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View Full Version : Bump Stop Length?



FrozenZJ
03-23-2009, 01:55 PM
I need to extend my bumpstops a bit but I'm not sure how long I need to make them. I was just planning on making the stock ones longer. This is for the front. I'm running a 5.5" spring with 33" tires with future plans for 35"s. I'm thinking I need to limit about 2" or so.

I went out and flexed it but because of the spring being compressed and the blowing snow, I couldnt really get a good idea of how long it should be. I'm guessing maybe 4" or so overall extra length.

Here are the pics. I also cut off some of the fender but I dont want to cut off the flare part.

Thanks!

Here is the tire stuffed. It also just rubs the firewall a bit. I figure a BFH could help that.

http://img9.imageshack.us/img9/9021/1042457.jpg

Same position just a shot from the other side. Its got more droop, just need a better ramp.

http://img23.imageshack.us/img23/5845/1042459.jpg


And one sitting level..

http://img11.imageshack.us/img11/797/1042462.jpg

SirFuego
03-23-2009, 02:09 PM
Flex it out like you did.

From the side that is stuffed, measure the distance from the bumpstop cup to axle spring perch. Notice I said, bumpstop cup -- that's because the rubber portion compresses quite a bit. As an aside, if you use a forklift or something of the like, you need to lift the right rear tire to check clearance on the left front tire (and vice versa for the other tires).

Add that much (and perhaps a little more to account for the fact that you probably want to steer when you are flexed out) bumpstop to the axle spring perch. I'm suggesting to extend them from the axle side, because if you extend the bumpstop post too much, you can run into rubbing issues with that and the coil spring.

Repeat this process until you get your suspension dialed in. A BFH on the inner fender goes a long way, too.

Hockey pucks work very well as cheap bumpstops. They measure 1" high.

This is how my front bumpstops are setup:
http://www.wnyoffroad.org/thegallery/data/media/18/DSC00267.JPG

Also keep in mind that limit straps/chains on both sides of the axle to limit axle droop can also help to reduce/eliminate tire rubbing. They also come with the nice added benefit of prolonging the life of your shocks.

Derek33
03-23-2009, 02:11 PM
Also keep in mind that limit straps/chains on both sides of the axle to limit axle droop can also help to reduce/eliminate tire rubbing. They also come with the nice added benefit of prolonging the life of your shocks.

Im curious as how droop helps reduce or eliminate tire rubbing?

FrozenZJ
03-23-2009, 02:11 PM
Hockey pucks, thats a good idea. I was just planning on cutting the metal and extending that part.

I might have to flex it again when the weather breaks or something. I really couldnt get an eye on how much gap I had when it was stuffed.

SirFuego
03-23-2009, 02:27 PM
Im curious as how droop helps reduce or eliminate tire rubbing?
Limiting droop can.

Think of the axle/tire combo as an "H". With the vertical lines being the tires and the horizontal line being the axle. Now rotate the "H" clockwise about 10 degrees or so -- this is equivalent to "flexing".

Notice that the bottom of the right vertical line (i.e. the drooped tire) moved not only lower, but it also moved left. Notice that the top of the left vertical line (i.e. the stuffed tire) moved not only higher, but also moved right.

Now rotate the "H" clockwise a bit more -- notice that as this rotation continues, the top/bottom of the tires move not only vertically, but horizontally. Now try this for different "pivot points" along the axle -- you will notice that this trend is always true.

So the more one side droops, the closer the stuffed tire gets to the inner fender. So if you limit droop, you can reduce the flexing angles and therefore reduce the potential for tire rubbing.

SirFuego
03-23-2009, 02:36 PM
Also, a good "rule of thumb" is to match your lift height with your bumpstop extensions. So if you are at 5.5", you can start with adding 5.5" of bumpstop and tweak as necessary.

Derek33
03-23-2009, 04:47 PM
I gotcha. Thanks for the explanation.