Rotational weight gains/losses

venster

What difference would it make shaving off 100g from each wheel on my bike for alpine climbs

Reason I ask is that I'm running beaded Gatorskins that are supposedly about 300g each - like the idea of superior p******* protection.

But am off to the the gentle slopes of the Alps in August and wondered if it would make much difference if you're grinding up going 6mph... and would rolling resistance come into it if you're not going fast ( ie 23 v 25)....

ugo.santalucia

Not much difference, little more than their weight difference, I would say... contrary to most people belief it's not up the slopes of the Galibier that light wheels and tyres offer the best performance, but on mixed terrain where there is constant need for acceleration

turnerjohn

venster wrote:

What difference would it make shaving off 100g from each wheel on my bike for alpine climbs

Reason I ask is that I'm running beaded Gatorskins that are supposedly about 300g each - like the idea of superior p******* protection.

But am off to the the gentle slopes of the Alps in August and wondered if it would make much difference if you're grinding up going 6mph... and would rolling resistance come into it if you're not going fast ( ie 23 v 25)....

If your worried bought flatting get a set of Conti 4 Seasons...fair bit lighter....or set of GP4000S or PRO3-4s...your notice the difference and appriciate it on the longer climbs

trtimothy

I'd be more worried about the fact gatorskin tires have dreadful grip for the descents than their weight going uphill. Swap to something better like gp4000s or pro3-4s.

You're unlikely to puncture in the alps, the roads are far better than the UK in my experience, just remember don't hold your brakes on on the descents as you'll heat up your rims and blow your tires. Don't brake on the straight bits or on-off (sort of like ABS).

jibberjim

Whilst the weight will make no difference.

Good tyres will make a noticeable difference.

venster

Oh right, seems more pros than cons for changing them. As I thought - although for different reasons !

I only bought the gatorskins because I went through a spate of punctures and was getting hacked off fixing them in the rain.

What about 23mm v 25mm going uphill..? Negligible again ?

trtimothy

I'd go with 23mm, 25 is overkill and in my opinion 'feels' slow, doubt it makes much difference though. Reckon 23s corner better as well.
On a side note If u want good training tires for uk I'd recommend the specialized roubaix tires though. 23mm tread 25mm casing. Seem really hard to puncture and roll/grip well. Certainly better than Gatorskins.

cougie

I think 25s corner better - they're a rounder profile ?

I'd go for Conti GP4000S = great tyre.

wallace_and_gromit

ugo.santalucia wrote:

Not much difference, little more than their weight difference, I would say... contrary to most people belief it's not up the slopes of the Galibier that light wheels and tyres offer the best performance, but on mixed terrain where there is constant need for acceleration

I find this surprising (though I am frequently both wrong and surprised), as in my experience, when cycling up an alpine gradient, if I stop pedalling, I stop moving very quickly indeed. By deduction, I conclude that I am accelerating throughout each pedal stroke. Thus, I would have thought that reduced rotational weight would be a greater saving uphill than simply the reduction in weight.

I certainly go faster on my new tyres and wheels than on the old set, but most of my routes have a lot of junctions and undulations, where genuine acceleration is frequently required, so the time savings may come from these. I've not really been timing my climbs this year, as I've been working on not chasing arbitrary targets, so don't have "before" and "after" data for any climbs.

As an aside, the GP4000s tyres are the canine's cojones. I can't recommend them highly enough.

Remarkable

Wallace and Gromit wrote:

I find this surprising (though I am frequently both wrong and surprised), as in my experience, when cycling up an alpine gradient, if I stop pedalling, I stop moving very quickly indeed. By deduction, I conclude that I am accelerating throughout each pedal stroke. Thus, I would have thought that reduced rotational weight would be a greater saving uphill than simply the reduction in weight.

I certainly go faster on my new tyres and wheels than on the old set, but most of my routes have a lot of junctions and undulations, where genuine acceleration is frequently required, so the time savings may come from these. I've not really been timing my climbs this year, as I've been working on not chasing arbitrary targets, so don't have "before" and "after" data for any climbs.

As an aside, the GP4000s tyres are the canine's cojones. I can't recommend them highly enough.

Try typing in your old wheels weight and new wheels weight into this website:

http://www.analyticcycling.com/WheelsClimb_Page.html

The difference is marginal really on a long climb. As you say though, when accelerating out of junctions and on undulating roads the lighter wheels will make a greater difference.

Bar Shaker

Wallace and Gromit wrote:

I find this surprising (though I am frequently both wrong and surprised), as in my experience, when cycling up an alpine gradient, if I stop pedalling, I stop moving very quickly indeed. By deduction, I conclude that I am accelerating throughout each pedal stroke. Thus, I would have thought that reduced rotational weight would be a greater saving uphill than simply the reduction in weight.

I certainly go faster on my new tyres and wheels than on the old set, but most of my routes have a lot of junctions and undulations, where genuine acceleration is frequently required, so the time savings may come from these. I've not really been timing my climbs this year, as I've been working on not chasing arbitrary targets, so don't have "before" and "after" data for any climbs.

As an aside, the GP4000s tyres are the canine's cojones. I can't recommend them highly enough.

Your understanding is spot on, you are accelerating the wheel speed with every pedal push up a hill and rotational mass will play a part, as will wheel stiffness. The lighter the flywheel, the easier it will spin up with every pedal push. This is why the pros ditch their deep section rims and opt for light, stiff wheels for the climbs. My Elites made a big difference to my climbing.

Another vote for GP4000s. No punctures in two years and many thousands of miles, plus excellent grip.

styxd

Make sure you get some light weight inner tubes aswell.

bompington

Bar Shaker wrote:

The lighter the flywheel, the easier it will spin up with every pedal push.

Yes, but it then has less momentum than a heavier flywheel, so the energy in it gets you less far up the hill.

If you think of it from a pure physics point of view (which means assume for a moment that the system is 100% efficient, i.e. no friction etc):

- suppose you and your bike weigh 100kg altogether (OK all you weight-weenie climbing snakes, this is for the sake of a round number*)
- if you put in 400W for 10 seconds, you have put in 4000 joules of energy, and you can calculate that in a perfectly efficient system, that gets you 4m of height gain. It makes no difference where you distribute your weight, if you put in that energy it has to go somewhere.
- now you do have factors like rolling resistance, hub internal resistance and air resistance in the real world: I suppose these could differ slightly if you are pedalling in a jerky, speed-up-slow-down style, but by how much? I doubt it's significant.

Pros, I assume, use lighter wheels because the bike's lighter overall, or perhaps for the placebo effect of believing that rotational weight is important.



*Me and my pig-iron steed together weigh almost exactly this :oops: