wheels choice for SC race car

[rsrdave]

Hi Guys ,I have asked about wheel size for my 1980-SC race car (not street driven) with a 993 on PMOs making 304bhp at the wheels and big reds brakes all round .
I have been advised fronts 8x18 225 or 235/40/18 and rears 9x18 265/35/18 or 275/35/18 package .
My question is for the SC wheels choice is ,are 18" the way to go or 17".If you don't take in to account tire availability ,which is the best way to go for a race car .
cheers Dave

[WPOZZZ]

With Big Reds, will 17s fit? If they do, I would go with that. I'm not sure what you want to spend on wheels, but I would go with CCWs as they are relatively inexpensive and available in custom sizes.

[wildcat077]

Dave,

I have full 996TT brakes on my narrow bodied 89 Carrera and i have 17 inch Fikses with 225/45/17 and 255/45/17 Dunlops ...
Have room for 235's in front and 275's in the rear.
Not sure 35 aspect ratio 18's are a good choice as it would be like driving with elastic bands on your wheels !

Cheers !
Phil

[IROC]

Originally Posted by rsrdave

Hi Guys ,I have asked about wheel size for my 1980-SC race car (not street driven) with a 993 on PMOs making 304bhp at the wheels and big reds brakes all round .
I have been advised fronts 8x18 225 or 235/40/18 and rears 9x18 265/35/18 or 275/35/18 package .
My question is for the SC wheels choice is ,are 18" the way to go or 17".If you don't take in to account tire availability ,which is the best way to go for a race car .
cheers Dave

What do your class rules say? Personally, I'd go for anything that will get you somewhere in the neighborhood of 245mm of width in the front and 275mm in the rear. You'll need it.

[Bill Verburg]

Originally Posted by rsrdave

Hi Guys ,I have asked about wheel size for my 1980-SC race car (not street driven) with a 993 on PMOs making 304bhp at the wheels and big reds brakes all round .
I have been advised fronts 8x18 225 or 235/40/18 and rears 9x18 265/35/18 or 275/35/18 package .
My question is for the SC wheels choice is ,are 18" the way to go or 17".If you don't take in to account tire availability ,which is the best way to go for a race car .
cheers Dave

you can use 17 or 18, but for track use 18 w/ lower aspect ratio will be better.
275/40 x17 & 275/35 x18 are both equally on the tall side at 25.5" but the 35 series will be a better track tire.

8" front ET25-31 and 9" rear ET 12-15 or if rules allow 9.5" ET19 rear.
Hoosier 245/35 & 275/35 should fit w/ a little work. You might even get 285/30 in there but that should really have a 10" wheel.
Hopefully Gary R will chime in as to the 18" Hoosiers he ran on his SC?

[Jeff Alton]

If you want to run a Hoosier, the 255/35/18 is wider than their 275..... and it is shorter....

17 or 18 will work fine, have used both.

Cheers

[Bill Verburg]

Originally Posted by Jeff Alton

If you want to run a Hoosier, the 255/35/18 is wider than their 275..... and it is shorter....

17 or 18 will work fine, have used both.

Cheers

Good call Jeff!

I had never noticed that, the 245/35 and 255/35 x18 are a good match



i'd still much rather have a 35 series tire than a 40 series

[KTL]

I'll second CCW wheels. These are a VERY nice wheel for the $ spent.

[Jeff Alton]

Bill,

I never noticed the width in the spec sheet until we had them under the car, then I went looking at the specs.... great cheater tire.

Cheers

[Jeff Alton]

Here is the 255/35/18 R6 on a 18x9.5 wheel.






CCW makes good wheels, have a sets of monoblocks for the 996. There three piece stuff is good too. We don't sell them, but they are good quality.

Cheers

[brentrussell]

Dave,

Are you running Slicks or do you have to run DOT tyres?
If Slicks.... why not run 18" and use Porsche Cup Tyres? They run a 650mm diameter, 24 Front and a 27 Rear.
18" Wheels in your required offsets for the SC will be harder to find than 17" in my opinion.

Cheers

Brent

[Jeff Alton]

Most track wheels will be three piece, so getting the offset correct is not an issue in either 17 or 18.

Cheers

[petevb]

Originally Posted by Bill Verburg

you can use 17 or 18, but for track use 18 w/ lower aspect ratio will be better.

What makes you believe that Bill? General practice, or more specific information?

I ask because I've been working through this issue recently, having 17s, 18s and 19s for the car. I noticed that Michelin is very specific with the GT3 cup cars, strongly recommending the taller side-walled slicks on the rear vs the shorter ones.

They make three slicks for the rear of the rear engined GT3 type track cars, having the equivalent of a 3.8", 4.4" and 5" sidewall height, all 18" wheels. They say:

They recommend the 3.8" sidewall for near stock cars- "(not for "serious" race-prepared cars like Carrera Cup or SuperCup cars)"
They recommend the 4.4" sidewalls for GT3 cups and similar
They recommend the 5" sidewalls for GT3R, GT3RS and RSR cars.

They suggest the taller sidewall tires put power down better.

Obviously a lot of design goes into these slicks that is different than street tires, but I wonder. My 17s have a 4.2" sidewall, the 19s a 3.6" sidewall. I don't run the same type of tire so comparison is difficult, but I wonder if the taller sidewall might give some of the benefits the Michelin slicks see.

Any thoughts?

[Bill Verburg]

Originally Posted by petevb

What makes you believe that Bill? General practice, or more specific information?

I ask because I've been working through this issue recently, having 17s, 18s and 19s for the car. I noticed that Michelin is very specific with the GT3 cup cars, strongly recommending the taller side-walled slicks on the rear vs the shorter ones.

They make three slicks for the rear of the rear engined GT3 type track cars, having the equivalent of a 3.8", 4.4" and 5" sidewall height, all 18" wheels. They say:

They recommend the 3.8" sidewall for near stock cars- "(not for "serious" race-prepared cars like Carrera Cup or SuperCup cars)"
They recommend the 4.4" sidewalls for GT3 cups and similar
They recommend the 5" sidewalls for GT3R, GT3RS and RSR cars.

They suggest the taller sidewall tires put power down better.

Obviously a lot of design goes into these slicks that is different than street tires, but I wonder. My 17s have a 4.2" sidewall, the 19s a 3.6" sidewall. I don't run the same type of tire so comparison is difficult, but I wonder if the taller sidewall might give some of the benefits the Michelin slicks see.

Any thoughts?

Cup cars are a world of their own, they run extreme camber, extreme spring rates and have power to spare compared to all us normal types not to mention very efficient aero packages. When using slicks there is no such thing as aspect ratio as for DoT R or street types, also heat buildup in the Cups is a real concern the taller tires can handle it better

back in the early 2000s they ran 245/645 & 295/680 on 10 & 11 and continue to use 24/64-18 & 27/68 -18 on 9 & 11 basically the same sizes on the late Cups, late RSR use 27/65 -18 & 31/71 -18 on 11 & 13 but these sizes depend on the series too.

I believe that when Porsche made the move to taller tires on their street cars, they did so to get the advantage of lower aspect ratios w/o having the total tire package be too short for the cratered lanes we call roads in this country. The taller tires will also last longer for the same tread compound


After a lot of experimentation 993 Cups settled on 245/645x18 & 285/645x18 which is equivalent to 245/35 & 285/30 on 8.5 & 10

964 Cups used Toyo 245/45 & 255/40 or Pirelli 245/620 x17 & 265/630 x17 on 8 & 9.5 depending on the series

A shorter sidewall will in general run at a lower slip angle and as a result have more grip and run cooler.

[petevb]

Originally Posted by Bill Verburg

Cup cars are a world of their own, they run extreme camber, extreme spring rates and have power to spare compared to all us normal types not to mention very efficient aero packages.

Yea, I'm wondering where the crossover into that world is. I've got the same power, potentially the camber, and I run the cup wing so similar downforce. So how far away are we?

I currently run the car a lot softer than a cup car, and don't feel I could make my car work at their spring rates with my current tires. One wonders if they are using the tire as the spring, a-la F1, which is why they set the cars up so stiff...

I think the larger slip-angle on the taller sidewalls suits my driving style perhaps. When the 17s go away the breakaway is not nearly as abrupt as the 19s, however I not using the same tires so could be completely off.

[Bill Verburg]

Originally Posted by petevb

Yea, I'm wondering where the crossover into that world is. I've got the same power, potentially the camber, and I run the cup wing so similar downforce. So how far away are we?

I currently run the car a lot softer than a cup car, and don't feel I could make my car work at their spring rates with my current tires. One wonders if they are using the tire as the spring, a-la F1, which is why they set the cars up so stiff...

I think the larger slip-angle on the taller sidewalls suits my driving style perhaps. When the 17s go away the breakaway is not nearly as abrupt as the 19s, however I not using the same tires so could be completely off.

In the northeast 18 is the most popular track tire size, the Caymans and 997s use 19s but seem to eventually migrate to 18. There are a lot of legacy 17s around and the latest fad is the 275/35 x15 for the the 911s.

Your car is a far cry from those that most of us drive.

I'm sure that the tire is a significant part of the springing on the Cups, before they repaved LRP the Cups had a lot of trouble getting the power down, acceleration, braking, cornering were all a series of hops from bump to bump.

[rsrdave]

Hi Guys ,thank you for all your post and info .I have decided to run 18s 8x18 9x18 and borrowed a set for the cars first outing 235/40/18 265/35/18 and went well .
cheers Dave

[dsfnctn]

[JohnJL]

Originally Posted by Jeff Alton

Here is the 255/35/18 R6 on a 18x9.5 wheel.






CCW makes good wheels, have a sets of monoblocks for the 996. There three piece stuff is good too. We don't sell them, but they are good quality.

Cheers

Hi Jeff,
What model/year is the green car? Do you know the offset on that rear wheel?