CHAPTER 19 ■ WHEELSSlick tires provide maximum contact in dry, flat conditions. For this reason, professional racecars use
slicks. But, under wet, gritty, or uneven conditions, slicks tend to lift up and lose traction. That’s why most
professional races are immediately halted (or delayed for tire changes) upon rain.
Grooved tires are similar to slicks, but with strips and patterns cut out of the tread. They provide decent
traction on flat surfaces. On gritty or wet surfaces, the grooves direct particles away from the contact points
and the grooves allow the tire to flex a little more. Because of this balanced performance in wet and dry
weather, grooved or pattern-treaded tires appear on almost all street automobiles.
Knobby tires have aggressive bumps throughout. They’re fantastic in uneven or loose soil conditions.
Because household terrain isn’t designed for lunchbox robots, knobby tires provide surprisingly good
performance throughout the home. However, the bumpy tread leads to noisy, side-to-side walking behavior
on flat surfaces. Knobby tires wouldn’t be appropriate for precise, calculated movements or for pushing
contests on flat surfaces.
Tire Diameter
Believe it or not, the diameter (think “height”—see Figure 19-6) of the tire is probably the most important
characteristic of a robot’s tires. The obvious effect is on how tall the robot will be. But, there is a much more
significant effect.
The diameter of a tire radically affects torque and speed. The larger the diameter of the tire, the greater
the resulting speed. The smaller the diameter, the greater the twisting (pushing, pulling) force.
If your robot is going too fast, switch to smaller diameter tires. If your robot is unable to move due to a
large mass or lack of motor power, again, switch to smaller diameter tires. Conversely, if your robot is going
too slowly or tends to spin its wheels when starting to move, switch to larger diameter tires.
Figure 19-6. A variety of tire diameters