touring wheels upgrade

[rareposter]

Cyclist magazine has a good explanation of it all:

https://www.cyclist.co.uk/in-depth/do-l ... ight-frame

[Jdsk]

Cyclist magazine has a good explanation of it all:

https://www.cyclist.co.uk/in-depth/do-l ... ight-frame

I wouldn't recommend that.

It confuses mass with weight.

And it feels as if there's a germ of truth struggling to escape from this if only it could:

Andy Ruina, professor of mechanical engineering at Cornell University, puts it quite simply: ‘The top of the wheel is going twice as fast as the bicycle is. And the opposing direction [the bottom of the wheel] doesn’t cancel out that speed.

‘Consequently it has twice as much kinetic energy so it takes twice as much force to get it going and it makes the bike slow down twice as much.’

Jonathan

[531colin]

...............

Andy Ruina, professor of mechanical engineering at Cornell University, puts it quite simply: ‘The top of the wheel is going twice as fast as the bicycle is. And the opposing direction [the bottom of the wheel] doesn’t cancel out that speed.

‘Consequently it has twice as much kinetic energy so it takes twice as much force to get it going and it makes the bike slow down twice as much.’

Jonathan

OK, lets accept that.

Thing is, that twice as much force is still an absolutely tiny amount of force.....remember my "thought experiment" where with finger and thumb you can spin a bike wheel? So with finger and thumb you are exerting enough force to overcome the friction of the bearings, the inertia of the wheel, and the air drag of the spokes (etc) ....not only that, but you are giving the wheel enough momentum so that it carries on spinning despite bearing and air drag.
I don't know about the rest of you, but I couldn't get a bike going with finger and thumb, its hard enough with 2 legs.
Then we don't just pretend that this tiny amount of force (to accelerate the wheel) is enough to notice, we further pretend that there is a real detectable difference between the tiny amounts of force to accelerate wheels of marginally different weights.
I think the whole thing is a crock, dreamed up by marketing departments to separate the gullible from their cash.

Disclaimer; I'm just a simple biologist, trying to make sense of life.
If theres anybody out there who actually understands this stuff, I'm happy to be put right, and I'm sorry if my (ab)use of the terms has upset anybody's sensibilities.

[rareposter]

I think the whole thing is a crock, dreamed up by marketing departments to separate the gullible from their cash.

Yeah but it's been repeated so many times for so many years (even way back in the 90's, people were trotting out the old "a pound off the wheels is worth two off the frame"), it's become cycling lore, handed down by generations.

Much the same as "the unique riding characteristics of steel" and "carbon breaks" and "max HR is 220-age".

It's all nonsense but it just gets perpetuated year on year, marketers jump in on it too.

Add on a bit of placebo and psychology ("I've spent £800 on these wheels, they MUST be great!") and various bits of science (of varying degrees of being actually science-y) plus related factors like aerodynamics, stiffness, the tyres that are mounted on said wheels and you can see how it all gets really confusing.

[pwa]

I think if one were able to push around a fixed wheel (i.e. no freewheel) that wasn't touching the ground, just rotating in the air, and then tried to apply braking through the pedals by resisting the cranks going round, you would find a wheel with a very heavy tyre a little harder to stop than the same wheel with a light tyre. The difference might be small, but I think you would notice it. And the difference when pedalling forward might be tiny, but you do it sixty times a minute, 3600 times an hour.

I hastily add that weight is not top of my list for wheel requirements. Freely spinning hubs, good seals, reliable spokes and adequate robustness all come above lower weight, with lightness only being looked at when those other factors are dealt with. I just avoid unnecessary weight.

Regarding cost, I think every wheel I've ever bought could have been substantially dearer if I had gone for all the dearer options on my tick sheet. I pay enough to get quality, and don't pay the extra for a fancy label and ten grams less. XT rather than XTR, Ultegra rather than Dura Ace.

[Pendodave]

If adding up wheel physics, then tubes (or not), tyres and aeroness are all part of the system, and all contribute to an improvement in speed or robustness. May also be a lot cheaper than a new wheel.

[531colin]

I think if one were able to push around a fixed wheel (i.e. no freewheel) that wasn't touching the ground, just rotating in the air, and then tried to apply braking through the pedals by resisting the cranks going round, you would find a wheel with a very heavy tyre a little harder to stop than the same wheel with a light tyre. The difference might be small, but I think you would notice it...........

The original fallacy was;
accelerating a wheel on its own from rest with your fingers, you could be able to tell the difference between a heavy and a light bike wheel
....so, in exactly the same way, you can tell the difference between heavy and light bike wheels when accelerating the rider, bike, and luggage on the road.

This is just a new fallacy, for exactly the same reason, which is that the minor differences you can expect to feel when decelerating a wheel on its own would also apply to decelerating not just the wheel, but the rider, bike, luggage

[531colin]

.......... And the difference when pedalling forward might be tiny, but you do it sixty times a minute, 3600 times an hour.

You would (theoretically) expect to feel a difference if you accelerated sixty times a minute, not if you simply maintained your speed.
(so that on an alpine climb in a race, there might be some small gain from using light wheels, not only that, but the jerkier the climbers pedalling, the more advantage there is from light wheels)

[pwa]

.......... And the difference when pedalling forward might be tiny, but you do it sixty times a minute, 3600 times an hour.

You would (theoretically) expect to feel a difference if you accelerated sixty times a minute, not if you simply maintained your speed.
(so that on an alpine climb in a race, there might be some small gain from using light wheels, not only that, but the lumpier the climbers pedalling, the more advantage there is from light wheels)

I am a "lumpy" rather than smooth climber, sadly.

[Nearholmer]

If you want wheels that are easier to accelerate/decelerate, you can reduce the mass, but it’s more productive to reduce the radius, because the rotational inertia is proportional to mass, but proportional to the square of the radius.

This may be of no help to anyone, but it is quite interesting (well, interesting-ish).

Personally, I can certainly feel the difference in inertia if I swap between heavy tubed tyres (the dreaded Marathon Plus) and light tubeless tyres on my bike, but I wouldn’t say one is better or worse than the other, just different.

As to the pulsing effect of pedalling, a setup with greater rotational inertia theoretically ought to be better, less tiring, not more tiring, because it provides greater flywheel effect, smoothing out the pulses.

[Chris Jeggo]

I did this stuff at A-level. As regards the inertia of the bicycle as a whole, adding 1kg to the circumference of a wheel is equivalent to adding 2kg to the bicycle frame. Or you could say it's equivalent to eating a 2kg meal! Or a 1kg meal plus a litre of beer.

I decline to provide proof in the form of a page of equations, but note that the Wikipedia article "Rotational energy" states "The rotational energy of a rolling cylinder varies from one half of the translational energy (if it is massive) to the same as the translational energy (if it is hollow)."

[ANTONISH]

Isn't this about touring wheels where reliability is a prime concern ?

[simonhill]

Consequent to a question about tyres (and as mentioned by me, weights) on this forum, I have dragged this one up again.

I admit my Physics is limited and tempered by the all too dangerous addition of common sense.

So......

What about 531colin's theory that there is very little difference in getting a light and a heavy wheel spinning.

To paraphrase:

Two bikes upside down. One with heavy wheel and tyre, one with both lightweight.

A flick of the finger will get both spinning with very little effort, a couple of further flicks and they are spinning at a fair speed.

The effort required in either case is minimal compared to that required to get the whole bike going (pedalling or pushing).

If it takes so little energy to get the 2 different weight.wheels up to speed when the bikes are upside down, why is weight in the wheels so important.

If this was explained I missed it and am happy to be told to go to the back of the class.

[Jdsk]

Consequent to a question about tyre weights on the touring forum, I have dragged this one up again.

I admit my Physics is limited and tempered by the all too dangerous addition of common sense.

So......

What about 531colin's theory that there is very little difference in getting a light and a heavy wheel spinning.

To paraphrase:

Two bikes upside down. One with heavy wheel and tyre, one with both lightweight.

A flick of the finger will get both spinning with very little effort, a couple of further flicks and they are spinning at a fair speed.

The effort required in either case is minimal compared to that required to get the whole bike going (pedalling or pushing).

If it takes so little energy to get the 2 different weight.wheels up to speed when the bikes are upside down, why is weight in the wheels so important.

If this was explained I missed it and am happy to be told to go to the back of the class.

I don't think that there's any disagreement about the physics... for rotational movement it's the moment that's relevant rather than the mass. For ascending in a gravity field it's the mass.

But IIUC it doesn't seem to make much difference for real HPVs in real-world conditions.

Jonathan

[simonhill]

In English please?

Is the following true?

Apart from the weight they add to the overall weight of the bike, heavier wheels and tyres make very little difference to pulling away or rolling.

Someone has written on the touring tyre thread "So pulling away at a junction, 1kg on a tyre feels like 2kg on the frame". Is that untrue,?