Backspacing explained The article Imagine a top view of a wheel with the mounting surface centered between the edges... this is 0" of offset, or 0" of back spacing.... Now move the mounting surface to the outside of the wheel... like a front wheel drive car... that's negative backspacing... ie...the wheel moved "in". Now the opposite... the mounting surface is on the inside of the wheel and you have the "deep dish" look, this is positive offset, because the wheel is out from the car. Positive or negative offset is "bad", it moves the center of the wheel away from the center of the steering axis, and causes stress... Most factory wheels are about -0.5" to -1.0" offset... they are set in, because the ball joints are inside the mounting surface and they are the steering axis. Going more than about +1 offset will cause more rapid suspension/steering wear. John Donovan ************************************************************************************ Backspacing is the distance from the point where the wheel mounts to the back of the rim. More backspacing puts the wheel/tire closer to the vehicle. Less (of course) moves it out. If you move 'em too far in either direction, you'll put more stress on the bearings. Another popular measurement is "offset". As I recall, that's the distance of the mounting point from the center of the wheel. A positive offset means the point is closer to the outside than the center. There's a writeup in the Oct '97 issue of `4-Wheel & Off-Road' The stock TJ "gambler" style wheels have about 5.5" backspacing, the ARs that I replaced 'em with have 3 15/16". I'm told that 4.5" will fit 33x12.5 with no rubbing. James CE Johnson ************************************************************************************ Backspacing is the distance from the rear edge of the rim to the mounting surface. Offset is the distance from the rear mounting surface to the center of the rim. An 8" rim with 4" backspacing has 0" offset. A 10 " rim with the same backspacing has a + 2" offset. An 8" rim with +4" offset has 0" backspacing. Harry Brosofsky
john: do u remember chrome reverse rims from the 60's & how tough they were on spindles & balljoints ?
Cool I was just comming in to this Thread to ask about Backspacing and i run into this....Good Explanation! But what would be good for a '65skylark (coupe) that's on 17''wheels?
I'd have to disagree with Harry, an 8" rim with 4.5" (not 4")backspacing is 0" offset, he forgot to add the rear lip which is generally agreed to be .5" although some are closer to .375".
Take the backspacing of your orginal wheel. If it is centered in the wheel well and I believe it is then you can do a calculation from it. If your wheel was a 6" wide wheel and the backspacing on the wheels is 4" then when you go to an 8" wide wheel you will need to incease the backspacing by 1" to 5". The wheel is growing by 2" so you want half of the growth (1") as backspacing and half of the growth(1") as front space. This will maintain the postion of the wheel with respect to the hub. essentially it will make the wheel an inch closer to each side of the wheel well. Mark
