Help with relationship between wheel width and backspacing

[Stinkbug]

I current have 15 x 8 wheels with 4” back spacing. since I have added a Swayloc up front and outboarded my rear shocks, I am rubbing when flexing the suspension. It seems that an additional less backspacing would do the trick.

Here is what I am considering…

15” tires are becoming less and less available as manufacturers phase out old model tires and bring in their new and improved version. It is not news that my favorite MT/r are no longer available.

What I am running into is a smaller number of bead-lock wheels are available in 5 x 4.5 pattern. Even fewer with a 3 1/2 backspace. Those that I am finding are 8.5 or 9” width.
Since this is likely the last set of wheels my TJ will see, now might be the time to switch to a 17” wheel despite the additional costs of tires and wheels and loss of sidewall.

That is a long build up for what is probably a very simple question…

Will having a new 1/2 or 1” inch wider wheel negate the 1/2 inch less back spacing and put me in the exact same place I am now? In other words, will a 15x8 with 4” backspace be the same as a 15x9 with 3 1/2 backspacing when it comes to clearing suspension components?

 

[Jerry Bransford]

The backspacing dimension itself is not affected by the wheel width at all. The backspace dimension is only the distance between the inner-most edge of the wheel and the wheel's mounting surface. You ca have the same 4", for example, of backspacing regardless of if the wheel is 8", 10", or even 12" wide. This is an especially useful dimension, as opposed to the Offset dimension, since it tells you directly how far into the wheel well the wheel's inner edge protrudes... as in how close it is to the frame and suspension components.

The yellow tape measure below is measuring the wheel's backspacing.

 

[Stinkbug]

The backspacing dimension itself is not affected by the wheel width at all. The backspace dimension is only the distance between the inner-most edge of the wheel and the wheel's mounting surface. You ca have the same 4", for example, of backspacing regardless of if the wheel is 8", 10", or even 12" wide. This is an especially useful dimension, as opposed to the Offset dimension, since it tells you directly how far into the wheel well the wheel's inner edge protrudes... as in how close it is to the frame and suspension components.

The yellow tape measure below is measuring the wheel's backspacing.

View attachment 500945

Thanks Jerry, I am clear on that part of the equation and should have stated that in the original question. Maybe I am overthinking it like I normally do but I was wondering if the additional wheel width lets the sidewall bulge out more and negates some of the gains I will get from less backspacing…

 

[Jerry Bransford]

Thanks Jerry, I am clear on that part of the equation and should have stated that in the original question. Maybe I am overthinking it like I normally do but I was wondering if the additional wheel width lets the sidewall bulge out more and negates some of the gains I will get from less backspacing…

Wheel width doesn't really affect tire width at its mid-point up its sidewall which is the tire's stated width is measured at. Wheel width really only affects the tire's mounting width. And the wider the wheel the more air pressure the tire requires to stay safely seated against the wheel. Which is why most of us who air our tires way down stick to the narrower widths of acceptable width wheels. Which is why I run 8" wide wheels for my 35x12.50 tires. 10" would work but I can safely air down more with an 8" wide wheel than I could with a 10" wide wheel.

 

[Stinkbug]

Wheel width doesn't really affect tire width at its mid-point up its sidewall which is the tire's stated width is measured at. Wheel width really only affects the tire's mounting width. And the wider the wheel the more air pressure the tire requires to stay safely seated against the wheel. Which is why most of us who air our tires way down stick to the narrower widths of acceptable width wheels. Which is why I run 8" wide wheels for my 35x12.50 tires. 10" would work but I can safely air down more with an 8" wide wheel than I could with a 10" wide wheel.

Like you I am enjoying my Walker Evans beadlocks. however, I am running into fitment issues at this point in my jeeps modification (plus I could never find that elusive 5th wheel I have been searching for)

From what you wrote, can I assume that if sticking to a beadlock, the that the 1/2 increase in rim width to 8 1/2 on a 17” wheel or an additional 1” width on a 15” will be fairly nominal when it comes to airing down to the 8 pound range?

 

[Jerry Bransford]

Like you I am enjoying my Walker Evans beadlocks. however, I am running into fitment issues at this point in my jeeps modification (plus I could never find that elusive 5th wheel I have been searching for)

From what you wrote, can I assume that if sticking to a beadlock, the that the 1/2 increase in rim width to 8 1/2 on a 17” wheel or an additional 1” width on a 15” will be fairly nominal when it comes to airing down to the 8 pound range?

What fitment issues are you having with your WE wheels? My WE wheels are 15x8 with 4" of backspacing with 35x12.50R15 tires, 4" of lift, 1" body lift, and zero fitment problems. To me they are perfect.

 

[mrblaine]

What fitment issues are you having with your WE wheels? My WE wheels are 15x8 with 4" of backspacing with 35x12.50R15 tires, 4" of lift, 1" body lift, and zero fitment problems. To me they are perfect.

Didn't you have to add a small spacer to move the WE rims off of the calipers in the big brake kit?

 

[mrblaine]

Like you I am enjoying my Walker Evans beadlocks. however, I am running into fitment issues at this point in my jeeps modification (plus I could never find that elusive 5th wheel I have been searching for)

From what you wrote, can I assume that if sticking to a beadlock, the that the 1/2 increase in rim width to 8 1/2 on a 17” wheel or an additional 1” width on a 15” will be fairly nominal when it comes to airing down to the 8 pound range?

The tire sidewall bulge is also dependent on brand. I've run into vastly different amounts of sidewall rub doing outboard jobs depending on tire.

 

[Jerry Bransford]

Didn't you have to add a small spacer to move the WE rims off of the calipers in the big brake kit?

I did in the beginning but it must have self-clearanced itself. The last couple times my wheels were removed by a tire shop trying to get rid of a tire shimmy I noticed the spacers had been removed at some point but not by me.

 

[Stinkbug]

Didn't you have to add a small spacer to move the WE rims off of the calipers in the big brake kit?

I have the same wheels as Jerry and didn’t install a spacer. Maybe I should have but I didn’t. The only thing I had to adjust for the 15” brakes was to chamfer the unit bearing surface so it would seat properly in the rotor. But I will be the last guy to debate anything about brakes with you and Jerry.

What fitment issues are you having with your WE wheels? My WE wheels are 15x8 with 4" of backspacing with 35x12.50R15 tires, 4" of lift, 1" body lift, and zero fitment problems. To me they are perfect.

The were perfect when I had the same set up as you, once I added the Swayloc (thicker than my AntiRock) and outboarded the rear shocks is when is started having interference issues of the tire on the shocks and swayloc.


Edit: - Is it critical that I buy new wheels? No, but I lightened the load in the garage selling off old parts and accessories that I thought I needed years ago but don’t and saved the pennies towards getting this TJ project completed and dialed in after 15 or so years.

 

[Jerry Bransford]

The were perfect when I had the same set up as you, once I added the Swayloc (thicker than my AntiRock) and outboarded the rear shocks is when is started having interference issues of the tire on the shocks and swayloc.

Less backspacing or a small spacer.

 

[Stinkbug]

Less backspacing or a small spacer.

Less backspacing was always the answer as mentioned in the original post. I was just trying to figure out if having a wider wheel along with the new shallower backspacing would have a meaningful effect. Maybe it results it more tire bulge negating the 1/2” less backspacing the new rims will have?

It seems the answer is I will just have to try it and see…

 

[Jerry Bransford]

Less backspacing was always the answer as mentioned in the original post. I was just trying to figure out if having a wider wheel along with the new shallower backspacing would have a meaningful effect. Maybe it results it more tire bulge negating the 1/2” less backspacing the new rims will have?

It seems the answer is I will just have to try it and see…

Again, a wider wheel has nothing to do with the wheel's backspacing which indicates its clearance between its inner edge and things it could come in contact with. The backspacing has nothing to do with and is unrelated to the wheel's width.

 

[Stinkbug]

Again, a wider wheel has nothing to do with the wheel's backspacing which indicates its clearance between its inner edge and things it could come in contact with. The backspacing has nothing to do with and is unrelated to the wheel's width.

I guess I am just not getting it… So having a wider wheel does not translate into having more tire bulging on the sidewall? Assuming everything else about a wheel is identical. Will the same tire on a 8” or 10” wheel will cause no more or no less interference?

 

[Jerry Bransford]

Will the same tire on a 8” or 10” wheel will cause no more or no less interference?

Essentially the same. The tire's 12.5" width is measured half way up the sidewall and the wheel width at the tire's mounting beads has an insignificant effect on it. That's why we make a lot of specific backspacing recommendations based on the tire size but without regard to the wheel width.

 

[Stinkbug]

Essentially the same. The tire's 12.5" width is measured half way up the sidewall and the wheel width at the tire's mounting beads has an insignificant effect on it. That's why we make a lot of specific backspacing recommendations based on the tire size but without regard to the wheel width.

That clears it up… Thank you.