DavidM

I was just looking for tyre info on the web and found this from one of the sites. What grabbed me was the comment about running +2psi at the front in order to reduce understeer (I read the same thing 2 weeks ago in a Bob Jane tyre book). So what it's saying is that more pressure you run, the more grip you have. I know this goes agaisnt simple logic that sais the lower the pressure, the bigger the contact patch (and hence more grip).

Though, from my experience more pressure = more grip. We're talking about 30psi versius 40psi range and the more pressure I run (within reason), the less flex a tyre has. Less flex means that more 'thread' actually staying on the road, and hence the tyre does not 'fold' on itself. This in turn gives mroe grip then when the tyre flexes and folds.

Still, any new thoughts on this? Why would the following state that adding pressure in the front will reduce understeer?

"It is recommended to shave the tires to 3/32" to 4/32" for serious competition use.

Shaving to less than 3/32" will increase performance but reduce tire life.

Hot pressures in competition will run from a minimum of 36# hot to a max of 46# hot, 40# hot is a good starting point.

Running 2# to 4# higher pressures in the front tires will reduce understeer in most cases.

Remember that the tires will build up pressure in competition. Usual pressure build up is from 3# to 9#, this must be taken in account when setting cold pressures."

naishou

I don't think dogmatic statements like that carry any weight. What model tyre are we talking about, on what car, at what starting pressure? If your pressure is too low then increasing it will increase grip. If it's too high then increasing it will reduce grip

DavidM

I don't think dogmatic statements like that carry any weight. What model tyre are we talking about, on what car, at what starting pressure? If your pressure is too low then increasing it will increase grip. If it's too high then increasing it will reduce grip

Yes, you're right on all accounts but on the site it does not mention much about the pressures. Oh, and this is Toyo RA-1s that had the above snippet of text so we're talking about semi-race rubber.

On the other hand Bob Jane booklet mentions the OEM pressures as the starting point for the 'bold' statement "more pressure = less underseer".

naishou

Probably right for family cars on tall tyres with pressures set as a compromise between ride and handling. Performance cars with performance tyres? Who knows? Race rubber? You should have them at the optimum pressure to begin with, and if you do then raising it can only make things worse.

My Formula Ford runs 18psi hot in the fronts and I can tell you that if it even goes to 19psi I can feel a dramatic loss of grip and increase in understeer.

2kturkey

My experience on the S02s was that I always needed to run the fronts at least 4psi higher otherwise I had fairly massive understeer. Could just be my driving style though.