems to show up a green eyes monster.
> 
> What do you do with your disposable each week that is sensible.


He spends it training on how to get the perfect torque setting without ever needing a torque wrench.


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## bpsmith (26 Dec 2017)

Based on your examples @SkipdiverJohn, using the first call that I could find, it would take an additional 36 mins for the same rider to travel 80km on a 7kg road bike compared to a 16kg MTB and that’s on the flat!


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## delb0y (26 Dec 2017)

I find stopping to take photographs, or have a look round, or a drink or a cake, has quite an effect on my speed. That must be where I'm going wrong. I suppose adopting this aero-tuck thing might mean I don't see the things that make me want to stop and have a look round anyway, so it follows an aero tuck would make me faster. Would spoil cycling massively, of course. But I'd be faster.


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## SkipdiverJohn (26 Dec 2017)

bpsmith said:


> I think that you need to factor in that you don’t ride at a constant speed on the flat for your whole ride very often. Let’s have the stats for the difference in time it takes for your 16kg MTB to get to 20mph, compared to a 7kg road bike? Let’s also have the stats for the same bikes travelling up an 8% average climb?
> 
> EDIT: Forgot to ask why losing body weight and losing bike weight are mutually exclusive?



OK, so if I was to ride a 7kg road bike I would have a rolling weight of 97kg as opposed to 106kg on the MTB. That's 8% of the total, which would give some increase in acceleration, although it would not be anything like 8% faster as aerodynamics would be constant. Climbing a gradient would be harder/slower, no arguments. However a heavier bike/rider combination also has more momentum once up to speed so do not lose speed so quickly once you stop pedalling. You might have a hard slog up a hill, but once over the crest you can bomb down the other side. What you lose going up you gain going down, so long as you can take advantage of it without braking.
Losing body weight and bike weight are not mutually exclusive. However losing body weight is totally free whereas losing bike weight can get very expensive, once it gets to obsessional levels involving mere ounces rather than pounds.


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## bpsmith (26 Dec 2017)

delb0y said:


> I find stopping to take photographs, or have a look round, or a drink or a cake, has quite an effect on my speed. That must be where I'm going wrong. I suppose adopting this aero-tuck thing might mean I don't see the things that make me want to stop and have a look round anyway, so it follows an aero tuck would make me faster. Would spoil cycling massively, of course. But I'd be faster.


You’re right, of course, if that’s what you enjoy out of cycling. You’re also not trying to suggest that not doing those things won’t make you any faster.


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## screenman (26 Dec 2017)

delb0y said:


> I find stopping to take photographs, or have a look round, or a drink or a cake, has quite an effect on my speed. That must be where I'm going wrong. I suppose adopting this aero-tuck thing might mean I don't see the things that make me want to stop and have a look round anyway, so it follows an aero tuck would make me faster. Would spoil cycling massively, of course. But I'd be faster.



I have never wanted to stop whilst out on the bike.


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## SkipdiverJohn (26 Dec 2017)

bpsmith said:


> Based on your examples @SkipdiverJohn, using the first call that I could find, it would take an additional 36 mins for the same rider to travel 80km on a 7kg road bike compared to a 16kg MTB and that’s on the flat!



You're not comparing like with like though. You're assuming knobbly tyres on the MTB and an upright riding position vs slick tyres on the road bike and an aero riding position. I was only talking about the difference in weight Try running the numbers again for an upright position on both bikes and at least commuter type tyres on the MTB, which is what most riders would use for longer journeys. No-one is going to use knobblys on a 50 mile ride.


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## bpsmith (26 Dec 2017)

SkipdiverJohn said:


> OK, so if I was to ride a 7kg road bike I would have a rolling weight of 97kg as opposed to 106kg on the MTB. That's 8% of the total, which would give some increase in acceleration, although it would not be anything like 8% faster as aerodynamics would be constant. Climbing a gradient would be harder/slower, no arguments. However a heavier bike/rider combination also has more momentum once up to speed so do not lose speed so quickly once you stop pedalling. You might have a hard slog up a hill, but once over the crest you can bomb down the other side. What you lose going up you gain going down, so long as you can take advantage of it without braking.
> Losing body weight and bike weight are not mutually exclusive. However losing body weight is totally free whereas losing bike weight can get very expensive, once it gets to obsessional levels involving mere ounces rather than pounds.


You’re missing the fact that your MTB has knobbly MTB tyres and not smooth road tyres. There’s a serious loss straight away. You’re also missing that you’re more aerodynamic with narrower drop bars compared to wider flat upright bars. There’s also the geometry of the frame to consider. It’s clearly not totally down to weight with the examples given.

What about the difference between snug fitting road gear compared to flappy baggy MTB clothing too? (This ones a joke btw )

With regards to being able to make up the lost time from climbing, when descending the other side, I think we all know that’s not possible. A significant amount more time is lost in climbing than can be gained when descending.

With regards to losing weight being free, I beg to differ. Yes, it’s physically possible to just stop eating in order to lose weight, but keeping your fitness and muscle power intact when losing weight requires quality food with the perfect balance of what your body needs. That actually doesn’t come cheap. If you’re 175cm tall and 70kg, it’s tough to lose the 9kg difference and still ride fast.


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## screenman (26 Dec 2017)

SkipdiverJohn said:


> You're not comparing like with like though. You're assuming knobbly tyres on the MTB and an upright riding position vs slick tyres on the road bike and an aero riding position. I was only talking about the difference in weight Try running the numbers again for an upright position on both bikes and at least commuter type tyres on the MTB, which is what most riders would use for longer journeys. No-one is going to use knobblys on a 50 mile ride.



I have done 100 + on knobblies. So has my son and I would imagine his wife as well. Thinking about it I know of loads of cyclist who have done the same.


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## SkipdiverJohn (27 Dec 2017)

I just ran the figures for a more realistic 150 watts power, for a 90kg rider on a 7kg bike and on a 16kg bike, both on clincher tyres (my MTB tyres are ancient 1.75" commuter/touring pattern), both riding up on the bar tops. For an 80km trip, the 7kg bike comes out at 181 minutes journey time, the 16kg bike comes out at 184 minutes.
So a fancy £3-4k super-light carbon bike saves a whole 3 minutes compared to my £20 secondhand old steel workhorse!


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## Gravity Aided (27 Dec 2017)

Wider tires, same pressure and same tread, may be faster, due to the decreased friction of less tire deformation.


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## cyberknight (27 Dec 2017)

2 average minute saving over 9.7 miles comparing road bike vs aforementioned MTB with 450 ish feet of climbing on my commute.


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## SkipdiverJohn (27 Dec 2017)

cyberknight said:


> 2 average minute saving over 9.7 miles comparing road bike vs aforementioned MTB with 450 ish feet of climbing on my commute.



Which rather tends to prove the point that the journey time savings of having a very light and expensive bike are pretty minimal, unless the rider of the light bike rides on drop bars and the rider of the heavy bike is in a sit up and beg position. Commuters and pleasure cyclists (as opposed to speed merchants just trying to go as fast as possible) tend to sit up for the better view rather than just go hell for leather in a low position.


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## cyberknight (27 Dec 2017)

SkipdiverJohn said:


> Which rather tends to prove the point that the journey time savings of having a very light and expensive bike are pretty minimal, unless the rider of the light bike rides on drop bars and the rider of the heavy bike is in a sit up and beg position. Commuters and pleasure cyclists (as opposed to speed merchants just trying to go as fast as possible) tend to sit up for the better view rather than just go hell for leather in a low position.


My mtb is drop bar conversion with same bike fit as my road bike though so same aero effect, differences are rolling resistance, time to accelerate and weight on hills, plus m more knackered to do that time so im effectively putting more watts out to get those times.By the end of the week my legs are toast on that bike.


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## delb0y (27 Dec 2017)

I'm looking forward to trying out the new Giant Toughroad v the Tricross over the coming weeks and months. The weight is about the same, so it'll be a very un-aerodynamic position and very wide tyres versus the opposite. Be interesting to see the real world difference. I suspect those two factors will make the cycling much harder work, but I'm rather hoping the lower gearing will get me up some hills on which this year I've had to get off and walk up, and I'm hoping to tackle a lot more bridle-paths. So it might be harder, more enjoyable, slower, less enjoyable... may even be faster... although I suspect not.


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## bpsmith (27 Dec 2017)

SkipdiverJohn said:


> Which rather tends to prove the point that the journey time savings of having a very light and expensive bike are pretty minimal, unless the rider of the light bike rides on drop bars and the rider of the heavy bike is in a sit up and beg position. Commuters and pleasure cyclists (as opposed to speed merchants just trying to go as fast as possible) tend to sit up for the better view rather than just go hell for leather in a low position.


This thread is about the 2 example bikes being ridden to get the most speed out of them. If people choose not to use the drops and not ride for speed as their goal, then the modified MTB with road type tyres will naturally be similar over a flat route with no stops or in traffic for the commute.

My argument is that a light road bike compared to a heavy MTB, being used how they are intended and with the components they are sold with (including tyres), will be faster. It’s misinformation to suggest otherwise.

You’re argument centres around a road bike being ridden like a MTB, half heartedly whilst taking in the views, and a MTB being equipped with road tyres on a flat route without ever changing pace. I won’t argue against that type of comparison, so will end it there.

The overall fact, that we are sure to agree on, is that we should all equip our bikes and ride them how we like, ignore how much money anyone else has spent on their bikes, and enjoy ourselves. Far too much negativity in the world to let that get in between us cycling fans.


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## derrick (27 Dec 2017)

SkipdiverJohn said:


> No-one is going to use knobblys on a 50 mile ride.



I have a few times, loads of people do.
https://www.strava.com/activities/1246175983


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## bozmandb9 (27 Dec 2017)

Run all the numbers you want. When I was using my winter bike, an 11kg Whyte with touring geometry, I got dropped if I tried to ride with my sons team training ride. Now my 6.8 kg BMC is fixed, I can stay with them. I know the weight may be only one factor. Your computations aren't taking into account geometry and the effect on aerodynamics (except basics like tops or drops).


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## FishFright (27 Dec 2017)

OP can I see your maths? I'm guessing the issue is with the way the simulation works.


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## Smokin Joe (27 Dec 2017)

SkipdiverJohn said:


> You might have a hard slog up a hill, but once over the crest you can bomb down the other side. What you lose going up you gain going down,


No you don't, because the ascent is taking far longer than the descent so the gain on the way up on a bike that is 3kg lighter will not be made up by having the extra weight on the way down because of the much shorter time it gives you any advantage. I've ridden for long enough to know that losing 3kg off the bike makes a noticeable difference to average speed, whatever someone's lab calculations come up with.


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## Ajax Bay (27 Dec 2017)

bpsmith said:


> it would take an additional 36 mins for the same rider to travel 80km on a 7kg road bike compared to a 16kg MTB and that’s on the flat!





SkipdiverJohn said:


> You're not comparing like with like though.


Online after a lovely, sunny 75km this morning with an excellent coffee stop and good company.
Yes, unusually @bpsmith's contribution did not add value.
Keeping all else the same, at 150w power for a 90kg rider the difference in time between riding 80km on a 7kg bike and a 16kg bike (on the flat) is less than 2 minutes (172.1 minutes < 173.7 minutes) according to calculations provided using:
http://bikecalculator.com/what.html [= 0.3kph slower]
Not off topic, dropping 10kg of bodyweight (or cycle weight) saves 2 minutes.
Each kg lost/saved suggests an increase in speed of 0.04kph. Compare that with saving rolling resistance by choosing decent tyres - 4 watts is easily available (2w each wheel) which will imply a speed increase of 0.3kph.
Changing Gatorskins to GP 4000S II suggests 7w . . . . . . per tyre (many other makes are available).


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## bpsmith (27 Dec 2017)

Ajax Bay said:


> Online after a lovely, sunny 75km this morning with an excellent coffee stop and good company.
> Yes, unusually @bpsmith's contribution did not add value.
> Keeping all else the same, at 150w power for a 90kg rider the difference in time between riding 80km on a 7kg bike and a 16kg bike (on the flat) is less than 2 minutes (172.1 minutes < 173.7 minutes) according to calculations provided using:
> http://bikecalculator.com/what.html [= 0.3kph slower]


I will assume that you are inferring that I generally do add value, so I appreciate that. Feel free to state otherwise though. 

You’re right about the difference that solely weight makes, all else being equal. The comparison here was comparing 2 completely different bikes though, hence my comparison encompassing said differences.

More importantly, how was your ride today? Wish I had experienced a gloriously sunny morning in the saddle. #ProperJealous!


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## Ajax Bay (27 Dec 2017)

The 'unusually' was an edit, though quite a quick one, as I thought without it I was being harsh (for the season of good will). Please infer what you prefer. 
This was the scenario I focused on (quote from the OP):


itaa said:


> you will be just as fast on a cheap $50 Used 15kg mtb with NICE tyres . . . than someone on a 7kg $5k bike . . . - as long as you have the same Aero Drag and aren't going up-hills.


That is: on the flat, same aero drag (ie position) - just different weights of bike.
View: https://ridewithgps.com/trips/19768982
5 degrees, maybe 6, and only one 30m flood (about 8" deep; feet unclipped and at downtube changer level).


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## Ajax Bay (27 Dec 2017)

Dogtrousers said:


> Additional weight is of no benefit at all going downhill.


Why do well-built people on steel bikes always seem to descend relatively quickly, then?


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## GuyBoden (27 Dec 2017)

Hopefully, the more I weigh, the slower I will be riding, thus enjoying the scenery more...............


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## derrick (27 Dec 2017)

SkipdiverJohn said:


> No-one is going to use knobblys on a 50 mile ride.



I have a few times, loads of people do. Not quite 50 but close,
https://www.strava.com/activities/1246175983


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## bpsmith (27 Dec 2017)

Ajax Bay said:


> The 'unusually' was an edit, though quite a quick one, as I thought without it I was being harsh (for the season of good will). Please infer what you prefer.
> This was the scenario I focused on (quote from the OP):
> 
> That is: on the flat, same aero drag (ie position) - just different weights of bike.


Ok. Certainly leaves me with zero room to infer whatsoever. The edit kind of backfired it appears. Feels free to unedit accordingly. 

The scenario contradicts itself as a MTB cannot have the same aero drag or be ridden in the same position. We focused on different elements.


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## Bollo (27 Dec 2017)

Dogtrousers said:


> @Bollo have you got your "proper cyclists don't ride expensive bikes" jar? I have a deposit I want to make.
> 
> No not that sort of deposit.


Ewwww! Naughty step for ‘trousers!


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## Randy Butternubs (28 Dec 2017)

Dogtrousers said:


> Acceleration due to gravity is independent of mass. You must know that.



Err, only on the moon surely?

On Earth (which has an atmosphere) acceleration due to gravity is tempered by aerodynamic drag. Generally speaking, for heavy/dense objects this drag is small relative to the weight. Which is why on Earth a bowling ball falls faster than a feather but on the moon they fall at the same rate.


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## Randy Butternubs (28 Dec 2017)

Dogtrousers said:


> Your choice of bowling ball and feather is a poor one because they have different cd as well as different mass.
> 
> Insomnia edit. But you do have a point. For two riders of identical CD the deceleration due to drag will be inversely proportional to mass. So a heavier rider will experience the same drag force but less deceleration. How significant this is I don't know. Hopefully I'll get to sleep before figuring it out.



I chose the bowling ball and feather example as it was famously used during the moon landing...or was it a hammer and a feather? You are right though - it isn't a great example. A better one would be a balloon filled with air vs one filled with water - they both have the same drag coefficient and obviously the one filled with water will accelerate far faster under gravity.

A rider is a bit different since a bigger, heavier rider will generally have greater drag. I think an increase in weight should lead to a comparatively small increase in drag though. For simplicity's sake consider a cube with length _l _sides - the mass will rise proportionally to _l_^3 but the frontal area only to _l_^2.

Anecdotally, when I freewheel down hills (heavy rider, cheap bike) my much lighter brother on a far, far fancier bike has to pedal to keep up.


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## Randy Butternubs (28 Dec 2017)

Dogtrousers said:


> I did get to sleep in the end. With thoughts of frontal area and terminal velocities buzzing around in my head.



I'm so sorry. No one should have to go to sleep with maths in their head.


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## Ming the Merciless (28 Dec 2017)

In an atmosphere, objects of different masses, but of similar surface areas and profiles, will achieve different terminal velocities.


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## huwsparky (29 Dec 2017)

As I understand it the main benefit a heavier cyclist has going downhill is the momentum carried as the road evens out. That's certainly where it's very noticeable to me as I (as a relative lightweight) having to pedal to keep up whereas my heavier riding buddies carry their momentum better coming off the decent.


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## Alan O (29 Dec 2017)

Dogtrousers said:


> Additional weight is of no benefit at all going downhill.


That's pretty much what Galileo worked out, long before bicycles were invented. If you dropped fat me off the Tower of Pisa together with skinny Chris Froome, we'd hit the ground at the same time - ignoring air resistance. And if you account for air resistance, Froome would get down quicker.


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## Alan O (29 Dec 2017)

huwsparky said:


> As I understand it the main benefit a heavier cyclist has going downhill is the momentum carried as the road evens out. That's certainly where it's very noticeable to me as I (as a relative lightweight) having to pedal to keep up whereas my heavier riding buddies carry their momentum better coming off the decent.


Yes, there's greater momentum going into the flat.


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## Alan O (29 Dec 2017)

Ajax Bay said:


> Why do well-built people on steel bikes always seem to descend relatively quickly, then?


I'm a well-built person who rides steel bikes, but I haven't noticed any speed advantage going downhill.


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## Randy Butternubs (29 Dec 2017)

This is a bit sloppy but:

a = acceleration
F = resultant force 
m = mass
g = gravitational constant (about 10m/s^2)
D = drag force (it changes based on several factors including velocity but I think for this we can say it is constant)

acceleration = force/mass
a = F/m

Assume that the only significant forces are gravity and aerodynamic drag. Gravitational force = gm. Therefore:

acceleration = (gravitational force - drag force)/mass
a = (gm - D)/m
= g - D/m
acceleration = gravitational constant - (drag force/mass)

So when comparing, say, a 50kg and a 100kg object the 100kg one will accelerate faster unless the drag force acting upon it is double. This seems unlikely thanks to the square-cube law - volume (and so mass) increases far faster than surface area. I don't know anything about aerodynamics though so I'm happy to be corrected. I'm also using free-fall as an example but rolling down a hill shouldn't be fundamentally different.


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## Ajax Bay (29 Dec 2017)

Randy Butternubs said:


> This is a bit sloppy
> D = drag force (it changes based on several factors including velocity but I think for this we can say it is constant)
> I don't know anything about aerodynamics though


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## gilespargiter (31 Dec 2017)

According to my, admittedly anecdotal - but repeated observations; people seem to be considering completely the wrong factors concerning why a solid person on a steel bike descends more rapidly.

To relate such an anecdote in a definitely tongue in cheek way but including what seems the main key fact.

I find that when approaching the latter parts of an ascent such as say, Pen y pass over yr Swyddfa, one finds that those on lovely carbon cycles wearing super - shall we say- "streamlined" kit tend to look over their shoulders and upon noticing someone like me, with my carradice and steel frame they then go flat out eyes popping - guts busting. Although it is of course obvious that I must have been winding them in for a considerable distance. If they then avoid the ignominy of pretending to take pictures at the top, the next thing I observe is their super light frames flapping and twisting around in such a way that they can scarcely keep hold of them. At this point the main problem I have is giving them a wide enough berth as I streak past like an arrow on my ancient 531 steel. 
On hills like that I have no fear of having to repeat the maneuvre as by the bottom I'am seldom less than a mile in front.

Clearly the thing here is the stability of the frame when descending. I have noticed this as an issue on some very high end frames, some of which I have managed to have a much closer inspection of at the bottom.


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## classic33 (31 Dec 2017)

Not very "aero", but managed 55+ freewheeling downhill on it. 50mph limit, speed cameras set off.





And it's steel!


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## Gravity Aided (31 Dec 2017)

In this eventful life, I have been both the skinny guy and the "solidly built" guy, and the difference has seemed to be more on the climbs.


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## bpsmith (31 Dec 2017)

Gravity Aided said:


> In this eventful life, I have been both the skinny guy and the "solidly built" guy, and the difference has seemed to be more on the climbs.


And which build have you enjoyed being the most?


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## SuperHans123 (31 Dec 2017)

Ajax Bay said:


> Why do well-built people on steel bikes always seem to descend relatively quickly, then?


Seems to describe me...Fatty on a Cronk


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## Ajax Bay (31 Dec 2017)

gilespargiter said:


> yr Swyddfa


S?W? Trying to baffle us with Welsh?


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## classic33 (31 Dec 2017)

Dogtrousers said:


> Sorry, but I'm calling BS on this whole self-aggrandising "I scalped a roadie" anecdote.
> 
> Are you expecting us to believe that carbon frames have more flexibility than steel? So much so that it's possible to observe such flex (on a downhill no less, so without much power input) as our hero "streaks past like an arrow"?


Not watching where he's going!


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## Ice2911 (31 Dec 2017)

Just ride and enjoy


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## Levo-Lon (1 Jan 2018)

My ride to work is 6.8 miles via some road and cycle way route 
Full sus bike 11.6kg around 40 mins
Hybrid bike around 10kg 28mins
Road bike 7.6kg 25mins and i do a longer route all on road of 8.9 miles.

So i think the findings are BS..


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## SkipdiverJohn (1 Jan 2018)

meta lon said:


> My ride to work is 6.8 miles via some road and cycle way route
> Full sus bike 11.6kg around 40 mins
> Hybrid bike around 10kg 28mins
> Road bike 7.6kg 25mins and i do a longer route all on road of 8.9 miles.
> ...



So, on the figures you've quoted:-
Full-Sus MTB = 10.2 mph.
Hybrid bike = 14.5 mph.
Road bike = 19 mph.

You haven't stated what sort of tyres are fitted to each bike, and the comment about "all on road" for the road bike implies the other two were ridden on a route that included some sort of off-road tracks. How fast would your road bike be if you took it down the same route as the other two?
It's no good comparing apples with pears. If you want a meaningful result, all three bikes need to be ridden on exactly the same route and allowance made for any differences in tyres. The big difference between the full-sus and the hybrid can be accounted for by the suspension. The one time I've ridden a (cheap BSO type) full-sus MTB, it seemed like half the pedalling effort was being absorbed by the suspension rather than producing forward motion. That experience has made me very anti-suspension on bikes.


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## bpsmith (1 Jan 2018)

Agree on comparing the bikes on the same route, but disagree on the rest. How can we say a 16kg MTB is as fast as a 7kg Road bike, if we’ve made the MTB as much like a Road bike as possible, whilst also riding the Road bike in the same position as an MTB.

Surely we need to change the argument to a 16kg Road bike compared to a 7kg Road bike if you want to compare Apple’s with Apple’s?

Otherwise there’s some serious misinformation going on.


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## SkipdiverJohn (1 Jan 2018)

Are we trying to do a simple weight vs average journey time comparison here, or are we introducing other factors also? You seem to be coming at this from the standpoint that road bikes are naturally better because they are lighter, have lower rolling resistance tyres, and offer a different riding position. However, you can only maximise those advantages if you ride a route which allows you to get full speed up without the risk of bike damage or coming off. My guess is that if all three bikes were ridden over both routes and an average speed calculated, the differences would be greatly diminished. The full-sus would likely gain a couple of mph on a smoother road and the road bike would lose a couple of mph on the track route, but it would make less difference to the hybrid. It would be interesting if meta lon actually did these 2 alternative routes on all three bikes and then posted up the journey times.


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## Alan O (1 Jan 2018)

Comparing rides with different bikes involves so many variables that it doesn't make a lot of sense to deduce that it's the weight making the difference (although it's probably a part of it, you can't tell how much). Wouldn't a better way to do it be to ride the same bike multiple times over the same course with different weights attached to it? It still wouldn't reach the double blind ideal, but it must be better.


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## bpsmith (1 Jan 2018)

There are no other factors being introduced since the opening posts where its suggested that a 16kg MTB is as fast as a 7kg Road bike, only to then force both bikes to be ridden with the same tyres and in the same positions, plus ignoring all other differences between the said bikes...until now when the track factor was added. The assumption being that it’s a dirt track and not a tarmac cycle track, which we actually don’t know which at this point.


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## Winnershsaint (1 Jan 2018)

And I thought football forums were the home of b***ocks! I'm not a brilliant cyclist but I've got a very nice bike, in fact I've got two to choose from if I'm honest. They don't make me go faster, in fact my fastest average speeds were on my alloy Cube currently perched on the turbo which hasn't been on the road for around three years. I bought them because I wanted to and there should always be room for a new bike, but that's my business. I get a bit peeved with constant debates such as this on here and other social media which is thinly disguised criticism of those who choose to spend their disposable income on more expensive bikes, so what! I could understand the carping if there was a undercurrent of 'my bike's better than yours', but I am not aware of it. Oh and I wear ridiculous clothes too. They don't suit but are most comfortable and suitable for road cycling.


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## Ajax Bay (1 Jan 2018)

itaa said:


> -Want to go fast?
> a good aero position
> a good set of tyres with good rolling resistance,
> fitting clothes
> ...


I have taken excerpt quotes from the OP.
Conditions: Same aero drag; same quality of tyres (or even the same tyres); "aren't going up hills"; same route/roads/weather; same power output.
Each extra kg will cost less than half a watt (at 30kph say), or to put it another way, ceteris paribus, riding the 7kg super bike will 'save' the rider 29 seconds over 30km - according to bikecalculator.com
http://bikecalculator.com/


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## bpsmith (1 Jan 2018)

So why buy a MTB if you want to make it ride like a Road bike?

Assuming that the half a watt cost per kg is correct, are we actually suggesting that somebody weighing an additional 90kg would actually be less than 5 mins slower over 30km all other things being equal?

If that’s true, I am amazed.


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## mjr (1 Jan 2018)

bpsmith said:


> So why buy a MTB if you want to make it ride like a Road bike?


Maybe there's no space for more bikes, maybe they need the frame strength, maybe it's something else. Who cares?


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## mjr (1 Jan 2018)

Dogtrousers said:


> I was looking at my bike today and thinking. It's pretty fancy. I've spent a fair bit on it over the years. Some of the expenditure is hidden, in that I've tried and given up on things, some is quite evident. Frame is Reynolds 725 tubing (which might mean something to someone, but not to me). Good rigid altus rack, Altura rack pack with spare clothing. Hand built wheels, have been rebuilt multiple times. The last in a series of a zillion saddles that I've tried. Some of the expenditure is on small things, like the outsize drinking bottle that I prefer, or the BTwin handlebar bag, that I just don't think can be bettered. Wider handlebars that I found way more comfortable. Lots of small bits of fanciness aimed at making long rides more comfortable and convenient.
> 
> And now I find I've been wasting my time and money on tuning my fancy bike to how I want it. I could have been riding a random MTB as it would make no difference at all. What a fool I've been.


Look on the bright side: all those creature comforts haven't made you any slower, at least not directly.


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## Smokin Joe (1 Jan 2018)

All else being equal a lighter bike will be faster than it's heavier counterpart, unless the law of physics has changed since I last looked.


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## Ajax Bay (1 Jan 2018)

bpsmith said:


> Assuming that the half a watt cost per kg is correct, are we actually suggesting that somebody weighing an additional 90kg would actually be less than 5 mins slower over 30km all other things being equal?
> If that’s true, I am amazed.


"All other things being equal" (includes aero drag co-efficient, remember, which it wouldn't be unless the extra 90kg was a bloody great weight under the saddle) 6 minutes slower.


Smokin Joe said:


> All else being equal a lighter bike will be faster than it's heavier counterpart, unless the law of physics has changed since I last looked.


Yes, but only a very, very small amount - less than 0.1kph per kilo at 30kph [Conditions: Same aero drag; same quality of tyres (or even the same tyres); "aren't going up hills"; same route/roads/weather; same power output.] Had you a particular Law of Physics in mind?


Ice2911 said:


> Just ride and enjoy


+1


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## bpsmith (1 Jan 2018)

Ajax Bay said:


> "All other things being equal" (includes aero drag co-efficient, remember, which it wouldn';t be unless the extra 90kg was a bloody great weight under the saddle) 6 minutes slower


You’ve finally arrived at the point. All things cannot be equal when comparing a MTB with a Road bike, or when comparing different weights.


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## Ajax Bay (1 Jan 2018)

bpsmith said:


> You’ve finally arrived at the point.


No, I've been there all along: the premise articulated in the OP which was pointing out that *bike weight per se* doesn't matter much (see conditions above).


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## bpsmith (1 Jan 2018)

Ajax Bay said:


> No, I've been there all along: the premise articulated in the OP which was pointing out that *bike weight per se* doesn't matter much (see conditions above).


It's like pulling teeth. Bike weight is one argument. Suggesting a MTB and a Road bike are exactly the same is something very different.


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## Ming the Merciless (1 Jan 2018)

Smokin Joe said:


> All else being equal a lighter bike will be faster than it's heavier counterpart, unless the law of physics has changed since I last looked.



Remind me about the conservation of momentum and which bike has more momentum all other things being equal.


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## Ajax Bay (2 Jan 2018)

Smokin Joe said:


> All else being equal a lighter bike will be faster than it's heavier counterpart, unless the law of physics has changed since I last looked.





YukonBoy said:


> Remind me about the conservation of momentum and which bike has more momentum all other things being equal.





Dogtrousers said:


> All other things being equal (including power input) they will both have exactly the same momentum. But the lighter one will have greater velocity.


OK, include power input. Both twins (one on a 7kg bike, one on 15kg bike, ceteris paribus) start from rest (zero momentum) and accelerate (same power) to 30kph (8.3m/s). Relative acceleration will be inversely proportional to mass (say 80kg v 88kg) and the time taken to get to 30kph will be proportional - shall we say the power each twin generates allows them to get to 30kph in 10 seconds and 11 seconds respectively. As an aside please note the rider of the heavier bike now has more momentum: 11% more. Each twin cycles for an hour at the same power that, with equal aero drag, etc, etc (only difference is mass) achieves about 30kph. 30km later the twin on the lighter bike has to wait for about 30 seconds for her brother (who weighs the same as her btw). The second or two extra taken to accelerate to 30kph is negligible.
HTH (and @bpsmith - go to a dentist that pulls teeth with an anaesthetic)


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## derrick (2 Jan 2018)

Ajax Bay said:


> OK, include power input. Both twins (one on a 7kg bike, one on 15kg bike, ceteris paribus) start from rest (zero momentum) and accelerate (same power) to 30kph (8.3m/s). Relative acceleration will be inversely proportional to mass (say 80kg v 88kg) and the time taken to get to 30kph will be proportional - shall we say the power each twin generates allows them to get to 30kph in 10 seconds and 11 seconds respectively. As an aside please note the rider of the heavier bike now has more momentum: 11% more. Each twin cycles for an hour at the same power that, with equal aero drag, etc, etc (only difference is mass) achieves about 30kph. 30km later the twin on the lighter bike has to wait for about 30 seconds for her brother (who weighs the same as her btw). The second or two extra taken to accelerate to 30kph is negligible.
> HTH (and @bpsmith - go to a dentist that pulls teeth with an anaesthetic)



This is all good under perfect conditions, But in the real world. I ride with a guy who rides a S5 when he is on that bike we can ride 100 mile+ and stay together, but he also has an old steel bike that he rides not very often (Thank F****) i will drop him in no time at all.

Edit. it does not matter if he has a dump before hand either.


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## mjr (2 Jan 2018)

derrick said:


> This is all good under perfect conditions, But in the real world. I ride with a guy who rides a S5 when he is on that bike we can ride 100 mile+ and stay together, but he also has an old steel bike that he rides not very often (Thank F****) i will drop him in no time at all.


I'm confused by that because it seems like he's not a friend (is only called "a guy who rides") but it also seems like you're upset by dropping him. If he's a friend then it doesn't seem hard to ride a bit slower and if not who cares? It seems like a contradiction.

I also suspect the electric motor and area recumbent position on his C5 matters more than the weight of the bike.


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## derrick (2 Jan 2018)

mjr said:


> I'm confused by that because it seems like he's not a friend (is only called "a guy who rides") but it also seems like you're upset by dropping him. If he's a friend then it doesn't seem hard to ride a bit slower and if not who cares? It seems like a contradiction.
> 
> I also suspect the electric motor and area recumbent position on his C5 matters more than the weight of the bike.


It does not seem to take much to confuse you.


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## Ajax Bay (2 Jan 2018)

Well I read the S5 as SS ie single speed, to start with but suspect that @derrick is relying on chatters (exempt @mjr ) recognising that an S5 is made of carbon (so a '7kg supperbike' example).


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## Milkfloat (2 Jan 2018)

Dogtrousers said:


> I hope he wasn't riding his supperbike at dinner time. That would be a terrible faux pas.



Does that not depend on how he is dressed?


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## Ming the Merciless (2 Jan 2018)

Ajax Bay said:


> OK, include power input. Both twins (one on a 7kg bike, one on 15kg bike, ceteris paribus) start from rest (zero momentum) and accelerate (same power) to 30kph (8.3m/s). Relative acceleration will be inversely proportional to mass (say 80kg v 88kg) and the time taken to get to 30kph will be proportional - shall we say the power each twin generates allows them to get to 30kph in 10 seconds and 11 seconds respectively. As an aside please note the rider of the heavier bike now has more momentum: 11% more. Each twin cycles for an hour at the same power that, with equal aero drag, etc, etc (only difference is mass) achieves about 30kph. 30km later the twin on the lighter bike has to wait for about 30 seconds for her brother (who weighs the same as her btw). The second or two extra taken to accelerate to 30kph is negligible.
> HTH (and @bpsmith - go to a dentist that pulls teeth with an anaesthetic)



Continue with your assumptions and apply them for relative deceleration and what do we end up with? Given that the aero drag and rolling resistance are decelerating both riders all the time. Plus aero drag is not increasing linearly.


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## mjr (2 Jan 2018)

Dogtrousers said:


> I hope he wasn't riding his supperbike at dinner time. That would be a terrible faux pas.


Indeed. The faux pas should be danced between dinner and supper.

View: https://www.youtube.com/watch?v=bVIsPm2KH58


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## vickster (2 Jan 2018)

Interestingly the OP @itaa hasn’t been back to comment


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## Ajax Bay (2 Jan 2018)

YukonBoy said:


> Continue with your assumptions and apply them for relative deceleration and what do we end up with? Given that the aero drag and rolling resistance are decelerating both riders all the time. Plus aero drag is not increasing linearly.


I'm not sure I know what you mean by 'relative deceleration' - do you mean in order to stop at the end of 30km? In this model neither aero drag nor rolling resistance are 'decelerating' the riders: their speed increases from 0 to 29.5/30kph and stays there. Those two forces are countered by the drive (equal power = equal drive force) provided by the riders, overmatched during the initial acceleration and then matched, exactly. Aero drag increases exponentially but 1) it's the same (in this model) for both riders and 2) the speed is constant so the aero drag is constant. Perhaps you could "continue with [my] assumptions and apply them" yourself; and share that with us? What do you end up with?


vickster said:


> Interestingly the OP @itaa hasn’t been back to comment


Well, not that interesting, but I know what you mean (at least I think I do ).


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## vickster (2 Jan 2018)

Ajax Bay said:


> Well, not that interesting, but I know what you mean (at least I think I do ).


Posted Christmas Day, I wonder if alcohol might have been involved


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## bpsmith (2 Jan 2018)

vickster said:


> Posted Christmas Day, I wonder if alcohol might have been involved


Quite possibly but, all things being equal, we all drank exactly the same on Christmas Day.


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## vickster (2 Jan 2018)

bpsmith said:


> Quite possibly but, all things being equal, we all drank exactly the same on Christmas Day.


I had 3 glasses of wine. I was not drunk enough to post a thread which has now run for 8 pages with no further comment from the OP


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## raleighnut (2 Jan 2018)

vickster said:


> Interestingly the OP @itaa hasn’t been back to comment


They were last on here at just short of 7pm on Thursday but didn't comment/post in this thread.


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## Ajax Bay (2 Jan 2018)

Worth looking at the OP's post history to understand where the road bike v MTB rant (kernel of truth/fact nevertheless) came from. 9 year old MTB with new tyres and a 'below entry level' road bike (bought for £26 - a bargain btw) which he is considering converting to a flat bar.


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## derrick (2 Jan 2018)

vickster said:


> Interestingly the OP @itaa hasn’t been back to comment


Maybe he is still having a dump.


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## Ming the Merciless (2 Jan 2018)

derrick said:


> Maybe he is still having a dump.



But is he doing it in an aero tuck?


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## Ming the Merciless (2 Jan 2018)

In your model they accelerate to 30km/h a second apart. The heavier bike / person combination is now in the slip stream of the lighter / bike combination. They are putting out the same power and due to reduced drag the heavier rider / bike combo will now accelerate faster than the lighter rider and be able reach a higher speed (for the same power input) than the one in front. In fact they will be able to draw level as much as matters. So the riders will finish together.


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## mjr (3 Jan 2018)

YukonBoy said:


> But is he doing it in an aero tuck?


Yes, a dump tuck.


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