D'oh

Yesterday I ran in my 8th AutoX, and got to use my race tires for the first time. It was an interesting experience.

In short, let me just say that I was definitely faster than before, but I had a much harder time recognizing the limit than I did in my street tires. I now know why people say to AutoX for a while before going to race tires (I figures 7 events was "a while" for me).

So, I'm running 265/35-18 on all four corners (on 8" rims). Driving to and from the event with VDC on caused no problems, and running with VDC off caused no problems either. We did four runs, each consisting of two laps around the course. The first lap was a warm up, and the second was "on the clock". I typically start off pretty easy, and then gradually try to get on the throttle earlier and brake later each time around. After my first three runs I still couldn't tell where I was hitting the limit of the tires. I therefore decided to just go nuts on the fourth runs. Needless to say this strategy did not pay off with respect to time, but I definitely was able to roast the tires at practically every corner. By the end of the two laps I had practically driven the sidewalls off the tires. Ah well, it's like tightening screws, "Just tighten 'til it breaks and then back off a 1/4 turn." Next time I'll know better where to back off.

The car felt very well balanced when driven properly, but I had a much harder time feeling the limit than I did in the street tires. I think this was partly due to the extreme tire width compared to the wheel width. As was mentioned by others, it made the feel a little "soft" and more difficult feel the limit. Obviously with practice I will be able to do much better.

My best time ended up being about 1-1.5 second faster than normal (when I compare my times against the other cars that haven't changed), but I still have to knock another second off my times before I can compete with my buddy in his S2000. Ah well, at least I've finally caught up with Gen1 RX-7's on race tires.

-D'oh!

PS. I ran 39 PSI cold in front and 35 in back. By the end of the day I was 45 in front and 39 in back. I think that final lap really did a number on the tires.

Here's before picture of my tires:

D'oh

And here's an "after"

-D'oh!

mball

Do you have pics of the wheels on your car? Where did you buy your wheels and how much do they weigh? How much gas did you run in your tank? I will be autocrossing my Z for the first time this weekend and I was wondering about the gas level.

D'oh

I've got a few threads floating around asking basically the same thing as you.

I ended up going with the Enkei RPO2J wheel in the 18x8x35mm size. They are about 19lbs and $225 each. I bought mine from Discount Tire (a local store) but next time I'd probably use Discount Tire Direct because my local store is a madhouse and it took a few times to get things right. I still haven't picked up my concentric hub rings (the center bore on the Enkei is larger than the Z's hub, so you either need to be careful tightening the lugs or get the hub rings to take up the slack).

I am running 265/35-18 Kumho V700 race tires (about $180 from TireRack or $220 installed from discount tire).

I was unfortunately running at about 3/4 Tank of gas, and I never bother to get rid of the jack and spare tire either, so there was a bit of extra weight. Also, I took a fellow Z owner (300ZXTT) for a ride on my last lap. He was impressed with the torque of the 350, but not so much with my driving (I did warn him that I was going to find the limit of my tires, though).

Still no picks of my car with the wheel mounted, so I'll try to take care of that next time.

-D'oh!

mball

Discount tire direct didn't have those wheels. I found them at another site for $275. To bad I don't have a store near me. Thanks for the info.

D'oh

Try calling DTD (I'm assuming you checked their website?). One of the guys there should be able to order them for you at that price. If fact, Todd (I think that's the guy) posts here quite a bit and he was the one that gave me that price (approximately that price anyway).

Good luck.

-D'oh!

mpowers

iTrader: (7)

Try lowering you'r tire pressure, Its a bit high, start with 32 hot for the front and 28 hot for the rear. I am avid autocrosser an have ran kumho before. Now running michelins my tire pressure is 27 front and 23 rear hot. Or take you a tire pyrometer with you and check the temp of you tires from inside out. It will help you to determine weather or not you are running too much air.Ie if the middle is hotter than the outside to much air.

Track_350Z

Cool D'oh!

Thanks for the update. I'll be running 8" F & 8.5" R for BS. I'm torn cause Kumho is 265 & Hoosier is 245. I'm thinking about running 245 Hoosiers up front and 265 Kumhos in the rear. What do you think?

Is the tire wear in your photo the inside rear or outside front?

2003z

iTrader: (7)

I got my rpo-2s from discount tire direct. Just because they dont show it doesnt mean they dont have it. Todd also got me my kuhmo's with them, and they don't sell those either.

D'oh

Are you running those pressures on a Z? I'm guessing by your pressures and handle that you have an Mcoupe or similar?

At the risk of telling you something you already know how to solve, here's my dillemma: The Z has extremely slight negative camber in front, and therefore it is practically impossible to run pressures that low without completely wiping out the outside sidewall. Part of the problem was my driving and the large tire size, but even when I was taking it easy I was encroaching on the sidewall. I'm definitely open to suggestions on how to fix this, but unfortunately, I don't think lower pressures will be possible unless I drop a tire size (and possibly not even then). One of the members does have a pyrometer though, so I am hoping on getting some additional info from that. Just by hand, I could tell that the outside was significantly hotter than the inside. Couldn't really tell about the middle though. What do you think?

I think that is an interesting choice in tires. I've heard the Hoosiers are stickier, so you may be getting a very good combination of good turn in and stickiness in the front with a good meaty tire on the back (and one that is less expensive). I'd be interested in hearing how that turns out, since it sounds like a good compromise between performance and cost. The only issue might be rotation since the fronts will most likely wear out much sooner than the rears.

The pics are showing the ouside of the fronts. Interestingly, the outside of the rears are just about as bad (although the sidewall is in much better shape). The inside of the fronts and rears are almost new. Some of the little rubber "feelers" are still there.

-D'oh!

mpowers

iTrader: (7)

Yes I am running them on a 350Z although my size is diffrent, 245/45r16, they came from my 300ZX that I had sold. Waiting on a set of new wheels to come in. But this is not the only 350Z I have had th chance to help set tire pressure on. Driverdogs' 350Z
runs 255/40r17 and we are getting better performance out of lower pressure and better tire wear. Rember to trie checking your tires temp it will tell you what pressure to run. The only question I have is the side wall wear from the front or rear tires?
My guess is thats its the front, and you'r plowing the nose of the car into corners. Tire pryometer is the key to setting the best pressure for the car but 45psi hot and 39psi in the rear is two high. Check out the pic you took, he inside to the out side of the tire has a lot more wear than the inside indicating over driving and too much pressure.

D'oh

Cool, thanks for the tips.

The sidewall wear is from the front. The rears wear much better. I'll try lowering the pressure at the next event.

With that taken care of, I think "over driving" will be my biggest obstacle

-D'oh!

Blue Liquid

Hey D'oh, I wonder if running a wider wheel would cure some of the issues with heavily scrubbing the outside shoulder. On my last car I ran the V700 on a 15x7.5 wheel, and the tire was a 205/50-15, so the tire was nicely stretched over the wheel and sat relatively flat on the wheel, with no sidewall bulge whatsoever. It looked much wider than most 205 width tires on narrower wheels. I realize buying new wheels is probably out of the question though. And I think running lower pressures will exacerbate the sidewall roll-over problem. It sounds to me like you simply are running into a problem of too wide of a tire for an 8 inch wheel.

If my plan works out right, I'll be running 245/45-17 Yokohama AO32 on a front wheel of 17x8.5 and a 275/40-17 tire on a 17x9.5 rear. I think it'll be interesting to see how the tires look strapped onto relatively wide wheels, at least compared to the 8 inches you're running. When I purchase this set-up, I'll take some actual measurments and pictures and maybe we'll see a significant difference between your 265's and mine, perhaps more so in the front, since I'll be running a narrower tire on a wider wheel.

Also, your V700's look just like mine after a day at the track or after an autocross. You get that rib of rubber building up along the edge. awesome.

mball

How did your Z handle with the same size tires front and rear? I autocrossed mine for the first time last weekend on the stock tires and I was suprised how easy oversteer was to provoke. I have autocrossed several different kinds of cars and I think that only my Miata has been easier to provoke oversteer. I was thinking about going with the same tire sizes that you have, but i am wondering if staggered race tires would be a good idea. As far as pressures go, my previous autocross car was a 91 Sentra SE-R that i ran 195/55/14 V700s on the stock 5.5 in wide rims. I had to run the fronts up around 45 to prevent them from rolling onto the sidewall. They were still gripy. I ran stock pressures in my Z for the first run and then dropped the rears down some to lessen the oversteer.

I finished 2nd of 5 in my class. I was only 1 second (on a 60+ second course) behind a 944 turbo on race tires. I beat the other 944 turbo on race tires that was there by about a second. I can't wait to drive the Z on some sticky rubber. I bet it does wonders for it.

D'oh

Blue Liquid:
I'd run a wider wheel if I could, but that would bump me out of the stock SCCA class, and I don't think I'm ready to start modding yet. The tire dudes actually gave me 8.5" wide wheels initially (by accident) and offered to let me keep them, but I had to have them changed so I wouldn't be breakin the law.

mball:
I've had a hard time causing oversteer in the Z, but that may be due to my crappy driving style. I'm fairly certian I take the car too hard into the corners, which puts me on the edge of the fronts and makes me loose some of the cornering capability. The AutoX isn't so bad, since second gear has quite a bit of punch to it. However, when I was at Laguna Seca I seemed to be plowing around the corners much too often. Again, probably due to my poopy driving, but I've heard may others complain about the Z's understeer as well. I also found the car to be much more balanced in the rain, probably since it was easier to get the rear tires loose with the throttle. In any case, I had been trying to balance the car better before I got my race tires.

So, when I replaced my stock street tires I got 245/40's in front and 245/45's in back. It really seemed to help balance things a bit, but it could also be because I was getting a little better behind the wheel. I decided to get equal size race tires so I could rotate them more easily and also so I would have an easier time getting the rear end around. Of course, now that I have the race tires I'm learning all over again.

-D'oh!

mpowers

iTrader: (7)

D'oh, just got back from an scca event in viginia beach and ran driverdogs 255's on my car to see where to set the pressure at. Ended up with 30 psi hot in the front and 24 psi in the rear for best grip and wear. Ended with a second and half lead on an s2000 and over three seconds till the next z and won the class!
Any way try a similar pressure and good luck to you.

D'oh

Wow, I don't know if I can bring myself to run pressures that low, but I appreciate the info.

I'll try and work my way down a couple PSI each run until I reach numbers close to that.

Thanks again for the help.

-D'oh!