mixed wheel sizes

[Lowaholic]

Hey all. I'm not too sure if this have ever been figured out on this site or the old one, but I'm planning on getting new wheels soon for my truck, and I really want to go with 17"s front and 18"s rear. I know I'll have to change gears to match. I've got 3.73s all around now, but was planning to go to probably 4.10s in the rear to compensate for the 18"s. Has anybody ever pulled this off or does anyone know what formulas to use to figure it out? Or just how exact the math has to be (ie-.000s, .0000s, etc)? Thanx for any replies

 

[ABLITZ]

on a AWD truck/car you dont wanna run two different sized wheels,it will burn up the transfercase.i dont know if changing the gears would make up for the difference.maybe someone else might know

 

[Crazy J]

you can pull it off if you're very careful in your tire selection, you'll need tires that have the same diameter. check out tirerack.com to see the specs of the tires. it's a lot easier this way than to try and gear the rear differently.

 

[BillC]

You can run different size wheels and tires on an AWD vehicle, if, and I stress IF, you match the tires and wheels to the differential gearing. The idea is that you want to have the front and rear driveshafts spinning at the same rate at all times. So, you need to match the gearing and tire sizes to make each wheel/tire cover the same distance for each driveshaft revolution. The formula for calculating this is:

front tire diameter/front diff ratio = rear tire diameter/rear diff ratio

Or:

rear tire dia = front tire dia x rear diff ratio / front diff ratio

As an example, if you run a 24" tall tire on the front with 3.42 gears, and your rear diff had 3.73 gears, you will need a 26.18" tall rear tire.

For anyone who doesn't believe me, read up on Summit Racing's QuadraDeuce. It is running a SyTy AWD system AND different size front and rear wheels and tires.

 

[Lowaholic]

woohoo now there's the kind of answer i was lookin fer
the only trouble now is figuring out how close they would have to be or within what kind of tolerances? When I first started thinking about this a few months ago I figured they would have to be REAL close like within probably thousandths at worst, but then again how many AWD cars and trucks are out there with uneven tire pressures? I'm thinkin that should be enough to cause damage? Well i'm off to do some math for now...

By the way, that Quadradrive is sweeet- heres the link ~> AWD '32

 

[7dhamper]

woohoo now there's the kind of answer i was lookin fer
how many AWD cars and trucks are out there with uneven tire pressures?

By the way, that Quadradrive is sweeet- heres the link ~> AWD '32

Look at the AWD Lamborghini Diablo VR4, it has a Vette tire package: 17's on the front, 18's on the rear (I think). I'll try to find a link...