What race tire size for DE on 15x7's

[caproader]

Guys,

Now that I'm spending so much time waving cars around to pass at DE events, I guess it's time to ask for race tire advice.

I have a set of 15x7 cookies that I want to use on my 73 T coupe with a2.7 MFI engine and stock bars (torsion and sway).

What is a reasonable tire size if I do not want to roll the fenders or change the alignment from street specs? The car is slightly lower than original spec.

What brand and model number gives the best compromise between tire life and tire traction? Because it is my first race tire, I'm inclined toward tire life before trying to knock off the last tenth of a second.

All advice and thoughts happily accepted.

John Meyer, The Capitalist Roader, and proud member #322
73 S sportomatic Coupe, 73.5 Targa, 73T with 2.7 MFI
1969 912/5 Irish Green Coupe in pieces

[304065]

15x7 Cookies have the same offset (23.3mm) as Fuchs. As such, I would not go any larger than 205 at each corner.

On my narrow body 1971 race car I usee 225s but these require rolling of the fenders and I am, as you might expect, using very aggressive camber settings that are not suitable for street driving. I also have about 35mm of offset on a seven.

The danger with a 23.3mm offset seven is that the additional width is offset to the outer face of the tire, which places it in closer proximity to the fender lip. The Factory fit sevens under the 911R by using a 49mm offset that basically put the additional inch of width on the inside of the rim. This resulted in a narrowed rear track which was compensated for by the additional rubber. Obviously this was less than desireable which is why the Factory started flaring (even the 911R had larger flares than the LWB) with the S-T and didn't stop until the RSR.

It's hard to make a narrow body work well for really going fast. My advice would be to use 205's and accept a slightly lower limit which is probably appropriate anyway in light of your decision not to modify (i.e. all race cars must be thought of as economically and historically expendable)

[Eric911S]

Hello: What I use are the Kumho Victoracers 225/50/15 on 7" wheels. These work very well and last a long time. The tracks that we run here are old airport circuits and are hard on tires. The Kumho are less expensive than Toyo or Yokohama tires. Kumho have a new tire as well the V700 and it works well and can be gotten in a 45 series tire. The Kumho's are a forgiving tire and give you alot of feedback which is good for new track drivers. Another option are Falken tires which I have driven on a Nissan Z and they seemed not as sticky as the Kumho. Lastly make sure your car is not lowered too much since you don't have bigger torsion bars then it will roll more so you may have a rubbing problem in the rear of the car. The front will be fine. Thanks Eric

[caproader]

Guys,
Thanks for the thoughts. In the short term, I plan to borrow a friend's set of race tires mounted on 15x7's and take a trip up and down the street to see if they rub.
Many thanks for your help.

John

[304065]

How will you tell if they rub, by the burned paint 2" up the fender? By the torn and distorted sheet metal?

When the tires rub it's not pretty.

[nullh20]

If the rear tires rub inside the fender above the lip you should see rub marks on the tires.

Just driving up & down the street probably isn't enough though- you want to be sure you aren't going to have issues on the track in high body roll situtations when suspension travel is maxed.

[Earl Green]

You might need to check the oil lines for the front cooler and spring plate bolts after you drop the car off the jack.

R Gruppe #259

[Eric911S]

Hello; You won't have any rubbing on the spring plate bolts or the front oil lines. If you use the 225/50/15 tires. If you want to check clearance get 5 of your biggest friends and lean on the rear of the car to check for rubbing. Lift your engine lid so they can sit on the engine shelf and also push down on the bumper. This will work very well with stock torsion bars but not so well with larger bars. If your car is close to stock height you should be ok. If lowered to the max then you will have rubbing already with your stock 195/65/15 tires. Good luck. Thanks Eric

[304065]

Mr. Green, considering that your 7R's have their additional width on the inside it is no surprise to me that you had to relocate the oil lines and grind down the spring plate bolts. However, the questioner is asking about ATS "Cookie Cutters" which have a 23.3mm offset, unlike your 49mm offset rarities. Therefore, I would think it much more likely that his problems will be encountered on the wheel arch, not on the inside as yours.

[Eric911S]

Hello: I was just responding to his question about the later offset wheels. I'm sorry if I affended you. I have raced these cars for 16 years and know what fits on them. I use the 7x15 phone dial wheels,cookie cutter wheels and Fuchs 911 part number 7x15 wheels. If you use the 7R wheels they will break if used for track wheels- not when they will. As a racer I use the wheels that I can buy cheaply and are strong. Mr Green I would not have bent the oil lines to fit the wheels, I would have used spacers instead. Caproader, I would use the cookie cutter wheels and have fun at the track. Thanks Eric