Lighter wheelset question - Page 2

Wrong. It's an equation of motion. It is perfectly applicable to the situation at hand.

So, when you did your little race car experiment, did you actually do measurements? Did you actually make sure to hold variables constant between tests and account for those variables that you couldn't hold constant?

As for the numbers, Mark McM's numbers show there is very little difference in performance between various MOI. The difference is on a level that is likely undetectable by the rider (especially given that with optimum aero wheels, the aero contribution is an additional 0.5 mph at 25 mph, a difference in velocity that requires a bike computer to be revealed, i.e. it isn't discovered by the seat of your pants).

The thread wasn't about racing, but since you bring it up, might you explain, then, how it is that pro riders can win races....sprints, even.....on 7 kg bikes with unlight wheels when they can ride 6.8 kg bikes with their choice of light wheels? Technically your inch argument is just subjective flotsam. If you're going to argue for an inch, then you also have to discuss the differences in Crr as result of the paticular path a rider follows and the random surface structure of a road (implying a random Crr); the effects of varying meteorological conditions for each rider; possible aero effects resulting from position in the spring leadout and throughout the rest of the sprint; rider's energy status at the end of a race; varying inflation pressures for tires on the different bikes; and so on.

When racing you often make choices because those choices might help, not because they definitely will. You make choices because said choices might have very few downsides and are therefore, in your judgement, worthy risks.

None of that has anything do with the marginal benefits of low MOI wheels.

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OK, I won't be able to convince you, and I won't put any more effort in it.

But just think about the fact that many competitions restrict the weight off bicycles ...



About the race-cars (not that it matters here): I was involved in the measurements ( I needed different data), and it was done on 2 identical cars. First time the second car was slower, (with the heavier tyres), 2nd time they had identical tyres and the second car was faster ...

It all happened in the timespan of 1 hour, and there where no special weatherchanges, no other changes at the cars, same pilots per car ...

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This topic drives me nuts even more than Kirby Palm's BS crank length formula of 21.6% of inseam.

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The 'importance' of rotating wheel weight on bikes is the biggest scam being perpetrated by bike companies at the moment; probably even more than bike (and component) weight (at least bike weight actually means something when riding up hills).

Automotive analogies can't be used here, because of the massive differences in car wheel and motor revs, relative to weight, even in 'non-race cars'. For example, if a 1500kg car is generating 300,000w, that's a ratio of 200w-per-kg. Compare that to a 75kg guy on a 7kg bike, who 'might' generate 1000w stomping out of a corner in a crit: that's 12.2w per kg. Can you see the difference?

Bike wheel aerodynamics and stiffness are far more important that the mythical external rotating mass, and these can be sacrificed by light, box-shaped rims.

My fastest-feeling wheels are my uber-stiff, 2.2kg sets with 30mm-deep rims. I've tried many lighter wheels (sub-1500g) which feel as though they "spin up" way slower because they flex like shid!

Mine are a set of really nice Campagnolo Delta box section rims laced with 36 double butted spokes. I made a set with left hand rear Revolution spokes and fronts, and it felt much 'softer'.

The stiffness of your rear wheel will make you a better climber. If you could somehow shave 275 grams of your existing wheel set, I will bet my next paycheck that hill will be just as hard.

A stiffer wheel in the back without flex will get you up that hill a lot quicker and it will be noticable whether its 275 grams less or 275 grams more.
A heavier wheelset will have somewhat of an advantage on the flats. How much don't know. There are others arguing this point through out this thread.

Just my $.02 worth.

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You'll have to use science to convince me. Actually, you'll need scientific proof that what I say is incorrect. I state and maintain that on a bicycle, wheels with lower MOI do not provide performance benefits that humans can detect regularly. I also maintain the above equation is absolutely correct. Further, I maintain that you're reading the equation incorrectly. In fact, the equation describes any acceleration of a bike/wheel combo in a plane. Further, solution of the differential equation provides solutions in terms of velocity. If you state the velocity form as a differential, you solve it to get solutions with respect to position. In fact, not only does the equation explicitly give acceleration and velocity (with manipulation, position), it can be used to give solutions in terms of momentum and energy.

This is just Newtonian mechanics, vetted over the course of the last 400 years.

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36 spokes? Nice. I only started using 32 because they became 'standard', not that I'd notice the extra stiffness with 4 more spokes.

I have a two-bit theory as to why deep (and usually heavier) rims may feel to some as though the accelerate slower.

Lighter-steering bikes feel zippier to accelerate, espeically when riding off the saddle, and I figure the slight gyro effect of deeper rims slows the steering a fraction, hence, making the bike bike feel a tad more sluggish.

Hey? Hey? Hey?

Maybe, although bikes don't generate much in terms of gyroscopic effects. Lighter wheels do make themselves known when you're throwing your bike back and forth, and that lighter feeling could be confused with feeling like the bike is accelerating up the Angliru like a goat steamin' on PCP.

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Yep, that sounds more like it.
Back to my croanies and writers to workshop my two-bit theories

Even when I was lighter than I am now, I have always used 36 spokes. 4 spokes are only 28 grams but make for a stronger wheel.

Lighter wheels typically perform better but not always. Sometimes lighter wheels can perform worse depending on the situation. Pursuit wheels are lighter than sprint wheels and will not withstand abuse like heavier wheels.

I have found that smaller tires make a huge difference. If you go from a 360 gram to a 195 gram tire it makes a huge difference on hills. The lighter tires will not last as long though. When I raced in road races I typically used a 195 gram or 250 gram tire on the rear and a 250 gram tire on the front. I trained on tires that were 360 grams.

Rigidity is key. Typically there is a balance between rigidity and lightness. Too rigid and things break but you have more power. Too loose and you lose some power and things can break too.

It is not unusual for a beginner to want lighter equipment and think that is the key when conditioning is critical. Avoid the temptation to but new equipment.

Someone who is in excellent condition will win on a Schwinn Varsity and the person who is not can have a carbon fiber bike and lose miserably.

you arent going to see much, if any gain from a lighter wheel, but you will from a more aero wheel. The difference from a 20mm rim to a 40 or 50mm is definately noticeable, and obviously even more so with a disc/deep dish up front

F = ma
On a wheel F= (m v^2)/r
The acceleration on a wheel is v^2 /r.

The acceleration of an object that follows a linear path and does not change direction or velocity has zero acceleration. In a wheel it always has acceleration because there is always a change in direction.

Anyone who rides the track and maintains the same speed throughout the bank knows that it takes a lot of energy to maintain that speed and can feel the acceleration at the end of the bank when it goes into the straight away.

A very heavy flywheel is hard to get moving and once it is moving it is very hard to stop. It has a gyroscopic effect. A wheel that is light does not take very much energy to get it going nor much to stop it.

Way too much emphasis on gear, not enough on the ride, the rider, the engine, the person.