Bumpstop extension length

[Elio S]

Does anyone how to calculate bumpstop extension lengths?? I have a WG Grand Cherokee with 2" block lift, standard suspension and 245/70 r 17 mud terrains on it. It's original tyre size is 235/65 r 17 highway tyres. I disconnected the sway bar today to try and get a little bit of extra flex, and the tyres ended up hitting the guards on compression. I do plan on getting some sway bar disconnects and extending the bumpstops in the near future, but have no idea as to how much I should extend them. Plans further on down the track will include removing the spring blocks and fitting a 3" spring lift, and although at the moment I'm happy with my current tyre size, I won't rule out possibly going up to 265's when these ones require replacing.

Cheers

Elio

[AV8]

Don't know how to calculate that but I do have lots of WJ parts, axles, diffs, JKS discos, Bar Pin Eliminator. Will post them in for sale section in a couple of days. Wooders should be able to advise you on your questions.. He's THE professore :). PM if interested., first cut.

Sal
Bella Vista

[AV8]

From IRO

In Stock


Extend your bump stops with our custom length bump stop spacers (price is per pair). We recommend extending your OEM bump stops because simply put, they are the best bump stops available short of expensive pneumatic or hydraulic units that require lots of custom fabrication to install. The OEM bump stops are very progressive meaning they are very soft at initial contact, but get progressively firmer to stop even the hardest of hits without brutal, part breaking, metal to metal contact. The best part is they are designed to be used without even knowing it from the driver's seat.


If you choose a custom "non-stock" length, please allow 5-10 business days to ship.


How to choose the length:


Actual lift height:
It is very important that you do not use the manufacturers advertised lift height for any calculations. Always use a hub to fender measurement with the vehicle loaded they way it is typically used. If you usually carry tools and spare parts, have them in the vehicle when you measure. Also fuel weighs about 8lbs per gallon so measure with a full tank for bump stop purposes. Hub to fender measurment is measured from the center of the tire/wheel vertically to the bottom of the fender or fender flare. Measure on flat ground and measure all 4 corners because they always vary from side to side. Average the left and right measurements, but keep the front and rear measurments separate. Hub to fender measurements on a stock WJ Grand Cherokee are about 18.2" rear and 18" front. OEM distance to the start of the bump stop is roughly 1.5"


What is your goal?


OEM uptravel:
If you just want OEM suspension uptravel then extend your bump stops by your actual lift height (see hub to fender measurement procedure above).


Extra uptravel:
If you want a little bit of extra uptravel then extend your bump stops by a little less than your lift height. For example for a 4" actual lift height extend the bump stops 3.5", or whatever you think is best for you. We think 1/2" additional uptravel is great for general use.


Maximum tire clearance:
If you are looking for maximum tire clearance then use an RTI ramp, trail obstacle, or other method to cycle the suspension. You must have your lift kit and tire combination in place to use this method. Simply cycle your suspension to the maximum travel you want to allow (remember to cycle your steering lock to lock). Then measure from the middle of your bump stop to the bump stop pad. This is the amount to drop your bump stops. Remember to consider the worst case scenario. For example, going downhill will push harder on the front bump stops, or as one tire droops more the other tire stuffs more even after contact with the bump stop (because of the location of the bump stops). So you may want to add 1/2" or more to your measurement, or be sure you measure using worst case scenario. We do not recommend extending bump stops more than your actual lift height (see hub to fender measurement procedure above).

[Elio S]

Yep, I'm thinking 2" extensions are the way to go at the moment. Should stop tyre contact with the gaurds, and allow for a little extra up travel when I get around to putting the 3" lift in

[Wooders]

I'd disagree a little with the IRO statements and methods. But would be pretty boring to read so I'll leave it alone ;)
The primary job of the bumpstop is to protect the coil (and to lesser extent the shock) from over compression.
If you over compress the coil it can lead to premature sgiing and even failure (cracking) of the coil.
Adjusting the bumpstop is different depending on if a new or is used or a spacer.
Since you have used a spacer, I would advise adjusting the bumpstop by the same thickness as the spacer (at best marginally less).

[Elio S]

I'd disagree a little with the IRO statements and methods. But would be pretty boring to read so I'll leave it alone ;)
The primary job of the bumpstop is to protect the coil (and to lesser extent the shock) from over compression.
If you over compress the coil it can lead to premature sgiing and even failure (cracking) of the coil.
Adjusting the bumpstop is different depending on if a new or is used or a spacer.
Since you have used a spacer, I would advise adjusting the bumpstop by the same thickness as the spacer (at best marginally less).

What I got out of the IRO site was to basically if I lift 2" then I should extend the bumpsotps to 2" or 1 1/2" if I want a little extra travel. What I was thinking was, as I've already got a 2" block lift, I'll put 2" bumpstop extensions in, and when I finally upgrade to a 3" suspension lift, those 2" extended bumpstops should still effectivlly do their jobs.
This is how it sits at the moment. http://i276.photobucket.com/albums/kk26/Zook/1510760_10152164455670905_7021620920997807625_n_zp se3f2f95c.jpg As you can see the tyre is hard up against the gaurd

[Wooders]

Remember what I said about the primary job of the bumpstop is to stop over compression of the coil.
OK with a coil spacer you are effectively adding the entire thickness of the spacer as non-compressible material betwen the bumpstops. ie you must extend the bumpstops the same amount to maintain the same coil protection.
If you then add different coils you then should further allow for any additional coils wraps and any increase in coil wire thickness.
Make sense?

[Elio S]

Remember what I said about the primary job of the bumpstop is to stop over compression of the coil.
OK with a coil spacer you are effectively adding the entire thickness of the spacer as non-compressible material betwen the bumpstops. ie you must extend the bumpstops the same amount to maintain the same coil protection.
If you then add different coils you then should further allow for any additional coils wraps and any increase in coil wire thickness.
Make sense?

Yes it certainly does. Explains the bent leaf spring I got 4wding with a previous Suzuki I used to own