[atomicjoe23]

How do you go about figuring out the correct length of the rear lower 4-link arms. . .I'm building a JeepSpeed Cup/CORR/SCORE inspired desert Jeep XJ and I'm going to be using boxed lower rear 4-link trailing arms and I need to figure out the right length to make them.

JeepSpeed Cup limits suspension travel in the rear to 15" I believe (the JeepSpeed website rules section is not opening at the moment for me to double check) and CORR rules specify a minimum ride height of 10" as measured from the ground to the lowest protrusion on the bottom of the truck (i.e. the truck must be able to drive over a set of 10" blocks with the tires inflated to 20psi). I'm not sure what the stock ride height is at the moment or what ride height that I'm going to be looking for but I'm sure it will be more than 10" but I don't want the thing jacked sky high either. . .looking for more of the desert racer/pre-runner look. Wheel base will be between 104-116" and I'm looking at a front and rear track width of ~70". I will be using 15x10"; 16x10" or 17x9" wheels with either 33x12.50 or 35x12.50" tires and I will have a curb weight of ~3750 lbs. . .give or take.

I'm not sure how much of the above information is necessary but if someone can point me in the right direction as far as customized chassis design goes I would greatly appreciate it.

Thanks!!!

[balloo93]

So your are doing a coil over conversion in the rear?

The lengths you need can't really be given if this is a custom one off setup. You would have to determine how to mount and where to mount the arms and that will give you necessary lengths.

[AznDrgn]

There are 4 link calculators available, just google or search on pirate. It'll take into account wheel base, travel, COG, and how much the axle will tend to walk under the vehicle or push it forward.

[Oizarod115]

The 4-link calcuator is an interesting tool. Unfortunatly a lot of the parameters for it are inconvenient (who knows their exact CG, especially when you haven't built the truck yet?), and a text-book 'correct' geometry 4-link is 99% gaurenteed to not even come close to fitting in the avaliable space. However, I can't knock it too bad, as it's still a good idea to run any design through it to quickly verify things. But, at the same time I do not like how it is too 'easy', and really takes the understanding out of the process, and would much rather see someone learn the 'hard' way by modelling it on paper.

Anyways, I'd says shoot for a lower length of about 40-44" and an upper length of 30-32". Just so you can get a tape measure and realize how much work it'll take to make this fit. Remember that you want your arms as flat as possible. And about 8" of seperation vertically at the axle side as a minimum. And you don't want your AS to be absurd either way as the truck wil behave strange. Also, you failed to identify exactly what type of 4-link you're building (single triangulated, dual, panhard/5-link parallel), and that changes things a lot. Only ONE of them is worth building if you have any intention of going fast. Or even going slow...


Confused?

[paulmatyn]

http://www.jeepforum.com/forum/f37/dez-racer-xj-build-367176/

talk to skullver. here is his jeepspeed build thread.

[ktmracer419]

dont jeepspeed rules also say you need to keep leafs in the back and coils in front like from the factory?

[600dollarXJ]

Originally Posted by ktmracer419

dont jeepspeed rules also say you need to keep leafs in the back and coils in front like from the factory?

someone already told him that in his thread at naxja

[EricsXJ]

I might be wrong but I take it he's building a JeepSpeed "inspired" rig - not one to actually be used in JeepSpeed. But honestly IMO leafs ARE a better setup for that application where big flex isn't really needed.

[ktmracer419]

Originally Posted by 600dollarXJ

someone already told him that in his thread at naxja

gold star for being observant

[skullver]

actually the jeepspeed cup class is relatively unlimited, I think the main requirement is the motor type must have come with the body style, no V8 xjs. Coilovers and custom suspension are allowed and necessary to be competitive. That being said I gave you a longer more detailed suggestion on one of the other forums, good luck and get that wallet ready for a major draining


copied and pasted:
I were you I would look into the ranger trailing arms/triangulated 4-link rear suspensions and base yours off of that as they are similar in trackwidth and wheelbase, just be prepared to drop some serious coin on shocks, figure $700-$900 per shock, with a rear trailing arm/4-link I would run a 2.5(at least)/14-18" travel coilover and a at least 2.5" 3-tube bypass, so just the rear your looking at around $3200. To go through the trouble of the rear trailing arm/4-link and still have a solid axle in front capable of relatively little travel seems silly though, but to do it right you would need around the same shock set-up so there goes $6400 in shocks alone, no real way around that if you design everything right, you will need the shocks to compete. Once you get a good amount of controlled travel well then you will need the extra $$horses$$ to utilize the suspension so look at a stroker/ mucho head work as the XJ never came with a V8 so using one would be illegal.

I don't seem to remember seeing a travel limitation for the jeepspeed cup unlimited series but I'll look around again, regular jeepspeed is 10"/12" and you need an approved suspension manufacturer, not so with the cup class. I see it being really hard to keep it close to that weight with all that suspension, look into building the main cage from 2" dom to be safe as it will break the 4k lb mark. I think you would have a really hard time trying to compete in both corr and jeepspeed as they have a whole different set of requirements but I wish you luck, keep me posted, sounds like a cool plan.
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[atomicjoe23]

All,

thanks for all the replies and suggestions.

Skullver. . .I got your post on the other forum and thanks for the suggestions it definitely will help me get started.


Oizarad1115. . .I'm going for a triangulated rear 4-link set-up.

I've got Herb Adams Chassis Engineering book but unfortunately it is currently packed away in a box in preparation for an upcoming move so it's inaccessible at the moment.

What do you guys thinking of using an '05-08 Tacoma 4WD IFS set-up with a Chaos Fab Uniball long travel suspension system w/extended 4340 axles for the front (or better yet something like ESB Fabrications long travel race front suspensions for the Tacoma 4WD IFS set-ups)!!!

[Jason, aka: Jeepin.com]

I think it's an abomination and wrong on every level conceivable.

[skullver]

Originally Posted by atomicjoe23

What do you guys thinking of using an '05-08 Tacoma 4WD IFS set-up with a Chaos Fab Uniball long travel suspension system w/extended 4340 axles for the front (or better yet something like ESB Fabrications long travel race front suspensions for the Tacoma 4WD IFS set-ups)!!!

for one it would be impossible to adapt the the driver side front output of the XJ transfer case, the taco xfer case for IFS exits from the center and the differential is centered, you could use Ford TTB 4wd beams if you really are stuck on IFS as they have the differential on the driver side. Sounds like the most economical thing to do would be to start with an easier platform, tacoma, exploder, ranger etc, no use re-inventing the wheel so to speak. Not to mention you will not be able to get a good amount of travel from any 4wd IFS set-up, unless you have at least $5k(probably more) to spend on spindles/porsche plunging custom cv shafts etc like the 4wd pro-trucks(corr). But hey, innovation is the mother of creation(or however that goes) so have at it if you are a true glutton for punishment, it will be a long, bumpy, expensive road that may end up leading to knowhere, but I must admit it is similar something I was kicking around before I did my research and sourcing for parts, my conclusion was to start with something with a frame and keep it 2wd Good luck though, don't let anyone disourage you but make sure you do all your research before you pull the trigger so to speak.

[Oizarod115]

Originally Posted by atomicjoe23

Oizarad1115. . .I'm going for a triangulated rear 4-link set-up.

I've got Herb Adams Chassis Engineering book but unfortunately it is currently packed away in a box in preparation for an upcoming move so it's inaccessible at the moment.

What do you guys thinking of using an '05-08 Tacoma 4WD IFS set-up with a Chaos Fab Uniball long travel suspension system w/extended 4340 axles for the front (or better yet something like ESB Fabrications long travel race front suspensions for the Tacoma 4WD IFS set-ups)!!!

Is that book any good? I was going to buy it but never got around to it, it might be out of print now...

And IFS is a lot of fun. However, I have only ever ONCE seen it on a cherokee, it was a ford TTB setup. And once on a comanche, which was S-10 stuff, but 2wd (street truck). I don't cruise the desert racing comunities, so their might be more out there, but I'd think they'd be TTB if anything. The TTB is cheap and can be adapted easily enough as it mounts like a much more conventional suspension setup. The S-10 IFS setup I saw involved putting a comanche cab on a highly modified S-10 frame as it was NOT possible to position the arms in an acceptable place otherwise. As would be the case with many IFS setups. I am sure it is possible and have looked into it quite a bit with the intention of sometime doing a AWD street truck. Nothing will be easy though. But if you understand how it works and have the time/money/skill it can be pulled off.

[atomicjoe23]

Originally Posted by skullver

I don't seem to remember seeing a travel limitation for the jeepspeed cup unlimited series but I'll look around again, regular jeepspeed is 10"/12" and you need an approved suspension manufacturer, not so with the cup class. I see it being really hard to keep it close to that weight with all that suspension, look into building the main cage from 2" dom to be safe as it will break the 4k lb mark. I think you would have a really hard time trying to compete in both corr and jeepspeed as they have a whole different set of requirements but I wish you luck, keep me posted, sounds like a cool plan.
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JeepSpeed Cup rules are still not functioning on the JeepSpeed website!