Spring under (I know people are curious)

2 words come to mind when you try to pull that much travel out of a solid axle panhard setup front end. bump steer. because of the panhard bar the front axle will be moving so far to the left and right as it moves through the travel range you start losing the ability to steer effectively. if you're hitting big travel and aren't going in a straight line get ready for some fun.

ok well on that note..... how much travel can you get before you have too much bump steer?
 
depends who you ask. put someone who's driven differant fast desert cars into a jeepspeed, and they can feel it and be annoyed by it at 10.
 
The Krellwitz/Skilton Class 3 Wrangler has 12 - 13 inches of travel in front and about 18 in the back if I remember correctly, and that Jeep has proven solid axles can be very fast. Building a Jeep w/ 12 inches of travel front suspension coupled with a spring under rear getting 14 - 15 would be failry easy and mathmaticly speaking, would be about 20% faster than a car with 10 in front and 12 in back.

As far as investing time into a unibody vehicle goes, every single modern trophy-truck style prerunner becomes a unibody after the body/cage/frame are connected. Nothing wrong with unibodies and Skilton's old Don-a-vee Cherokee proves links, unibodies and solid axles can be fast and also last for 2 decades.
 
The Krellwitz/Skilton Class 3 Wrangler has 12 - 13 inches of travel in front and about 18 in the back if I remember correctly, and that Jeep has proven solid axles can be very fast. Building a Jeep w/ 12 inches of travel front suspension coupled with a spring under rear getting 14 - 15 would be failry easy and mathmaticly speaking, would be about 20% faster than a car with 10 in front and 12 in back.

As far as investing time into a unibody vehicle goes, every single modern trophy-truck style prerunner becomes a unibody after the body/cage/frame are connected. Nothing wrong with unibodies and Skilton's old Don-a-vee Cherokee proves links, unibodies and solid axles can be fast and also last for 2 decades.
i agree with you chris.. so what would we have to do to convert an XJ to leaf under? in your experiance
 
The Krellwitz/Skilton Class 3 Wrangler has 12 - 13 inches of travel in front and about 18 in the back if I remember correctly, and that Jeep has proven solid axles can be very fast.

Nothing wrong with unibodies and Skilton's old Don-a-vee Cherokee proves links, unibodies and solid axles can be fast and also last for 2 decades.

FAST or "Fast for what it is"??? There is a difference......apples and oranges.
 
18-20" on a straight axle front end? Might have a little bump steer and your oil pan would be non existent.

I should of made my post more clear. I didn't mean or claim a XJ pulling that much travel. Should of made that clear. :cheers:
When I said just because we are straight axle it shouldn't matter..I mean to say just because we are straight axle doesn't mean we shouldn't link the rear??? Say you jump your truck...your rear should touch down first. So more rear travel = helpful! As far as going over whoops & such, sure you probably won't use all the travel but its there for when you do use it!
Yes I agree more front travel would be great but you can only go so far before BS comes into. I'm aware & already know of this! Does this mean extra rear travel isn't helpful? HELL NO!!

Don't get me wrong, it would get tons of street cred but you can only polish a turd so much.

As for the polishing a turd comment. Maybe your hearts not into like others are. I agree you can grab a ranger throw 5000 down & have a nice capable prerunner, but whats the fun in that? The uniqueness of a baddass jeep that can hold its own it sick! You know this because you've built a sick ass jeep! Unibodys can be strengthened. Plating & cages go a long way! Especially when your not out beating it every weekend.
J: sorry if it sounds like I'm being a dick, thats just how I wrote it lol! Didn't mean to come off like that.


Im gonna guess you have never ridden in a linked truck before. The only trucks I have seen with 30"+ of travel are trophy trucks. Also properly valved shocks will help you go alot faster than more travel will. And to much travel can actually make you go slower if you don't have the horse power to back it up

Yes having a solid front axle does make it different. Why do you think the guys who link there jeeps either put beams on them or want to put beams on them
We all know about properly valving shocks in here....I think just about everyone in here is building/have build or have a jeep thats being used as a prerunner/desert truck or what have you!! But since you know so much on that matter, please tell me something...Why would use be straight axle matter? All that means to me is less front travel! The rear travel will still be useable, sure maybe it won't be all the time but it will be useable!
And to make it clear no ones chasing travel numbers in here. We are inquiring about spring under since a few JS have been built that way in the past! If you have no experience with it and cannot contribute to better the thread, then please have a nice day!
And no I'm never been in a linked truck before. But I can bring up 2 expos & countless rangers that have been purpose built & are still daily drivers, that are pulling 24"+ of rear travel...Full on trophy trucks?? They are far from it!! Next time I post I'll make sure to post exact numbers for you though!
I'm sure with a simple search you could find plenty of trucks that aren't trophy trucks pulling rear travel like that!
Oh and these 4.0's with the right gears will have more than enough Torque to keep you moving! Torque would of been the right word since horse power is a derivative of torque! No need for more "power" to have more travel, sure it'll help you go faster but it isn't needed! Thats absurd, but I know what you ment! You can go plenty fast with the power available.
More travel isn't going to slow you down either, if you think it is please explain it to me!


I'm aware that 10-12" in the front is about it without going crazy and yes bumpsteer comes into play! That still doesn't give me a definitive reason why spring under in the rear is a bad idea or shouldn't be done! And X-over steering setups will help eliminate some BS! I see no reason a XJ with 12" of travel up front shouldn't be SU in the rear!
This is a far cry and obivously will never happen or be proved, but I'm willing to bet if you have 2 equal jeep XJ's, with the only variance being one is SO & one is SU. I'm willing to bet the SU would be faster!
 
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The way I look at it personally is until you can out drive the vehicle at hand theres no need to upgrade right? unless of course you want to for the fu*k of it. We are out driving the jeep at this point!
The XJ is SO & we are getting ready to set it up, so before we conformed to what everyone else does. We thought of upgrading possibly, thats the reason for the thread!

Thanks to those who are contributing though (chris, skull, silver, ect). We are truely trying to get useful information on the subject not argue about it!
 
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i agree with you chris.. so what would we have to do to convert an XJ to leaf under? in your experiance

I would think the easiest route would be to buy Nationals or Deavers designed for spring under. I don't know of any junkyard/bastard pack that could be made to work, and for the purpose of going fast I would just spend the cash on the good stuff.
 
I'm aware that 10-12" in the front is about it without going crazy and yes bumpsteer comes into play! That still doesn't give me a definitive reason why spring under in the rear is a bad idea or shouldn't be done! And X-over steering setups will help eliminate some BS! I see no reason a XJ with 12" of travel up front shouldn't be SU in the rear!


OK. You should have come at it like this from the beginning.....spring under (I will be doing to my Bronco) would help the springs last longer as you wouldn't go into negative arch on full compression and would allow you more uptravel in the rear. I don't say it's a bad idea.....I say if you are searching for 18-24" travel out back with 10-12" up front, your rig won't drive any better or be any faster. You don't need to land the back first if jumping (its not an airplane coming in for landing, haha) and to be honest, depending on your springs and valving, you may not gain anything for the first few inches of travel anyway (as the shackle swings and play is taken up). I say go spring under if you can (and give us a good write up) but don't expect to be any faster than your front will allow. :cheers:
 
I would think the easiest route would be to buy Nationals or Deavers designed for spring under. I don't know of any junkyard/bastard pack that could be made to work, and for the purpose of going fast I would just spend the cash on the good stuff.

hey chris... with your experience how much travel can you get out of the front of an XJ with the stock location of the shock mount?
 
I know some Jeepspeed racers have run 12" travel shocks in front at roughly 6" lift over stock. I think some shocks run shorter than others and it would be a tight fit, but it can be done. And when I say 12" travel shock, I mean a 2.5 or 3 inch body race shock that uses a T&J's style upper mount in the fender well and pushing the custom fabbed lower shock mount down as low as possible on the axle.

Hope that makes sense. The only other option is to take out the inner fender and build an engine cage (like I-beam and Grimm have done) but the inner fenders are a HUGE part of the Jeep's structure so plan accordingly.
 
I know some Jeepspeed racers have run 12" travel shocks in front at roughly 6" lift over stock. I think some shocks run shorter than others and it would be a tight fit, but it can be done. And when I say 12" travel shock, I mean a 2.5 or 3 inch body race shock that uses a T&J's style upper mount in the fender well and pushing the custom fabbed lower shock mount down as low as possible on the axle.

Hope that makes sense. The only other option is to take out the inner fender and build an engine cage (like I-beam and Grimm have done) but the inner fenders are a HUGE part of the Jeep's structure so plan accordingly.
yeah i know what you mean... and by the way its Tyler, the guy you built the beam for. i'm the one that want to go leaf under also i'm just trying to get some info on how to.
 
OK. You should have come at it like this from the beginning.....spring under (I will be doing to my Bronco) would help the springs last longer as you wouldn't go into negative arch on full compression and would allow you more uptravel in the rear. I don't say it's a bad idea.....I say if you are searching for 18-24" travel out back with 10-12" up front, your rig won't drive any better or be any faster. You don't need to land the back first if jumping (its not an airplane coming in for landing, haha) and to be honest, depending on your springs and valving, you may not gain anything for the first few inches of travel anyway (as the shackle swings and play is taken up). I say go spring under if you can (and give us a good write up) but don't expect to be any faster than your front will allow. :cheers:
Ya I should have been more clear in my OP. Right now we can go decently fast with what we have. Chris, speedbump, yamadevil have seen the XJ first hand. We are pulling roughly 10-11" of travel, using 2.0's...ect!
We have & can go pretty damn fast through some rough stuff & the only thing thats holding back is the rear.
No we don't have deavers right now & I'm sure the rig would handle the fast stuff better & the rear wouldn't be holding us back if there was deavers back there.
But since we are setting it up anyway, we figured it might be worth it to go SU. It sounds like its worth it, theres just some research & stuff that needs to be done.
 
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