Rolling resistance?

[dastott]

Hi guys. Please forgive me if this is a stupid question but I was wondering about rolling resistance and different gradients, speeds and road surfaces. Recently started running the fastest ‘durable’ clinchers (Michelin Power Competition) with latex tubes, 23mm on front and 25mm on back. Do rolling resistance gains or losses vary with different gradients, speeds and road surfaces? Cheers

[pdlpsher1]

It should be linearly proportional to speed. Weight will increase RR, as does a rough road surface. But for the same weight and road surface it’s the speed that determines the amount of RR. The gradient will have no effect.


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[alcatraz]

It varies with speed, weight, tire, tube, tire pressure and road surface.

If you're climbing you're transferring the rr from the front to the rear and vice versa.

Good choice of tires I think (apart from the sidewall puncture protection). One thing that I find interesting is that the tubed tires on bicyclerollingresistance are tested with a heavy 100gr butyl tube and the results are with the tube's rr included. If you normalize the tube tire numbers and reduce them by 1-1.5w which you can do by putting in a thin latex tube, you'd get a different order of "best tires".

(This is me thinking about it, not reading papers on the subject.)

[dastott]

Interesting, thanks. So, another tyre (GP4000S or Schwalbe One V-Guard, for example) might be faster than the Michelin with latex tubes? They have marginally higher RR with the heavy tubes.

[mrlobber]

From personal experience, Michelin Power Competition can't be called durable by any standards, I did have 3 tires, all got dooming sidewall cuts within first 500 kms. Michelin Power Endurance (subjectively) has very close rolling resistance to Competition (both with latex tubes), but you can expect at least 10k of mileage out of them.

[dastott]

Thanks for the input. Actually just had my first sidewall cut on the Michelin Power Competition the other day. Have done almost 5000kms on that rear tyre though, so not too bad. Will look into the Michelin Power Endurance.

Behind my question is a choice I am wrestling with. I have a local hillclimb race coming up and I am wondering about wheel choice, option 1 or 2:

1. 1000g carbon tubs with 22m Conti Sprinters
2. 1400g alloy clinchers with 23mm front and 25mm rear Michelin Power Competition with Vredstein latex tubes.

Both are shallow box section. Would normally run the tubs but getting punctures is not unheard of on this forested climb (never happened to me though), and it’s a bit messy with autumn debris at present.

FWIW, the climb is 9km at 7.7%, mostly steady gradient but twisty with a reasonable road surface (a bit rough in places). I will be trying to win the race, hence the question…

[Marin]

the climb is 9km at 7.7%,

500g extra will cost you about 10s on that climb.

Try this, it gives quite realistic results: http://kreuzotter.de/deutsch/speed.htm

However, you'll probably be riding at a speed where aerodynamics already make a huge difference - riding upright instead of in the drops will cost you almost a minute!

[dastott]

Thanks! So wear the aero helmet and not the lighter climbing helmet. I will be in the drops and on the hoods mostly. Because it is in dense forest I imagine the wind effect would be somewhat less?

[alcatraz]

Interesting course. Depends on your avg speed.

If you expect to avg 35km/h then maybe aero will trump weight.

If you expect 25km/h then probably weight will trump aero.

At what speed do these curves intersect you ask? Better use some form of caculator like the previous poster suggested.

38mm carbon tubs with corsa speed tires would probably be quite sweet in a situation like this.

[bikebreak]

Thanks for the input. Actually just had my first sidewall cut on the Michelin Power Competition the other day. Have done almost 5000kms on that rear tyre though, so not too bad. Will look into the Michelin Power Endurance.

Behind my question is a choice I am wrestling with. I have a local hillclimb race coming up and I am wondering about wheel choice, option 1 or 2:

1. 1000g carbon tubs with 22m Conti Sprinters
...…

Conti Sprinters for uphill race?? in my experience those are close to 300g
try vittoria corsa speed or veloflex record, either under 200g

I use corsa speed on front wheels with caffelatex sealant. If the road debris flats it despite the sealant it would have flatted the clincher too
If you use the tubular tape you can swap out a tire just as fast as swapping a tube. maybe faster.
it's a little heavier than glue

[Marin]

Tubular tape also increases rolling resistance.

Regarding rr vs. aero, my calculation above used a speed of 18kph, and even there aero is a huge factor.

[bm0p700f]

Mathematicaly speaking gradient reduces rolling resistance but the effect is small.

Power to overcomeRolling resistance = Crr*m*g*cos(theta)*v

Theta is the angle to the horizontal.

[Alumen]

the climb is 9km at 7.7%,

500g extra will cost you about 10s on that climb.

Try this, it gives quite realistic results: http://kreuzotter.de/deutsch/speed.htm

However, you'll probably be riding at a speed where aerodynamics already make a huge difference - riding upright instead of in the drops will cost you almost a minute!

That says it all... I don't want to be the wise guy, but for that 10s I would spend more time on my fitness.

Other then that, I would go for lightweight / low RR all the time, aerodynamics in climbs is not for us mortals.