sdrake

Thanks for the continued info.

I understand your point... guess that's why we see used PSS9's with low miles for sale from time to time.

Looking at the StarSpecs, you reccomend the 225 on the front compared to the 205 stock size? If that's the case would it be a 225/50 or do you have to adjust the ratio?

On the avitar pic, both are mine - 96 cab stock with 41k and a 65 Pontiac GTO restored stock.

Thanks again to all

nile13

225 on the front, absolutely It would be 225/25-17 to keep approximately the same tire diameter.

993 understeers fiercely with 205/255 combo. 225/255 makes it more neutral. My previous cab ended up with that tire combo, Bilstein HDs and H&R springs and Turbo sway bars for suspension. That was a street car with very occasional autocross, the combo seemed pretty decent, albeit the springs and shocks didn't really work together perfectly.

sdrake

Just want to confirm this before I order these tires.

Stock 205/50/17 has a diameter of 636.77mm
The 225/25/17 you mention above has a diameter of 544.06...

Shouldn't I go with the 225/45/17 with a diameter of 634.23? That's within .4% of stock.

Final question - is there any problem with these tires clearing with the 20mm additional width on a stock 17 in cup wheel?

thanks

bart1

Yes, order the 45 profile.

trophy

No clearance problem, I have had a 255/40r17 on the front of my car without issues.....

nile13

Sorry, my fingers are usually faster than my brain. Of course you'd go with 225/45-17 on the front. I don't think there are any 25 ratio tires made

Sorry

You will have no clearance issues. I've ran these on the front and I think quite a few of us here do, that's where I got the idea in the first place.

sdrake

Tires on their way for the stock wheels - For the price, and my skill level, going with the StarSpecs.

On install, what is everyone's suggestion on camber and other variables. I plan on driving only in good weather - roughly 75% street - 25% autocross.

I've read that -2 to -3 degrees is that way to go onthe front???

thanks

race911

305/25-19. Yes, I've checked as the 305/30s I have on the back of the C4S now run 1" tall.

(And there are undoubtedly many tires of 25 or less aspect ratio for the Donks, Boxes and Bubbles running 22-??? inch rims.)

Fünfer

What is the right approach for tire pressure?
I did my first autocross recently with my local PCA chapter, and several of the experienced autocrossers/racers told me to take air out of the tire. We actually lowered it to below 30. I have 18" Advan08 on the car, which are pretty nice. But I am confused about what the right thing to do would be. To add air, or to let air out, and why?
Any thoughts?

fast_freddy

I had PS2's until the beginning of summer 2009 and was cleanly ahead of all other cars in my class with my local car club by one second. I switched to RE11's and was the same speed, I didn't get that much slower and the "competition" that much faster within one month and remain there. Once these tires are done so am I with them. They slide all over the place and have terrible turn in. I have not driven the Yokohama's on my car but have driven on them mounted on a 996, they were quite fast, had terrific turn in and nice progressive feedback. They're a bit heavy though. Who am I kidding though about the weight...

I drive 18" wheels (Volk's in avatar) so I believe Star Specs are available for them. I have no idea about 17's though.

nile13

Ah, air pressure. The basic religious debate of racers everywhere, I think

Well, there is no right answer. Essentially, think of it this way. There is a range of pressures at which a tire would work well on a given surface for a given car setup. Let's say that for a specific tire it would be from 30 psi to 40 psi. In that range you sort of (not exactly) get more grip if you lower the pressure. This is similar to effectively softening the springs at that end of the car. Outside of that range any lowering or increasing will cause a fairly quick loss of grip.

So, why are things not simple? Because they depend on car setup, temperature, humidity, surface, hell, they depend on the course itself as well. On a colder or wet day you want a soft spring and lower pressure to get some grip and to heat up the tire quicker. On a hot day on concrete surface you want more pressure to not overheat the tire by the end of the run.

The bottom line? I know what the "right" pressures are for Kumho V710 for my 2,100 lb CSP Miata on a broken asphalt of an old airfield where we run. it happens to be 28 front and 25.5 rear (0.5 psi is an inside joke, it gives me psychological advantage as in "our amplifiers go to 11"). The same tire on a different car on the same surface on the same day will be different. I just went to Hoosiers A6 and started with 33/31 pressure, which seems to be close to the truth for that tire, but it'll take me 4-5 events to even begin to feel how they work.

So... the bottom line is - ask local PCA people who might run Advan 08s what they do for pressure. Take it as a starting point. Put chalk marks on the sides of your tires. See what they look like after a few runs. If tires do not work their shoulders, lower pressure.

Remember, in a 993 the front to rear balance is most important as you'll end up steering the car with your right foot once you get fast. You can't just get "ideal" grip on one end and be happy, you have to be cognizant of what the other end is doing. And, oh, btw, tire pressure seriously depends on your driving style. You see the equation with many unknowns? I do.

cgfen

Nile13, interesting discussion, thanks.

I'm currently using either Ventus V12's or AD07s
Both sets are close to being used up and next tires will either be AD08s or Ecsta XS ku36s.
i run a wide body car so sizing is a bit more challenging.

AD08 would be 235 / 295
Ecstas would be 245 / 315

Right now i like the AD07s better than the V12's for everything other than NVH.
The yoko's grip / wear / resist heat smearing better than the V12's, (they better for nearly 2X the price!
V12's work well for 2 - 3 AX laps, then smear. I don't like them so well at a 20 minute track run session.

For pure street type tires used on the AX or small track environment, i think the yoko's are hard to beat......................... but the Ecstas also seem appealing.

Do you have any feedback directly concerning the Ecstas as compared to the yokos?

Thanks

Craig

nile13

Craig, I've driven a Miata on Kumho XS. Did not like it one bit. Nor did the owner. I don;t think XS holds a candle to either Z1s or AD-08s. And I say it as a big Kumho fan (now almost a former Kumho fan, unfortunately).

BTW, all street tires need to be sprayed after a few runs. Especially in Cali where it's hot and I think you guys run on concrete? They get very greasy very fast. At local PCA events where they divide groups into sub-groups and the runs are about 2-3 minutes apart sometimes... it's pretty bad even on race rubber and sheer terror on street rubber on a heavier car (I've ran my previous 993 cab on Azenis for several events).

Fünfer

Mike, thanks for your additional comments. I have been putting chalk marks on the sides of the tire to see how far they roll in the corners. And by taking air out they are getting to the little arrow on the side, yet are not going any further. So I guess that was the right move. The place we auto-cross at is typically pretty cool. It is near the coast and pretty much always foggy - typical CA coastal climate. So taking some air out of the tire makes sense to help heat up the rubber. I am definitely not at the point where I am getting the maximum out of the car and my stock C2 setup. I have a lot of learning yet to do; to get smoother and faster. It sure beats a day in the office and I am having a blast trying to get better and faster!!!

nile13

Funfer, you're just not pushing hard enough

In my experience a 993 on street tires works them rear tires pretty hard. You kind of point with the steering wheel and then finely position the car with the gas pedal. Especially in longer steady state turns. Which mean that the rear is always slightly sliding. Plus I have not figured out a way of braking a heavy car on street tires without getting... umm... hot.