Reply to "Wheel fitment"

Jim

The distance a tire/wheel combination extends outwards (compared to other tire/wheel combinations) can be computed with this formula:

(tire cross-section ÷ 2) - off-set

This defines where the edge of the tire's sidewall is in relation to the hub. That dimension should fall in the range of 102mm to 112mm up front or 149mm to 159mm in the rear or the tire shall rub the fender arch. The outer sidewall limits can vary by 10mm due to tire diameter, ride height, camber adjustment and whether or not the fender arches have been “rolled”. I prefer to use the conservative limits 102mm (front) and 149mm (rear) as my limits, because I like "wiggle room".

check out the latest posts on the last page of sticky #8 for a detailed explanation.

Going in the opposite direction, if you stuff the front tire/wheel too far into the wheel well it just won't look good and it won't match the rear tires which are rather limited in where they can be situated within the wheel house. Stuffing the front tire inward reduces the track width (which reduces cornering traction) and alters the scrub radius too.

In general 18x8 wheels for the 225mm front tires will be fine with 12mm off-set unless the car is going to be lowered beyond the European ride height. The factory front 15x7 wheel off-set was 6mm. 12mm off-set will reduce the factory track width by 1/2 inch. This is better however than the 18mm off-set of the factory 15x8 wheel which is popularly used as a front wheel.

The way I like to proceed is to increase the amount of front tire offset as little as possible, in order to maintain the front track width as wide as possible. Then recess the rear tires to match the front tires if possible. The problem however, there's minimal opportunity to adjust the position of the rear tires. For instance tires 26.6 inches in diameter or more run into the issue of possibly rubbing the mufflers on their inner edges. 18x10 or 19x10 wheels for the 285mm rear tires are therefore limited to -6mm to zero off-set. -6mm is the factory dimension for the 15x10 wheels. That off-set extends the outer edge of the 285 tire close to the edge of the fender arch and increases the rear track width by 2 inches. Zero off-set of the rear tires recesses them by 6mm (1/4 inch). Rear track width is still 1-1/2" wider compared to the track width using the factory 15x8 wheels. At zero offset, a 285mm tire should have 1/4 inch clearance on either side, with the muffler on the inner sidewall and with the outer fender on the outer sidewall. In other words the tire is centered between the muffler and the outer fender.

The front tire's sidewall should be about 15mm recessed inside the fender, and the rear tire's sidewall should be about 8mm recessed inside the fender. Not a bad match, better than a lot of tire/wheel sets you'll see on Panteras. The front track loses only 1/2" width, the rear track gains 1-1/2" width. Both help the Pantera stick in corners. The tire diameters will be in the ball park allowing the chassis stance to be set properly (level) while the front and rear tires are equally centered within the wheel arches. No clearances are being pushed to the limit, everything has a little "wiggle room". In other words, you've got a combination there in which both the chassis' engineering and the car's appearance were taken into consideration.