Jason Judd

How do I figure out what is the correct size slick for my car?

I'm currently running Hoosier R6's...275/35/18 up front on 9" rims...and 295/30/18 in the back on 11" rims.

I've got a 968 which weighs in about 2,650 lbs.

It's set up with Motons, and has about 3 degrees negative camber up front, and about 2 degrees negative camber in the back.

I'd like to try running slicks, but I don't know the correct compound...or the right size!

Sheesh!

This seems like such a newbee question...But, I don't know how to figure it out!!

Can somebody help me out?

Thanks!

Bryan Watts

Size should be easy...measure your current tires and then look up the slicks. You may even be able to find a chart for the Hoosiers that lists the actual measurements, since they are normally inflated from the measurement listed on the sidewall. Unlike R-comps, slicks are, for the most part, the size that is written on the side. And as if that isn't enough, it's not hard to find a chart for most slick manufacturers that gives the measured tread width, sidewall height, sidewall width, and diameter for a slick mounted on the optimum wheel size. Most charts will also list the acceptable wheel widths and the optimum width for a given slick size as well.

Compound...takes some time to figure out. At your weight, you would probably end up running a medium compound most of the time. The person you buy your slicks from can make a recommendation for a specific compound for a specific slick.

Camber...doesn't matter what you are running now, you'll want to take tire temps and adjust the camber for the slicks. Slicks tend to have a lot more spring rate (sidewall stiffness) than R-comps, so your optimum camber and air pressure will very likely change.

What kind of slicks are you considering running? Depending on what you want to run, I can likely give advice of a good supplier and link you to a chart showing size information. We've run Hoosier, Dunlop, Pirelli, and Yokohama slicks on our current car over the years.

333pg333

Also Jason, in general slicks have quite a lot more outside diameter, meaning that they're a taller tyre. This may have an effect if your car is very low with inside fender rubbing. You may need to raise your ride height. Just using your avatar as a guide I would think you'd be ok....but it also depends on the slick.

eg your fronts have an OD of 25.5" whereas the Michelin Porsche Cup with a 270mm tread width is 26.85". That's quite a bit of difference. I raised my ride height recently by only 2cms which is .78" The car looks like a 4x4 now by comparison so it's amazing how such small increments can make big differences. Just an FYI IMHO.

Geoffrey

Jason, you'd have to check clearance, but the following tires would likely fit

Dunlop 235/650 front and 265/660
My first choice for performance although the rear taller profile may be an issue on your car. Also, the taller profile will change your overall gearing, probably to the negative side.

Michelin 24/64 front and 27/65 rear
Fronts are Cup size tires and will work great. Rear tires were awful when I tested them

Pirelli 246/645 front and 285/645 rear
Should be an Ok tire, but availability has been a problem

Yokohama 250/650 front and 280/650 rear
Good slick for a newbee. Very forgiving slick with a soft sidewall. 280 is a front tire for a sports prototype and not recommended for the rear of a 911 (although we have run them on the rear of a 911)

Hoosier Cup slick 250/650 front and 285/645 rear
New slicks with great support from Hoosier

In general, the larger profile you can run in the rear (660 - 680, etc) the better the car will be, the longer the tires will last, and the more load the tire can handle. The tires I listed above should fit under your rear qtr panels and then you can see if you can run a taller profile, like a 680, however, your gearing may suffer unless you can install shorter ratios.

Jason Judd

Geoffrey,

Thanks for all that info!

I'll work with that and see what fits under the car; as that seems to be one of the key factors with these tires.

Jason

cooz

pay me the $8.00 you owe me and i'll tell ya what ya need to know!

cooz
aka
norm m

Jason Judd

Cooz,

If you would remember things correctly...It's YOU who owes ME the $8...and now it has compounded interest!

And, by the way, go get a tent, for some shade...so you stop sweating all over the place, too! You're scaring the children!!

333pg333

ewww....

So Jason, did you decide what to get yet?

Jason Judd

Patrick,

I'm going to try Hoosier's 250/645/18 front and 285/645/18 for the rear.

I'll see what those are like and let you know.