How does backspacing affect handling? 3.75 vs 4.5 backspacing for 31 x 10's?

[kayakbrian]

First, I'm new here and I just want to say thanks for such a great resource. Been driving the XJ for about 3 years but I'm doing my first big XJ build so everything is new to me.

I'm going to be running 15 x 8 steelies and 31 x 10.5 KO2's on a 3" lift and will never go to a bigger on tire size. My current backspacing choices for the wheel I'm looking at are 3.75 and 4.5.

First, does anyone know for sure if 4.5 backspacing will or won't rub the LCAs with this wheel / tire combo?

Next, I can't get a good sense of how backspacing affects performance? Wider stance obviously affects stability, and I seem to drive at 30 degrees more often than I should, so stability sounds nice. But I've also read that backspacing affects handling and parts wear. We do a LOT of freeway driving and if there are negative handling aspects or extra wear on parts between these two backspace choices that would definitely factor into my decision. Lots of opinions out there but it's hard to decipher what is real and what isn't!

Thanks for any replies, especially if you run this setup. appreciate it.

 

[maxbraketorque]

I've got 31x10.5" on 15x8x3.75" backspace now, and I will be moving to 15x8x4.5" backspace on 32x11.5".

I've got long arm suspension, so I don't know if 4.5" will clear stock LCAs, but its not the end of the world the tires rub.

I've not had any problems with highway driving. I routinely cruise at 65+ mph on straight stretches and on twisty mountain roads.

3.75" backspace creates a very large scrub radius. This cause lots of tire skid on full lock turns such as in parking lots. From a practical perspective, its not a problem. Just a little skid. I suspect that large backspace also increases the tendency for death wobble, but I have no direct experience with this.

From the perspective of looks, I feel like 3.75" make 31x10.5" tires stick out too much. The tires stick out at least 1" beyond stock fenders on a late model XJ.

 

[RCP Phx]

On "lil sis" I run 31.50 x 15's on factory Gambler rimsky which are 4.5" backspacing with short arms and do not rub!

 

[Tim_MN]

I doubt the minor difference between the two backspacing choices will have any observable handling differences. Less backspacing does cause greater wear on the unit hub bearings.

Most XJ Cherokee owners run about 4.25 to 4.75 backspacing.

 

[Winterhawk]

15x8 with 4.5 bs is 0 offset. With a 31x10.5 tire your scrub radius is 22mm from stock. Regardless of what most people say it will indeed affect handling.

 

[RCP Phx]

The only advantage to less backspace is body roll stability.
The dis-advantages are increased wear on the unit bearings, ball joints, and tie-rod ends by increasing the steering load! You also may have to deal with fender coverage laws.

 

[jeep ride]

I had 15 x7 4 inch backspace on my 98xj with 31 1050 because of inspection laws.

 

[XJEEPER]

I've run 16x8 TJ Rubi wheels with 1.25" billet spacers on two XJ's, for 2 decades and 140k miles combined.

This combo nets me a total backspacing of 4".

In that timeframe, I have not experienced accelerated ball joint wear (I don't run cheap stock BJs) nor have I experience accelerated unit bearing wear. FWIW

 

[Ewenm]

ive been running 15x8 rims with 3.75 back spacing for 17 years with no issues what ever

oh ok so off roading i get more muck up the side of my vehicle.

and once had my arm resting on the open window and got wacked in the elbow by a stone
ouch that hurt

 

[phissure]

I have the setup that OP wants to do, but I have no idea what my backspacing is. How do I measure it?

 

[RCP Phx]

I have the setup that OP wants to do, but I have no idea what my backspacing is. How do I measure it?

It should be marked on the rim!

 

[XJEEPER]

I have the setup that OP wants to do, but I have no idea what my backspacing is. How do I measure it?

Backspacing is measured from the wheel mounting surface to the rim bead area where the tire bead contacts the rim.

Using the "offset" terminology, this measurement references the distance that the wheel mounting surface is offset from the wheel center point. Measured in negative and positive offset.