A very interesting series of posts here about pressures, but in the end, I have to agree with PDX_racer - higher pressures are the norm, especially on the Z.

Yes, you can run the stock pressures of 35 psi. I did it and tries varied pressures from 28 in the rear to 40 up front - all on the stock tires and wheels. When you're not pushing the car to the limit, stock tires and pressure are fine.

I'm running RT-615's now and regularly run 40 - 45psi in the fronts. It DOES help the understeer problem.

It's not "internet lore" - it's the time tested technique of every autocross organization and top autocrossers around the country.

 

I must not have pushed it to the limit consider my low pressure got me 5 raw FTDs in 2.5 years.

The 4-6psi higher than stock pressure theory works good on a normal car, but I think it is absolutely pointless on a good handling car with stiff tires. The whole purpose of inflating the tires is to prevent them from rolling over. If you are not rolling on it, what is the problem? But hey, whatever you feel is comfortable. I have run as low as 26psi on my 710s with moderate success.

 

I'm sure there are, WA is usually wet a lot. What do you use for rain?

 

I was kidding there Dave.

 

How is your 3000+ pound car not rolling over on 26psi?

 

FTD in a Z What are you running against - kids on Mattel BigWheels?

j/k I only dream of FTD. Hell, I'd like to have a PAX FTD or Stock FTD or even a Ladies FTD. I'd consider myself lucky to even see another Z get FTD.

I know where I rank against some of the best local drivers and I know where they run against some of the National Tour and National Championship drivers -- I have a hard time envisioning a Z pulling out an FTD very often. You must have found the Nirvana of Z setups or you've got one heavily modded Z. What class do you run in?

 

Complete stock car in B Stock, only thing that is not stock are the tires. I run in a club with about 100 cars, medium size field i guess. I run in AS or BS (I get bumped since my class is usually empty).

I think I got 2 or 3 on the V710s, another 2 or so in the RA1s.

I ran my 710s consistantly at 29psi, I was perfectly happy with them. They rolled very little, I used the complete tire and I was happy with it. The only place I use 35psi is for the street, and I found that to be too high usually.

With the right course and some good luck, the Z can do okay in autox. I am not saying it will win nationally, but it shouldn't disappoint neither. I have battled through tight courses, wide open courses, dry courses and wet ones, it's all about luck. I think one of my FTD was in damp condition. Also there are other compeittive Zs in the area too, so I am not hte only one.

Oh yeah I struggled so hard at the last event in a 1st gear course, I barely beat a MR2 NA that was bumped to my class. It was bad....

 

i drive too slow to not roll it? my 235/40/17 looks like they are flat all the time, but they still do okay. rolling on the sidewall a little bit is okay, it's not the end of the world

 

So you have no mods other than tires?
Sorry, but your competition must be lacking. The people in my region who get the top pax and raw times are all national level competitors. Is there no one driving an RX-8?
A 350Z got raw FTD in our region once last year.....Michael Bright, he's also a great driver, been driving the Z for like 4 seasons now. Ohlins shocks, custom straight ti from cats back, now racing in BSP. He's on this board....

 

No other mods that I know of, although I was challenged twice down in NJ.

I am not doubting there are better drivers out there, but the competition are not exactly Porsche club autox neither. It's not easy to get a FTD, you have to have everything working right. I have raced against national level drivers, I have beaten and got beaten by them. For the most part, the average is still between 3 and 10 overall. I am not too worried about it given the fact that I still use 3 years old RA1 and I am more concerned about time trials than autox. I won the first autox in 2007, yet I struggled at the last event. It's all about luck.

Oh and this post is about tire pressure, I still say try different pressure and see what fits your driving. I just drive slower if the car plows. I dont think I have varied my tire pressure by more than 1 psi since I got the Z.

 

Then please explain....

And

Also, on a slightly different subject, can you please elaborate on this:

 

On the same set of tires, I have never changed the tire pressure more than 1 psi. If you have to set your tire pressure 5 or 6 psi higher on one axle than the other, then your car is probably not balanced or you are not doing something right.

It's a lot more fun doing track days than autox. I meant to tell the poster how much more fun he can have at the track when you can use all of the car.

 

It seems that I would agree with what you are saying with the higher pressure. I did start my fronts at 37 after the first run and after they rolled over really bad I upped them to 40 and it seemed to help. Next time I will go a bit more extreme like 42 and lower the back to like 38.

On another note when running a tire like the V710 I could see how a lower pressure like mid 20's for those would be much more acceptable. Which makes sense because they are "more of a race tire". That is a completly different situation. I mean to find a good pressure for a stock street tire "T1-R, RT-615, Kumho MX". In my case the T1-R

I have been thinking and if I were to adjust the front sway bars to full stiff and the rear to full soft wouldn't this result in reduction of understeer "pushing".

 

Toyo's have notoriously soft sidewalls so you will definitely need to bump the pressure up.

 

As I said, I used 35psi for my Rt-615. I use even less for my Toyo RA-1, and I can tell you the RA-1 have softer sidewall than the 615s. These modern tires are not like the ones back in the days, you don't need tons of tire pressure to get full traction out of it.

 

finally.... a thread that is interesting and informative!!!

anway, are there are tire reps/manufactuers that can support any of these speculations with tire psi and use???? Be nice to see a Toyo, Hoosier, Flaken rep on this forum!!

I have ran a handful of open track days on my stock tires. Stock being Pilots in the rear and Ectas on the front. I bump all four tires to 39 first thing in the morning on cooler days. Hot track days I set them at 36 first thing. Monitering them all day never getting over 44psi front or rear. Seems "slippery" or "loose" in the rear if I creep over that magic 44 mark.

 

I think personal preference has a lot to do with it. Plus differnt car requires different tire pressure, you should be looking at tire temperature.

 

Tire manufacturers don't even make recommendations for street use, no way to expect much in terms of autoX/road use. It's too dependent on the car and the car's setup.

As for track days, that's whole 'nother subject. The pressures we run at an autocross would definitely be way too high for track use.

 

Michelin does have a recommended pressure and tire temp for the GT3...

 

Well there you go.

710s are NOT street tires.