Tire Pressure 101

My thought was that when the track builds rubber and gets grippier, my speed is scrubbed on exit when the hopping starts. In the rain, I’m able to corner faster than everyone because my high COG becomes advantageous.

Dry track - Entry: Good response from steering input. Apex: slight oversteer. Exit: hopping.

It’s hard to generalize the symptoms as every corner doesn’t act like this but this is my issue with high speed sweepers. I actually don’t feel like I have an issue in tight hairpins. That’s where I usually make up lost time in other parts of the track.

Anyone has the links to these articles? Would be an interesting read…
I can search the internet archive, but a start to the site / blog would be great.

Would like to know what grip means to you all. Tire grip? If so which tire. Or is grip referring to the overall “state” of the kart/

Ok I’ll take a stab at this. Grip in a kart: a force placed by the tire to act opposite inertia/momentum through friction with the surface it is contacting. i.e. in a corner, inertia/momentum wants the go kart to keep going in the same direction while the tire’s contact with the ground is counteracting those forces.

Btw I am not a physics expert so I could be using these terms totally wrong.

In terms of tires, a tire has a set amount of grip it can provide. If that amount is exceeded by the forces mentioned in my definition of grip, the kart slides. After input from others in this thread, I understand how tire pressure is important. If the temperature (Edit: largely managed by pressure) of the tire is not in the ideal range, the grip it can provide changes.

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Turns out Nick Firestone is the great grandson of Harvey, who founded the tire company. As to access to the articles, I’ve reached out to Nick to see how this might be done. At the time he charged a subscription fee. If the articles were in book form, the book would be substantial. He wrote very clearly and included color pictures to illustrate numerous points.
As I trust we all know, when a track rubbers-up and your chassis is still tuned for a clean, dry, green track, you will go slower. I do club racing and the best we ever get is a clean, dry, green track. Given that condition, I try for my best lap times when the “national” teams are at our Tucson track once a year. A day or two before their official Friday practice, I go out with the ones that are practicing early – and really scrubbing our track surface before rubber begins to build. Using Nick’s approach of having a higher psi (within the manufacturer’s operating range) and coming in hot with the same psi in all 4 tires, I had my best lap time ever driving my Rotax with MG Yellows when I came in right off the track with tire pressures at 14.7, 14.7, 14.8, and 14.7.

Hmm, interesting that you believe that too much grip (binding?) only occurs when the IR is set down. I’ve always thought that there was a case for increased rolling resistance on the OR due to the OR’s high slip angle, even though the IR is lifted.

You’re correct, you can have binding by overworking the outside tire to the point it can’t twist properly and produces more rolling resistance. I find that only really happens in pretty high-grip situations on softer tires. For the type of racing most people are doing, the track conditions won’t be so that you encounter that; usually the kart will overload the outside tire and just slip rather than bind and twist. I would say that the modern tire with a stiff sidewall is less likely to do that as well. The softer sidewall tires will probably suffer a bit more from that. I know we experienced it more on older spec MG Yellows or even Bridgestone YHCs if the track conditions were grippy and hot enough.

Pretty sure Col from K-Racer did a good video on this exact phenomenon.

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