How much time does extra weight cost on Alpe d’Huez?

1.8kg loss saves about 2% time on a long climb like Alpe d'Huez (assuming that the wind was constant) – 1:54 on a 50ish min climb

bike presumably was 6.8kg (UCI minimum)
rider – very rough guess but based on him being a good Tour De L'Avenir rider was probably in the region of 70-75kg
kit say 2.5kg for shoes, helmet, shorts, jersey)
full water bottle .75kg

So that's around 75+6.8+2.5+.75 = 85kg total weight

so the 1.8kg in question is 2.11% which you'll notice is very close to the difference in time which is what I've always reckoned.

Of course if you're riding on a course that requires a lot of acceleration and deceleration, that may be different (since you're constantly burning off energy as heat from braking and then having to put it back in.

friction works the same – I've seen stuff saying you could 'gain' a few hundred metres over a 10mile TT (for the same expended power) just by switching to a ceramic BB.

Edited, so future generations can't see my mong-ness.

I rode my steel HT in an Enduro yesterday, along with heavier components (but same tyres/wheels), its about 3lbs heavier than my Ti version.

Certainly felt harder work, especially the last lap 'pushing'…

eh? That makes no sense Njee!

If you fitted a BB that was almost impossible to turn, rode up Alpe D'Huez and then fitted a silky smooth, free spinning one and rode up again at the same power output, which climb would be faster?

I think the theory (and practice) is that if you expend 300watts for 30 minutes then, with the ceramic BB (or other bearings), you would travel x hundred metres further in that time due to lower friction losses in the drivetrain. or something.

Oh yeah, what am I on about, wwaswas makes sense, less power expended overcoming friction.

friction works the same

have you seen the SRAM TT rear mechs with 13 & 15T jockey wheels to reduce the friction?

i thought it has been excepted for a while that, 1kg reduction in weight is equal to 1 min over a 30 min climb, as a basic measurement – which is roughly what this experiment shows.

This report has been posted before several times. Makes interesting reading but:

1. Water in the tires is not goin gto be the same as a fixed weight.
2. That rider is going to be pedaling much better (i.e. more evenly) than the average rider and so will lose less energy to this.

njee20 – Member
Surely the thing with ceramic BBs is that your power output is higher, same with jockey wheels. Only ceramic wheel bearings would allow you to go faster for the same power output.

Depends how you look at it – rider power output is the same.

So… how much does 1.8kg of weight loss affect the average unfit forty-something MTBer on his 2hr trail-centre blast?

😉

1. Normal bike + 1.8L extra water in tyres(!)

Surely the system is much more complicated than merely assuming you're increasing rolling weight by 1.8kg? 'cos the water is naturally going to rest at the bottom of the tyres, and you'll have friction and whatnot causing it to flow.

Seems like a poor test, lead weights would have demonstrated better.

friction works the same – I've seen stuff saying you could 'gain' a few hundred metres over a 10mile TT (for the same expended power) just by switching to a ceramic BB.

Friction and gravity (for the purposes of a climb) are linear forces, this is why at greater speeds it's all about aerodynamics, as a small improvement can result in a better return for the same improvement.

Only doing the test once for each scenario comes no where near the criteria for a valid scientific experiement.

Aye, double your speed and (approx.) quadruple your aerodynamic drag.

On the flat there is some certain velocity at which your aerodynamic drag is equal to the sum of all other frictional forces (i.e. mechanical) acting to slow you down, I think it's about 12-14mph. The faster you are, the more you have to worry about your aerodynamic drag.

Not too much of a problem for me.

Downhill racign seems insane on this issue.

There's Steve Peat only runnign 3 Ti rotor bolts at each end to save weight and make himself faster yet he has to (on pain of disqualification) wear clothing that is loose and adds more air resistance than could possibly be saved by losing three small bolts.

Rough estimate: volume of tyre = .23 ^ 2 * pi * 6.22 * pi = 3.24 litres, so each tyre was 30% full.

Not the same as fixed weight at all.

Friction and gravity (for the purposes of a climb) are linear forces, this is why at greater speeds it's all about aerodynamics, as a small improvement can result in a better return for the same improvement.

i'm not sure if i understand what you said.

by this do you mean that the wind resistance is higher than the friction resistance, so a 5% improvement in aerodynamics while give a bigger gain than a 5% reduction in friction?

or that its harder to reduce the friction?

There was a thing on Bike Radar about the benefit of using a TT bike/aero helmet vs a normal road set up, admittedly they used a very handy rider, doped Aussie TT champ IIRC, but it was quite a big variation.