Lift Install and Bumpstop

[YonderNorthwest]

Gearing up to do a small lift install. Bought a set of 2" JKS springs and some 0-2" lift monotube fox shocks (merry christmas to me). I think I've got the removal and installation of springs and shocks figured out thanks to some detailed threads here on the subject. I've also got access to a lift for an afternoon that should make it that much easier.

Where I'm getting a bit confused is the subject of bumpstops and extensions. Shocks have a compressed length of just over 12", and my understanding is that is shorter than the stock length that came on the jeep. I installed new Bilstein 4600 shocks a couple of years ago and refreshed the bumpstops while I was in there.

If my new shocks have a shorter compressed length than what I have on there now, am I going to need to extend my bumpstops to protect them? Normally I would just fire the parts cannon at it and buy them regardless of if they were needed or not, but it's that time of year and money is a bit tight...

Thanks

 

[Ir0nH3@d]

you wont know the exact bumpstop adjustment needed until you install the shocks and cycle the axle with the coils removed. even if the shocks don't require as much bumpstop, you may need to stop axle movement to keep the tires out of the fenders or the steering components from making contact.

 

[YonderNorthwest]

you wont know the exact bumpstop adjustment needed until you install the shocks and cycle the axle with the coils removed. even if the shocks don't require as much bumpstop, you may need to stop axle movement to keep the tires out of the fenders or the steering components from making contact.

Even if I'm keeping the same 31" tires I've been running with no lift?

 

[jjvw]

Even if I'm keeping the same 31" tires I've been running with no lift?

Stock compressed shock lengths were 13" front and 12.2" rear. If your new shock compressed lengths are close to that, there isn't anything to do.

If these new shocks are shorter compressed lengths, then you have an odd choice of new shocks for reasons other than bumpstop concerns.

 

[YonderNorthwest]

Stock compressed shock lengths were 13" front and 12.2" rear. If your new shock compressed lengths are close to that, there isn't anything to do.

If these new shocks are shorter compressed lengths, then you have an odd choice of new shocks.

Just looked at the product specs again. Rear shocks are 12.850 compressed and front shocks are 13.250 compressed. So about a quarter inch in the front and half an inch in the rear....

 

[jjvw]

Just looked at the product specs again. Rear shocks are 12.850 compressed and front shocks are 13.250 compressed. So about a quarter inch in the front and half an inch in the rear....

Then don't waste time on the bump stops if they are stock. The jounces will still do their job and you will have full shock travel.

 

[YonderNorthwest]

Then don't waste time on the bump stops if they are stock. The jounces will still do their job and you will have full shock travel.

Perfect. Thanks for the quick answers.

While I've got you here... It looks like I'm going to have 7" of shocks travel in both the front and rear. Do you know how that compares to the factory setup? I've got an anti-rock that gives me good articulation. Any concern about over-extending with only 7" of travel?

 

[jjvw]

Perfect. Thanks for the quick answers.

While I've got you here... It looks like I'm going to have 7" of shocks travel in both the front and rear. Do you know how that compares to the factory setup? I've got an anti-rock that gives me good articulation. Any concern about over-extending with only 7" of travel?

Stock shock travel was 7.5" front, 7" rear.

The Antirock will not restrict travel and the shocks have always been the limit to travel.

 

[Ir0nH3@d]

wait a sec, you are adding lift height but going with shorter shocks that have less travel? that seems like a mismatch

 

[YonderNorthwest]

Stock shock travel was 7.5" front, 7" rear.

The Antirock will not restrict travel and the shocks have always been the limit to travel.

My understanding was that the antirock was allowing more travel than connected, stock sway bars. Sounds like with 7" of travel on 2" lift springs I am going to have a bias toward uptravel. But that's assuming my bias is 50/50 as it sits now.

Thanks for the info.

 

[jjvw]

My understanding was that the antirock was allowing more travel than connected, stock sway bars. Sounds like with 7" of travel on 2" lift springs I am going to have a bias toward uptravel. But that's assuming my bias is 50/50 as it sits now.

Thanks for the info.

Your factory front sway bar restricts articulation. The Antirock does not restrict articulation. It is ultimately the shocks that allow as defined the limits of the articulation.

This is mine with 12" shock travel on both ends and its articulation is not being restricted by the sway bars either.

 

[jjvw]

wait a sec, you are adding lift height but going with shorter shocks that have less travel? that seems like a mismatch

0-2" JKS springs. That is a different discussion from his existing shocks and bump stops. The greater the spring lift, the more he will screw up the shock travel bias, eventually to the point that he ought to consider longer shocks appropriate to the new ride height.

 

[YonderNorthwest]

0-2" JKS springs. That is a different discussion from his existing shocks and bump stops. The greater the spring lift, the more he will screw up the shock travel bias, eventually to the point that he ought to consider longer shocks appropriate to the new ride height.

wait a sec, you are adding lift height but going with shorter shocks that have less travel? that seems like a mismatch

Wanted the 2" JKS springs not for the lift but for the dual rate. Hoping they will limit sagging when I pull my trailer. Ordered the 0-2" Fox shocks because I wanted something firmer than the Ranchos but softer than the Bilsteins. Figured 0-2" shocks for a 2" lift would be the way to go. Seems I didn't do enough research before my purchase.

 

[jjvw]

Wanted the 2" JKS springs not for the lift but for the dual rate. Hoping they will limit sagging when I pull my trailer. Ordered the 0-2" Fox shocks because I wanted something firmer than the Ranchos but softer than the Bilsteins. Figured 0-2" shocks for a 2" lift would be the way to go. Seems I didn't do enough research before my purchase.

Dual rate springs are a gimmick. Shock sizing ought to be measured after the ride height is established, rather than based on lift height. How do you know Fox shock valving is in between Rancho and Bilstein?

 

[YonderNorthwest]

Dual rate springs are a gimmick. Shock sizing ought to be measured after the ride height is established, rather than based on lift height. How do you know Fox shock valving is in between Rancho and Bilstein?

I checked out a spreadsheet somebody posted on here and the spring rate for the JKS dual rates is higher in the "firm" coils than the other springs listed there. My thinking was that they would resist added tongue weight better than the constant rate springs. Any manufacturer claims about improved ride quality or the like are not what I am after.

If this wasn't my daily driver, I would like to be able to install the springs, then measure, then order the shocks. Unfortunately that isn't how I can go about this.

Do you think my theory on the springs being better for dynamic weights is flawed somehow?

Edit: And as far as the shocks go; I don't know that for certain. Just basing it off of the limited feedback from folks on here who have run fox shocks. I have a heavy rig and an antirock. This made me think the soft riding Ranchos would not be a great option on road. The Bilsteins are reputed to resist body roll better, but be a pain in the ass (literally) on logging roads. Figured the fox's might be a good in-between.

 

[jjvw]

....

Do you think my theory on the springs being better for dynamic weights is flawed somehow?

...

Food for thought....

The maximum tongue weight for a TJ is 200 lbs. A Rockjock 4" coil is effectively about 130lb/in and is the lowest rate coil I am aware of for the TJ. This means the maximum tongue weight of 200lbs will sink the rear about .70".

A pair of 200lb/in coils will sink about .5".

I have measured multiple times at the gas station that the ride height difference between an empty vs a full tank of gas, typically 14-16 gallons, is about .25".

If your concern is the control of dynamic movements, then you need to move your focus onto the shocks and sway bars. The coil prings do not control movement. In which case, you need to begin by having shocks that are sized appropriately for the ride height. Followed by valving that will control the movements in a manner that satisfies you. Sway bars won't do much to control movements induced by tongue weight, though.