Wheel backspacing

[pathybuilder]

I apologize for bringing up an old thread again, but this seems like the most straight forward thread on backspacing here. My question is around how a 10" rim is not recommended. So...I just measured my stock chrome wheel, measures 15x7 with 4.75BS. I was running 31/10.50/15 with no frame rub. Now I want to upgrade to 33/12.50/15 or 33/13.50/15 Most 12.50 tires recommend a 10" rim. 13.50 definitely needs a 10" rim. So the difference between the rim and the original 10.5 tire is 2.5" divided by two, because the tire will sit evenly on both sides of the rim = 1.25". 1.25" tire offset + 4.75" BS gives me 6" So the inside of the tire sits 6" from the wheel mounting surface. This should be your critical measurement.

 

Now, if I run a 33/12.50/15 on a 8" rim... 12.5"-8" = 4.5". 4.5"/2 = 2.25". Therefore 6"-2.25" = 3.75" which is why 3.75 is the recommended backspacing for running a 12.5" tire on an 8" rim.

Now if I run the same 33/12.50/15 on a 10" rim....12.5"-10" = 2.5". 2.5"/2 = 1.25. Therefore 6"-1.25" = 4.75", I would think that running 4.75BS with a 12.5" tire on a 10" rim would be the same as the running 3.75"BS with a 12.5" tire on an 8" rim. The centre of the tire is still going to be in the centre of the rim which as long as the distance from the wheel mounting surface to the inside of the tire is 6", it should be the same.

Now if I want to run a 13.50 tire, not considering fender trimming or steering components - which are being addressed BTW. 13.50"-10" = 3.5". 3.5"/2 = 1.75" Therefore 6"-1.75" = 4.25". I would need to run 4.25"BS with a 13.5" tire on a 10" rim. This is going to stick out 1" further than a 12.5" tire on 8" wheels with 3.75BS. Don't get me wrong, I understand that running a wider tire will be harder on your steering components and wheel bearings, but I don't think the rim width has anything to do with that, just the backspacing.

 

I hope this doesn't make things more confusing for people. If it does I'll just delete it, I promise. Wheels and Tires are expensive. I'd hate to order something that isn't going to work.

[Chadius]

Where can I get some rims with 3.5 back spacing? I can't narrow summit results by the model. Do I have to do it by the bolt pattern? If so what is it?

[nunya]

6x5.5 lug pattern

[SpecialWarr]

Those are LUG-centric, yes?

[ebayfish]

Make sure to check the center hub bore too, you need at least 100mm(about 4") many Chevy rims are only 87mm, thus won't fit around your from hub.