Rim backspacing and offset.

[2000Cherokee]

i am picking up a 1988 Xj to use as a street xj build and i am trying to get rims so they dont stick out past the wheelwells at all. if possible i would like to keep them inside the wheelwells a bit so when i lower it a little i will not be hitting the flares. right now i am looking at the mustang bullit wheels that are in the 18x9 size if i go with the deepdish style i can get them with an offset of +34 and with backspacing of 6.41". or i can go with the regular rim lip still in the 18x9 size but they have an offset of +24 and backspacing of 5.85

now my question is how much if any will these rims stick out past the fenders? or will they be the same. if possible i would like to run a wider rim in the back for wider rubber since this will be a 2wd cherokee with a stroker motor and possibly a turbo so it will be putting down some power. but when i get into the wider rims the offset and backspacing chenges alot and i have no idea of how to tell how far out they will stick

so for the front i am looking at these
(regular lip)18x9 offset=+24 backspacing 5.85

rear
(deep dish)18x10 offset=+22 backspacing 6.38
(deep dish)18x10 offset=+45 backspacing 7.27

how would i tell if these rims would stick out the same? i would like to run a regular lip in the front and deepdish in the back just not sure how it would look

Thanks for any help

 

[streetpirate]

I had to do this when i bought my rims too, jack it up, remove the tires on one side, hang a string with a weight on the bottom from fender flare, the furthest point away from the hub that you want them sticking out, and measure the distance.

10" wheel, minus the backspacing, and thats how far the rim will stick out from the hub, and add ~1/2" for tire clearence.

once you know what size tires you are going to run (i would do stock mustang sizes to keep the height low, less rubbing when you lower it.

go to www.1010tires.com/TireSizeCalculator.asp

 

[Beej]

Even running a low profile tire on 18's, I'm pretty sure you won't be able to run a wheel of backspacing more than the 5.85. I don't think you could do the 6.38 (6.375), that's 6 3/8", I'm pretty sure the sidewall of a tire on a wheel with that backspacing will be too close to the leaf springs in the rear, especially lowered. Of course if you are planning on ditching the leafs for coilovers or a rear coil conversion, this may not be an issue for you. If you aren't though, this may be a consideration. I'd go with a 9" wide wheel if I were you, but to each their own...

You probably will want the wheel & tire diameter to be no less than 26", otherwise it may look too small on the vehicle, even lowered.

Also, no offense to streetpirate, but I think his rims stick out too far. They are definitely farther than what you described you want. He's heard that before though...

Ditto on the tire calculator, and if I were you, I'd double check those mustang rims. I thought they were 18x8's not 18x9's.

 

[Michaelarchangelo]

It depends on the width of the rim. If it is a 8" rim, then you could run more than 5.85.

 

[Beej]

It depends on the width of the rim. If it is a 8" rim, then you could run more than 5.85.

Backspacing figures do not change according to the rim width. Larger rim widths with the same backspacing increase width via frontspacing, no?

 

[Michaelarchangelo]

No but it does change the offset.

 

[streetpirate]

Also, no offense to streetpirate, but I think his rims stick out too far. They are definitely farther than what you described you want. He's heard that before though...

HEY! YOU TRY TUCKING 12" OF RUBBER WITH $100 BUDGET FOR WHEELS!

 

[HillbillyLes]

Backspacing is just that... the distance on the inside of the rim from the mounting face to the (inside) lip of the rim. The space from the hub mounting face inside to the leafspring or inner fender will not vary depending on the rim width. That is a given distance unless a wider axle is used or the springs set in and inner fender massaged... no matter WHAT the rim width.

On a Cherokee, the stock rim has a backspacing of 5.5". I am running 32X11.5 tires on stock XJ steelies (5.5 inches backspacing). I have less than 1/2" clearance between my inner tire and the leafspring. 6.5 inch backspacing would set the inside of the tire/rim an inch closer to the leafspring which obviously would not work.

For an 8-10 inch wide rim, a backspace of 4.5" to 5" (max) depending on the tire width would probably give enough inner clearance without the "wide-track" look.

I am in the same boat as I want to upgrade from my 32X11.5s to 33 or 35X12.5s so will have to get some wheels with less backspacing in order not to rub on the inside.

HbL
::

 

[Beej]

Backspacing is just that... the distance on the inside of the rim from the mounting face to the (inside) lip of the rim. The space from the hub mounting face inside to the leafspring or inner fender will not vary depending on the rim width. That is a given distance unless a wider axle is used or the springs set in and inner fender massaged... no matter WHAT the rim width.

On a Cherokee, the stock rim has a backspacing of 5.5". I am running 32X11.5 tires on stock XJ steelies (5.5 inches backspacing). I have less than 1/2" clearance between my inner tire and the leafspring. 6.5 inch backspacing would set the inside of the tire/rim an inch closer to the leafspring which obviously would not work.

For an 8-10 inch wide rim, a backspace of 4.5" to 5" (max) depending on the tire width would probably give enough inner clearance without the "wide-track" look.

I am in the same boat as I want to upgrade from my 32X11.5s to 33 or 35X12.5s so will have to get some wheels with less backspacing in order not to rub on the inside.

HbL
::

I agree with all of that except that stock rims have 5.25" of backpacing, not 5.5"...

 

[Michaelarchangelo]

Hmm, Im running a 17x8 with 6.295" backspacing and no problems.

 

[Beej]

Hmm, Im running a 17x8 with 6.295" backspacing and no problems.

What size tires?

I ask because I have stock 15" wheels with 31's and the sidewall is about 1/2" away from my leafs in the rear.

 

[Michaelarchangelo]

235s, they are just the tires that came on the rims for now.

 

[Beej]

235s, they are just the tires that came on the rims for now.

Do they rub your control arms at all at full lock?

And, what are they from? Its an unusual backspacing measurement...

 

[Michaelarchangelo]

Ive tried to get them to rub, but they haven't. They are from a 2005 mustang

 

[Beej]

Ah yes, I remember now, I think you had pics up here once, no? They must stick out about the same as the stock wheels too. I was looking at a set of those this morning, it would be great if they had a 5" backspacing...

 

[Ed A. Stevens]

I will steal a little from the FAQ Project, with thanks to Boatwrench & Yuccaman ... and a few others (let me know if this helps?):

Back Spacing: Back Spacing is the distance from the inside (closest to brakes) lip of the wheel to the mounting surface that bolts up to the hub or axle.

Standard Back Spacing (OEM or Factory rims): Standard backspacing is the smallest backspacing that can be built without reversing the shell. It is also the backspacing that has been calculated as the best average of brake clearance and steering geometry. Standard backspacing is what is supplied from the factory with stock production rims and places an importance on looks as well as steering geometry. The OEM or Factory Cherokee wheel back spacing is 5.25-inches for the typical 7-inch wide aluminum rims.

Reduced Back Spacing (lower number): Reduced back spacing moves the wheels outward from the axle hub flange, resulting in a wide track, (track is the distance from one side outer wheel edge to the opposite side outer wheel edge). Reduced back spacing increases the load on bearings, ball joints and steering components through an increase in leverage. The increased leverage is because the ball joint pivot point is fixed and has not been changed and the arc of the centerline of the wheel/tire sets further out from the hub. This causes the tire to move in a larger arc. Front tires turning in a larger radius arc may cause clearance problems with the non- trimmed fenders at full lock.

Deeper Back Spacing (increased number): Deeper back spacing moves the wheels inboard closer to the centerline of the vehicle, increasing the potential for large tires to contact the frame at full steering lock (requiring the steering stops to be adjusted out for a larger turning radius to eliminate the unwanted contact). Deeper back spacing is desirable with wider than standard axles, but could cause tire rubbing on Lower Control Arms (LCAs) and wheel interference with brake components on standard or OEM width axles.

Clearance: The best way to space tires out farther away from the springs or the body is through the use of longer or wider track axles. Custom axles are more expensive than custom wheels so changing backspacing becomes a desirable option. Decreasing or reducing the backspacing, thus moving the wheels outward from the vehicles is a less expensive compromise to restore the steering lock and inner fender well clearance when installing larger and wider tires. Another way to gain tire clearance is through fender trimming which is covered in another section.




Need more? Try this link ...

http://www.rsracing.com/tech-wheel.html

 

[Michaelarchangelo]

Ah yes, I remember now, I think you had pics up here once, no? They must stick out about the same as the stock wheels too. I was looking at a set of those this morning, it would be great if they had a 5" backspacing...

Nope, that wasn't me. They do stick out about the same as the stock rims. Why do you want them with a 5" backspace? You could always go with a spacer.