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Bumpstop sizing help

X

XJ_NorCal

NAXJA Forum User
Location
Patterson, CA
Ok guys I've searched/googled and simply cannot find a decent explanation on how to properly size your jeep with new bumpstops after a lift or with mods.

I've got a 1998 XJ on 31×10.50's with 3.75 inches of backspacing, stock fender flares and 4.5 inches of lift. My front tires have bent my flares a little so I know I need bumpstops. I also just purchased 33×12.5 KM2's and BW flat fender flares and I'd prefer they not tear my fenders apart. How do I figure out the proper size bumpstops?
 
To do it right you need to flex your Jeep out and take measurements. You also should remove the shocks for this. You may even find your shocks are the wrong length!
 
XJ_NorCal said:
This may sound stupid but measure what exactly?
Click to expand...

Gap between the bump stop and the corresponding pad on the axle. I had to run Daystar bumps at full length to clear the fenderwells (fender openings are hacked with TJ flares) on my XJ with 4.5" lift and 33x12.50 General Grabber X3s (run "large" at 33" actual height).
 
There is so much more to this.......
What control arms do you have?
Make sure the sway bar is disconnected.
Make sure your not hanging from the brake lines.
Don't use the shocks as bump-stops or limit straps.
 
I'll add that at 5.5", I run a 3" lower with a +1" upper bump-stop.
 
RCP Phx said:
There is so much more to this.......
What control arms do you have?
Make sure the sway bar is disconnected.
Make sure your not hanging from the brake lines.
Don't use the shocks as bump-stops or limit straps.
Click to expand...

RC Adjustable Uppers & Lowers

So far I've gathered the following...

1. Disconnect sway bar and remove shocks
2. Flex one side of the front axle until just before my tire makes contact with my fender. (i should probably rotate my tires to ensure clearance at all angles as well)
3. Measure distance from bottom of current bump stop to corresponding pad. (this is the distance that I need to extend my bump stop by)

Repeat the same for the rear minus rotating the tires.

Does this sound right?
 
two_door_rob said:
Don't need to remove the shocks for bump stops. Leave them in so you can make sure the shocks don't bottom out.
Click to expand...
Yes and no. Depending on mod, lift height, shock specs., may need to bump stop and replace shocks accordingly.

Actually, it is better to disco at least one end of the shocks to check droop and use limit straps if necessary.
 
If the shocks are the proper length there is no need to remove them, but I guess we don't know that. OP what's your shock situation? Now's a good time to figure that out if you haven't already
 
two_door_rob said:
If the shocks are the proper length there is no need to remove them, but I guess we don't know that. OP what's your shock situation? Now's a good time to figure that out if you haven't already
Click to expand...

I've got the RC 4.5" lift kit (short arm) with control arm drop brackets for the lower control arms. I have the standard shocks that come with that kit so I'm assuming they are the correct length.
 
i always recommend adding to your bumps at the striker pad (bottom of the coil) rather than getting all of your bump from the stock tower (top of the coil). two reasons... adding all of your bump to the top makes it extremely long, putting a lot of leverage on it. it can also bind on the coil/make them hard to install/remove.

if i remember correctly... i added 2" of rigid bump to the striker pad for a 31" tire. 4" for a 35" tire. this was with the stock bump in the tower (which compresses basically to nothing), a more rigid bump stop replacement in the tower (like the daytar ones) may require less bump on the striker pad. your shock choice and amount of trimming will also be of concern. be sure to check full lock to lock as well.
 
The shocks that they throw in with lift kits aren't necessarily the right size. They should be close, but probably won't be perfect. Tire size, fender trimming/flares and bumpstops all come into play when determining shock length. Do a search for "how to measure for shocks" if your still not sure, post up here.
 
RC data has always been a problem(along with stiff shocks), RC doesn't list any ext/comp lengths for their shocks!
 
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