Im getting some 36x13.5x17" Irok radials this weekend, and need to decide on wheels. 17x8 4.5" B.S. or 17x9 5" B.S.? I am leaning towards the 17x8.....that extra 1/2" of backspacing will probably come in handy. Any reason NOT to go with the narrower wheel? Im thinking Cragar Soft 8.

 

With a 9" wide rim with 5" back spacing or a 8" wide rim with 4.5" back spacing there would be no difference, both would give you the same amount of tire in the wheel well as well as out. The only difference would be that the wider one would make the tire a litle flater across the tread wile the narrower rim will make the tire seem a litle more round and tall. But not by muck seeing as its only a 1" difference between the two.

 

go with the 9" i have 17 x 8 bs 4.5 with 12.50 and i wish i would have got the 9" instead

 

you need wider than an 8" wheel for a 13.50 tire according to interco. i have 8" and wish i had 10" width.

 

This is incorrect.

The BS has NOTHING to do with the rim width (That's an offset issue).

A rim with 5" of BS has a 1/2" more BS than a rim with 4.5" of BS, no matter what the rim width is.

As a 4.5" BS rim is at least about what is needed, that would be my first choice for BS if I had to choose between the two above's BS figures.

4.75" BS is typically required for a 12.5" section width tire...and a 13.5" tire is going to protrude another 1/2" than a 12.5" tire, as discussed....so the 4.5" BS gives an extra 0.25" of that 0.5" difference, close enough if a little rub on full stuffage is not a disaster once in a while...but ideally, another 0.25" - 0.5" would provide more clearance.

That means that 4.25" might work better for full stuffage situations/full lock, etc...but frankly, 1/4" rub is not a big deal anyway....

Hope that helps.

 

I would disagree.

The tire will sit centered on the rim, with equal amount of the tire extending past the edge of the rim on both sides, and the back spacing is the amount of the rim that is on the back-side of the mounting surface. The wider the rim the less back spacing that would be needed.

Say we had a rim thats 10" wide with 4" of back spacing and also one that is 8" with the same back spacing of 4" both with a 12.5" tire mounted.
The tire on the 10" rim would sit 1" farther out than the tire on the 8" rim would.
The 10" rim rim would place 7.25" of the tire forward of the mounting surface while the 8" rim would place 6.25" of tire forward.

 

LOL.....TEEJ is right....4.5" is 4.5" period. Backspacing only refers to a distance between the wheel's mounting surface and the inner lip of the rim. It is independent of wheel width. A 9" wide wheel with 4.5" backspacing will stick out 1" further than a 8" wheel with the same backspacing.

It seems the consensus is that I would be safer and better of with a 9" wide wheel. No prob...its just that the Pro Comp 97 seems to be the only 17x9 4.5" BS steel wheel available and it is nearly double the price of the Soft 8.....but I think the extra 1/2" of backspacing will be worth it.

 

No, still wrong....its just not true.


12.5" tire, 6.25" inboard protrusion from center of tire, 2.25" of tire bulge out past inboard side of rim...no matter what rim, etc.

Slight differences may appear as the rim gets REALLY wide for the tire, etc...but, the reality of it is that the inboard side of the rim is 4" from the hub face....and, its a 6.25" trip from the middle of the tire, AND the middle of the rim, to get there....

The place the hub face mounts is NOT the center of the rim....and the BS says ONLY where the inboard EDGE of the rim is.....

So, as a 12.5" tire ALWAYS sticks one side 6.25" inboard from the tire's center line...

...and, as we KNOW the edge of the RIM is 4" from the brakes, etc....and that the inboard side of the TIRE has to be mounted to the inboard side of the rim...the rim's WIDTH is taken out of the equation.

So, if part of the journey inboard is shared by extra rim metal with the rubber, that's fine, but, the journey is the same 6.25" inboard from TIRE centerline distance anyway.



Please, trust me on this.

 

think about the word itself backspacing... it don't matter if the wheel is 15 inches wide if the back spacing is 4.5 it will have 4.5 inches of space on the back side.. or if it is 8 inches with 4.5 Backspacing it will have 4.5 inches of space on the back side.
the tire don't know where the "face" of the wheel is...

saying the BackSpacing changes with the width of the wheel is like saying if you take a 12 inch ruler and break 4 inches off the end of it and then say that the first six inches is no longer six inches because the rest of the ruler changed.

 

"It seems the consensus is that I would be safer and better of with a 9" wide wheel. No prob...its just that the Pro Comp 97 seems to be the only 17x9 4.5" BS steel wheel available and it is nearly double the price of the Soft 8.....but I think the extra 1/2" of backspacing will be worth it."

Good question, BTW - I was wondering about this myself.

Oh, and TEEJ, I saw this and thought of this thread.