Would a road bike be quicker?

[SimonC]

For a constant speed, all other things being equal (drag etc), a light and heavy bike would require the same power to maintain that speed.

But the heavier bike will require more energy to reach that speed, which in the real world is relevant because I'm sure we all dont ride at a perfectly constant speed. So riding away from lights and other stops, and slow downs will take more effort.

 

[HLaB]

I've similar gearing on my Sirrus and I find it good. When I bought the sirrus I had panniers and mudguards on it and took it on CTC rides it coped very well. In the end though I joined a faster club and whilst the sirrus remained a flat bar road bike for around a year it eventually became a dropped bar bike and I bought another 2 road bikes. My last one is a bit dearer (a Kinesis) but it was bought bearing mind the ability to have full guards and a rack fitted.

 

[chris667]

Eh? It's a triple with a 30x25 gear at the bottom. Shome mistake shurely.

No, 30/25 is what, 30-odd inches? That's quite high for a bottom gear, 52/11 is well over 120 which is more than is good for most people.

And it's too cheap.

 

[swee'pea99]

For a constant speed, all other things being equal (drag etc), a light and heavy bike would require the same power to maintain that speed.

But the heavier bike will require more energy to reach that speed, which in the real world is relevant because I'm sure we all dont ride at a perfectly constant speed. So riding away from lights and other stops, and slow downs will take more effort.

Eh? I don't understand, much less get, the science questions on University Challenge, but that is surely incorrect. Are you telling me that once you've achieved a steady 20 MPH, whether or not you have panniers full of lead makes no difference to the effort necessary to maintain that speed, other than the effects on wind resistance?

 

[Hont]

No, 30/25 is what, 30-odd inches? That's quite high for a bottom gear, 52/11 is well over 120 which is more than is good for most people.

And it's too cheap.

That's a fairly standard ratio for road bikes with a triple. It's a 52/12 btw, which is, agreed, quite high but again quite standard for a triple.

 

[chris667]

It may be standard for a lot of road bikes, but that still doesn't make it right for most people, and it's a particularly poor choice for a hybrid with 30mm tyres.

The way I see it this bike is the worst bits of a hybrid and a proper road bike.

And it's too cheap.

 

[jeltz]

Thanks, I all.

Its not about current budget its about how much money I need to get together to get a suitable bike for my needs. 2nd hand is a definite option and I'm watching ebay, the local rag, putting the word around.....

 

[jimboalee]

Eh? It's a triple with a 30x25 gear at the bottom. Shome mistake shurely.

The bike is good for a 13% incline.

 

[jimboalee]

[quote name='swee'pea99']Eh? I don't understand, much less get, the science questions on University Challenge, but that is surely incorrect. Are you telling me that once you've achieved a steady 20 MPH, whether or not you have panniers full of lead makes no difference to the effort necessary to maintain that speed, other than the effects on wind resistance?[/quote]

SimonC is correct.

A more accurate statement would be "The slimmer and more aerodynamic bike will be quicker".

Although it takes more effort to get to 20 mph, you can relax the power earlier when coasting to the next set of traffic lights because the higher inertia bike rolls further.

This is how a Touring bike works. ( Although they only get to 13 mph ).

 

[jimboalee]

For a constant speed, all other things being equal (drag etc), a light and heavy bike would require the same power to maintain that speed.

But the heavier bike will require more energy to reach that speed, which in the real world is relevant because I'm sure we all dont ride at a perfectly constant speed. So riding away from lights and other stops, and slow downs will take more effort.

Slow downs will take more effort on the brakes, not your legs.

A vehicle's Cd can also be evaluated by allowing it to coast down a flat road in neutral ( freewheeling ). The further and longer it rolls, the lower it's Cd. If the shape and aerodynamics are the same, adding weight will result in a longer roll, thus a lower Cd.
If the shape ( cross section area ) remains the same but the Cd is lower, Power will be lower due to Power being dependent on Cd x Area.

Do you remember stuffing plasticene in your Hot Wheels cars to make them roll further?

 

[jimboalee]

Shut up James, you're frightening the Newbies away

 

[carl9547]

very interesting thread there,sent me to bed an hour earlier than i planned..cheers young einsteins

 

[SimonC]

Slow downs will take more effort on the brakes, not your legs.

I kinda meant accelerating away again from those little slowdowns. All those little extra bits of effort add up on a long ride.

A vehicle's Cd can also be evaluated by allowing it to coast down a flat road in neutral ( freewheeling ). The further and longer it rolls, the lower it's Cd. If the shape and aerodynamics are the same, adding weight will result in a longer roll, thus a lower Cd.
If the shape ( cross section area ) remains the same but the Cd is lower, Power will be lower due to Power being dependent on Cd x Area.

Do you remember stuffing plasticene in your Hot Wheels cars to make them roll further?

I think in general there is so much more to consider than weight, such as frame and wheel stiffness, which is where your more exotic materials come in, the benefits are not just from light weight. Also, matching the kit to what you are using it for, no point having light flimsy wheels on say a cyclo-cross bike, cos they will last about 10 minutes as an example, or loading up a carbon frame with shed loads of panniers.

Also much more important to think about the weight you can lose from yourself as well as the bike.

Having said all that, having just discovered a crack in the chainstay in the Kinesis ally frame Ive been using this season, I'm buying a Planet X carbon fibre frame in white for road racing next season. Bling-bling. Always a silver lining.

 

[accountantpete]

Whoops - that will teach me to read posts and not glance at them Swee'pea

 

[swee'pea99]

Nay worries. At least I understand your posts.