[StokedXJ11]

Can someone explain to me how it is that bumpstops work.... and the job that they do?

[Wheelin98TJ]

They stop upward travel of the axle.

If you look at the front coils on your XJ, you'll see a cup with a rubber bumper inside the coils. Once the spring compresses enough, that rubber bump stop comes into contact with the axle. So the spring is not allowed to compress anymore which stops upward movement of the axle.

[Tirith]

Bumpstops do three things (at least as I see it): they prevent overcompression of the springs in your suspension; they prevent the shocks from bottoming out; and they keep your wheels from stuffing too far into your wheel wells. In short, they limit compression of your suspension.

You can see your bumpstops in the front of your XJ if you look inside the coil springs. They are the rubber/polyurethane things hanging down from the top (or mounted to the spring pad below). For the leaf packs in the rear, you should see a rectangular rubber block mounted above the packs.

It is essential to properly bumpstop your vehicle as you lift it. In general, the bigger the springs, the more bumpstop you will need.

HTH!

[StokedXJ11]

ok sweet, thanks.

[Tirith]

Here's some pics that illustrate them nicely. Note the aluminum "adjustable" bumpstop on the bottom coil spring pad, and the compression of the bumpstops in the other pictures. (They are designed to allow about an inch of "crush".)

[StokedXJ11]

so with these, you can run larger than normal tires. Like tires that would be to much for a specific lift: IE: 33" tires with a 3" lift on an XJ and the Bumpstops stop the tire from going to far up into the wheel well when the suspension compresses?

[Tirith]

Originally Posted by cammer427

so with these, you can run larger than normal tires. Like tires that would be to much for a specific lift: IE: 33" tires with a 3" lift on an XJ and the Bumpstops stop the tire from going to far up into the wheel well when the suspension compresses?

Correct. But while longer bumpstops allow you to run larger tires, they also limit suspension articulation. While this may be acceptable on pavement, it may be unacceptable off-road. By limiting flex, you will lift tires sooner, and become more tippy. It's a trade-off.

For instance, see below for some comparison pics of my buddy's XJ. The pics are before and after we installed bigger tires and more bumpstop. He is running about 4.5" lift, front and rear. The smaller tires are 30x9.5, the bigger tires are 32x10.5 TSLs (which actually measure closer to 33"). Note the addition of the aluminum bumpstops to the lower spring pads in the pics. We had to add three additional inches of bumpstop when we went from the 30s to the 32s (33s ) to keep the the tires from rubbing. That killed his uptravel, but it was either that, or trim the fenders, which he was unwilling to do. (The rig is a Daily Driver; he did not want to hack into the unibody, nor destroy the "stock" look of the rig.)

Anyway, you can see the loss of flex. It is definitely tippier, but it seems to perform better in the rocks with the bigger tires. We just have to be mindful that he is tippeir now.

[Tirith]

Last two pics.