Upgrading tires. What back spacing?

[Zuni]

After reading this and now I'm worried.
I ordered new wheels and plan on getting new tires
OEM on my Sport was 245/75R17, 17x7.5", 44mm or 45 OS, and I forget what the backspacing is for OEM.
New:
275/70R17 17x9, -6mm OS, 4.7" BS.
Are these going to stick out like crazy?
(Thanks and I hope I didn't hijack the thread. New member here, new Jeep owner as of last week. I've been meaning to post just an introduction thing)

Going from 44 to -6mm offset would be just short of 2 inches of back spacing difference. So that should be about 4.25 back spacing. A +6 offset would be about 4.75 back spacing I believe.

Sponsored

 

[Old Dogger]

Thank you Reinen. Maybe I'm mistaken but I believe a 275/70R17 is a 33"x11", not quite so large as 35"x12.5". (I will not claim to be anywhere near an authority on wheels tires or general mechanics/suspension)

I run them one mine, and this 275 is a 32" tire. 285's are 33's.

 

[Zuni]

If his chosen wheels are available in ~12-20mm mine weren’t, I was a bit nervous, but the tread doesn’t stick out past the extensions He’s OK to about the common 0 offset with extensions.

I was shooting for 0 to -6 offset for maximum clearance (0 would equal about 4.5" back spacing). I was wondering if I could tuck them in a little. My old jk had a 2" lift and 33x12.5x15s that stuck out at least 2". That puts a lot of stain on the unibearings. I had to replace the front bearings twice and rear once between 40,000 and 100,000 miles.

 

[Old Dogger]

Your question: I'm replacing my stock 285x70x17 Wildpeaks with 35x12.5x17 mudders on my 23 JL Rubicon. I believe the stock cast rims are 17x7.5 with a 6.25" back spacing/44mm offset. Can I use a 17x9.5 with a 5", 4.75, or will I need 4.5" back spacing?

Second question: I was shooting for 0 to -6 offset for maximum clearance (0 would equal about 4.5" back spacing). I was wondering if I could tuck them in a little. My old jk had a 2" lift and 33x12.5x15s that stuck out at least 2". That puts a lot of stain on the unibearings. I had to replace the front bearings twice and rear once between 40,000 and 100,000 miles.

Hopefully the below will help to somewhat clarify your questions:
1. The Width of the factory wheels are 7.5". The upgraded wheel width is 9.5" So you are adding 2.0" of width. Half of that will go to the inside and half will protrude outward. So 2.0" divided by 2=1" More wheel to the outside.
2. Lets review Back Spacing: The Factory wheel is 6.25. The updated Wheel is 4.5 Back Spacing. So that will move your wheel out a additional 1.75".
3. Lets review tire width: Your 285, is 11.5" wide. Your 35's are 12.5" wide. So half will go to the inside and the other half will protrude to the outside. 1.0" divided by 2-.5" added to the outside.

So your tire will protrude out this much further: Rim width 1", Back Spacing 1.75" and tire width 05" equals a total of 3.25 additional inches.

@Zuni

 

[2nd 392]

I was shooting for 0 to -6 offset for maximum clearance (0 would equal about 4.5" back spacing). I was wondering if I could tuck them in a little. My old jk had a 2" lift and 33x12.5x15s that stuck out at least 2". That puts a lot of stain on the unibearings. I had to replace the front bearings twice and rear once between 40,000 and 100,000 miles.

~0 offset with 12.50’s the tread will be even with XR flares with 8.5” wheels with the sidewall bulge past them. I would keep it as close to 0 as possible. 1” = 25 mm adjust accordingly for increased wheel width . IE 9 1/2” wheels ~12mm

 

[Zuni]

I run them one mine, and this 275 is a 32" tire. 285's are 33's.

Your question: I'm replacing my stock 285x70x17 Wildpeaks with 35x12.5x17 mudders on my 23 JL Rubicon. I believe the stock cast rims are 17x7.5 with a 6.25" back spacing/44mm offset. Can I use a 17x9.5 with a 5", 4.75, or will I need 4.5" back spacing?

Second question: I was shooting for 0 to -6 offset for maximum clearance (0 would equal about 4.5" back spacing). I was wondering if I could tuck them in a little. My old jk had a 2" lift and 33x12.5x15s that stuck out at least 2". That puts a lot of stain on the unibearings. I had to replace the front bearings twice and rear once between 40,000 and 100,000 miles.

Hopefully the below will help to somewhat clarify your questions:
1. The Width of the factory wheels are 7.5". The upgraded wheel width is 9.5" So you are adding 2.0" of width. Half of that will go to the inside and half will protrude outward. So 2.0" divided by 2=1" More wheel to the outside.
2. Lets review Back Spacing: The Factory wheel is 6.25. The updated Wheel is 4.5 Back Spacing. So that will move your wheel out a additional 1.75".
3. Lets review tire width: Your 285, is 11.5" wide. Your 35's are 12.5" wide. So half will go to the inside and the other half will protrude to the outside. 1.0" divided by 2-.5" added to the outside.

So your tire will protrude out this much further: Rim width 1", Back Spacing 1.75" and tire width 05" equals a total of 3.25 additional inches.

@Zuni

Not really worried about how far it sticks out. I'm worried about rubbing at full articulation. Although I realize my mistake with the rim width and am shooting for 9 or 8.5". Actually 285s = 11.22" wide.
So I figure safe would be half the width of the tires plus half the width of the rims in minus back spacing. ((12.5-11.2=1.3) + (9.0-7.5=1.5"))/2 equals 1.5" rounded up. So optimum back spacing would be 6.25-1.5=4.75. I think that should work. Offset would be: 44-(1.5"*25.4) =5.9mm.
They should stick out about 2.15".
I wonder if they would rub if I used 5" back spacing or 0mm offset?

 

[JT1]

Not really worried about how far it sticks out. I'm worried about rubbing at full articulation. Although I realize my mistake with the rim width and am shooting for 9 or 8.5". Actually 285s = 11.22" wide.
So I figure safe would be half the width of the tires plus half the width of the rims in minus back spacing. ((12.5-11.2=1.3) + (9.0-7.5=1.5"))/2 equals 1.5" rounded up. So optimum back spacing would be 6.25-1.5=4.75. I think that should work. Offset would be: 44-(1.5"*25.4) =5.9mm.
They should stick out about 2.15".
I wonder if they would rub if I used 5" back spacing or 0mm offset?

On a rubicon you can run 35x12.50 on factory wheels and not rub except for in the rear at the liner. Don't overthink it.. any backspacing less than the factory 6.2 will work.

Quadratec sells factory looking wheels in a 5.2" backspace in a 17x8.5 for pretty cheap.

 

[Old Dogger]

Not really worried about how far it sticks out. I'm worried about rubbing at full articulation. Although I realize my mistake with the rim width and am shooting for 9 or 8.5". Actually 285s = 11.22" wide.
So I figure safe would be half the width of the tires plus half the width of the rims in minus back spacing. ((12.5-11.2=1.3) + (9.0-7.5=1.5"))/2 equals 1.5" rounded up. So optimum back spacing would be 6.25-1.5=4.75. I think that should work. Offset would be: 44-(1.5"*25.4) =5.9mm.
They should stick out about 2.15".
I wonder if they would rub if I used 5" back spacing or 0mm offset?

Most run 9" Rim Width, with 4.5 Back Spacing. But, another favorite is 9" Rim Width, with a 5.2 Back Spacing. Either or should work just fine. Your scrub radius, will be better with the 5.2. Plus that will also be easier on your Ball Joints and hub bearings.

 

[Reinen]

Thank you Reinen. Maybe I'm mistaken but I believe a 275/70R17 is a 33"x11", not quite so large as 35"x12.5". (I will not claim to be anywhere near an authority on wheels tires or general mechanics/suspension)

Oh, I thought you were the OP and the OP is going to 35s.
Just plug your tire sizes & offsets into https://tiresize.com/wheel-offset-calculator/ and you'll get exact measurements.

 

[Zuni]

Most run 9" Rim Width, with 4.5 Back Spacing. But, another favorite is 9" Rim Width, with a 5.2 Back Spacing. Either or should work just fine. Your scrub radius, will be better with the 5.2. Plus that will also be easier on your Ball Joints and hub bearings.

That sounds like sound advice. That's about what I'm coming up with. My math told me 4.5 to be safe but I was hoping to tuck them in a bit more. The scrub radius I didn't even think about, another good pt. I wasn't worried though because I have 2" higher fender flares.

Sponsored