Front Bump Stop Extensions and Rancho RS5000X Shocks

TrueTexas

TrueTexas

TJ Enthusiast
Supporting Member
Joined
Feb 7, 2019
Messages
464
Location
The Woodlands, TX
I am adding a very minimal lift (1" - 1.5" expected) and am trying to determine what bump stock extensions (if any) are needed and which specific RS5000X shock to go with. Running 31" tires with the longer term potential of 32" tires at the most doesn't have me as much concerned about up-travel, it is really down-travel... let me try to explain.

This is for my TJ only, your dimensions may be slightly different - but shouldn't be by very much

The stock suspension at rest (curb height) has a delta of 13.375" between the height of the shock (17.5") and the height of the bump stop over the spring perch (4.125") - (17.5" - 4.125" = 13.375"). This means the Rancho RS5000X shock for 0" of lift (p/n RS55128) would fit fine as it has a compressed length of 13.050". This means that on full compression of the suspension, the bump stop will limit up-travel and the shock will not bottom out. It also means the suspension has an up-travel of 4.125" (bump stop allowed travel) and a down-travel of 3.53" calculated by 21.030" (fully extended shock length) minus 17.5" (curb height length).

So now let's look at it when we add 1.5" of lift and stay with the shock for 0" of lift. The curb height length of the shock increases to 19" and the bump stock limited travel goes to 5.625". Staying with the stock shock will allow the full range of up-travel as the delta remains at 13.375" and the shock is still only 13.050" fully compressed. As far as the wheel goes, this doesn't change from stock as the upper limit of travel is the same as it was with the stock suspension, it only starts from a lower position. However, using the Rancho shock for 0" of lift will now significantly limit down travel to 2.03" calculated by 21.030" (fully extended shock length) minus 19" (new curb height length). Assuming the shock limits down-travel, this means down-travel has been reduced significantly. We can debate for hours why this is not a good thing on a 4WD vehicle.

Ok, so now let's look at moving to the next size up Rancho Shock, the one that states 2.5" of lift (p/n RS55239). In this scenario, the compressed length of the shock is 14.430". This means we will need a bump stop extension of min 1.055" (14.430" - 13.375" to stop the shock from bottoming out during suspension up-travel. I am not a betting man so I would opt to go for a 1.25" to 1.5" bump stop extension. This will limit the up-travel to between 4.125" - 4.375", which is equivalent or slightly better than stock. in this scenario, down-travel ends up at 4.840" calculated by 23.840" (fully extended shock length) minus 19" (new curb height length w 1.5" lift). The down travel is now better than the stock setup, making the vehicle much more compliant off road.

Everything about this points me in the direction of the Rancho RS5000X for 2.5" lift (pn RS55239) and a 1.25 - 1.5" bump stop extension. My questions to the experienced on this forum are:

1. Do you see any flaws in my logic?
2. Would you go with a 1.25" or 1.5" bump stop extension and if so, do you have any recommendations - I like the metal 1.25" JKU ones for the bottom spring perch
3. Would you mount the spacer on the bottom spring perch or above the bump stop cup.
 
Last edited:
Fully cycle the axles/tires without the springs and see what really happens with clearances in the real world. 32" tires need bump stop extension on the front with stock fenders.

The ideal shock length is the one that has its overall travel split in half. Whatever you do, do not sacrifice the up travel. The down will follow.

The front bump stop extension should be added to the axle side. The rear can be added to the frame side by extending the cup.
 
Thanks @jjvw cycling the front suspension is my next step to get exact measurements for the bump stop extension so I can maximize uptravel but not bottom out the shock and ensure the tire doesn't hit the fenders.

I agree that travel should be split up and down. Staying w the stock size shock, down travel becomes really limited - about 2". Going with the longer shock will keep down travel at around 4" but requires a bump stop extension for the reasons above.

Do you think I am good to go to get the 2.5 lift shock and then figure out my bump stop extension from there?
 
Were it me, I would do a preliminary cycling to find the minimum bump stop requirements for everything but the shocks. From there, you understand this enough to make a good choice on the optimal shock lengths. A few details to keep in mind... Everything happening here is a balancing act of compromises. The optimal shock might require additional bump stop. A little bit of tire rub on metal is fine during full flex. That movement is generally slow speed. The same goes for the compressed shock at full flex. Use that travel is you can. Use the bump stops primarily to limit travel and prevent damage during high speed events.
 
  • Like
Reactions: TrueTexas
You need 1.5" of additional bump stop if you want to run RS55239's. This will give you a closer even bias, but you will sacrifice some up travel. Like Josh said, compromises.
 
Thanks @bobthetj03 . My math (first post) suggested between 1.25 and 1.5 inches of bump stop extension to run the RS55239s as well. With 1.5 lift and 1.5 bump stock extension, I shouldn't lose any up travel from stock but I will gain some down travel. My guess is that it should be fairly evenly split as well.

Now I just need to find some 1.5 inch bump stop extensions. I don't care about the material as much as I care that the bolt heads are recessed if I'm putting them on the axle pad.

Alternately, for only 1.5" do you think a poly spacer above the cup (for the front) would cause issues? That is easy to find (and cheap).
 
Still space the axle side. Exposed bolt heads are fine. The jounce will conform. One pair of jounces already has a recess in the middle. Put those up front.
 
TrueTexas said:
Thanks @bobthetj03 . My math (first post) suggested between 1.25 and 1.5 inches of bump stop extension to run the RS55239s as well. With 1.5 lift and 1.5 bump stock extension, I shouldn't lose any up travel from stock but I will gain some down travel. My guess is that it should be fairly evenly split as well.

Now I just need to find some 1.5 inch bump stop extensions. I don't care about the material as much as I care that the bolt heads are recessed if I'm putting them on the axle pad.

Alternately, for only 1.5" do you think a poly spacer above the cup (for the front) would cause issues? That is easy to find (and cheap).
Click to expand...

You really don't want to add anything to the upper cup because the springs will arch as they droop and hit the jounces. I use hockey pucks on the lower pad. You can drill a hole in them, then use a larger wood bit to recess the hole for the bolt head. 1.5" is the absolute minimum you need. I run 2" bumps and only have 1/2" of shock shaft showing at full stuff with the jounce bumper about fully compressed.
 
Dont forget that your bumpstops may change when you go to a larger tire. So If you are planning 32s in the future keep that in mind when you are setting bumpstops.
 
Dont forget that your bumpstops may change when you go to a larger tire. So If you are planning 32s in the future keep that in mind when you are setting bumpstops.
Click to expand...

For sure. I am going to drill and tap the lower spring perch so when it's time to go to 32 inch tires, I can remeasure and drop in new bump stop extensions if needed. The 31s I have only have about 2k miles on them so there is time before that happens.
 
TrueTexas said:
I am adding a very minimal lift (1" - 1.5" expected) and am trying to determine what bump stock extensions (if any) are needed and which specific RS5000X shock to go with. Running 31" tires with the longer term potential of 32" tires at the most doesn't have me as much concerned about up-travel, it is really down-travel... let me try to explain.

This is for my TJ only, your dimensions may be slightly different - but shouldn't be by very much

The stock suspension at rest (curb height) has a delta of 13.375" between the height of the shock (17.5") and the height of the bump stop over the spring perch (4.125") - (17.5" - 4.125" = 13.375"). This means the Rancho RS5000X shock for 0" of lift (p/n RS55128) would fit fine as it has a compressed length of 13.050". This means that on full compression of the suspension, the bump stop will limit up-travel and the shock will not bottom out. It also means the suspension has an up-travel of 4.125" (bump stop allowed travel) and a down-travel of 3.53" calculated by 21.030" (fully extended shock length) minus 17.5" (curb height length).

So now let's look at it when we add 1.5" of lift and stay with the shock for 0" of lift. The curb height length of the shock increases to 19" and the bump stock limited travel goes to 5.625". Staying with the stock shock will allow the full range of up-travel as the delta remains at 13.375" and the shock is still only 13.050" fully compressed. As far as the wheel goes, this doesn't change from stock as the upper limit of travel is the same as it was with the stock suspension, it only starts from a lower position. However, using the Rancho shock for 0" of lift will now significantly limit down travel to 2.03" calculated by 21.030" (fully extended shock length) minus 19" (new curb height length). Assuming the shock limits down-travel, this means down-travel has been reduced significantly. We can debate for hours why this is not a good thing on a 4WD vehicle.

Ok, so now let's look at moving to the next size up Rancho Shock, the one that states 2.5" of lift (p/n RS55239). In this scenario, the compressed length of the shock is 14.430". This means we will need a bump stop extension of min 1.055" (14.430" - 13.375" to stop the shock from bottoming out during suspension up-travel. I am not a betting man so I would opt to go for a 1.25" to 1.5" bump stop extension. This will limit the up-travel to between 4.125" - 4.375", which is equivalent or slightly better than stock. in this scenario, down-travel ends up at 4.840" calculated by 23.840" (fully extended shock length) minus 19" (new curb height length w 1.5" lift). The down travel is now better than the stock setup, making the vehicle much more compliant off road.

Everything about this points me in the direction of the Rancho RS5000X for 2.5" lift (pn RS55239) and a 1.25 - 1.5" bump stop extension. My questions to the experienced on this forum are:

1. Do you see any flaws in my logic?
2. Would you go with a 1.25" or 1.5" bump stop extension and if so, do you have any recommendations - I like the metal 1.25" JKU ones for the bottom spring perch
3. Would you mount the spacer on the bottom spring perch or above the bump stop cup.
Click to expand...

Though the math says that we will need 1.25-1.5” bumpstop, cycling my suspension revealed I needed 2.25 ... the only reason I think I am going to get rid of mine. I dint want to loose that much up travel. The rear need exactly 1.5”, not bad.

BTW: I am running the 2” lift version.
 
TrueTexas said:
@Ericshere03. I am definitely going to cycle the suspension. In process of getting the springs out to get actual measurements. what size tires are you running w the 2 inch lift?
Click to expand...
32x11.50x15 ... I can easily run 33’s with all the bumpstop ... plus I have a 1” BL ...

Share your bumpstop length when your done... I feel my fronts are defective because they’re so long, compared to the 14.43” compressed length as advertised...
 
Absolutely. I will certainly follow up with all details.

I'm currently reconsidering my spring choice after receiving my Moog 3226/3227 springs. Both sets came all beat up and chipped from Moog because they seem to want to cheap out and not add any packaging between the springs allowing them to bang into each other in the box Don't think I want to pay for springs that are pre-damaged.

I also found a guy who is making me custom bump stop extensions out of UHMW-PE. If @Chris is ok with me sharing his details on the forum , I will do a write up on that as well
 
Ericshere03 said:
32x11.50x15 ... I can easily run 33’s with all the bumpstop ... plus I have a 1” BL ...

...
Click to expand...

Easily might be optimistic for 33s. Your goal is to always at least maintain 4" of up travel. 2" spring + 1" body is at the bare minimum. Your combination of parts might not allow for factory amounts of travel.
 
Do I need longer bump stops or extensions with a 2” lift on my 98 TJ?
Seems to me that if the I’m installing taller springs (OME HD 933 and 942) and longer travel shocks (Rancho RX5000S - RS55241 & RS55239) installing longer bump stops just negates the added travel in the suspension. Am I missing something?
Do I risk the spring going solid at full compression or hitting the limit on the shocks?
Only running 31” tires so not really worried about fender rub.
 
JeepFan1998 said:
Do I need longer bump stops or extensions with a 2” lift on my 98 TJ?
Seems to me that if the I’m installing taller springs (OME HD 933 and 942) and longer travel shocks (Rancho RX5000S - RS55241 & RS55239) installing longer bump stops just negates the added travel in the suspension. Am I missing something?
Do I risk the spring going solid at full compression or hitting the limit on the shocks?
Only running 31” tires so not really worried about fender rub.
Click to expand...

Basically longer bump stops are needed whenever larger or longer than stock complements are added. Longer bumps keep non stock parts from crashing into other things.

Shocks with a longer compressed length than stock need extended bump stops. Tires that are larger than about 31" need bump stop extension.
 
  • Like
Reactions: JeepFan1998
@JeepFan1998 just looking at the fronts, without a bump stop extension, the shocks will take the impact when they bottom out. This can cause damage to the shock piston or valving.

Bump stop extensions are used to prevent whichever of the following comes first
1. Shock bottoming out
2. Tire hitting the fenderwell

The shocks you have selected ( based on my measurements) will bottom out about an inch before the bump stop hits the spring perch. So although you would need to cycle the suspension to make sure the tire isn't going to hit, you are already looking at needing bumpstop extensions.

The reason to cycle is to make sure you don't put too long of an extension in that will limit your max possible up travel. You are already gaining more up travel than stock so loosing some of that to prevent other damage should hopefully keep you equal to or slightly better than stock.

For the front, general consensus is to apply the extension to the spring perch because of potential interference w the spring. On the rear, you can put them above the jounce cup

Is there a reason that you don't want to put in extensions? Is it drilling and tapping the spring perch or cost? If cost, I've got a guy making some for me out of UHMW-PE at a very reasonable cost. He is getting ready to offer them for sale. PM me if you want his contact info once you know the lengths you need.
 
Top Bottom
Back