Scottie

I am in the process of further upgrading the wheels and tires on my C4. After searching I have learned that the new wheels and tires have to be within 6%. Ok, what is the 6%? Is it within 6% front tire circumference to rear or 6% new wheels and tires to OEM?

Computamedic

I'm pretty sure the 6% figure relates to the difference between the front and rear tyre size. Whether it relates to diameter or circumference is immaterial - it's the same issue. It's the PDAS system on the C4 that gets upset about front and rear axles running at different speeds. In reality, as long as you stay with a similar overall diameter you'll find it hard to stray anywhere near 6% difference. Just adjust the aspect ratio of the tyre to suit the size of wheel you choose. There are lots of tyre size comparison web sites (like this) where you can compare your chosen size with the standard size.

Regards

Dave

newsboy

I believe that the 6% is the allowable deviation from the circumference of the original 16" tires that were original equipment on the car.That is what the PDAS is set for. You will find that a most low profile 17" tires are almost the same as the original 16" So within spec's and no problem

Computamedic

Page 214 of Adrian Streather's book confirms that Steven is correct. The PDAS calculations are based on the OEM wheel/tyre combination and allows for a maximum 6% variation. It would be quite difficult to exceed that figure however since the overall radius of the tyre varies very little provided the correct aspect ratio is used.

Taking the standard front tyre of 205/55x16 the variation when going to a 205/50x17, a 225/45x17 or a 225/40x18 is significantly less than 1% in all cases.

Regards

Dave

tbennett017

Also as a caution, be sure your front and back are as close in diameter as possible. If not you will be causing the driveline to compensate and possibly wear much more quickly.

Scottie

Thank you all fellas, I will heed your advice and stay as close as possible to OEM AND front to rear.

Dave White

I went to 17"s years ago and have never had a problem. An interesting note is when I had the original wheels on(16"s) and the rear tires were very worn, I would occasionally get a flash from the differential light at high speeds, probably due the the diameter difference.