Technical FAQ: Significance of rolling resistance, tire patching

Have a question for Lennard? Please email him at veloqna@comcast.net to be included in Technical FAQ.

Dear Lennard,
While I absolutely agree that Heine has way more variables than you do for tire rolling resistance testing, for most riders, I find your analysis to be something akin to the medieval debate about how many angels can dance on the head of a pin.

You used the example of fingernail polish. For the vast majority of riders, that delta won’t matter.

Heine has shown statistically significant results when he examines supple casings. Those translate into speed differences for real riders.

Your analysis was undoubtedly significant to Paris-Roubaix. I would like you to translate them to a 55-year-old age grouper riding on a “typical” road surface.

FWIW — I am not 55, but — as a physicist, I do appreciate the geeky tech details.
— DeVon

Dear DeVon,
Your point is well taken in the sense that for the 55-year-old age-grouper, a watt here or there in rolling resistance is not going to make much difference. However, in the gravel-tire test we just did, the difference between the slowest and fastest tires was 17 watts, or 34 watts for the front and rear tires combined. Putting out 34 more watts than other riders certainly can make the difference between being dropped, or not, for 55-year-old age groupers.

Keep in mind that all of the tires in our tests were high-quality, supple, relatively pricey tires. Stiff, inexpensive, heavy tires, like OE spec tires on less expensive gravel bikes, would suck up considerably more of the rider’s power yet. And some riders are so concerned about flats that they use super-thick, “thorn-proof” or “thorn-resistant” inner tubes or even tire liners like Mr. Tuffys, which would add lots of watts of power drain to any tire they were used with.

If the 55-year-old age-grouper were going to compete in gravel races, which I certainly would have been doing at 55 if my heart had not given me a big wake-up call at that age, I would argue that just a few watts could make a significant difference. Just staying up near the top of the results and not coming near the slowest tires in the test, the Challenge Strada Bianca Pro TLR 36 tire in our test would require 6 watts less to roll at 35kph than a Challenge Gravel Grinder Pro TLR 36 or a Schwalbe G-One R Evo Super Race TLE 40, 7 watts less than a Panaracer Gravel King SS 38 TLC, and 8 watts less than a Specialized Tracer Pro TLR 42, a Schwalbe G-One Speed Evo Super Ground TLE 38, a Specialized Pathfinder Pro TLR 42, or a WTB Byway TCS 34. Double those for the two tires and stretch it out over 100 or 200 miles of gravel racing, and the extra energy required from the rider becomes quite significant.

Consider that the winner does a 200-mile gravel race in around 10 hours, and the last finisher does it in about 20 hours (plenty of 55-year-old age-groupers finish in this kind of time). The riders average 20mph and 10mph, respectively, to accomplish this. At those speeds, their tires won’t absorb as much energy as they did at the 35kph (21.75 mph) used in our test, though the winner’s tires will be close. Estimating that the 20-hour finisher’s tires have half the rolling resistance that they would have at 21.75mph would be conservative, since one can be fairly certain that a lot of time for these riders will be spent stopped at feed zones and with mechanical problems, and their average moving speed would be well over 10mph. So, if, say, that 8-watts-per-tire difference between four tires and the winning tire was cut in half to 4 watts for the lower speed, then the two tires together absorb 8 watts more. Over 20 hours (1,200 minutes), that’s 160 watt-hours (Wh) of energy, around the capacity of a small e-bike battery.

Using bikecalculator.com, an 80kg (176-pound) rider will go 200 miles into a 10kph (6mph) headwind on a 2 percent grade in 20 hours by averaging 160 watts of power output. This is not an unreasonable estimate of power output for a rider of this weight over 200 miles of gravel riding, and 8 watts would constitute 5 percent of it. I don’t think anyone would intentionally give up 5 percent of their power for 20 hours. Again using bikecalculator.com, increasing power output in the above example by 8 watts would chop 40 minutes off of the finishing time. I’m guessing that many 55-year-old age-groupers would gladly switch tires to take 40 minutes off of their race time.
― Lennard

Dear Lennard,
Thanks for the well-reasoned answer about tire testing methodology. “And for a bit more comfort and almost the same speed, I’d go with 32mm.” For what it’s worth, Alex Moulton did a lot of research on rolling resistance for his small-wheel suspended bikes, including low-speed instrumented testing (inside an aircraft hangar with no wind) and detailed collaboration with Dunlop. The size he chose for the AM series, where one tire had to satisfy a variety of customers? 32-369mm!
— Doug

Dear Lennard,
I recently purchased an inner tube patch kit and proceeded to patch three tubes. They all held air at first, but left overnight, all three deflated.
I would like to purchase a kit that works! Can you offer any advice on this subject?
— Charlie

Dear Charlie,
I’ve always had good luck with Rema TipTop patches and adhesive. Let the glue dry until it’s no longer wet—only tacky—before applying the patch. Don’t peel the clear plastic backing off the patch after applying the patch. Nobody cares what it looks like when it’s inside of the tire, and peeling that plastic layer off can peel up the edges of your patch.

I think your problem might have come in when testing your patches, not when patching them. I don’t recommend inflating patched inner tubes unmounted to test your patch; only inflate the tube when it is inside of a tire, else the air pressure can push the patch up off the tube. So, after patching an inner tube, mount it into a tire on a rim and inflate it. Then the high air pressure will tend to adhere to the patch better rather than trying to lift it off. I realize that it’s more work, and there is a risk that you’ll have to remove it again if you didn’t find and patch all the holes in the tube.
― Lennard

Dear Lennard,
Regarding bead breaking, all tubeless tires have very tight beads that can require a bead breaker to pry them loose. This is very common in motorcycle and car tires and isn’t a matter of sealant, but simply that for tubeless tires to work, regardless of the application, they need to have a bead that doesn’t stretch and that is very tight against the rim.

I’d expect to see the bicycle tool companies coming out with more bead-breaking tools soon.
— Rob

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.