Tire Slip Angle Example
This is a video I found on You Tube showing a tire flexing as it is turned on a rolling conveyor belt. You can see the bulge and deformation on the inside bottom corner of the tire as it is steered from a straight ahead direction. This is an example of how slip angle works. You can’t see the difference in steer angle vs. the difference in tire tread angle, but the deformation is an indication of this.
I’d like to shift gears a little here and get away from tire construction and physics on how the tire works a get to a little more practical application on tire prep and maintenance. You have to watch when mounting tires. Some tire manufactures will build camber into circle track tires, so it makes sense that tires need to be mounted to be run in a certain way. If you are running Hoosier tires there is a small oval serial number code that needs to get mounted towards the infield. Another thing to mention at this time is that a dirt racing tire should not be flipped to put sharp edges forward after the tire get worn down. Tire cords will take a stretch in a certain direction and should not be turned and run in a different direction. It’s similar to a torsion bar, once it takes a set in one direction it will go dead if it gets twisted in the opposite direction.
If you are new to the sport, you will probably walk through the pit area and see people tearing away at a dirt racing tire with a big 7 inch grinder. Tires will harden up as they run or if they even just sit. Grinding a tire with a grit anywhere between sixty and one hundred and twenty grit disks. This will take the top layer off the tire and expose the softer more supple rubber underneath. I often use the analogy of the top layer being like a callous on you foot. The top layer is hard and the skin under it is soft. This is especially important when running in a spec tire class, where the tire compound is too hard for the conditions of the track. You need to continually keep the surface of the tires as soft as you can. I also like to use a tire grinder that rotates at a relatively low RPM. A grinder that rotates too fast car actually put heat into the surface of the tire and hardens it up as you are grinding it. Also I like to use one of those flat foam back up pads on the grinder and keep it flat on the tire. The goal here is not only to take off the very top surface of the tire, but keeping the tire surface flat and even, with nice sharp edges at the leading edge.
Next time maybe we will touch a little bit on grooving and sipping. Try to have fun even though racing is done for the year, Till next time.