What do you all recomend for AutoX tire pressure. Right now I have 41 in the front and 37 in the rear. Hopefully I can negate some of the push with this setup. What setups have all of you used and how did you find them to work?

PS: This is on the stock potenzas on the touring 18s.

 

On the stock potenzas I ran pretty high, 48, 42. I kept up fairly well with some BS'rs on R compounds at the Midiv in St. Louis on the first day, on streets I was only 1 second out of first.

I actually enjoyed the car on streets on an autocross track, not the grip you get with R compounds, but they were a lot crisper than the V700s I am running now. Hoosiers are nice and crisp, but I am going to try to make Kumhos work.

 

What size Kumho's are you running? I just ordered some 265's for my 18x8" wheels that I think can be jammed on there, just not sure how "mushy" they will be.

I've run a few AutoX on the OEM tires and a couple track days as well. I found that when the front tires got above 44 or so at the track days, they began to loose grip.

I then got some Yokohama AVS ES100 245/40-18 when my front tires wore out, and they also seemed to work well in the low 40 PSI range. The wider size seemed to help balance the car a bit.

My rears have been left in the upper 30's.

These pressures are when hot BTW.

Just replaced my rear tires with Hankook Ventus K104, but haven't used them on the AutoX. Hopefully I'll have race tires by then time the next one rolls around.

-D'oh!

 

on my r-compund tires I run 44 all around. I tried lower pressures in the rear, but it seemed to be a lot more loose, at least to me.

 

I'm not an expert, but I was running low 40s up front, and down to about 35 in the rear last time out. This was with temps in the mid/high 90s, so I had to go that far down on the rears to be able to accelerate out of turns without fishtailing all over the place due to lack of traction

 

I run 245 V700s all the way around currently, will try some new sizes out next year if I can get the new 710s.

 

I was running 42 all around and I just ran 42 F 37 R this weekend. The rear felt a little looser but more controllable exiting the turns. I was definitly getting more wheel spin with the higher pressure in the rear. I think it turned in a little better too.

When hot, I was closer to 44 F 39 R.

That's on the stock tires.

 

I have noticed that my pressures in my 18s are way different from those the Zs with 17s are running. I belong to a club that fortunately hosts many practice events. I've gone in both directions with pressures... first high, then low... and back again.

I'm stepping out on a limb here... because I've found my sweet spot at a lot lower pressure than the rest of the group. Temperatures have been in the mid-80s... I start with 34F/28R.

Higher pressure in front seems to promote the car's John Deere like tendency to plow... lower pressures allows the tire to roll over too close to the end of the tread... 34 leaves you a quarter inch of tread left to roll over on. Higher pressure in the rear doesn't seem to allow me to make use of the Zs torque advantage... 28 seems to be the break point... lower than in the rear makes the rear too squirrely... the rears never get close to the end of the tread on the sidewall.

I'm not saying I have any facts and data to support coming to my conclusions other than getting closer to the faster participant's times. You can give my pressures a try... I've logged approximately 30 runs coming to the pressures I'm running. Our OEM tires are never going to totally satisfy us at A/X events, I figure my best bet is to compromise the pressures and work on my input as a driver. Good luck!

BC

 

the last autoX i went to this guy told me to go to a parking lot and put a chalk line on the tires from the outside edge down to the rim of the wheel or close to it. Then take a sharp turm(until it breaks loose) and note where the chalk gets rubbed off to. As you can tell so far this is all about tire roll so now just repeat untill the chalk line gets rubbed off to the edge of the tread.

 

White shoe polish is probably more common than chaulk. Marking the tire to the end of the tread on the sidewall should be adequate... you shouldn't have to go all the way up the sidewall.

If you mark up to the end of the tread... return to grid... and the mark has disappeared... you are definitely running too low a pressure. I started out with a borrowed baseline recommendation from another Z driver... I think I was advised 42/36... I worked on the pressures from there.

It's difficult to find a place other than an A/X to actually test pressures... I like to get a composite reading from negotiating a series of turns in a fashion typically found on an A/X course... without breaking any laws.

I'm told there is more to getting tire pressures correct than marking tires and trying to get tires to utilize the full available tread surface doesn't always net the perfect pressure. I tend to believe this... since my 18s in the rear never got within 5/16s of the end of tread... but running less than 28lbs. made the rear wag way too much.

Do people still use pyrometers to come up with proper tire pressures?


BC

 

I see people using pyrometers quite often.

IMO they are a much better way of determining pressure than using a mark on the tire because you can actually see what's happening on the middle and inside of the tire as well. Usually, people use the pyrometer to also check camber, but since ours isn't adjustable we don't have much option there.

Of course, it's much less expensive to buy some chalk or shoe polish than it is to get a pyrometer.

-D'oh!

 

I was using 41 in front and 38 rear, stock 17"s, hot. Rear still not using all the thread. Try 37,36,35 next time.

 

I have been running the same range others with 17s have reported -- I'm not convinced it's right. I was hoping a large differential in pressure would tame the understeer, but not to be... With Stillen bars (front full soft; rear full hard) the car rotates pretty nicely, but the basic understeer is still prevalent. I suspect it will be up to me to learn to drive the car the way it wants to be driven, rather than the way I would like.

I'll be on 275/40 Victoracers for the rest of the season, and I'll report back on that set-up.

Brian: I didn't know you lived in Puyallup, too!? It's interesting that you are finding low pressures so effective... BTW, I have a pyrometer which we can share at the next event.

 

How many 350Zs are there in Puyallup, WA?

 

Last weekend I kept working on pressures at autocross event.

I left 41F, and I went all the way from 39 to 31 for the rears. I defenetely felt huge difference in handling and my times dropped from 49s to 45s in 5 runs. I still not using all the tire (stock 17") so I'll quite possible try 28 next time for the rear.

Weather - sunny mid 80s.

I unload EVERYTHING I can from the car before the run. That includes spare, jack, tools, and mats.

 

Lateapex,

We moved out to Puyallup in the Spring... over in Gem Heights. I'll take you up on the pyrometer offer.

You are quite welcome to try my car with my tire pressures at the next practice.

BC

 

Lateapex,

You mentioned that you were running the 275/40 Victoracers, that's on 17's right? I was just wondering what wheel sizes you've got to run that size on. Are you running that on all 4 corners?

 

Yes, I'll be running 275s all around, on the MB Motorsports 9" competition wheels. The tires should be here this week, and I'll try them out next weekend.