What tire pressure for Z1 Star Spec's for AutoX
 

I just got my Star Specs mounted on my extra set of rims and I will be doing an AutoX this Sunday on concrete surface. I assume these tires have a stiffer sidewall than the stockers I have been running at AutoX. Any idea of a good starting pressure to go with?

..need to know if you are still on a staggered setup or are you square.

If square, my experience from last season was about 2 psi higher in the rear. 36F 38r is a good start cold . Then start to adjust, if loose add some air to rear. If pushing add to front. Mine Star Specs are on 8.5" RPF1s and are 245x45x18, square.

Oh, and the sidewalls are probably much stiffer than what you were running before.

I went from the stock RE050s big difference.

Yes, I am also on square setup, 245/45/18 on G35 coupe 8" rims. This will be my first run on square setup.

Thanks.

..concrete usually has much more grip than asphalt too, so the dynamics could be different. I think you'll be pleased with the Star specs. Are you running STR class with SCCA?

Hey man, how do you like the Star specs? Over other tires you have had?

Star specs
 

I'm very happy with them. They turn in great and have excellent traction. They aren't too noisy either. I'd only recommend them though if you want to run street tire classes in SCCA solo 2, otherwise I'd go with a quieter less stiff tire.

I'd go opposite what he said, 38F, 36R... and vary from there. But the Z likes more air pressure in the front then the rear...

The groups I have been running are not SCCA but some use their rules. Last year BS, so I guess this year CS? Everything is stock (wheels are technically not but close enough). This week is an S2000 group. Another group is a time trials only group to simulate more of a road course environment on a huge pad, with very laid back schedule so you can get in a ton of runs which is a lot of fun at higher speeds. There is an SCCA group that also runs but I have not run with them yet. I am trying to get in a lot of seat time this year with no major mods planned for the car, just working on modding the driver.

On my stock R040's I had been happy running 36 PSI with a little less in the rear. I know at my first AutoX one of the Z guys (on this board) was running below 30 PSI with the stiff sidewalls he had, but they could have been R comp I am not sure

I would second that after driving on the Star Specs for a couple of days, a little more noise and stiffer ride. I will definately be putting my street wheels and tires back on for daily driving.

psi
 

Well that worked when I ran a stagered setup with the OEM RE050s...but when I went to square with stiffer sidewalls then I needed more rear psi as it was quite loose coming out of turns.

So based on other high performance tires, what do you guys think? I have BFG G-force KDW's. Just trying to figure out if the star specs are better than these?

Good writeup in Grassroots Racing magazine this month using times around a skidpad to optimize tire pressures and comparing street tires to R compounds. (Conclusion 2 second rule of thumb is accurate even with sticky streets) Never tried it myself, but it seems like a good objective methodolgy.

Yes, having driven 2 cars on star specs, they are much better tires then KDWs.

jbh1, I have also recently bought some G35 18x8s (30mm and 33mm offset) to use in the summer/AX. Was thinking about the Star Specs myself. I'd be interested in your experience with different tire pressure from this weekend if you'd care to post your results and satsifaction level. Also do you have any VDC issues with the square set up? Thanks ,Rich

No VDC issues with the square setup so far, I have driven about 200 miles around town on them. The change in tire size was less than 3% from stock so it should be ok, 245/45/18 on all 4. I will try to post after the event tomorrow if I get a chance to play with pressure.

My G35 rims are 18X8 7 spoke but all are 30 offset, not 2 that are 33 offset. Now my stock Z wheels are 8" in front with 30 offset and 8.5" in rear with 33 offset.

OK,
I am back from the AutoX. I don't know if I can give you much feedback on pressure. I ran 35-37 during the day. Possibly best when tires were a little warn started the run with 35 and finished with 37 when I was done.

What I can tell you is I am much more competitive than I was, even in my heavy roadster (3600 lbs). Keep in mind this is only my 5th event so this is all relatively new to me. There were a ton of miatas and S2000's plus vetts. I was faster than 1/2 of the S2000's and 2/3 of the Miatas. Only 1 vette beat me (Z06) but the other 2 were just not driving well. This is only counting the cars on street tires, the R comp cars were much faster.

The square setup is definately better for me. The understeer is gone but it is certainly not heavy on oversteer either. My suspension is all stock.

I am excited about future events. I am sure some of my good times are that these tires are brand new and they will probably fall off as I run them event after event.

Now I need help with my brakes, my pads are not lasting long at all.

jbh1, Thats good feedback, thanks for posting it. I wasn't really considering a square setup, but will now throw that in the mix for my future set of "sticky" street legal tires. I've got to find a set of TPMS for my new wheels, buy some tires, and I'll be good to go. I'm still trying to decide whether I'll only use my better tires for AX use only and take them on and off as needed or whether I'll leave them on all summer.

Square is nice because you can rotate the tires from front to back. I don't have TPMS in my second set of wheels. I think if you have 2 sets of wheels that have TPMS its not going to work becasue the car has to be reprogrammed by the dealer to recognize the new sensors, then it will not recongnize the old sensors. I think there is a sticky in the tires and wheels section that describes this. I put back on my street tires this week and the car is much more comfortable driving around, but I have to swap back today because I have a time trials tomorrow.

jbh1, I didn't know that about TPMS. I'll go search and read up on that. On the plus side if I skip the TPMS on the AX tires, I'll save some $. With my different F&R offsets, I don't think I will rotate front to rear. Thanks for the TPMS heads up.

FYI,
I ran 35 front and 33 rear on a time trials event yesterday. I think I could have gone a little lower on the front maybe.