Widening Wheels

[TERMINATORSAINT]

Good afternoon,

I have the 1999-2004 Mustang SVE 03 Cobra Wheel - 18 x 10 Machined, and want to run the Toyo R888R 315/30/18. The wheel offset for these wheels is +20 MM.

If I were to have these wheels widened to 11 inches for example, would they just mount up and there not be any clearance issues? Would a spacer be applicable in this instance?

The car will have H&R Race Springs and the B8 Bilstein Shocks installed with rolled fenders.

Hoping the cobra gods can give me some guidance.

Thank you for looking!

 

[DCguy]

When wheels are widened they will typically cut the barrel toward the inner edge since the bore and spokes of the wheel are more toward the outer edge. Then they'll add whatever amount of material and weld the inner edge back on to that, effectively widening the wheel.

Forget offsets - backspacing is what's important here when you're concerned about clearance. First thing is find out what your wheel backspacing is.

So if you have an 18x10 with 5.5in of backspacing (for example), this means that from the wheel bore's edge (the surface of the wheel that contacts your brake rotor) to the wheel lip of the inner edge of the wheel is 5.5 inches. Find some photos of this its easier to grasp.

Widening a wheel means adding backspacing. So if you added 1in to your 18x10 it will become an 18x11 with 6.5 inches of backspacing....which means you will have more tire going into your wheel wells. If you run quad shocks you may have some contact issues there. In such a case, a wheel spacer (or removing the quad shock) is required.

From there you can figure out your wheel offset, but in general terms adding backspacing will effectively increase your positve offset. So if we add 1in in wheel width thats basically 25mm of offset we've just added. If you're already starting out with a +20mm offset, this means you'll have a +45mm offset which isn't great. You'll have wider wheels but the outside edge of the wheel is going to be unchanged relative to where it sits under the fender. So either way, when widening wheels, typically spacers are always needed, unless you have a very rare wheel like an 18x10 with a 0 offset.

In this case I would go with a 1/2 spacer at minimum, maybe even 5/8 to help push the wheel outward for a better fitment and, potentially, clearance. What that means is that you'll need to install 3in wheel studs if you haven't yet....and open ended lugnuts.

It might just be easier to buy a set of 18x10.5 for the rears if you're just trying to stick to factory style 5 spokes.

 

[fitforspeed]

If I’m not mistaken I believe your offset is a measurement from the wheels mounting face to the centerline of the wheel. So the positive offset would increase by 1/2 essentially becoming +32.7mm


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[fitforspeed]

You can run a 315/30r18 on a 10 inch wide wheel. Physically it will mount and be ok. Recommended is 11 inch for proper fitment. 10.5 is what the AFS reproduction wheels are. I’ve run both a 10 and a 10.5 with 315 Toyo r888r’s with no issues. Rolled fenders recommended and grind down the factory irs mounting bolt in the inner fender well or buy a low profile version. Having wheels widened is not cheap though and including shipping and down time it all adds up. If you really love the wheels then go for it. Taste in wheels may change over time and you could end up having a fair amount of money tied up in a relatively cheap Chinese wheel. I say save your money and buy a nice set of custom forged wheels when you can.


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[TERMINATORSAINT]

When wheels are widened they will typically cut the barrel toward the inner edge since the bore and spokes of the wheel are more toward the outer edge. Then they'll add whatever amount of material and weld the inner edge back on to that, effectively widening the wheel.

Forget offsets - backspacing is what's important here when you're concerned about clearance. First thing is find out what your wheel backspacing is.

So if you have an 18x10 with 5.5in of backspacing (for example), this means that from the wheel bore's edge (the surface of the wheel that contacts your brake rotor) to the wheel lip of the inner edge of the wheel is 5.5 inches. Find some photos of this its easier to grasp.

Widening a wheel means adding backspacing. So if you added 1in to your 18x10 it will become an 18x11 with 6.5 inches of backspacing....which means you will have more tire going into your wheel wells. If you run quad shocks you may have some contact issues there. In such a case, a wheel spacer (or removing the quad shock) is required.

From there you can figure out your wheel offset, but in general terms adding backspacing will effectively increase your positve offset. So if we add 1in in wheel width thats basically 25mm of offset we've just added. If you're already starting out with a +20mm offset, this means you'll have a +45mm offset which isn't great. You'll have wider wheels but the outside edge of the wheel is going to be unchanged relative to where it sits under the fender. So either way, when widening wheels, typically spacers are always needed, unless you have a very rare wheel like an 18x10 with a 0 offset.

In this case I would go with a 1/2 spacer at minimum, maybe even 5/8 to help push the wheel outward for a better fitment and, potentially, clearance. What that means is that you'll need to install 3in wheel studs if you haven't yet....and open ended lugnuts.

It might just be easier to buy a set of 18x10.5 for the rears if you're just trying to stick to factory style 5 spokes.

Thank you very much for the explanation! Sounds like holding out for the AFS machined 10.5’s might be the best bet. I really like the original wheel design in 18’s.

 

[TERMINATORSAINT]

You can run a 315/30r18 on a 10 inch wide wheel. Physically it will mount and be ok. Recommended is 11 inch for proper fitment. 10.5 is what the AFS reproduction wheels are. I’ve run both a 10 and a 10.5 with 315 Toyo r888r’s with no issues. Rolled fenders recommended and grind down the factory irs mounting bolt in the inner fender well or buy a low profile version. Having wheels widened is not cheap though and including shipping and down time it all adds up. If you really love the wheels then go for it. Taste in wheels may change over time and you could end up having a fair amount of money tied up in a relatively cheap Chinese wheel. I say save your money and buy a nice set of custom forged wheels when you can.


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I appreciate your response! Some good points, the investment would be steep. I like those AFS 10.5’s. Hope they release them soon. Yeah I think I’ll just hold out and go with a 10.5

 

[98 svt]

I run a 305/35 18 on 10" wheels. A 315 would work for sure.