Best backspace/width/offset for 37 inch tire and 2.5 inch OME?

[NMAZ]

Howdy,
I'm looking to run 37 inch tires with a 2.5 inch heavy OME springs. I know there will be rubbing, and I know I'll likely need some panhard bars and maybe upper and lower arms. My question is what what wheel specs will help minimize the rubbing? I'm looking to copy some folks that have had success and not reinvent the wheel (pun intended).

Thanks,

-Randy

 

[Road Apple]

To fit 37”s I’m installing a 3” suspension lift and a 1” 4Crawler body lift. The front axle will be moved forward 1.25” with Eimkeith RAM brackets to help clear the firewall. The rear axle will be moved aft with extended lower and adjustable upper control arms.

The wheels are
17x8.5
Backspacing is 4.5”
Offset is 0mm
Which are both stock numbers.

Thinner tires will help.
I chose 37/12.5R17 tires
13.5 tires will be harder to clear

Button head bolts will help inside the fenders
Front coil spacers to level the truck will help

 

[Broski]

To run 37s with a 2.5" lift you will need to do some cutting or run large Bump stops. 3.5" back spacing will help clear the frame and inner wheel well on the rear.
There are many variables that make a difference, how heavy or lite your Reg is and there is a big difference in size from one brand 37" tire to another

 

[Broski]

To fit 37”s I’m installing a 3” suspension lift and a 1” 4Crawler body lift. The front axle will be moved forward 1.25” with Eimkeith RAM brackets to help clear the firewall. The rear axle will be moved aft with extended lower and adjustable upper control arms.

The wheels are
17x8.5
Backspacing is 4.5”
Offset is 0mm
Which are both stock numbers.

Thinner tires will help.
I chose 37/12.5R17 tires
13.5 tires will be harder to clear

Button head bolts will help inside the fenders
Front coil spacers to level the truck will help

To fit 37s you don't need to move the front axle forward to clear the firewall or exhaust. It will help clear the rear lower outer wheel well where the bolts are that you speak of. If you do then you have to cut the front of the wheel well, the bumper and the radiator support.
This is all documented in Box rockets build thread.

 

[Road Apple]

To fit 37s you don't need to move the front axle forward to clear the firewall or exhaust. It will help clear the rear lower outer wheel well where the bolts are that you speak of. If you do then you have to cut the front of the wheel well, the bumper and the radiator support.
This is all documented in Box rockets build thread.

@Broski, I did my homework. Yes, @Box Rocket has documented this, which is why I’m moving the axle forward in a similar way. He states, “These will give better tire clearance at the firewall.”

Adam documents moving the axle forward in his MUD build thread in post #674.

Build - Box Rocket 1995 FZJ80 Build

Looks good but man it's crazy how even 37's look small/normal on these

forum.ih8mud.com

Adam also documented his DIY bracket install on Expedition Portal on post #541.

“After the bumpstops are sorted, the last step will be to relocate the front axle ~1.5" forward. I plan to do this using the method Darren McRae has been using in Australia for some time now with the Slinky kits and factory radius arms. New plates are welded in to the frame bracket for the radius arms and new holes drilled farther forward. These will give better tire clearance at the firewall. Don't want to move it to far or there are clearance issues with the front panhard.Rocket

Box Rocket 1995 FZJ80 Build

After the bumpstops are sorted, the last step will be to relocate the front axle ~1.5" forward. I plan to do this using the method Darren McRae has been using in Australia for some time now with the Slinky kits and factory radius arms. New plates are welded in to the frame bracket for the...

www.expeditionportal.com

I’m using the @eimkeith bracket, who also has documented the help given moving the axle forward saying, “The other aspect that I was interested in was relocating the axle forward to create more firewall clearance for larger tire sizes.”

FJ80 / FZJ80 RAM

Did you “need” to move the axle forward? No. But it will help according to these two knowledgeable members.

 

[NMAZ]

To run 37s with a 2.5" lift you will need to do some cutting or run large Bump stops. 3.5" back spacing will help clear the frame and inner wheel well on the rear.
There are many variables that make a difference, how heavy or lite your Reg is and there is a big difference in size from one brand 37" tire to another

Is that 3.5" back spacing with an offset of 0, and an 8.5" wide wheel?

Thanks

 

[Broski]

@Broski , I did do my homework. @Box Rocket has document this, which is why I’m moving the axle forward the same way he did. He specifically mentioned, “These will give better tire clearance at the firewall.”

He documents moving the axle forward in his build thread in post #674.

Build - Box Rocket 1995 FZJ80 Build

Looks good but man it's crazy how even 37's look small/normal on these

forum.ih8mud.com

Adam also documented his DIY bracket on expedition portal on post #541.

“After the bumpstops are sorted, the last step will be to relocate the front axle ~1.5" forward. I plan to do this using the method Darren McRae has been using in Australia for some time now with the Slinky kits and factory radius arms. New plates are welded in to the frame bracket for the radius arms and new holes drilled farther forward. These will give better tire clearance at the firewall. Don't want to move it to far or there are clearance issues with the front panhard.Rocket

Box Rocket 1995 FZJ80 Build

After the bumpstops are sorted, the last step will be to relocate the front axle ~1.5" forward. I plan to do this using the method Darren McRae has been using in Australia for some time now with the Slinky kits and factory radius arms. New plates are welded in to the frame bracket for the...

www.expeditionportal.com

I’m using the @eimkeith bracket, who also has documented the need to move the axle forward. says, “The other aspect that I was interested in was relocating the axle forward to create more firewall clearance for larger tire sizes.”

FJ80 / FZJ80 RAM

Did you “need” to move the axle forward? No. But it will help according to these two knowledgeable members.

I never said you didn't do your homework. I personally ran 37s interco trxus tire that are one of the only true full 37" tall tires with out moving the axle. The tires never rubbed the firewall or the exhaust. My Reg is a dedicated wheeler and I run the hardest trails. I am how on 39s and have moved the axle foreword the same way Box Rocked did. In other words I have a lot of experience with this.
The point is when you move the axle forward for 37s you well be cutting in the front as documented in Adams thread.
I was just trying to be helpful and don't want other readers to think they have to move the axle to run 37s .
Cheers

 

[Broski]

Is that 3.5" back spacing with an offset of 0, and an 8.5" wide wheel?

Thanks

Not trying to be a smart a**, reading up on wheel back spacing and off set well help you under stand the difference. For there to be 0 offset the back spacing has to be half the wheel width.

 

[jkeithw]

I might be wrong, but I think part of it has to do with extended bump stops and radius arm rear mount heights. I like to maintain as much uptravel as possible (and avoid extending the bumps.) And, since I relocated the pivot downward, the two in conjunction put the tire closer to the firewall at the top of its travel arc vs. say a 3-4" suspension lift with extended bumps and the original rear pivot height (relative to the frame). Does that make sense?

That said, I'm also doing a 25mm forward bracket based on some user feedback about the current 30mm version of my RAMs.

 

[NMAZ]

Not trying to be a smart a**, reading up on wheel back spacing and off set well help you under stand the difference. For there to be 0 offset the back spacing has to be half the wheel width.

lol, this is why I only have only posted a few messages and have been on for years. thanks for the info you did give.

 

[jkeithw]

Not trying to be a smart a**, reading up on wheel back spacing and off set well help you under stand the difference. For there to be 0 offset the back spacing has to be half the wheel width.

well, almost - the wheel width is always measured inside the bead walls, whereas the backspace is measured from the WMS to the innermost edge of the wheel. Typically wheels measure around 1/2" wider than their actual width because of the flange or wall thickness where the wheel meets the bead.

So you could have a wheel that is 8" wide, 0 offset, and 4.25-4.5" of BS, for instance.

 

[Broski]

well, almost - the wheel width is always measured inside the bead walls, whereas the backspace is measured from the WMS to the innermost edge of the wheel. Typically wheels measure around 1/2" wider than their actual width because of the flange or wall thickness where the wheel meets the bead.

So you could have a wheel that is 8" wide, 0 offset, and 4.25-4.5" of BS, for instance.

Thank you for the clarification, you are correct.

 

[NMAZ]

If not 0, what is the recommended offset?

 

[Broski]

I might be wrong, but I think part of it has to do with extended bump stops and radius arm rear mount heights. I like to maintain as much uptravel as possible (and avoid extending the bumps.) And, since I relocated the pivot downward, the two in conjunction put the tire closer to the firewall at the top of its travel arc vs. say a 3-4" suspension lift with extended bumps and the original rear pivot height (relative to the frame). Does that make sense?

That said, I'm also doing a 25mm forward bracket based on some user feedback about the current 30mm version of my RAMs.

This why in post #3 I said that there are too many variables, each Reg will be different.
I also think people confuse the inner wheel well with the fire wall. The fender bolts to the inner wheel well which sets in front of the fire wall.
All that being said I like your products, there well thought-out & built. I am finally getting the PHC ket that I bought from you installed.

 

[NMAZ]

Do these fit the bill? Pro Comp Xtreme Rock Crawler Series 97 Steel Black Wheels 97-7983S3.5

Wheel Diameter:17 in.
Wheel Width (in):9.000 in.
Wheel Bolt Pattern (app):6 x 139.70mm
6 x 5 1/2 in.
Offset:-38.00mm
Backspacing (in):3.500 in.
Center Bore Diameter (mm):107.95mm

 

[Broski]

Do these fit the bill? Pro Comp Xtreme Rock Crawler Series 97 Steel Black Wheels 97-7983S3.5

Wheel Diameter:17 in.
Wheel Width (in):9.000 in.
Wheel Bolt Pattern (app):6 x 139.70mm
6 x 5 1/2 in.
Offset:-38.00mm
Backspacing (in):3.500 in.
Center Bore Diameter (mm):107.95mm

They are the same size wheel that I am currently running and work well. With a 12.50" wide tire they still tuck. Off the top of my head I can't remember the correct bore size necessary to fit over a full float rear hub.
If you are not running factory flares the wheels will stick out side the body.

 

[NMAZ]

Thanks Broski! Gotta say, the work you've done on your suspension looks pretty freaking sweet.

-Randy

 

[jkeithw]

I just got home and was able to find the back of the envelope where I made offset notes for our 80 - I don't have direct experience with these fitments yet (I'm going 16"/35" initially on our truck) but my notes were -25 to -12 ET on 8/8.5 width, and -12 ET on a 9" to clear the inner fender well in the rear and minimal trimming to the flares. (more experienced folks may want to chime in here)

 

[Road Apple]

Off the top of my head I can't remember the correct bore size necessary to fit over a full float rear hub.

Center bore is 106mm