Spyerx

Hi all, sort of newbie... I have yet another question regarding tire pressures and wear. My 997.2 C2 is lowered with H&R springs and was aligned as best as possible w/o changing the control arms. Overall, my rear tire wear is pretty even. The car is mostly driven hard in the canyons of LA when I drive it, not a whole lot of commute, and no track miles.

I'm using the pressures (cold, set at about 60f) from the manual, the "lower load" pressures. I have 19" wheels, so cold 34/40. When these get HOT, the rears can get up to almost 50, fronts up to about 38. Tires are Pirelli P-Zero N2 rated (I think).

I've been reading a bit here and I have seen pressures and f/r differential recommendations all over the map.

Here's my question: Has anyone here varied these much to the benefit of handling/comfort for the street? Particularly the differential, to give the front end a bit more bite on turn-in?

Thanks

CORSASCHNELL

I have played with my tire pressure a few times, it takes a keen sense to notice the difference. My Indy recommends lowering front and rears by 4 PSI to make tires last longer, I did but found the handling a bit lazier and not as sharp.

The one set up I liked was to keep the fronts to factory spec but lowered the rears by 5 PSI, it gave the car a nice predictable roll in sharp turns, like the back end is planted with no sign of over steer.

Try this set up and see if works to your taste.

Mike in CA

I run 33 front and 38 rear. This helps a bit with hot pressures and it drops the front/rear differential in favor of a little more grip in front relative to the rear. It also helps the ride a little on the roads around here. I could probably drop the rear another pound or two but my tires are wearing well and the ride/handling is to my liking. When autoxing I do a lot of pressure adjustments as the tires heat up to keep the pressure in the optimum range for my track Sport Cups. For the street, though, it's not practical to be constantly changing pressure so you're stuck with a compromise among wear, grip, and ride. Experiment within a reasonable range around factory specs to see what suits you, but go too far afield and you risk reduced wear or performance or both.

Edit: You probably know this stuff already but just in case, this info from the Tire Rack might be useful:

http://www.tirerack.com/tires/tirete...jsp?techid=58&

http://www.tirerack.com/tires/tirete...jsp?techid=147

dasams

These are the cold temps recommended by Big O Tire company at last week's track day. They were kind enough to purge and fill with nitrogen. As this was only my second track day, I don't have enough experience to say whether traction would have improved if I started with a lower or higher pressure. Dave

Dadio

While we're on the subect of tire pressure, with the nitrogen gas does the TPMS reading match the pressure the tires were set to when they were refilled with the nitrogen ? And does the reading stay constant after the tires are fully warmed up ?

Mike in CA

Although 33F 38R works well for me on the street, given the pressure gain from heat that you are likely to experience at the track, that seems a little high for cold pressure, but I'm guessing Big O was erring on the side of caution. It would help if you knew the optimum hot pressure for whatever tires you have and then work from there. For example, per Michelin, the optimum hot pressures for my Sport Cups are 32F 36R and they recommend starting with cold pressures of 25F 28R. My experience has been that the tires seem to work best with something close to those hot pressures. The Sport Cups are R compound with stiffer sidewalls so those numbers wouldn't necessarily apply to a street tire. Starting at 33 38 what kind of hot pressures did you end up seeing at the end of a run?

Mike in CA

Nitrogen expands with temperature just like any other gas so pressure will go up and down. Nitrogen molecules are bigger so there is less permeation of gas through the rubber and loss of pressure over time. Because it doesn't support the presence of moisture it inhibits corrosion and allows for more consistent pressure changes with temperature, which is why it's good for racing and track applications. Pressure is pressure so TPMS will correctly read the what's in the tires.

Spyerx

Mike - really great insight and info, appreciate the links to the tire rack articles. Will definitely play a bit with my pressures next canyon run.

great stuff!

PJorgen

Using N2 in tires has advantages, but there is a lot of misinformation about it. Mike is correct in that it expands with increasing temp like any other gas.

However, N2 is not "bigger". Remember air is about 78% N2, and O2 and CO2, the other main components of air, are actually larger molecules than N2. In addition, N2 will hold water vapor just like any other gas. The primary advantage of using N2 is that it is commercially available with very little water vapor in it.

It's the water vapor that causes large changes in pressure with changes in temperature, because water vapor is not an ideal gas since it changes phases (liquid to gas) in the range of temperatures encountered in our tires.

So, use dry N2 to fill your tires if you can. However any other dry gas would work just as well.

Mike in CA

My understanding is that nitrogen won't permeate rubber as easily as oxygen and is less likely to lose pressure in a tire over time but I'm no doubt incorrect that it's due to size. Also, the fact that nitrogen is an inert gas and oxygen is an active one, as well as being a component of water contribute to the advantages of nitrogen. Thanks for the clarification and correction on the other issues.