And when you are looking to buy shocks, they give the compressed length of the shock in the descriptions?
One little picture explains quite a bit
- Thread starter Chris
- Start date
Yep. Rancho 5000X example:
- Compressed Length: 13.690
- Extended Length: 21.470
- Travel Length: 7.780
JC123
TJ Enthusiast
Does this only come into play with a lift? Do I need to worry about it when shopping for replacement shocks for stock/non-lifted Jeep?
If the Jeep is stock, then buy stock length shocks.
That being said, I don't know if there is room on a stock TJ with stock bump stops for a longer compressed shock.
Stock shocks are....
Front
13" compressed
7.5" travel
20.5" extended
Rear
12.2" compressed
7" travel
19.2" extended
Last edited:
So yesterday I had typed a few questions about how and/or why all this stuff works and if it was all needed. For some reason I never hit the post reply button but after reading so much more today I felt it would be better to just see if I got it now. Feel free to correct me where I'm wrong. Anywhere I put *-* is just me extending something beyond what most people would do.
The bump stop size needed is more related to tire size (than lift height) to prevent interference with the body and other parts. *-* On a 12 inch lift the stock TJ tires would probably stay away from the body with original bump stops. *-* On a stock suspension 33 inch tires would need much longer bump stops.
Bump stop size will affect suspension flex. *-* The 12 inch lift with original bump stops could allow the stock tires to rub the upper shock and spring mounts. *-* The stock suspension with longer bump stops wouldn't let 33 inch tires rub the upper shock and spring mounts.
Wheel offset/backspace can affect interference with the upper shock and spring mounts when the suspension flexes.
The shocks need just a tad bit more travel (in each direction) than the suspension so they can handle the complete movement without being destroyed.
Keep the soft jounce out of the picture until the correct bump stop and shocks have been figured out.
Put the soft jounce back in to keep from hearing metal contacting metal when getting crazy in your Jeep.
The bump stop size needed is more related to tire size (than lift height) to prevent interference with the body and other parts. *-* On a 12 inch lift the stock TJ tires would probably stay away from the body with original bump stops. *-* On a stock suspension 33 inch tires would need much longer bump stops.
Bump stop size will affect suspension flex. *-* The 12 inch lift with original bump stops could allow the stock tires to rub the upper shock and spring mounts. *-* The stock suspension with longer bump stops wouldn't let 33 inch tires rub the upper shock and spring mounts.
Wheel offset/backspace can affect interference with the upper shock and spring mounts when the suspension flexes.
The shocks need just a tad bit more travel (in each direction) than the suspension so they can handle the complete movement without being destroyed.
Keep the soft jounce out of the picture until the correct bump stop and shocks have been figured out.
Put the soft jounce back in to keep from hearing metal contacting metal when getting crazy in your Jeep.
That's pretty good. To re-phrase, clarify and add a few things....
Lift height, in and of itself, has no determination of the bump stop extension until the coils get so long that bump stop is needed to prevent coil bind. Coil bind is when the coil is compressed into a solid mass. This can lead to the wire overlapping and a permanently damaged coil. This scenario is hard to achieve in anything close to a normal build. It's actually still an unusual scenario with coil spacers, but worth checking to make sure.
31" and larger tires need front bump stop extension. A stock Rubicon with the front sway bar disconnected will be able to mash it's stock size tire into the front fender sheet metal at full flex. Once the bump stops are extended to keep the tires out of the front sheet metal, a change in lift height (in and of itself) will not have an effect on the bump stops.
The rear wheel opening is larger and the compressed shocks will usually be what determines the required rear bump stop extension.
As lift is added to an existing shock, the up travel increases the same amount as the down travel decreases. To correct this, a longer shock is needed to restore the down travel, but at the expense of the previous gain in up travel. The goal, at the very least, should be to restore the stock shock up and down travels. A longer shock will have a longer compressed length (and often more overall travel). This longer shock will require bump stop extension in order to prevent over-compression. Over-compression is what causes shocks to blow up, bend, break a bar pin or tear off a mount. All of these are common shock problems that are entirely preventable.
Another consideration is the front track bar hitting the diff cover. Many aftermarket combinations of these two parts can create an interference which can lead to a broken track bar, non-existent steering and possible death.
The common theme here is the prevention of an interference. The purpose of the bump stop is to limit up travel before parts crash into other parts. When the bump stops are extended to prevent the first thing that interferes, all the subsequent interferences will be covered. This is why some Jeeps get away with some lousy track bar and diff cover combinations, because something else needed more bump stop extension.
Shock length and tire size are the two most common things that will require added bump stop. The lift height has far more to do with restoring travel that has been lost due to the required bump stop extension from larger tires, longer shocks, or some other cause of interference resulting from non-stock parts.
Extended bump stops are not a bad thing. They are simply a requirement needed to make our modified Jeeps work they way they are supposed to. Once you understand this, you will be able to build a well balanced and functional suspension. This understanding will also open up a whole new level of modifications like outboarded shocks, making full use out of replacement fenders, and finding ways to reduce the amount of required bump stop extension.
Lift height, in and of itself, has no determination of the bump stop extension until the coils get so long that bump stop is needed to prevent coil bind. Coil bind is when the coil is compressed into a solid mass. This can lead to the wire overlapping and a permanently damaged coil. This scenario is hard to achieve in anything close to a normal build. It's actually still an unusual scenario with coil spacers, but worth checking to make sure.
31" and larger tires need front bump stop extension. A stock Rubicon with the front sway bar disconnected will be able to mash it's stock size tire into the front fender sheet metal at full flex. Once the bump stops are extended to keep the tires out of the front sheet metal, a change in lift height (in and of itself) will not have an effect on the bump stops.
The rear wheel opening is larger and the compressed shocks will usually be what determines the required rear bump stop extension.
As lift is added to an existing shock, the up travel increases the same amount as the down travel decreases. To correct this, a longer shock is needed to restore the down travel, but at the expense of the previous gain in up travel. The goal, at the very least, should be to restore the stock shock up and down travels. A longer shock will have a longer compressed length (and often more overall travel). This longer shock will require bump stop extension in order to prevent over-compression. Over-compression is what causes shocks to blow up, bend, break a bar pin or tear off a mount. All of these are common shock problems that are entirely preventable.
Another consideration is the front track bar hitting the diff cover. Many aftermarket combinations of these two parts can create an interference which can lead to a broken track bar, non-existent steering and possible death.
The common theme here is the prevention of an interference. The purpose of the bump stop is to limit up travel before parts crash into other parts. When the bump stops are extended to prevent the first thing that interferes, all the subsequent interferences will be covered. This is why some Jeeps get away with some lousy track bar and diff cover combinations, because something else needed more bump stop extension.
Shock length and tire size are the two most common things that will require added bump stop. The lift height has far more to do with restoring travel that has been lost due to the required bump stop extension from larger tires, longer shocks, or some other cause of interference resulting from non-stock parts.
Extended bump stops are not a bad thing. They are simply a requirement needed to make our modified Jeeps work they way they are supposed to. Once you understand this, you will be able to build a well balanced and functional suspension. This understanding will also open up a whole new level of modifications like outboarded shocks, making full use out of replacement fenders, and finding ways to reduce the amount of required bump stop extension.
Last edited:
@jjvw you should write a primer on this topic. Your posts are very useful and informative but they are spread on the forum across your build thread and threads like these. I would love to see them all together in one place if you can find the time to write it. Doesn't have to be immediate, of course, feel free to take your time ... me, and many other people (and esp new Jeep owners who come from driving regular cars without doing the research) will really benefit from your wisdom accumulated over the years!
Someday, I'll get to help setup a relatively stock TJ and take the pictures that are usually missing or less clear.
Mine isn't very familiar looking to a new guy anymore, which can make things more confusing than it needs to be.
I'm hardly an expert, and these things didn't make sense to me until Unlimited04 and Mudb8 (Dave) explained what bump stops do, why they matter so much and what they teach you.
Last edited:
OP
I agree, it would be absolutely invaluable to have a sticky that explained how all of this worked and tied in together. Travel, bump stop, compressed lengths, extended lengths, etc. Basically a thread that would explain what all of this stuff means and how these numbers work together.
It's a very daunting subject for new TJ owners, and I get it, because I was there once as well. Most people don't even have any idea that they're suppose to set their bump stop and cycle their suspension. They genuinely don't know what that's important.
But yes, it would be really beneficial to have a stock TJ to explain it with, then maybe do a 4" lift install with 33s or 35s, and explain how all the variables have changed now that bigger tires have been added, a lift, etc.
The information is out there, but it's scattered about in such a way that doesn't make it an easy read for new owners to follow. It needs to be all nicely organized and compiled into one sticky thread, so that others can actually follow along and make sense out of it, without having to bounce from thread-to-thread.
It's a very daunting subject for new TJ owners, and I get it, because I was there once as well. Most people don't even have any idea that they're suppose to set their bump stop and cycle their suspension. They genuinely don't know what that's important.
But yes, it would be really beneficial to have a stock TJ to explain it with, then maybe do a 4" lift install with 33s or 35s, and explain how all the variables have changed now that bigger tires have been added, a lift, etc.
The information is out there, but it's scattered about in such a way that doesn't make it an easy read for new owners to follow. It needs to be all nicely organized and compiled into one sticky thread, so that others can actually follow along and make sense out of it, without having to bounce from thread-to-thread.
As much as there is on youtube, I only saw one video of a guy cycling the rear of a suspension (on a JK). Kind of surprising.
You'd think Bleepin' Jeep would have this covered over and over, but those guys are always surprised when their half baked projects chew up tires.
I spent months trying to understand this stuff as I was searching for my TJ. I still have plenty of gaps that gets filled in when I read threads like these. There is so much I still don't know.
New Jeep owners (and I'm very much in this category) should understand that properly building a Jeep is a time consuming process and it's not just bolting on the stuff you buy irrespective of what generation Jeep it is. I understand that quite a few buy Jeeps for looks and heritage reasons, but even they would only gain by understanding things like how a suspension needs to be setup.
So for shits and giggles I decided to try to measure my situation on my TJ. In the front, it looks like from above what I think is my bumpstop to the top of the spring mount area, is 9inches. 7 inches from the bottom of the bumpstop(I think that’s what that’s called). And my shock length as Chris showed in his pic was 6.5.
So based on that information, and my remedial understanding , my shocks are a bit too long. I’m not doing any off roading any time soon, so this will be fine for road driving I’m assuming .
And my back length was 9.25 about, and the shock distance was a little over 5.
My plan at some point was to follow the steps to cycle the suspension, but this was a quick measure while I had it in the lift working on another project.
So based on that information, and my remedial understanding , my shocks are a bit too long. I’m not doing any off roading any time soon, so this will be fine for road driving I’m assuming .
And my back length was 9.25 about, and the shock distance was a little over 5.
My plan at some point was to follow the steps to cycle the suspension, but this was a quick measure while I had it in the lift working on another project.
If the shock exposed shaft is shorter than the space between the steel cup and the axle pad, then the shock is the bump stop. The difference between those two measurements is how far the axle is able to crash through the shock.
I personally do not agree with the justification that a street Jeep does not need proper bump stop extension. Speed bumps, pot holes and other road imperfections exist. And we are often hitting those things at a far higher speed than what typically happens off road. Adding weight in the form of passengers or cargo only reduces the up travel and increases the opportunity for over-compression.
The immediate fix here is to extend the bump stops. A better fix might be a combination of a shorter shock along with the appropriate bump stop extension. This is where it is important to identify and establish the upper limit of the suspension travel. This will help in the selection of the optimal length shock for your specific setup.
OP
What's funny is that in the world I come from (BMWs) people would put coilovers on their M5 (just like I did), lower it a little, and drive around town. In those scenes, there is no such thing as a bump stop, shock travel, etc. People would have no idea what you're talking about.
So when you bottom out your lowered BMW, you just take the fender out with you. Though I will say, even with all the potholes I hit, that never happened.
However, I also wasn't running 35" tires that stuck out wider than the fender anyways!
But those Honda guys with the stupid little "wrapped" tires and wheels out past the fender... those guys need some serious bump stop!
So when you bottom out your lowered BMW, you just take the fender out with you. Though I will say, even with all the potholes I hit, that never happened.
However, I also wasn't running 35" tires that stuck out wider than the fender anyways!
But those Honda guys with the stupid little "wrapped" tires and wheels out past the fender... those guys need some serious bump stop!
Thanks jjvw.
I guess I wasn't too far off but I didn't even think about coil bind, the track bar and the differential cover. Three things that were never a potential issue in my CJ days but make sense today.
I guess I wasn't too far off but I didn't even think about coil bind, the track bar and the differential cover. Three things that were never a potential issue in my CJ days but make sense today.
An interesting detail here is that these shocks have what appears to be a jounce or cushion to protect it from a hard impact. It's probably better than nothing, but the force of full compression is still being transferred through the compressed shock and into the shock mounts. Why not move that force into the bump stops and let the shocks be shocks?
Even if the final up travel is minimal, it still makes sense to me to include some component designed to limit the up travel as a way to prevent damage elsewhere.
I have a feeling my stanced Honda Civic would look different than most.
OP
I totally agree. I'd rather be safe than sorry.
I just find it rather amusing that other than in the off-road world, no one really has any idea what a bump stop is or what it's intended purpose is.
Even in the road racing and track car world? That seems like something that would matter during a hard corner at high speed.