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General Articles - Extras

Bumpstops Explained

Article written by Moab Man

Date Added: 05/31/2006

Repeatedly you will see the question posted, ?How much lift do I need to fit X sized tire??

This is where the lowly bumpstop?s are often misunderstood. You can lift a vehicle as high as you would like, but without bumpstop extensions you can still only fit a tire to the maximum that the bumpstop?s will allow.
Follow along as I illustrate what I mean...

Between the coil spring perches (blue) you can fit any size spring or mount any lifted leaf to the axle. This will allow larger tires to be ?fitted? on the vehicle. Here is where the bumpstop (red) comes in.
If you compress the suspension (with or without a lift) with the stock tires, or maximum size allowed, on a stock vehicle this is how it looks.
Now add a larger size tire without extending the bumpstop?s and the tires will go into the fenders possibly damaging the fender, tire, or both.
By adding a bumpstop extension, the tire will be kept away from the fender.
So how do you figure out how much extension you need? Although there isn?t an exact science to this, the following will get you in the ball park.

You have to know what the maximum (actual) tire size is that can be fit on a compressed suspension. Example: 30.25?
What is the actual size of the tire you?re putting on? 32.5?
What is the difference between the two figures? Divide by 2. Example: 2.25? / 2 = 1.13? (1.13? is about 1 1/8?)
Round up to 1.25? and this is approximately the bumpstop extension you will need to allow the tire to come up to the same point as it did with the stock tire.

Although this gets you in the ballpark of how much extension is needed, but is not an exact science. Variables are the shoulder of the tire used, backspacing of the wheel, and the amount of lateral movement in your suspension.

Final Thoughts

Hopefully you now have an understanding of the role bumpstop?s play in proper tire fitment.

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