How to determine proper length of rear lower 4-link arms?

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!!!

i thought jeepspeeds had to run rear leafs

redneck23ms said:

i thought jeepspeeds had to run rear leafs

Click to expand...

They do and you must have stock wheelbase o 99.4 to 103.4" wheelbase. He said inspired by Jeepspeed but he will not be legal if he don't follow the rules:

http://209.85.173.104/search?q=cache:I0Gjxl5JptEJ:www.jeepspeed.com/2006%2520JeepSpeed%25201%2520Rules.doc+jeepspeed+track+width&hl=en&ct=clnk&cd=1&gl=us

http://www.jeepspeed.com/rules/rules.shtml also jeepspeed rules state wheel travel of 10" front and 12" rear, must retain stock wheelbase max 33" tires etc and must use stock wheels or american racing wheels.

up to 16x8 too, and you need to get your brackets and some adjustable arms, and tweak your pinion angle after its mocked, and before you tack.

sorry, i should fix that, you need to have your brackets on, and then you mock up your axle and set the pinion angle, then measure your arm lengths. then tack everything, then disassemble and finish.

I found out that Dirt-Tech makes a boxed lower trailing arm specifically for Jeep Cherokee XJ JeepSpeeder's. . .it's 50" long from the center of joints.

Now I just have to figure out how long the upper links should be!

You really need to look at a 4-link calculator and make sure the whole thing is setup correctly, you can't just get numbers from other kits and expect them to work well.

There is a lot that goes into a good 4-link. Link lengths, vertical & horizontal separation at both the frame and axle ends are all very important.

Ralph XJ & Starboard M. . .thanks for the reminder about checking that stuff out and for the link to the 4-link calculator.

I would for sure double check that stuff. . .the 50" trailing arms from Dirt Tech are specifically for JeepSpeed XJ application (I've talked with Dirt Tech about this application and the use of it with their Ford 9" rear with 4-link brackets). . .it turns out that in talking with Dirt-Tech that someone else has already got a 4-link set-up for an '84-01 XJ and they are asking him if it's OK to send me his email so that we can chat about his set-up).

Anyway thanks again everyone. . .good or bad thoughts about my ideas are all appreciated!!!