Tread on Tires and Bicycling
From: Christopher Wallace
Subject: CCM Tire tread
Date: June 22, 2005 11:55:35 AM PDT
To: CHI-CRIT-MASS@UIC.EDU
Part 1
Tread is not understood well, Here are some basics: the more tread you have the less you will stick to the stone that pavement is made of. If you are on soft soil, tread will dig in to the mud or soft dirt and offer less slippage. Tread is a combination of rubber columns, walls, peaks, towers, and AIR spaces between them. The air spaces between tread offer less rubber to touch the stone pavement. Now for some reason intelligent people believe that you can dig into stone with rubber ( this amazes me, Rubber is softer than Stone, It will NOT dig into it!) With this idea that tread cuts into stone, they then think they will get more adhesion on pavement with less rubber (Remember the air gaps between tread) touching the stone the road is made of. Tread does offer some benefits as I describe in part two, but tread does not help you stick to stone pavement.
Racing tires for NASCAR, INDY, CART, NHRA drag racing,AMA motorcycle racing, go-carts, and rock climber shoes, all use tread less rubber. Tread less rubber places the most amount of rubber on the stone surfaces and sticks to the stone much better than any tread will. The rubber compounds are designed to deform slightly to the shape of the rock and grasp as much stone surface as possible. This is why they stick so well.
Tread knob towers, or walls, or peaks, can all bend over when a load is applied to them, this is bad for adhesion. Start with the idea of a knobby tread tower. It strikes the ground with the front edge of the tower then as you roll forward the whole top is in contact with the pavement. Continue rolling and the tower lifts off the pavement rear edge first. When we accelerate the towers get bent over and the back edge is the only part touching pavement. Think about this: instead of the whole top of the tower touching the stone surface, now just a little edge is touching. There is almost no rubber touching the pavement at all. Now place side loads of turning into a knob and you will see you have very little rubber from the knobby touching the ground, PLUS there is a lot of air around and between each knob. When I get in to a hard turn on a knobby, I can hear the tire slipping on the surface as it makes a louder noise than when I am rolling in a straight line.
RAIN: A car will start to hydroplane in deep water at 45 miles per hour. Do I really have to go much farther with this explanation on why it is hard to hydroplane on a bike? Who here goes 45 mph on their bike in the DRY much less the rain?
When slick tires first came out there was an add in Cycling Magazine where a person in full motorcycle protective crash leathers and a full face helmet was leaned over 45 degrees on pavement while running through a puddle. The tire company was trying to show the tire would stick on wet pavement. I thought it was a hoot that the rider was still afraid of the photo shoot test that they wore leathers.
During rain any petroleum based and steel surface will become slick to rubber. Paint is made of oil and will be slick, oil on stone will become slicker, polished steel lids on streets will become slicker. Sorry no tire will stick to any of that.
Snow is cool, a thin slick tire will cut and push though snow and get to rock pavement, stick nicely. Only steel studded tires will stick to ice, but they suck on stone pavement.
Wet Grass is where tread is soooooo cool. Now how often are you carving up the park grass on your knobbies in the morning dew or after a rain, or during a cycle cross race? If you are off road in soft soil GET some knobbies. If you want to stick to stone pavement the tread will not help.
Part 2
Tread is cool. A slick tire will stick to little flakes of glass and pound them into the rubber. Most do not cause flats, they just cut up the rubber and are annoying. Some will cause flats. Tread on the other hand will bend over in a turn and allow glass to be scrubbed out as the tread slides across the pavement and some glass will pop out. The air spaces between knobs are impossible for little glass flakes to stick to. Now we all get flats from bigger glass pieces, wire, screws, thumbtacks, and thorns. Bigger objects will defeat tread benefits.
Source: Chicago Critical Mass Mailing List
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