Inner Tubes & Rolling Resistance (Road Bikes)

[Dansky]

I have been wondering how changing to either a latex inner tube or a lighter butyl version would affect rolling resistance, as stated in a few cycling articles.

It would seem (to me) that tubes would have nothing to do with the actual contact patch that a tire is making with the road surface, but I would like to hear others' input.

Thoughts?

 

[dabac]

Rolling resistance comes mainly from the amount of material that's being kneaded by the little "wave" that forms around the contact patch, and the tube, as it's in direct contact with the tire, is indeed part of that material.
Imagine if you ran tubeless, then the only thing being forced to change shape as the bike rolls along would be the tire. With a tube, that too gets added to the equation.

 

[CAMPYBOB]

What dabac said.

The compression and friction (minimal as it may be) of the tire and tube...and the particular working combination of a specific tire and a specific tube...will yield either more or less Watts consumed/Crr at some specific speed zone.

 

[danfoz]

What these other guys said... latex inner tubes are more supple than butyl and can deform more readily. It's the same reason higher thread count tires usually run faster as well.

Dave Ryan, one of our respected forum members did some tests on rollers with an an SRM and latex vs. butyl innies. There was an approx 10-15watt savings to maintain the same speed in favor of latex. The same findings have been verified on other forums by other folks tests.

15 watts is very real "free" speed. Some riders may take a month of hard work on a training plan to realize such an improvement. A nice gain for the small price of having to inflate one's tires each day.

 

[531Aussie]

10 to 15 watts?! Hmmm, that sounds VERY high.

The Bike Tech Review guys found a difference of anywhere from 1w to about 3w (I'm not scouring through the numbers again to get the exact difference ), depending on the tyres or tubes used.

Scroll down to the "butyl vs latex" bit; but the differences in the main results list rarely exceed 2.5 Watts difference
http://www.biketechreview.com/tires_old/images/AFM_tire_testing_rev9.pdf

 

[danfoz]

Originally Posted by 531Aussie
10 to 15 watts?! Hmmm, that sounds VERY high.

The Bike Tech Review guys found a difference of anywhere from 1w to about 3w (I'm not scouring through the numbers again to get the exact difference ), depending on the tyres or tubes used.

Scroll down to the "butyl vs latex" bit; but the differences in the main results list rarely exceed 2.5 Watts difference
http://www.biketechreview.com/tires_old/images/AFM_tire_testing_rev9.pdf

http://www.cyclingforums.com/t/494099/rebuild-a-powertap-wheel-and-calibration#post_4066048

Dave notes it's just a comparison btw, not rigorous Crr testing.

One thing to note, that the rougher the road gets the more advantageous anything "supple" will be in terms of power savings i.e. tires and/or tubes. Technically I imagine a ball bearing rolling along glass would have the lowest Crr, but we know tires that don't deform easily over road chatter tend to roll like bricks.

Here's another link which looks to put the advantage somewhere in between the biketechreview data and Dave's observation: http://bikeblather.blogspot.com/



The Continental4000s is run with both latex and butyl for a difference of 8 watts - for a pair of tires. The biketech data is per wheel, so double whatever the number is to calculate what the rider is saving.

In addition, we know the biketech data is using Michelin latex, but we don't know what latex/butyl Dave was running or what tubes the blog poster above is using. There's a lot of room for error comparing the findings, and I might be carelessly throwing wild numbers around, but it's probably safe to say latex is faster than butyl.

It could probably be argued 6 or 8 watts is pretty meaningless but that's just the inner tube, and added to a faster tire (a training tire vs. a race tire, fiddling with tire pressures, etc.) it could add up to something substantial. Philippe Gilbert once said "training is a lot, maybe 50%, then the rest is all the small things, one percent here, one percent there...". I'd put the training number slightly higher myself ;P

 

[dhk2]

I've seen that biketech chart as well, and also think a savings of 6-8 watts total @ 40 kph is more likely. But of course watts lost to Crr depend on both speed and weight, so anytime we talk savings, also the weight and speed should be specified since the losses would be roughly proportional to both of these variables. EG, allowing for a 20 lb bike, a 220 lb rider going 40 kph would in theory have 4 times the power lost as a 100 lb rider @ 20 kph. And of course the tire used affects the savings.

Also, if Dave Ryan did his testing on rollers, believe that would yield a higher result because riding small rollers result in more sidewall deflection than on a flat road. That factor alone could likely account for the difference in watts saved.

But with the GP4000s, even 8 watts for a 200 lb load at 25 mph is a good savings. Since that's the tire I use, believe I need to get a pair of latex tubes and see what they are like. I don't race, but that kind of potential savings might make a difference in the Weds speed limit sign sprints.....probably should capitalize the "might" here. But as far as watts saved/dollar spent, this looks like a good investment.

 

[CAMPYBOB]

The ONLY difference I ever noticed when using latex tubes was...how often I had to pump my tires back up to pressure.

 

[531Aussie]

Hmm, I see. Thanks.

I might have to rethink things

In fact, I might get some RIGHT NOW!

 

[531Aussie]

What about the theory that latex is so supple that it's more likely to squeeze out of slightly loose-fitting tyres and pop?
True -- I read that

 

[danfoz]

Well they are pink.

And yeah they do try to sneak into every nook and cranny so definitely require a bit more care when installing. As far as feeling anything, if one can notice the difference in ride quality between a Rubino and a CX then possibly, it's the same degree of subtlety. It's one of the reasons tubbies felt nicer than clinchers, they all came with a built-in latex innie. Some asses however are just too beat up to tell the difference

 

[CAMPYBOB]

Quote by 531Aussie:
"What about the theory that latex is so supple that it's more likely to squeeze out of slightly loose-fitting tyres and pop?"

It's not what squeezes out of latex that matters...it's what you can squeeze IN it!



Yeah...THAT'S supple!

 

[531Aussie]

Ha.
True

 

[Dansky]

For some reason the term "Silicone Valley," just came to mind.

 

[oldbobcat]

Originally Posted by 531Aussie
What about the theory that latex is so supple that it's more likely to squeeze out of slightly loose-fitting tyres and pop?
True -- I read that

If the tires are that loose, it doesn't matter what the tubes are made of.