Of all the promises of free speed in triathlon, one of the easiest ways to get faster in your races is in your choice of bicycle tires. True. Engineers in the laboratory have proven that some tires are indeed faster than others.
How do they know this? Real experiments using real bikes and real tires.
A while back, I was looking into a category of triathlon-related ideas that I was calling Stuff We Know for Sure That Really Works (SWKFSTRW for short) and at that time, caffeine was one of those things.
While sipping through the caffeine literature, I saw a throw-away line from an interview with Chris Leito about the known fastest bike tires. In this era of hyperlinks, I dutifully went down the rabbit hole and looked in, deeply.
It turns out that there really are faster tires and slower tires, and the difference is one that you will notice.
Actual laboratory tests by actual laboratory people have proven that the rolling resistance of tires varies greatly and very greatly impacts your effort—and thereby speed—on the bike.
How much? In precise, engineering, laboratory terms—a lot.
The Math Proves It
Consider one test sample from a most excellent posting on Bike Tech Review http://www.biketechreview.com/tires_old/images/AFM_tire_testing_rev9.pdf, in which Al Morrison used rollers to determine the Coefficient of Rolling Resistance (CRR, if you want to speak Laboratory). The lowest CRR tires, Vittorio Pisto Evo CS Tubular (the name has more CRR than the tire) cost the rider 10.8 watts per wheel in rolling resistance. That is, it takes you 10.8 watts of pedaling power just to overcome the tire’s rolling resistance. Bueno.
In this same sample, in 134th place (yup, he tested 134 tires) the highest CRR (greatest resistance) tire, whose name I won’t mention, takes 24 watts per tire to overcome rolling resistance.
Now, for the math: 10.8 watts per wheel, that means I have to multiply by two because bikes have two wheels (two-wheelers, that is), so rolling resistance of the Vittorio Etcetera Etcetera tire for one bike with two wheels is 21.6 watts.
The tire Whose Name I Won’t Mention takes 24 watts per tire, times two = 48 watts per one bicycle.
That’s 26.4 watts more than two low-CRR tires.
So, what’s 26.4 watts to you, the triathlete?
If your threshold power is 200 watts, 26.4 watts is 13.2%. Wait, can’t be true. Lemme check the math.
No, it’s true: 13.2%.
How does that translate into free speed, which the first sentence of this article promised? Ah, back to the math.
Speed on the bike depends on a few factors in addition to CRR:
· Weight of the bicycle and rider
· Road surface.
There is a precise mathematical formula that describes all this elegantly:
Pounds of Pizza X all my Missed Workouts X being Too Cheap to buy anything with Carbon in it = Maybe I can make it up in Fast Tires if I can get them on Sale.
Let’s take these factors in turn.
Weight of the bike and rider—I think this goes into the category of Stuff We Know for Sure That Really Works. A lightweight bike is faster than a 44-pound Schwinn Varsity lead sled. And the triathlete who drops a couple of pounds without sacrificing power is going to be one happy triathlete.
Aerodynamics—Some say that, riding at 20 miles per hour, you spend about 90% of your power fighting the wind. The next time you are riding on CO Highway 93 or US 36 on a breezy day, the crosswinds that toss you around like you are in a cage fight will remind you in an unforgettable way. All things being equal (that is, not compromising your ability to create power, not to say being able to run off the bike), more aero is better.
Road surface—The polished aluminum of laboratory rollers is smoother than real roads, even our wonderful Front Range highways (what evil genius invented chip seal, anyway?). While you, the triathlete, can do something about the combined weight of you and your bike, and about how aero you can go before you feel like you are folded into a small suitcase, the race course is the race course and you ride on the surface that the race director tells you to. “Aha!” you engineers out there say, “But you have to account for road roughness in your CRR comparison tests!” Okay, fine. Uncle.
In this other great posting, again using rollers (the same kind I ride on—I wonder how often he falls off while watching episodes of The West Wing), Tom Ahnhalt actually does adjust the data to account for real road conditions. Check it out. http://bikeblather.blogspot.com/2013/02/tire-crr-testing-on-rollers-chartand.html
All that remains which you can easily impact is CRR, which means selecting fast tires to get the free speed. The trick here is to inflate your tires properly for the road surface. More is not better. Anything higher than 120 psi (less if you weigh less than 130 pounds) just gets transferred as up and down motion and slows you down.
And back to tire-versus-tire comparison, tubulars and clinchers are all mixed up in the ratings, so tubulars are not inherently better in the CRR category.
Tubes Matter, Too
These same laboratory tests prove that latex tubes make the tire faster. Regular, standard, bike shop tubes are butyl, not latex. Latex tubes cost more, and latex tubes with extra-long valves (such as 80 mm for your 303s or other deep dish race wheels) probably will only be available on line.
For once, you don’t have to sacrifice money for speed. You can find many of the fast tires at prices similar to Tires We Won’t Mention. That’s just purchase price. The tradeoff comes…now.
Many of these fast tires do not last very long. That makes them expensive, over time. Alas, they are supple, and that suppleness comes from being a bit thin. In addition to having a short lifespan, they may also be a bit prone to punctures. So, there you have it. You can shave lots of minutes off your bike leg with fast tires, but if you flat during the race, your advantage just evaporated like spilled vulcanizing fluid. Maybe better to just shave your leg? That’s up to you.
But you might think about throwing down your credit card for a pair of fast tires and latex tubes and keep them in a safe until race day. Thirteen point two percent. That’s (almost) free speed.
The hunt for Stuff We Know for Sure That Really Works continues. Send in your ideas for SWKFSTRW and we’ll expand the list.