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2018 SRT
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Discussion Starter · #1 ·
I just picked up a MOPAR donut tire/wheel to use as a spare. With it came a wheel spacer for use should I need to use it on the front of my SRT. When I mount it on the back of the wheel the spacer doesn't fit flush. It's got about 1/8" of slack/wobble. Referencing the second pic note the A, B and C. It appears the portion of the lug between "A" and "B" bottoms out on the spacer before "C" seats on the wheel. Anyone have any advice? Thanks.
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The wheel spacer is only to be used on the front unless you have an open differential. The wheel spacer allows the wheel to clear the 6 piston Brembo disc brake calipers. If you put the donut spare on the rear with a closed differential, it will think that wheel slip is taking place and it will lock up. This can potentially cause damage to the differential unit. You are supposed to place a front tire on the rear and the donut spare on a front wheel location.
 

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Guess I'm not getting it? The area between A and B should be seating on the wheel. Does the spacer bolt on to the car with it's own bolts, then the lugs in the picture are where you mount the wheel? Generally if using the stock lugs, the spacer is very thin

Looking at your picture, the back of the wheel would contact the face of the spacer, then the nuts would tighten until the shoulder of the nut (A toB) is pressing on the surface of the wheel. C shouldn't seat on anything, if it is seating on the top of the spacer, the lugs are too long

A Guy
 

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Discussion Starter · #5 ·
All, last night I realized my mistake. Duh! That said I do have a question relative to where it’s acceptable to mount the donut (front or back).

The MOPAR donut is a 145/80 x 18 with a 27.1” diameter. My tires are the factory size for an SRT…275/40 x 20. The diameter is 28.7”. Is the 1.6” difference problematic for mounting the donut on the rear? The only reference to the rear end on my window sticker is “All Speed Traction Control.” I don’t know if this translates into “open” or “closed” (Bob’s terminology).
 

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All, last night I realized my mistake. Duh! That said I do have a question relative to where it’s acceptable to mount the donut (front or back).

The MOPAR donut is a 145/80 x 18 with a 27.1” diameter. My tires are the factory size for an SRT…275/40 x 20. The diameter is 28.7”. Is the 1.6” difference problematic for mounting the donut on the rear? The only reference to the rear end on my window sticker is “All Speed Traction Control.” I don’t know if this translates into “open” or “closed” (Bob’s terminology).
Many cars that have traction control will use the ABS instead of the differential. On Challengers and Chargers, the closed anti-spin differential cover is finned. The open non anti spin differential cover is smooth. If you have an anti-spin (finned cover) differential, you should only mount the donut spare on the front. The front tire/wheel assembly is then mounted on the rear. Best to do some additional research and determine what type of rear differential you have. If your car is all wheel drive, you may not be able to safely mount a donut spare at all.
 

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Dodge has sold tens of thousands of limited slip rear diff M6 R/T Challengers with a spare either standard or optional and nowhere is there a warning or stipulation that the spare must be used on the front only.

It's not like you're going cross country with it, it's for emergency use only to get you to the nearest tire shop.

Even Modern Spare has addressed this and their spare is the same diameter as the factory spare and they
say it is not a concern:

My vehicle has a limited slip differential, will using the spare damage my car?

-No, it will not. There are many performance vehicles that come from the factory with both a limited slip differential (LSD) and a spare tire. As a general rule of thumb, a spare tire needs to have a diameter that is at least 85% of the diameter of the vehicles other tires.

At minimum, our products have a spare tire diameter that is 92% of the OEM tire diameter with many of our kits having a 95% + diameter relation to the OEM tire size.

Thus, you can be confident that any Modern Spare product will be well within the safe use range for your vehicle.





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