"Taking an ounce off your wheels is liking taking two ounces off anywhere else on your bike." "Start by getting light weight wheels, makes a huge difference in acceleration." These are are near-universal beliefs.

Those of you who recently spent $1500 on a wheelset to eliminate a few grams and are convinced your bike was radically transformed might not want to try the following experiment:

Prop up the front of your bike or put it on a stand and watch your speedometer while you grab the front wheel and give it a spin. If you want to get it up to the 20s you will probably have to yank on the spokes near the hub. Of course the effort to spin up the wheels is x2 of that, but its still really trivial -- you can do it with two fingers of one hand. At least I could, and that is with a $189 wheelset with 700 x 32 tires. You could also put your bike in its hardest gear and you will find that it takes little effort to get the rear wheel up to top speed with one hand. And that is bringing the wheel from standstill to max rpms much faster than occurs in any actual riding conditions. Unless you have a handcycle in your fleet you probably have far more strength in your legs than in your arms.

The effort to overcome the inertia of the wheels is a fart in a hurricane compared to what it takes to overcome the inertia of getting combined bike and rider mass up to speed, let alone to move that mass from elevation A up to elevation B. If you are racing its true that grams, seconds or fractions of seconds count, of course, but the difference from ultralight wheels is much less than it is commonly made out to be.

Don in Austin

interesting. I've been hearing that a lot, too and I was wondering what's the reason behind the belief that lighter wheels make the most significant difference.

Not that I really care but,you also have to remember that the racer types are bringing that mass up to speed many times over a 100+ mile ride.They are also bringing it up to a much higher speed than most of us mortals,it all add up over time.All those grams add up to alot of weight over a season.

If you are worried about every 10th of a second,it counts.

If you climb hills and are worried about those 10th's,it counts.

If you ride 100-200 miles a day it counts.

If somebody is going to give me a $10,000 bicycle and pay me to ride it,it counts.

For us mortal humans,it doesn't matter.You could put $2500 woven pigmy butthair rims on my bike,wouldn't make it any faster with me riding it.

Don, if you're saving a couple grams you're probably right. If you're switching from steel rims to alloy (and, I should note, probably spending about 1/10 of the number you quote), the difference is appreciable in about one second.

I don't have an ancient clunker bike with 5 pound wheels. however, I will try it on a MTB with 26 x 1.5s

Yes, what I was addressing was the minimal real world returns between an under $200 wheelset and a $1500 wheelset. A bike with steel wheels is probably going to be slow in many aspects.

Don

IMO, all benefits attributed to wheels are way overrated. That doesn't stop me from lusting after light aero wheels, however...for intellectual and esthetic gratification rather than for any material performance benefit.

Huh???? Its about the energy required to make the entire wheel accelerate -- plain and simple. Its true, of course, that weight on the rim has more of an effect on inertia than weight at the hub.
But the whole wheel spins together. If you spin the huib you spin the rim.

Don in Austin

I hear you! I have three CF bikes. But I am realistic about what the CF can do for my performance. Just fun to build them and got all the CF frames and other CF components cheap and un-branded from China.

Don in Austin

Everything counts. One fluid ounce of water in your water bottle counts, administering an enema on yourself before a ride would count, it's just a question of how much. Some folks talk about ultralight wheels as if they made a huge difference and that is what I take exception to, unless they are using standards such as draining a couple of ounces of water from their bottle makes a huge difference.

Don in Austin

My guess is that the high priced wheelset will have better hubs and a more aero profile which will effect performance. Probably more than weight alone. I will say that dropping 1/3 lb. from each of the wheels on my commuter (dumped the thorn-resistant tubes in favor of standard tubes) made a big impact on average speeds on my commute.

reduce the diameter of the wheel and the mass goes down too..

+1

That's also a case where it's much more than the weight alone. Thorn resistant tubes add a substantial amount of rolling resistance which I found to be far more significant than the increase in weight. As your wheel turns the tube is flexing in the region of the contact patch and flexing the thick rubber of a thorn resistant tube requires energy that ultimately has to come from the rider.

The wrench example is torque only NOT energy. Bad analogy.
What I mean by energy -- say watts -- is torque x speed. This is the same from the hub to the tire. If you have a friend who is a physicist or mechanical engineer you might run this by him/her.

Don in Austin

And an engineer should know that the energy needed is the same whether you are applying a small force through a large distance with a long wrench or a large force through a small distance with a short one.

In the case of propelling a bicycle it's easy to adjust the distance vs. force needed by choosing the appropriate gearing and Don is correct that comparing the energy needed to spin up the wheels vs. the energy needed to propel the entire bicycle and rider is the appropriate measure of how significant the wheel weight is.

Don is absolutely correct in my opinion. I'll bet that the tire makes a big difference with the expensive wheels also because who's going to put a Strada K on a $1500 wheel? But to play devil's advocate, he's really observing the force it took to spin the wheel (or pounds per sec per sec more precisely) and it occurred to me that the force needed to propel the whole bike at 20mph is only around eight pounds or so, so the energy isn't all that much there either.

I think if someone had a sloppy stroke like me he's accelerating on each pedal stroke, moreso than does a more polished rider. That's gonna add up, but the question is how much?

Maybe if someone had a trainer and a powermeter, and compared his power expended for the same distance with two different wheels it would be a decent experiment.

Weight and aerodynamics will always be a hotly debated topic. I have my opinions, as does everyone. Mine differ somewhat from my "buddies" but neither have any real scientific data to back our claims. The two buddies that I've debated this with a lot are racers (one real- one wannabe).

The real racer comes waltzing in one day sporting a new CF ride. Ceramic bearings- aero spokes (16), which weighed in a bit over 14 lbs. As he was telling me all the benefits of the components I listened, but not without a lot of eye eye-rollin'. You got to understand that he doesn't know much about bikes, but believes everything he's told by salespeople and his racer buddies. So, he's telling about the benefits of aero this, and aero that. How much it helped top speed, blah-blah-blah. I asked, "what do you do about them legs flailing around- do the aero spokes and wheels offset this?" Hummm. So he says it must be the ceramic bearing hubs then.

So I challenged him to a couple of (very non-scientific) tests. First a static spin test. Both front and rear wheels brought up to speed (his and mine) and allowed to spin down. Wouldn't you know it, my lowly Ultegra hubs (32) round spokes- 425 gram rims, and 100 gram heavier tire, spun about 30% longer on the front, and almost twice as long on the rear. I knew a part of it was the heavier tire and rim, but the most of it is because my lowly hub spun better. So I said...

"Static tests don't really benefit from aero stuff so let's do a coasting test." Just a couple blocks from me there is a five block long downgrade- not steep, maybe 3-4%. Starting from a dead stop I beat him to the bottom by nearly a block length and bested his top speed by almost 5 mph (could be some computer errors in there). I had on Levi's and he had on his wifes yoga gear- AKA bike clothes. He was so smug and sure at the outset that the only comment I could conjur up was, "you spent six grand on THAT?" Didn't hear from him for almost a month. LOL

Other buddy subjected himself to the same test. His equipment wasn't as good as the first guy's, but better than mine- he thought. His results were even worse.

Either should have waxed me in the coast test at least. Combined bike and rider weight for each of them was 10 lbs heavier than me and they had "aero gear." The static spin down test I kew I could win hands down. I had a heavier rim and tire combo and there ain't nothing that spins like a loose ball Shimano hub, and the Shimano free hub has less loss to friction and the action of the pawls.

However, I will take lighter weight every time I can within reason. I won't take lighter weight at a much greater hit on my wallet, and I won't sacrifice rolling resistance for weight. Lighter weight bikes are just plain more fun to ride! It matters not where you shed the weight, but generally there's more weight loss to be had in the wheelsets, so that's pretty much where everyone starts.

Now's when you ask, "what about losing 10 lbs body weight instead?" It ain't the same. I lose ten pounds or so after winter and start to get in shape. Yes there's less total weight you have to pull around, and the engine gets better, but it ain't the same. Give me five pounds off the bike anyday.

Lighter weight rims and tires do have some advantages but I doubt few of us will go fast enough to realize it. Descending at 45 mph or so the light stuff leans into the turns better. The gyroscope effect is less so it doesn't want to "stand up" and alter your line. This effect is real and I've felt the difference a few times. That was years ago. Now you won't catch me going 45 on a bicycle unless I go off a cliff.

The aero spoke thing? On the stand with the wheel maintaing 20 mph, you feel a lot more "wind" off the wheel with 32 round spokes than 16 aero spokes. Real world? I don't think there's any advantage until you get rid of the flailing legs and that big sail sitting in the saddle.

If you get through this long-windedness, thanks for allowing me to spout off!

rotating weight hurts you more than non-rotating weight (particularly rotating weight that is far away from the axis of rotation - so mainly the tire and rim, and to a lesser extent, the spokes). the issues are:
a) for what type of riding does it hurt you?
b) how *much* does it hurt you?

The more you are accelerating and decelerating, the more rotating weight will hurt you. If you are doing a time trial on a relatively flat, non-technical course, you're doing very little accelerating after you initially get up to speed. Same is true for just-out-riding in the countryside in a relatively flat area.
If you are doing a lot of climbing, stopping and starting in traffic, or in an environment where you have to accelerate quickly to attack or cover someone else's attacks, rotating weight matters significantly. But for many types of riding it doesn't.

Absolutely rotating weight means nothing cruising down the road at steady speed, means more the more you are changing speeds. But, even then its small compared with the forward momentum of bike + rider.

Don in Austin

Thanks, your rebuttal was much better stated than mine!

Don in Austin

Not at all. Yes you're accelerating and decelerating a little on each pedal stroke, but the energy requirements are independent of the weight. A heavy bike (or one with heavier wheels) will actually decelerate a little less than a lighter one due to its greater inertia. So while it takes more energy to accelerate the heavy bike you don't have to accelerate it as much and the energy needs are essentially the same for both. In both cases, the energy needed to keep going at the same average speed on level ground will be determined by air resistance, mechanical inefficiency, and rolling resistance.

The first is by far the most important and is unaffected by weight (in fact some aerodynamic wheels are heavier as a result of the deeper rims), the second is small and also unaffected by weight (although higher quality components may tend to be both lighter and a bit more efficient), and only the rolling resistance goes up slightly with added weight - but is a very small part of the total drag.

:

You could say this about any component on a bike, or the complete bike itself. Progress is made in incremental steps.

Don, I'm not one of the princess and the pea type of cyclist, I don't notice a difference in two wheelsets that are as close as 500 grams between my road bikes. I do notice a difference between the touring bike's wheelset and a roadie's wheelset because the touring bike's wheelset is possibly 75% heavier (Quick math and just the touring bike's tires are 75% the weight of the roadie's wheelset.).

Wheels are like flywheels, they store energy. The heavier the flywheel the greater is the energy required to spool up to a certain RPM in a finite amount of time compared to a lighter flywheel yet less energy is required to maintain the target RPM. The heavier flywheel will continue to spin longer than the lighter flywheel when power is removed.

Much ado about nothing for the average recreational cyclist. A & B club riders likely benefit from lighter wheelsets and tourers likely benefit from heavier wheelsets.

Brad

I think it takes more energy to accelerate and decelerate centered about a given speed than to maintain that speed without deceleration.

Mostly right I'd say, but my educated guess is that the flywheel effect would have little benefit for the touring cyclist. Perhaps enough to fractionally offset my sloppy pedal stroke, since it would tend to smooth that out.