Specific backspacing question (4.5" backspacing and 12.5" tires)

winfield

winfield

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Feb 14, 2023
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Greenbank, WA
Looking for help. I have a 97 TJ with a 4.5" lift. It currently has 15x10 wheels w 3.5" back spacing and 35/12.5 tires. The local Highway Patrol is hassling me because they stick out too much. A smaller tire will look goofy, so was hoping to switch out wheels. Question: Can I get away with 4.5" back spacing on a 15x8 wheel and 35/12.5 tire? Mostly road use, which is a sin here I'm sure. I've read everything I can on this forum, but am still a bit at a loss.

The lift and tire details:
Bilstein B8 5100 4.5" Front & 4.5" Rear Lift Shocks
Rough Country Long Arm Upgrade Kit for 4-6 in
Super Swamper 35x12.50R15 Tire, TrXus MT Radial RXM-11R
 
I’m going to bump this just to help it get attention but I just don’t have a lot of knowledge with backspacing to offer advice.
 
You'll have to adjust the steering stops for sure. The question I have is if the tires will contact the springs or not. I think you should be fine, but someone who has actually run this setup will chime in shortly and let you know for sure.
 
While not exactly your setup, I’m running 17 x 9 wheels with a 4” backspacing and 35x12.5-17 MTs They are mostly fine. It’s only when I’m at full lock that the edges rub a little.

4.5” BS will probably rub a bit more, but will probably be OK
 
Chris said:
You'll have to adjust the steering stops for sure. The question I have is if the tires will contact the springs or not. I think you should be fine, but someone who has actually run this setup will chime in shortly and let you know for sure.
Click to expand...

Thanks, Chris. I had read about putting washers in the steering stops and am not opposed to that. Hopefully someone stumbles on this who has run a similar setup and can answer on the springs.
 
winfield said:
Thanks, Chris. I had read about putting washers in the steering stops and am not opposed to that. Hopefully someone stumbles on this who has run a similar setup and can answer on the springs.
Click to expand...

Washers are not needed. If a tire rubs at full steering lock and it bothers you, then back off on the steering.
 
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Mike_H said:
While not exactly your setup, I’m running 17 x 9 wheels with a 4” backspacing and 35x12.5-17 MTs They are mostly fine. It’s only when I’m at full lock that the edges rub a little.

4.5” BS will probably rub a bit more, but will probably be OK
Click to expand...

Thanks, Mike. I appreciate the help.
 
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3.75" BS seems to be common for a 35x12.5 tire. Mine is running that now. But i will be changing to 17x7" wheels with 4" backspacing in the near future. The tires do rub at the far reaches of the steering and suspension travel and they will rub a bit more with less BS. But I know and understand where that will be and it doesn't concern me.

The interesting aspect is that the steering will improve some because the steering axis inclination will be closer to stock. Not enough people mention that when it comes to wheel backspacing.
 
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jjvw said:
3.75" BS seems to be common for a 35x12.5 tire. Mine is running that now. But i will be changing to 17x7" wheels with 4" backspacing in the near future. The tires do rub at the far reaches of the steering and suspension travel and they will rub a bit more with less BS. But I know and understand where that will be and it doesn't concern me.

The interesting aspect is that the steering will improve some because the steering axis inclination will be closer to stock. Not enough people mention that even it comes to wheel backspacing.
Click to expand...

Thanks, jjvw. This is helpful.
 
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Mr. Bills said:
I run 315/75R16 ("metric" 35) tires on 16x8 wheels with 4" backspacing - no rubbing with a single thin washer behind each steering stop. 4 1/2" backspacing would rub with those tires.
Click to expand...

Thanks, Mr. Bills. Looking at some 16 and 17 wheels to get more options. Sounds like 4" bs will be the magic number. Of course that means buying tires too. Ha!
 
winfield said:
Thanks, Mr. Bills. Looking at some 16 and 17 wheels to get more options.
Click to expand...
Sorry. I couldn't resist. :p
1n5wni.gif
 
winfield said:
Looking for help. I have a 97 TJ with a 4.5" lift. It currently has 15x10 wheels w 3.5" back spacing and 35/12.5 tires. The local Highway Patrol is hassling me because they stick out too much. A smaller tire will look goofy, so was hoping to switch out wheels. Question: Can I get away with 4.5" back spacing on a 15x8 wheel and 35/12.5 tire? Mostly road use, which is a sin here I'm sure. I've read everything I can on this forum, but am still a bit at a loss.

The lift and tire details:
Bilstein B8 5100 4.5" Front & 4.5" Rear Lift Shocks
Rough Country Long Arm Upgrade Kit for 4-6 in
Super Swamper 35x12.50R15 Tire, TrXus MT Radial RXM-11R
Click to expand...

I have this exact setup 35x12.5r15 with 4.5” BS.

For onroad it will work fine. I had no rubbing onroad. I did get rubbing off-road, so I added two washers to the steering stops and a 0.25” wheel spacer to the front two tires. This mostly alleviates the rubbing off-road, but 4” would be better.

The nice thing is 4.5” reduces the scrub radius, and that means it drives better onroad.
 
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