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sleeper55
05-30-2013, 11:43 AM
Looking to save some time and frustration figuring out a rear wheel size and right back spacing. Any imput would be great. My rear has been narrowed a total of 4 inchs.I just put a TCI 4-link in the car. I have drum brakes that are about a half inch wider than stock. The car is not tubbed. I would like to run at least a 17 inch wheel. Has anyone been through this and can tell me what type of back spacing I need on my wheels to get the fatest tire under it? I know there is a formula to get this figured out but I really suck at math. lol

chevynut
05-30-2013, 12:00 PM
I put together a spreadsheet that calculates this for you that has been widely used on the internet. You need to know the mounting surface width for any calculation. You said the rear has been "narrowed 4 inches" so I assume that's 2" per side. Does the 1/2" wider drum brake setup affect that width? The stock tri5 rear is 60" wide.

The largest tire you're going to squeeze in there without any tubs is a 275 with stock fenderwells and tubs. The fenderwell lips are about 71.5" wide inside (give or take 1/2") and the inner tub is 46.5" wide. The difference is 25" or 12.5" per side. If you allow 3/4" clearance on each side of the tire, you can use a 11" tire which is a 275 metric size. You could use a 9 to 10" wheel with that tire. I personally think an 8" wheel is too narrow.

You need to pick your wheel width and determine your actual wheel mounting width before you can begin to discuss backspacing.

BAM55
05-30-2013, 12:16 PM
Here is how you measure for your backspace. Put a straight edge on the mounting surface and measure towards the frame to the first thing that will touch be it leaf springs, frame or what ever that is your backspace. Then measure from the straight edge toward the fender and write those to numbers down and give them to the wheel guy. That is what you have to work with.

Lets say you have 5 inches on the inside and 7 one the outside. That tells me a 10 inch will fit because you have a total of 12 inches to work with. Now we have to figure out the backspace (the backspace is the mounting point of the wheel to the outer edge of the rear lip of the wheel). Since you have 5 on the inside if we did a 4 inch backspace you should be fine. You have a full inch for tire bulge that leaves us with six inched going towards the fender, again you should be fine because you had 7 to work with right? Nope there is a kink to this math. A 10 inch is really 11 inches wide. They measure from the inside of the lip of the wheels the tire mounting surface.lol So you are really going to have a 1/2 for tire bulge. Now you can chance it and run a 10 or move to a 9.5 wheel. I have a 1/2 clearance on my 55 210 an it never rubs I chanced it.lol My 55 210 is not tub but it does have the leaf pocket kit installed and my rear is narrowed. I have a 18x10 with a 4 1/2 backspace. My tire size is 285\40\18