Wheel upgrade

[annirak]

OK, you are obviously very keen to do this.

Here's the given.

Two bicycles accelerate from zero to 30 kph in three minutes. Both weigh the same with their riders - 90 kg.
However, bicycle A has wheels that are lighter than bicycle B, by 400 grams for the pair. Obviously bicycle B has the 400 grams placed elsewhere.
That weight saving is shaven of all areas of the wheel, ranging from tyres (radius 368mm) to hub (radius 36mm).
Bicycle B's wheels have a mass of 2500 grams and the mass is evenly distributed from radius 368mm through 36mm.

Calculate the energy each bike requires to accelerate up to the given velocity and also express it as a percentage difference.

Thank you.

Yes, yes, I have read your other post. I disagree with one or two of your assumptions, but I agree with your conclusion. What I don't agree with is that slower acceleration cancels out slower deceleration. They both make things worse.

 

[Justinslow]

Zzzzzzzzzzzzz

 

[Citius]

Heavy rims take exactly as much power as light ones to keep moving.

In case you missed it, this is what I have been saying throughout this thread.

 

[Yellow Saddle]

Yes, yes, I have read your other post. I disagree with one or two of your assumptions, but I agree with your conclusion. What I don't agree with is that slower acceleration cancels out slower deceleration. They both make things worse.

You are getting yourself deeper and deeper into hot water with your postings.

You said you would like to do the math, now do it and prove your point. If you don't like my assumptions, say so, change them to something more realistic and do the math. BTW, I've made the assumptions more realistic for you. Compare them to mine.

 

[S.Giles]

I've heard similar claims of improvements in audio amplifiers as a result of changing capacitors in the signal-path. Replace capacitor A with capacitor B and suddenly choirs of angels start to sing! Except nothing measurable has changed. (Note: Capacitor B is always more expensive than capacitor A, and the more expensive it is, the 'better' it sounds.)

I think this discussion is about human nature and human perception as much as it's about objective reality. I'm sure that people do experience something different, although IMO the difference only exists in their minds. If that perception makes them happy, that's a real gain!

 

[Justinslow]

So in conclusion, does this mean if I spend £200+ on a new wheelset (there's nothing wrong with my existing cheap wheelset) and save 500g I will get hardly any benefit from this change? Therefore it's not "worth" doing. Coz the physics and maths have confused me somewhat.

 

[vickster]

Placebo effect of having 'better' wheels and tyres not to be underestimated. If you have the money and want to spend on the bike, wheels and tyres most worthwhile

 

[Yellow Saddle]

So in conclusion, does this mean if I spend £200+ on a new wheelset (there's nothing wrong with my existing cheap wheelset) and save 500g I will get hardly any benefit from this change? Therefore it's not "worth" doing. Coz the physics and maths have confused me somewhat.

Sort of, but I'll refine it a bit.

But first, just read the preamble to my original calculation here.http://www.cyclechat.net/threads/road-racing-aero-wheels.173743/page-2#post-3523626
No need to go through the sums and arithmetic, just the preamble.

Then. Saving 500 grams anywhere on your bike will give you just about the same benefit. In other words, save it on the wheels or loose weight around your gut, the benefit is the same (within a very, very very small margin).

Further, whatever benefit there is to be had from weight savings, that benefit will be most visible when you do a lot of climbing and only then.

My attitude to all this is, most of us bike junkies want nice bikes but are all just to hung up on what the instrument weights. I say go ride, enjoy being out in the sunshine in the company of friends, have a beer afterwards and stop worrying what your bike weighs and certainly stop this wheel "uprade" nonsense. It is no different from a 20-year old putting bigger wheels and a big exhaust on his Subaru. Most people kinda laugh at them.

And then ultimately, whatever makes you happy makes you happy. And to finish off with a rider to that, if you really want those wheels and you are sure they will make you happy and more attractive to the opposite sex, then I'll happily sell you this pair here in the corner....spokes made from unobtanium, rim extruded from aircraft quality zircal, bearings fit for a Mars rover, painted by hand and polished to a fine gleam with crushed cherry pips.

 

[Yellow Saddle]

Placebo effect of having 'better' wheels and tyres not to be underestimated. If you have the money and want to spend on the bike, wheels and tyres most worthwhile

No, this is not what Giles and I have been saying.

 

[winjim]

Get a hundred fast cyclists and two identical bikes. Hide lead weights in one of the bike's wheels, and in one of the bike's frames. Randomly assign each rider to a bike and time them round a course. Do this double blinded so neither rider nor timer knows which bike they are using. Compare the times of the two groups using a meaningful statistical test. Repeat for different courses eg hilly, flat, etc.

Could somebody please do this and let me know the outcome?

 

[vickster]

No, this is not what Giles and I have been saying.

I don't really care about the maths, I just like new shiny things and I'm crap at cycling anyhow not helped by needing to lose 15kg off me bike weight is on,y important to me ultimately when I have to carry it up a flight of stairs. I am riding a sub 10kg bike today but then added mudguards, a rack, pannier bag with d lock. The weight of the wheels makes diddly difference, they just look nicer!

 

[uclown2002]

I got dropped on page 2.

 

[Justinslow]

I got dropped on page 2.

I got dropped going up a hill.........

 

[Citius]

Get a hundred fast cyclists and two identical bikes. Hide lead weights in one of the bike's wheels, and in one of the bike's frames. Randomly assign each rider to a bike and time them round a course. Do this double blinded so neither rider nor timer knows which bike they are using. Compare the times of the two groups using a meaningful statistical test. Repeat for different courses eg hilly, flat, etc.

Could somebody please do this and let me know the outcome?

A group of people are already doing this a couple of times every week. They are collectively called the 'pro peloton', I think

They've all got light bikes and light wheels - some of them even swap bikes and wheels several times each race. But the trouble is, the results are all skewed because the fittest guy with the best legs on any given day tends to win, regardless.

 

[Citius]

So in conclusion, does this mean if I spend £200+ on a new wheelset (there's nothing wrong with my existing cheap wheelset) and save 500g I will get hardly any benefit from this change? Therefore it's not "worth" doing. Coz the physics and maths have confused me somewhat.

If you switch to a wheelset which is 500g lighter, you will get 500g worth of benefit. There are websites which will calculate this benefit for you if you want - http://www.analyticcycling.com/ - although the simplest way would be to do two rides of identical profile and duration, one while carrying a full 500ml water bottle and the other one without. If you can detect or record a difference, then there's your benefit.

If the new wheelset is more (or less) aero, or if you are using lighter, faster rolling tyres, etc, then this will also affect things - but in strict terms of weight, then you should find the answer above.