BioMax's 4-link Article

The general idea is to have the bars near parallel to the ground a half travel. Wether it be one or the other, it would only be a few inches off at worst. You can screw up pretty bad and still have a driveable vehicle when you are done, so just try to get it as close as you can.

In a situation where the upper bars are shorter than the lowers, I set up the uppers to be parallel to the ground at half travel and then point the lower bars up a bit to get my i.c. This will eliminate as much of the pinion change as you can.

On a triangulated system, you would not calculate the angle of the bars into the bar length. Instant center is calculated from a side view only and from that view, you can not see the triangulation. So with theoretical equal length bars where the uppers are triangulated, the uppers will be longer.

Excellent, thanx, my 3rd four link from scratch and the first one i scrapped(worked like crap, threw the pinion all over). i'm pretty certain with all the advice this one will work nearly perfect. thanx again.

what if point C is mounted closer to the axle than point A, the distance the top bars are mounted to the axle is greater than the lowers(i noticed its usually the other way around) what affects if any is that going to have?

my lower tabs are 3 inches off the axle and the uppers will be mounted on a bar going over the pumpkin.(around 5 or 6 inches off the top of the axle. hope this will be okay or i'll have to bribe the laser guy into reprogramming longer tabs and cutting them out.

how do u set up 4 link bars for correct pinnion angle should it b notched and do u set it up laid out or at ride height thanks

You set it up for what it will be intended for. if u are going to be driving it at all levels which most of us do then i would set it up at half travel meaning if u have 10" of travel then set it up at 5" mark. But yes set the pinion angle with it at 5"

so should i set it up at ride height with say a -2degree pinnion angle

Originally posted by pootytang



what if point C is mounted closer to the axle than point A, the distance the top bars are mounted to the axle is greater than the lowers(i noticed its usually the other way around) what affects if any is that going to have?

If you move the tabs up of down on the rearend housing, but still keep the i.c. in the same place, you will create more or less, under-steer or over-steer. The changes will be minimal because of the placement of the i.c., but it will make some subtle changes.

Originally posted by wee-man



how do u set up 4 link bars for correct pinnion angle should it b notched and do u set it up laid out or at ride height thanks

Half travel is your best bet. Nate is right though, the intended use of the vehicle is more important than the available travel, but that could be a whole other conversation. As long as you don't have too much more than 14" of travel, half travel is best to set up your pinion and i.c.

As for pinion angle, I would go to airride talk.com, he has a really informative piece on calculating pinion angles.

hey biomax i do not post to much, i more or less like to absorb. but after reading all seven pages i wonder what the effects would be on a four link where the upper link bars are longer then the lower and point at an instant center such as a carrier bearing on a 2-piece drive shaft. i have not scene anyone address this.