I know you have 18x9.5 wheels on the back of your truck. You also have the 2" wheel adapters. Would the 17x11 wheels fit on the back with 7.5" backspacing. What do you think I would have to do to make them fit. Thanks for your help.

 

i think he has 5-lug wheel adapters, right?

 

My 18x9.5 wheels are +63 mm offset, so that's about 7.75" backspacing? With my adapters, it's about 5.75" backspacing (stock is 5.5"). The extra width, 9.5", of the wheel over stock, 7", pushes the edge of the wheel out to the edge of the fenderwell, 1/4" more wheel to the inside and 2.25" more to the outside. The real use for spacers is to put a wheel with more backspacing on and keep the effective backspacing close to stock, keeping the clearance on the inside.

Going with more backspacing moves the wheel inward toward the brakes. I don't think the trucks can take anything more than 7" backspacing.

 

ok I was incorrect on the backspacing a little. It is a 50mm offset. I am not really sure what the offset measures, is it the distance from the outer edge of the rim to the mounting surface or what? I used a online wheel calculator to determine that the wheel would have a 7.95 backspace with that offset. With the adapters that would put me at 5.95 of backspacing. These are zr1 wheels by the way. There is another version that has a 36mm offset which would put me at 5.5 backspacing. I assume I would have to have the finders modified for that though. Any input would be great.

 

This is going on a 6 lug truck?

Regardless, I just had a thought.
7.75" backspacing, 18x9.5", puts the wheels at the edge of the fender. I could have gone 18x10.5, and that would have put the backspacing at 8.25". Subtract 2" for effective backspace. That would put the 18x10.5 with 1/2" more to the inside and outside. 18x11 would be 3/4" more to the inside and outside with 8.50" backspace. All this with +63mm offset.

17x11 with +50mm offset is 8.00" backspace. So, if you use the same adapters I have, then your wheels would be 1/4" more to the inside and 1.25" more to the outside. Mine are at the edge of the fenderwell now, so your's would be sticking out 1.25" further, which may be what you want.

A 2" spacer/adapter would be the minimum I would use b/c the lug bolts are about 2.25" long and with the adapters I had to cut off 1/2" of the lug bolts to fit. That's fine b/c I still have plenty of room to tighten the down the adapter and have the lug nuts fit in the adapters. Any less of a spacer and the lug nuts would stick out and not allow the other piece of the adapter to fit.

You need to measure to see just how much backspacing is available before the wheel would touch anything. In your case, the 17x11 wheel needs more backspacing. (+63) or so would put you 3/4" more wheel on the inside and outside compared to my 18x9.5s. (+70, 9.00" backspacing, would put you 1.25" more to the intside and 1/4" more to the outside than mine. All this with 2" adapters.

Formula:
(wheel width)/2 + (offset/25.4) + .5 = backspacing

I'm about 95% sure I wrote all this correctly. Hope it makes sense.

 

Yes it makes perfect sense, I researched wheel offsets and backspacing last night. I ended up with the same figures you just gave me, I just wasn't sure if the rims would stick out or not. I didn't really want them to, I wanted them to be even with the fender well. I may consider having the fenders rolled and then beat out a little. I am getting the hotchkis springs and leaf springs with the wheels and spacers. I would like to change the offset of the rims but they only come in to offsets, 50mm, and 36mm. They are oem zr1 grand sport rims. Thanks for all your info it has been really helpfull.