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Mythbusters?!

May 7, 2010

In preparation for my participation in 100 miles of nowhere in a week and change, I mounted new tires from Ritchey, WCS Race Slicks on my road bike.

Bald is Beautiful

This got me thinking about tread patterns used for for the common 23mm all-around road tire for standard 700c road wheels.  Are slicks to be used primarily for racing, and only in dry conditions because they are unsafe?

My mind pictures bald automobile tires, and hydroplaning.  If road conditions are wet, should I have a pair of tires with tread designed for that condition?  I know from first-hand experience that tread and tread patterns make a huge impact in different conditions off-road.  But how about on-road?  Surely if I were a cyclist worth his salt, I would know the answer.  Sadly, I am not.

Bike guru, Sheldon Brown (who has since passed) has a great no-nonsense website about all things cycling.  He has an illuminating article about bicycle tires and hydroplaning that I used in researching this post.

Hydroplaning

Hydroplaning occurs when a layer of water becomes trapped between the tire and the road surface, causing loss of traction.

In a car, since four tires are in contact with the road, a square contact patch is best to maximize rubber to the road.  With a flat straight leading edge of tire to water, the tire is more likely to trap water underneath.  Automobile tires are also very wide, are run at lower pressures and much higher speeds than bicycle tires which traps water and affords less time for the trapped water to escape.  This is a real problem with airplanes landing on wet runways, so the airline industry has studied this extensively and has come up with a formula to determine when hydroplaning risk is greatest.  Crunching a few numbers with that formula, even at 120 p.s.i., similar to bicycle tires, a square-profile airplane tire would have to be traveling at 113mph before hydroplaning becomes a big risk.

What About Bicycle Tires?

Since bicycle tires are rounded in order to lean into corners, they push water away from the center much more effectively.  Also, rider weight is distributed on a relatively small contact patch, making the forces required to hydroplane on a bicycle tire impossibly high to cause hydroplaning.  If you look at the fine tread that is present on most bicycle tires, the irregularity of the road surface is much larger than that fine tread pattern.  The rubber will deform according to the texture of the road whether slick or textured.  So if it is impossible to hydroplane on a slick bicycle tire, why are they even manufactured with tread?

Not Necessary.

Because an uneducated public (previously me) will not buy them for fear of loss of traction.  Other manufacturers use different color rubber compounds to give the appearance of “tread” on a slick tire.  Myth busted!  Of course this just applies to road tires.  Once we venture on to the dirt (or mud), tread matters.

So now I have extra confidence in my slicks, as well as the bright folks at Ritchey that manufacture them despite us doofus public.  [“Race slicks” also sounds very dragstrip and top-fuel.  Competitors will shrink at the prospect of your raw, unadulterated POWER.]

Burnout, Baby!

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