Carbon wheels, why would you bother?

[Dusty Bin]

5. Rotational mass. I will stumble into this one with a little past experience. My previous track car was a Caterham R500, it weighted in with about half a tank of fuel at 480kgs. The difference between the magnesium wheels and light slick tyres vs. standard wheels or even mag wheels with non light tyres was immense. Bearing in mind this car was light and had a genuine power to weight of 500bhp / tonne, you could very much tell the difference.

We're not talking about cars though. And if you disagree with Newton's laws of motion, then good luck with that. Although you do seem to be talking in relation to wheel weight, rather than rotating weight.

Rotation mass does matter, the lighter the better. A lighter overall weight will make getting up hills easier, but having lighter wheels to achieve this, will also make accelerating take less power and overall any change in momentum.

Of course a lighter overall weight is better when climbing. But the specific benefits of lower rotating mass are massively over-stated, to the point where they are almost irrelevant to most riders.

A light non aero wheel out to take the same power to maintain as an identically shaped but heavier non aero wheel. But the advantages of the light wheel is the easier change in momentum, accelerating and braking. The heavy wheel will have more momentumn, so in theory will slow down lass quickly, but I don't necessarily see that as an advantage, especially if they take the same power to maintain at any given speed.

A light aero carbon wheel will take less power to change momentum i.e. accelerate, but will also take less power to maintain due to the aero advantages. Light and aero beats light and not aero. And light and non aero beats heavy and non aero.

That's my five penneth and some of it has even been scientifically proven...

If you are just going alongside flat at the same speed always, weight of wheels makes no difference, only aero will make a difference, but if you encounter any gradient or need to brake or accelerate then lighter comes into play, along with aero.

You seem to be confusing 'light wheels' with 'light rims'. The points I was making earlier related to 'light rims', in the sense that it doesn't really matter where the weight is on a wheel - or on a bike...

 

[jowwy]

Knew you wouldn't stay out this thread !

put bait on a hook, cast the line and one day you'll catch a big fish

 

[T.M.H.N.E.T]

i'm sure @Dusty Bin @Rob3rt @T.M.H.N.E.T will be along soon to disprove all of this with their superior technical knowledge and lamblast anything you say to negate their argument

Dubya tee eff? I've had nothing to do with these wheel threads. Nor do I care, until I'm buying wheels myself

 

[VamP]

Now here's an add thought; why would you bother buying carbon wheels if they are many times more expensive than aluminium and heavier?

I've been rim shopping (paging @fnar) and have been looking at these Campag wheels for a future project, they weigh 1550g and cost £229.

Whereas these Mavic carbon wheels weight 1630g and cost a whopping £2290! I guess they could have amazing bearings or something, but £2k worth of amazing bearings?

Am I missing the point?

Your linky doesn't work.

Carbon isn't necessarily more expensive. I've got some Far Sports heading my way and at £400 and 1070g they are cheap and light, and ever so slightly aero at 38mm rim width. They might even be decent, I live in hope.

Nobody will buy 1630g Mavics @ £2290. You can get 1000g ENVE for less than that.

Yes most people will do the cost/benefit thing, and some will allocate disproportionate weight to the Brand, but fundamentally most serious cyclists know the value of wheels and spend in accordance with their needs and wallet. As to the rim weight being more significant than the rest of the wheel, that's oft quoted but fundamentally debunked now. As Dusty Bin says, there is a small rotational effect, it is confined to the acceleration phase, and you won't notice it.

 

[mattobrien]

We're not talking about cars though. And if you disagree with Newton's laws of motion, then good luck with that. Although you do seem to be talking in relation to wheel weight, rather than rotating weight.

I have a feeling we are agreeing in a round about kind of way

I completely agree about rotating mass and that the further from the centre the greater the impact of the weight becomes on a change in momentumi.e. rims

In an ideal world the entire weight of wheels would be at the centre, where the affect of the weight will have as little impact as possible on the rotation of the wheel.

Fortunately I know the weight or my hubs, spokes and rims independently to each other, rather than a combined figure

 

[smokeysmoo]

I wouldn't

 

[Dusty Bin]

I have a feeling we are agreeing in a round about kind of way

I completely agree about rotating mass and that the further from the centre the greater the impact of the weight becomes on a change in momentumi.e. rims

In an ideal world the entire weight of wheels would be at the centre, where the affect of the weight will have as little impact as possible on the rotation of the wheel.

Fortunately I know the weight or my hubs, spokes and rims independently to each other, rather than a combined figure

ok, but in any situation where it is necessary to accelerate the rim - it is also inevitable that you will also accelerate the bike and the rider along with it. The point I'm making (which incidentally, is the same point that Isaac Newton made originally) is that it is the mass of the whole which is the critical factor - not the rotating mass of the rims. Any effort you put into accelerating the speed of rotation of the rims will be returned later in the form of slower (in the case of heavier rims) or faster (in the case of lighter rims) decelleration.

 

[Phil485]

They look cool!

Nuff said.

 

[VamP]

I have a feeling we are agreeing in a round about kind of way

I completely agree about rotating mass and that the further from the centre the greater the impact of the weight becomes on a change in momentumi.e. rims

In an ideal world the entire weight of wheels would be at the centre, where the affect of the weight will have as little impact as possible on the rotation of the wheel.

Fortunately I know the weight or my hubs, spokes and rims independently to each other, rather than a combined figure

You are really not agreeing about this at all. Read this, and if you still think rotational weight significantly matters afterwards, we'll talk

 

[Dusty Bin]

Love that link - and particularly the bit about 'cognitive dissonance'...

So, what do all these numbers mean? It means that when evaluating wheel performance, wheel aerodynamics are the most important, distantly followed by wheel mass. Wheel inertia effects in all cases are so small that they are arguably insignificant.

How can it be that wheel inertial forces are nearly insignificant, when the advertisements say that inertia is so important? Quite simply, inertial forces are a function of acceleration. In bike racing this peak acceleration is about .1 to .2 g’s and is generally only seen when beginning from an initial velocity of 0 (see criterium race data in Appendix D ). Furthermore, the 0.3kg/0.66lb difference in wheels, even if this mass is out at the rim, is so small compared to your body mass that the differences in wheel inertia will be unperceivable. Any difference in acceleration due to bicycle wheels that is claimed by your riding buddies is primarily due to cognitive dissonance, or the placebo effect (they paid a lot of money for the wheels so there must be some perceivable gain).

 

[mattobrien]

You are really not agreeing about this at all. Read this, and if you still think rotational weight significantly matters afterwards, we'll talk

Thanks for the link. If I read it correctly and I am very happy to be correctly of the things that can be changed / bought on the bike, aero matters most on wheels, followed by a factor of a round a tenth, by wheel weight.

Therefore aero matters the most and wheel weight matters much less. Wheel weight does matter, so if you are not able to improve other factors changing wheel weight will have a difference. I haven't mentioned significantly previously though.

I have actually bought wheels that weight roughly the same as my previous wheels, possibly a touch more, but have an aero profile. Don't get me wrong, I am not saying that wheel weight is all there is and perhaps my own actions have proven this, but there is an effect, even if much smaller than aero.

 

[GrasB]

Now here's an add thought; why would you bother buying carbon wheels if they are many times more expensive than aluminium and heavier?

I've been rim shopping (paging @fnar) and have been looking at these Campag wheels for a future project, they weigh 1550g and cost £229.

Whereas these Mavic carbon wheels weight 1630g and cost a whopping £2290! I guess they could have amazing bearings or something, but £2k worth of amazing bearings?

Am I missing the point?

By these do you mean Cosmic CXR80? If so... because the Mavic rims cut through the air much more cleanly than those Campag wheels.

 

[VamP]

Thanks for the link. If I read it correctly and I am very happy to be correctly of the things that can be changed / bought on the bike, aero matters most on wheels, followed by a factor of a round a tenth, by wheel weight.

Followed by rotational inertia by about a hundredth. Weight matters, obviously we are all quite obsessional about it, and it matters more on steeper hills, but it's nearly irrelevant whether it's at the rim or on your bum.

 

[Dusty Bin]

Therefore aero matters the most and wheel weight matters much less. Wheel weight does matter, so if you are not able to improve other factors changing wheel weight will have a difference. I haven't mentioned significantly previously though.

Nobody has ever argued that wheel weight doesn't matter. Specifically, it is rotating weight that doesn't matter.

 

[Rob3rt]

i'm sure @Dusty Bin @Rob3rt @T.M.H.N.E.T will be along soon to disprove all of this with their superior technical knowledge and lamblast anything you say to negate their argument

Go swivvel!