another tire question - 7x16 front and rear

Kemo · 08-14-2008, 01:04 PM

Im trying to get together a set of Autocross tires for my SC. After reading the rules, the tire width for a particular class is limited to 225 and the max wheel width is 7.5 inches.

I have a set of 4, 7x16 Fuchs that I can use for this, what is a good tire, with size, for this setup?

im thinking 225/45/16 in the back with 205/50/16 in the front? Plus, im just now understanding that tires heat up at different rates...im assuming that for Autocross you would want a tire to be ready to go fairly quickly right?

from searching, I see people running 7s and 8s or 8s and 9s. I havent seen 7s all around. is this a bad idea?

thx

racer · 08-18-2008, 05:51 PM

I would go with 225's all around. You get the bonus of being able to rotate the tires to even out the wear. Not sure about the rest of your suspension, but a set of adj. sways can help you dial out any under/oversteer as well.

Most 911 owners run a staggered set up (in part because the factory sold SC + newer cars this way) to reduce oversteer. Hence the 205/225 , 225/245 combos you see most commonly.

And yes, different tires take longer or short to warm up. Thats why most top AX guys run slicks, Hoosier or V710s. The rest are "also rans".

911st · 08-18-2008, 06:50 PM

A thought:

Pick up a set of cheap cookie cutter 15x7's and run 225/50's on all four.

I think Kumo Ecsta V710's are popular with the autoX crowd.

They are a bit wider and fit on a 7" rim a bit better.

Longer studs in the rear might be nice so you can run spacers.

KTL · 09:21 AM

Not a bad idea whatsoever. I and a friend both run all 16x7 with 225/50 all around. It's not the absolute fastest setup, but being fast is also about the driver. We do just fine keeping up (we pass a boatload more peeps than we let by) at our events. We haven't died yet with this setup that some feel is not quite proper. I like a car that has some high speed oversteer characteristics, and that's what my car's got plenty of. I have tamed it a bit with the adjustable rear sway bar.

The key to this setup working well is you MUST use spacers and longer wheel studs in the rear like 911st said. I have both 21 and 28mm spacers that I can use. The spacers give the rear more track width to better match the increase in track at the front. And like racer said, a big benefit is tire rotation to best manage the wear. These cars eat up rear tires at an alarming rate. It's nice to throw the fronts to the back and keep the wear on all tires somewhat even.

The reason I chose the 225/50 is because of the wide variety of tires to choose from. If 225/45 was more common in R compounds, I would use that size. I see the Yoko A048 is available in the 225/45 and would like to try that. Don't get me wrong, I still think the staggered setup is the best for a 911 because of it's rear weight bias. For people like me who are cheap and are content with being competitive but not the absolute fastest, spare no expense, this setup does just fine by me.

I do have some 16x8, 16x9 BBS wheels with Kumho Victoracers that I will use in the near future and we'll see how my times improve. I've been running the 16x7 225/50 setup because Hankook Z211 Rcompounds have been so cheap on closeout ($80 each). I've also run 16x8's all around with Michelin Pilot Sport Cup 225/50 and the car was quite fast with a rather poor weight balance and alignment. I'm sure I would have shaved 1-2 seconds easily if my car was better set up when I had those tires- LOTS of grip and wear very well.

Kemo · 08-25-2008, 08:33 AM

Thanks for all the info...

so if I go with the 225/50s all around, what length studs do I need and what spacer?

KTL · 08-25-2008, 08:56 AM

Well to get as much track width as you can in the rear, i'd recommend the 28mm 930 spacers with the 72mm studs (901.331.671.01 part #). That's what I have. The studs are a bit longer than the parking brake backing plate will allow for installation, so you have to bend the plate back a little bit to get the stud in the hub.

Most people choose to use the 21mm 928 spacers with 65mm studs (part # 911.331.671.00). These studs are an easier fit during installation. Do a search and you'll see the results people have had with this setup. Fits very nice, just not the most you can go for.