I just wanted to try and understand something better. I understand back space is the distance the rim bolts on to the inside edge of the rim... the less it is the more the rim is pushed out. I believe this distance is fixed. However I believe that rim width is independant of back space. For instance an 8" wide rim with the same back space as a 10" wide rim actually has all that width added to the outside of the wheel since adding it to the inside would change the backspace.

I often hear you need about 4.5" of backspace on a JK to run 35x12.5" tires. However if you look at a Rim with 8" width vs 10" width it changes where the tire rests. The center of the tire is in the center of the rim.

I was looking specifically at 2 Pro Comp rims, both 16" one 10" wide with 4.5" back space and the other 8" wide with 4" of backspace. If I am understanding this correctly the rim with 4" of back space is moving the tire out .5" but by using a narrower rim it is moved in by 1" and this results in the 8" wide rim with 4" of backspace actually causing more chance of interferance with suspension components/federwells or reducing turn radius since the tire is what causes the issues instead of th rim/wheel.

Am I understanding this correctly?

 

HUH? I need more coffee.

 

I think you got it right whatever I understood. two rims with the same backspacing, but different widht the one wider will stick out more than the narrower one. its not that complicated. and yes the more inches of backspacing would make the tire closer to the frame, resulting on possibly rubing. lets go over this a hundred times so everybody gets confused.

 

I think you're right.....

Think of it this way...........with a 4 in backspace and a 10 inch rim- you've got 4 inches towards the frame and 6 inches towards the outside: Conversely- 4 in BS and a 8 inch width-- you've got 4 in towards the frame and 4 towards the outside................................. of course there's a lil' shaved off one side of that calculation to account for the actual thickness of the mounting flange........

Dammm, its too dam early for math

 

DING DING DING DING DING DING DING.............................................. ....Give the man a prize!!!!!!!!!!!!!!!!!!!!!!!

 

OK, before I really understood this I always thought less backspacing means less chance of rubbing... but wheel width plays a part in that too and seems like it is just as important as backspacing.

So 2" wheel width = 1" back spacing when we are looking at only the inside of the tire from various components.

 

Use this chart.......



This shows the correlation between width, backspacing, and offset.

 

OK, before I really understood this I always thought less backspacing means less chance of rubbing... but wheel width plays a part in that too and seems like it is just as important as backspacing.

So 2" wheel width = 1" back spacing when we are looking at only the inside of the tire from various components.

I know that wider rims increases the foot print on the tread... but does it also push the sidewall out too? This would seem to take away from the 2" wheel width being the same as 1" of backspace.

I ran into this issue with my first Jeep, a CJ 7, where I put narrower rims on 35x15.5" Super Swaper SX tires (dedicated mud truck) and had horrible rubbing on the inside of my leaf springs. I am just wanting to make sure I avoid any amount of reduction in turn radius when I do a lift again.

 

But dont let him think it dont make No difference because it does....a 15 in wide tire on a 7 inch rim *could* fit..... but will 'roll' the tire instead of a flat tread (extreme example for sure) so your tire and rim widh should be *similar*

 

Here's a tech page with some helpful diagrams. The terminology was getting a bit confusing...
http://www.americanwheelandtire.com/tech.php