OK I checked the newbie section and did a search but there was no mention of tire pressure. My question is what is a good starting pressure ( +/- baseline from factory recommended) and how to adjust tire pressure to induce/control over or understeer.

There is a bunch of information on the internet but some are contradicting. For example some say to set starting pressure higher to prevent tire roll but others say lower to prevent over inflation. Yet other say to use a pyrometer to maintain optimal pressure. What temp are you even trying to maintain? Some say decrease pressure to increases grip while other say decreasing pressure reduces grip since this will induce tire roll. Then there is the old adage about using shoe polish to gauge tire roll. But with newer tires and stiffer sidewall construction it's not like I'm rolling +/- inch onto my side walls. The wear is so subtle it's hard to tell if I'm rolling too much or too little. Help, does anyone have a definite explanation/recommendation or URL link on tire pressure adjustment?

Johnny,

Which tire are you using? Because tire pressure and heat are different based on type of tire and brands.

I know that Hoosier R6 and R888 have a sweet spot at 36-38 psi hot. With a 3300 lbs car, I get there by starting at 28-30 psi cold. As soon as you go in pit, you check the pressure. It you are at the upper sweet spot temperature, whatever that is for you tires, then it is perfect. You don't want to drive too much under pressured since the tire structure won't have the internal support to stay rigid. That means you get too high tire temperatures and wear them down faster. But you also get better grip, for shorter time then. So autocross drivers sometimes takes this to an extreme.

About tire temperature, I am no expert. But where I have seen it in use is primarily to see if you have enough camber on your car. You want to make sure you wear the tires evenly. I don't think you need to measure temperature to find your right tire pressure.

PeO.

Johnny

Take a look at this Its very informative and will let you set up starting points and how to find the correct preasure. And how set up and temp and preasure are related....

http://www.tirerack.c...

Sean

Thanks Sean good documentation. Peo I'm sad to say I'm still running the mismatch set of street tires that came with the car. Fronts are Kumho Ecsta SPT and the rears Sumitomo HTR-Z III. I probably have another 2 or 3 track days on these tires before replacing. Still not quite ready to commit $$$ on r-comp or slicks plus an extra set of wheels. Will prob go with a nice set of summer tires like the new Michelin Pilot Super Sport. Thanks for the help.

BTW, Peo nice vids from Homestead. I see you keep your Vette well fed on a diet of GT-R, RS4, 911's, M3 and etc.

Johnny, for our cars (E46 M3), I typically would start out with 30 psi cold all around and make changes from there. Rule of thumb for our car is to never let the tires go above 40 psi (hot). Check your tire pressure immediately following a session, or better yet, have someone waiting for you in the hot pits, come in mid-session and have them check the pressure.

I highly recommend going with a square set-up for the track. Just so happens I have a set of original 18" M3 wheels (4) rears for sale, powder coated black - $400 :)

Johnny,

Looking forward to drive with you again (even if we have not been out on track in same group yet). The step to R-tires is longer than what one might initially see. Just to help you with argument to stay away

- You need a separate set of rims if you use the car as daily driver
- When you pull 1.25 G in the corners instead of 1G, you will find out that the car no longer is "in balance". The suspension is setup for street tires. Driving with R-tires will make your car feel soft. You will walk around thinking about coil over setups and stiff anti sway bars instead of caring for your wife.
- R-tires are more sensitive to the right pressure. If you have the wrong pressure you wont get 5 track days out of the tires, perhaps only 3. And $1000 for 10 hours of track is of course an effort.

But then, on the other hand, starting with R-tires are addictive. When loosing grip, I am still amazed how much grip you still have to correct things. (Unless you are completely off.) So, it does make me feel like a better driver. And it takes off 5 seconds on most tracks.

Smart - no, expensive - yes, addictive - so it hurts.

PeO.

Hey Johnny, I've read all the responses to your question. Here are my 2 cents to the mix. I have run everything from street tires to full on slicks! In my opinion, we are all out there having fun & not competing, therefore there is no better way to improve your driving skills than seat time with street tires! Street tires will communicate to you much better than R-compounds will and will teach you lots & lots of car control.
Once you can out drive your car & street tires, then & only then should you think of R tires. If you switch before, the tires will be doing the improvements, not YOU! I'm not sure if we have met, but you can ask anybody about the way I drive & I'm usually on street tires, Even now with a dedicated track car! If you improve your driving skills enough, you can keep up with your buddies on R tires and have fun in the dry AND the WET!!!
That is my advice, those PS2's you say you're going to get are probably the best street tires available, but they are pricey... I've been running on my turbo Miata the Ventus R-S3 it's Hankook's Extreme Performance Summer tire, it has a 140 tread wear & almost feels like an R-compound.
As far as PSI, Carlos is right as in most street tires are happy between 38-40 psi HOT. Hot is the important measurement, and your tires will have small triangles on the sidewall at the edge of the tread pattern. You want to gauge your air pressure to have the tire roll to that point! Not more & not less, the is the optimum roll marker.
So, whatever you do, I hope to see you out there soon...
Juan

Juan

I see that you are running the R-S3. I have been running TOYO Proxes R1R on my Supercharged RX8 for over a year. However, after reading the last Grassroots tire comparo they felt 3rd compared to the R-S3. Also, I'm running 245-40-18 due to my current wheel size 18x7.5 However, I purchased a new set of Enkei's RPF1 18x9.5 and will be pairing them with a set of 265-35-18

The R1R and R-S3 are about the same price. Not to mentioned that both are 140 tread wear.

Can you spare 2 more cents and help me decided if to stay with the R1Rs or get a new set of R-S3?

Thanks
Juan

Well Juan, I'll spare as many cents as you need...

I'll be honest, I've never run to those Toyos. I've always heard good thing about Toyo tires. So, I did a little research on some other forums and they all say the same thing. Both tires seem to give very similar performance, the only difference I can tell is with the heat. The Toyos seem to cycle out faster and apparently don't handle the heat as well. Like I said, I personally haven't run the Toyos, but I can tell you from experience that the R-S3's handle the heat very well (8 full hard track days on them so far). And I guarantee you I'm pushing the shit out of those tires, they even form a blue ring around the outer edge as proof! The R-S3's don't fade during a session and although there were a few negative reviews about their performance in the rain...I have lapped cars in the rain with those tires. Unfortunately, it's going to come down to your preference... They are both great tires, similar compounds & tread wear and cost. In my opinion after reading all the reviews and from personal experience, I think the R-S3 edge out the Toyos by a small margin. Those are my two cents any way. Please, let me know what you decide on and how they perform? I would like to get some direct feed back on your opinion. I hope this helped... When is your next rack event, I'd like to see your car on the track?

Thanks for the 2.5 cents. I still have a bit left on my R1R...maybe a track day or two...then to a fresh set of R-S3.

Next event PBIR NASA Sep 4th.