Porsche: Tire Modifications and Size Calculator
Adding a larger set of wheels and tires to your Porsche can improve not only performance, but the overall appearance of your car as well. Continue reading as this article will tell you what you need to know about tire modifications and sizes.
This article applies to the Porsche 928, Porsche 993, and Porsche 997 (1978-2012).
There are an incredible number of options available today for enthusiasts looking to replace their stock wheels and tires, but this doesn't mean that it has to be a daunting task. By conducting a little research and figuring out what you want from a set of wheels as well as tires, you can easily identify the best set for your particular needs. Essentially, the first step is simply deciding which kind of tire you need.
Step 1 – Determine your needs
Do you drive your Porsche only on sunny days or at the track? Do you live in a state where it rains a lot, or do you enjoy a little winter hooning? While most Porsche owners baby their cars and keep them garaged in the winter, summer tires aren't your only choice. You can go for an all weather type tire, or even keep a set of snow tires around (if you need to). For those lucky enough to live in warmer states or for those who garage their car in the winter, a set of summer performance tires can be maintained year round.
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Step 2 – Understanding tire sizes
Tire size has a huge impact on performance, and choosing the wrong size can have detrimental effects as well. If the tire is too big for your car, it can rub and wear out prematurely. If you want to move to a wider wheel and tire setup, keep in mind the total diameter of the package, and try not to stray more than 2 to 3 percent in total diameter from the original tire. For example, if you wanted to upgrade your factory 16" wheels to a 17" wheel, you would want to add a 225/45R17 front tire and a 245/40R17 rear tire because these sizes are close to the same diameter of the original tire.
Standard Tires |
Tires |
Rims |
ET** |
|
|
'87 Model Year Onward 928 S4 928 S4 Club Sport |
Front Rear Front Rear |
225/50 VR 16 245/45 VR 16 225/50 VR 16 245/45 VR 16 (with 17mm spacer) |
7 J x 16 H 2 8 J x 16 H 2 8 J x 16 H 2 9 J x 16 H 2 |
65 52.3 60 60 |
|
'89 Model Year Onward 928 GT |
Front Rear |
225/50 ZR 16* 245/45 ZR 16* (with 17 mm spacer) |
8 J x 16 H 2 9 J x 16 H 2 |
60 60 |
Step 3 – Choosing the right wheels and tires
Upgrading to a 17 or 18-inch wheel is quite common on Porsche 928s, and bigger sizes are possible. The problem with going too big is that you have a good chance of experiencing rub and premature wear, or even performance issues as well as damage. You will also want to take into consideration the wheel's offset. A negative offset can move the tire closer to the wheel wells, resulting in rubbing. A positive offset, on the other hand, moves the tire closer to the frame. The goal is to find the right spacing between the chassis and the body of the car to avoud any rubbing.
Step 4 – Other considerations
If you change your stock wheel and tire size to something bigger or smaller in diameter, you will need to have your speedometer as well as odometer calibrated to reflect the changes.
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