Offset rims on a AWD car

[DankDSM]

I have been thinking about handling with my car latley. I want to start road raceing and I know that the back end likes to drift around when off the gas. I thought a good way to solve this would be to have wider tires in the back. Maybe throw in a little offset and it should solve the problem. My worries are that this might effect the differental and gears in the transmission. So basically does anyone think this will work? Has anyone tryed it? I want some feedback before I go ahead and try this because i am using 18 inch racing harts and I am going to have to drop some serious money. Any advice would be apreciated. Thanks

Josh K

 

[president95]

You can't run different sized tires on an AWD car without damaging the VC. I wouldnt even run different brand tires that are the "same" size.

Same sized wheels, same brand, model, and sized tires on all 4 corners.

 

[Nors]

I think hes saying there may be slight differences in size...

 

[president95]

I disagree. Even the same tires that have worn slightly more than the other can have damaging effects.

As quoted from http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18

"As an example of different tire diameters resulting from tires worn to different tread depths, we'll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth. The new 225/45R17-sized tire has a calculated diameter of 24.97", a circumference of 78.44" and will roll 835 times each mile. The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8" shorter with a diameter of 24.84", have a circumference of 78.04" and will roll 839 times per mile. While the difference of 1/8" in overall diameter doesn't seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle's driveline. Obviously, the greater the difference in the tires' circumferences, the greater the resulting strain."


YOU may not notice a difference, but your car will.

 

[president95]

... Now, if the question was; "Can I run the same sized wheels/ (matching) tires with the rear having a different offset", he would be fine, as offset does not change the circumference. Offset is the distance between the true center of the wheel, and the point where the wheel mounts to the hub. That distance (measured in mm), is the offset.

 

[PieEyedPiper]

Good stuff president95, I'm in complete agreement.

 

[gsx rated98]

THE REAL DEAL, where are you getting your information from, that different size tires will not effect the VC? president95 has given a reference to his argument, where is yours?
Not trying to make argument, just would like to know where your getting your information from.

And yes, i do agree with president95.

 

[eclipsegsx1736]

There's quite a lot of info in here that needs to be cleared up. First of all, if the rear end is coming around on you with same size/type of tires all around, you need to figure out what you're doing wrong. Either something is incorrect with the car such as an alignment issue (camber settings?), or you need to drive differently. That being said, you can't expect to enter a corner hot and let off the gas mid corner in a car with modified suspension and expect the car to behave. Lift-off snap oversteer is quite common on an agressive suspension setup and can be avoided by driving differently or adjusting various suspension settings.

Second, if you're able to find two differently sized tires that have the exact same diameter than by all means you can run an offset tire setup, but I don't believe there are any combinations that will work. Regardless, you're doing it backwards. If anything you want a wider tire in the front. Your car shouldn't be set up to the point where you have to be so careful on a track to avoid snap-spin that you don't even push the car to the limit. Our cars, with their 50/50 torque split have a natural understeer tendency on-power. This can be somewhat tuned out with a tail-happy suspension setup, but the result is a scary car off-power (mainly on corner entry and during trail braking).

Just run the same size tire all around and figure out what is causing the car to oversteer, whether it's driver technique or set up or whatever.

 

[DankDSM]

I was not thinking of haveing a different roundness to the tire. I was more looking for a wider tire in the rear. These cars are nose heavy and more traction in the back cant be a bad thing. The main reason i asked this question is because i just rashed 2 of my rims and i have to replace them anyway. Thanks for the advice. I think i am going to call some wheel manufacturers to see if they can help me with sizing.

 

[eclipsegsx1736]

Ok, first of all you can't just get a wider tire without increasing sidewall height and affecting total diameter. The "40" in 245/40 isn't a fixed value, its a percentage of the tire width and therefore increases together with tire width. At least you got the nose heavy bit right, but being nose heavy usually means you would benefit from more front traction, as a nose heavy car (especially with 50/50 split) will want to understeer.