Any hard data on rotational weight?

[MaraudingWalrus]

Originally Posted by veggieburger

Marauding Walrus is one smart dude/dudette..

Thanks...I've got some paperwork that says that, some that says the opposite, and a whole lotta witnesses who think I'm a dummy. Who knows.


But one thing that I do know for sure is that this is an under-discussed element of the wheel/tire system.

The weight of the wheel doesn't tell the whole story. Where that weight is is what really matters... if you gave me two pairs of wheels with the same spoke count and lacing patern and one was 100g heavier than the other, but the heavier one had a 200g heavier hubset...I'd take that heavier wheelset because its weight is centered at the hub, not out at the rim.

I hope to eventually test enough similar wheels to be able to better convince someone that - at least where I live - complete wheel weight isn't as relevant. The two are often related, but not always.

Here in FL, we're not climbing jackdiddlysquat, so complete weight of things doesn't matter that much because we're not dragging it up anything.

I also have some other visions for using this device to try and get some numbers for aluminum vs brass spoke nipples, to see what kind of difference that makes from an energy standpoint, and things like cassettes or freehub bodies. Saving a few grams at the hub for many hundreds of dollars that it costs to spring for a DA or Red cassette should really be almost useless around here...

[cmg]

any place that lists the lightest 25-28-30mm road bike tires? I'm from the light at rim is all that matters group and coming from 180 gram tire or less. Big difference between conti supersonic 23 and cont gp4000 25mm.

[gospastic]

Originally Posted by cmg

any place that lists the lightest 25-28-30mm road bike tires? I'm from the light at rim is all that matters group and coming from 180 gram tire or less. Big difference between conti supersonic 23 and cont gp4000 25mm.

Compass Chinook Pass Extralight 700x28 - 229g
Zipp Tangente Speed R28 700x28 - 216g

[Mark McM]

Originally Posted by MaraudingWalrus

Results show that every time you go to spin that wheel up to 30km/hr in 10seconds the wheel by itself requires 3.1 watts of energy. The 23mm Corsa tire (and tube) require an additional 2.6watts of energy of the wheel by itself; the Lugano requires 3.4 watts additional; the Gatorskin requires 4 watts additional; the Protek requires an additional 10.3 watts to spin up to speed.

These are HUGE % variance between each other when just looking at the wheels by themselves. They're a considerably smaller % variance when taking into account the whole bike/rider system...but perhaps not an insignificant amount of actual watts. How many times in the course of your ride to you accelerate and decelerate? Saving two watts per wheel (so 4 watts total) every time I go to speed up is worth it to me to run Corsas over Gatorskins....and I'd wager it's something you and I can feel.

I'd wager that those choosing the 37mm Michelin Protek over the 23 mm Vittoria Corsa are looking at something other than rotating inertia.

And even among the other tires, the difference in rolling resistance - which sucks power all the time - is much larger than the power to accelerate. For example, the Continental Gatorskin took 1.4 Watts more to accelerate from 0 - 30 Km/h than the Vittoria Corsa CX. But the link above from www.BicycleRollingResistance.com shows that the Continental Gatorskin also takes 7.2 Watts more just to roll at a constant speed than the Corsa CX.

Rotational inertia is very low on the list for selecting tires.

[MaraudingWalrus]

Sure, rotational inertia is less of a matter than rolling resistance. Rolling resistance has been covered and written about and studied ad infinitum.

The question "Any charts that show what is gained and lost by lighter/heavier tires?" was explicitly asked.

I happened to have said chart. It exists. The differences are small, but completely legitimate and a real thing.



This information is largely totally ignored with wheels. It's also largely ignored with tires. It's real and it matters. Less than other things, but that doesn't make it completely insignificant.

If it didn't matter, weights for tires wouldn't be published or even measured.

This is literally the answer to the question that people didn't know they were asking when they ask what a given tire weighs.

[Mark McM]

Originally Posted by MaraudingWalrus

Sure, rotational inertia is less of a matter than rolling resistance. Rolling resistance has been covered and written about and studied ad infinitum.

The question "Any charts that show what is gained and lost by lighter/heavier tires?" was explicitly asked.

I happened to have said chart. It exists. The differences are small, but completely legitimate and a real thing.

Yes, that was the question. And the answer was about what is gained and lost by lighter/heavier tires is primarily rolling resistance. Rotational inertia is a secondary effect.

Originally Posted by MaraudingWalrus

This information is largely totally ignored with wheels. It's also largely ignored with tires. It's real and it matters. Less than other things, but that doesn't make it completely insignificant.

If it didn't matter, weights for tires wouldn't be published or even measured.

These two paragraphs are contradictory. If information is totally ignored, then why is it published? And if it matters and is published, why would it be ignored?

The reason that bicycle/component weights are published is not because people are knowledgeable about rotational inertia, but because weight is one of the easiest performance parameters for people to measure and understand. If you told most people about the CdA of a wheel or the durometer of a tire tread, they'd have no idea what you were talking about.

[MaraudingWalrus]

Originally Posted by Mark McM

Yes, that was the question. And the answer was about what is gained and lost by lighter/heavier tires is primarily rolling resistance. Rotational inertia is a secondary effect.





These two paragraphs are contradictory. If information is totally ignored, then why is it published? And if it matters and is published, why would it be ignored?

The reason that bicycle/component weights are published is not because people are knowledgeable about rotational inertia, but because weight is one of the easiest performance parameters for people to measure and understand. If you told most people about the CdA of a wheel or the durometer of a tire tread, they'd have no idea what you were talking about.

To the first point,

The amount of energy required to spin a wheel to speed is not a "secondary effect" of rotational weight. It's the primary effect. Increasing rotational weight directly increases rotational inertia.

Rolling resistance generally correlates with it, but they are wholly unrelated. Tires with more rolling resistance are generally heavier, but those two things are not linked directly. A heavier tire generally tends to not have as favorable a rubber compound for low rolling resistance, but it's rolling resistance isn't because of it being heavy.

You could theoretically have a supremely heavy tire with low rolling resistance. You could not have a supremely heavy tire with low rotational inertia.





To the second point,

perhaps this is as a result of misunderstanding of my use of pronouns rather than specific nouns. The information that is largely ignored is the effect of rotational inertia. Information about rotational inertia is not published, because largely nobody cares. The information that IS published is weights. People ask how heavy a wheel or tire is, and the reason that it actually matters is not, in this specific case, the reason they're actually asking.

Most people want a lighter bike because it's impressive to pick up a light bike. If it's lighter it has to be better, right?

In the case of a tire, yes a lighter tire is essentially always going to be faster -lighter tires are generally racier tires that are made of "nicer" rubber compounds - but that doesn't have to be the case for the wheel.

Wheelset A could be 100g heavier than wheelset B. Wheelset A has heavier hubs, lighter rims. B the opposite. But wheelset A will "feel faster" and get up to speed quicker, with less energy output, than B. Of course assuming all characteristics of the parts are identical aside from weight.

Looking at rotational inertia of a wheel allows one to look at a number that actually has some relevance. If wheel C is lighter than wheel D because it has a hub with an aluminum freehub body and holes drilled in it, that may not really actually matter in the real world.


Sure, people aren't widely knowledgeable about rotational inertia. However, when a tire's weight is published, rotational inertia is why its weight matters. Which is what I meant by saying that rotational inertia is the answer to a question people didn't know they were asking.




Again, rotational inertia is less important to performance of a tire than rolling resistance. I did not disagree with that point and perhaps wasn't clear on agreeing with it.

I also didn't intend to implicate - nor do I think that I did - that rotational inertia should be the be all and end all of absolutely any decision making process. However it's absolutely relevant to cycling in general (or really anything "cyclic") and absolutely relevant and the answer to the question of what's gained and lost by a heavier tire.

[makoti]

Originally Posted by 54ny77

heavier rolls just fine.

Mr Tull, is that you?

[benb]

I kind of have the opinion this is mostly feel and it's not really slowing you down all that much *within reason*.

We spend most of our time (on the road) at steady state, if you're actually fast by the time you're up at tempo/threshold/whatever pace the air resistance is dwarfing everything else, you can generally see this in your data if you're riding two bikes with similar PMs that you trust and/or swapping out the tires/wheels on the same bike with a PM. There is a temporary cost to accelerating the heavier setup but it's minor compared to the other costs since it only occurs when you're speeding up. And even the heavy setups are light enough they're pretty minor compared to the forces required to accelerate your body mass.

My main two points of comparison of the past 2 years are two drastically different bikes, there is a 10lb weight difference between them, but I've got a Stages on each. I was running treaded (file center/knob outside) 38c tires on the heavy bike last year and running some of the ultra fast Specialized Turbo 26c tires on the other bike. There was a pretty noticeable speed difference if I went and did say 10m at Threshold on the same stretch of road on the 2 bikes. There is a pretty big difference in rotational weight on this setup. Say maybe 2000g wheelset + 700g of tire on the heavy bike, 1500g wheelset + 450g of tire on the lighter bike.

This year I have 32c slick tires on the heavier bike.. those differences in speed are almost gone.

I can feel the "spin up" difference, and it is a lot of fun to have less rotational weight but other than a mental effect it's not making a huge difference.

Mark gave a great example above.. 1.4 watts difference in acceleration for the wheel/tire, 7 watts rolling resistance (constant), then you've got air resistance probably > 200w depending on the speed.

[Mark McM]

Originally Posted by MaraudingWalrus

I threw one wheel on my trifilar pendulum, and used the formulas described on the above mentioned wheelfanatyk blog post to calculate final results.

I used the same wheel, my ENVE Classic 45 laced with ACE3 spokes to a Paul High Flange front hub, using ENVE rim tape. I used the same tube with each different tire, and none of the tires were inflated to any pressure, they were just installed onto the rim.


I did three runs with each tire option and averaged the results.

I show results with no tire and tube (that'd be just the wheel with rim tape), a 23mm Open Corsa EVO CX, a 25mm wire bead Schwalbe Lugano, a 23mm Continental Gatorskin, and a 37mm Michelin Protek.




So, here's some background information/ comments/critiques on the "experiment" :



The end result, the watts column, is watts of energy required to spin that wheel up to 30km/hr in 10seconds. These numbers do not account for friction in any way - not bearing friction, not friction between the tire and the ground. These are just looking at overcoming inertia to spin the wheel in a theoretical situation in which all we are doing is spinning the wheel. It also doesn't really account for aerodynamic drag in any real way - given this test is done, in my case, in a garage and not a vacuum, I suppose there is some wind resistance, happening, but we're probably not achieving speeds of 30km/hr so that would obviously ramp up more at speed.

This also is obviously only the amount of energy required to spin that wheel by itself up to speed. The wheel, in the real world, is part of the whole bicycle rider system, so % variance between these wheels is lessened when taking the whole system into account, but it's worth noting the actual watts variance is not changed.





Results show that every time you go to spin that wheel up to 30km/hr in 10seconds the wheel by itself requires 3.1 watts of energy. The 23mm Corsa tire (and tube) require an additional 2.6watts of energy of the wheel by itself; the Lugano requires 3.4 watts additional; the Gatorskin requires 4 watts additional; the Protek requires an additional 10.3 watts to spin up to speed.

These are HUGE % variance between each other when just looking at the wheels by themselves. They're a considerably smaller % variance when taking into account the whole bike/rider system...but perhaps not an insignificant amount of actual watts. How many times in the course of your ride to you accelerate and decelerate? Saving two watts per wheel (so 4 watts total) every time I go to speed up is worth it to me to run Corsas over Gatorskins....and I'd wager it's something you and I can feel.


You can also check here for a spreadsheet of mine I'm updating with wheels I test to give data. It's not currently a very good spreadsheet and I haven't yet figured out a formatting that I like to show it in a way that makes clear obvious sense.



Also attached is a a photo of a Michelin Protek mounted to an Enve wheel...


in case anyone wanted to see that sacrilege

So, I took a look at the numbers you posted, and at first glance, they just don't add up.

The difference in mass between the wheel alone (797 g) and the wheel plus the Michelin Protek tire (1625 g) is 828 g = 0.828 kg, so this must be the mass of the tire. The tire is at the periphery of the wheel. We know that the effective translational inertia of mass located at the periphy of the wheel (for a wheel that is accelerated without slippling) is twice the actual mass: I(eff.) = 2 x M. Since all of the mass of the tire is inside the maximum periphery of the wheel, we know that it's effective inertia will be slightly less than twice its mass, but 2 x M is a good approximation. So the effective inertia of the tire is 2 x 0.828 kg = 1.656 kg

If the bike were accelerated from zero to 30 Km/sec (= 8.333 m/s), the energy change of the tire would be E = 1/2 I(eff) x V^2 = 1/2 x 1.656 kg x (8.333 m/s)^2 = 57.5 Joules.

If we assume that tire was accelerated with a constant power, than the accelerating power of P = E / T = 57.5 J / 10 sec. = 5.75 Watts.

But according to your data, the difference in power to accelerate the wheel alone (3.1 W) and the power to accelerate the wheel plus the tire (13.4 W) is 10.1 W. So according to your data, it takes 10.1 W to accelerate the tire alone. This is much higher than the known maximum power to accelerate the tire alone. I think there may be an error in either your measurements or your calculations.

I also question the formula in the Wheel Fanatyk web page to calculate moment of inertia - particular the use of the term 4 = gf/N: If the mass is measured in grams, there is no need to convert to or from Newtons of force.

As an aside, the paper referenced for the trifilament pendulum method of measuring moment of inertia was from an engineer at Barry Corporation. I worked for the Barry Corporation in the 1990s, and we did not use a trifilament pendulum for measuring moment of inertia. Instead we used a simpler single wire torsion pendulum. This Velonews article about measuring wheel moment of inertia also used a torsion pendulum.

[veggieburger]

Now you're just showing off.

[PepeM]

Originally Posted by benb

We spend most of our time (on the road) at steady state

Surely that depends on the terrain. Also, definitely not true in, say, a criterium.

[cmg]

you have to make easy to understand. so.... same wheels, same bike, comparing Tufo Calibra 23mm tires 145gram to Conti's gr4000 28mm 225-250gram tires. Spin up is easier on the Tufo but less rolling resistance on the Conti. So over the course of a 30miler with rolling hills, which would be faster? less effort, torque? flame on...

[benb]

Originally Posted by PepeM

Surely that depends on the terrain. Also, definitely not true in, say, a criterium.

Yes but if you look above the discussion is about values less than 10w.

Crits take place at high speed. I never even made it out of Cat 4 and I don't think I ever did a crit where the average speed was less than 22-23mph and there were always places on the course speeds went up to 30mph or more every lap.

At even 20mph little changes in position in the pack, bike fit, and which part of the bars you decide to ride on absolutely dwarf little 10w differences between inertial effects of wheel sets. I don't have a super nice SRM or anything but AFAICT you can't even see 10w variances reliably riding down the road with PMs because external factors constantly cause the #s to vary by more than that. Go by a tree that effects the wind and that is going to have an effect bigger than 10w.

We can debate it all we want but those little acceleration differences just really don't make a difference in how you do in the race. Get the fancy wheels and tires and save 10w for a few seconds each time you come out of a corner. Or move to the front and stick on the right wheel and you won't even be accelerating out of the corner at all since you'll be less affected by the pack "yo-yo" effects. Stay in the right place in the draft and you're saving 100w or more for minutes instead of seconds, etc.. Same thing if you're in a breakaway, if you can get clever and take pulls a little bit shorter than the other people, etc.. you'll advantage yourself more that way.

But no one is ever going to debate their is a great mental/placebo/motivational effect of the lighter wheels with lower rotational inertia, they feel awesome, they will probably help you put in a better effect just cause they "feel" like they have more of an effect than they do.

[Gummee]

Never underestimate 'feeling good' as it relates to 'doing well.'

I know there's a few pairs of wheels I enjoy riding more than others while racing CX (D/A c24 tubulars vs deeper section rims) because they are lighter and snappier. Makes me feel better, but I'm still old, fat, and slow.

M