anyone down for a J arms 101?

geoff

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I have been toying a lot with the idea of centermount arms. I know they arent necessary, i know simple setups work well with the right shocks, but centermount arms are sick. My roomate had his senior design project last semester so we did a 4link, and now on my project stating in august i think i am gonna do a centermount lower and J arm setup on my toyota.

I saw one truck posted by GEARS which looked good, and i liked yotapunks lowers, but it seems like more could have been done with the uppers. DrtDevils looks like a good start but the uppers could use some work. Of them, it seems that there wasnt too much real design other than build the arms and see how it does!.

The thing that i have been wondering is how to determine the lengths of the unparallel arms, and what kind of camber change are you going for? It seems that if there is some way to get an idea of what caster curve to aim for, then designing the length of the upper would be a function of the conceivable package size for the lower (dictated by steering setup) and factor in the appropriate camber curve. also what kind of racks are generally used, that wont break that is.
 

geoff

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is the motor moved back on that?

edit: nevermind

 

ntsqd

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My simple take on the various curves a front suspension travels in:

Camber - Want the tire contact patch flat to the ground at all body roll angles. The outer tire can pick up the outer coner of the contact patch as the body rolls. This will offset carcass squirm.

Castor - Want gain in compression and extension. Gain in extension should border on radical. Reasoning is that more castor angle increases the straight-ahead tendency of the vehicle. Nothing worse than jumping a 'darty' vehicle. Gain in compression should be mild. Sometimes you have to turn right at a landing. Excessive castor would fight you

Toe Change ('bumpsteer') - Want slight toe-in tendency in either direction from normal ride height.

I have no idea what it would take to achieve these goals. It's quite possible that some are mutually exclusive.
 

UndercoverFab

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kinda off topic but how wide is too wide when it comes to track width, on my first attempt at building a pre runner i built beams for my full size chevy and it was 8inchsonce i move i want to start on another one but with arms this time. also what would be considered to much change for camber in the complete range of travel, the beam truck stayed within +/- 2-1/2 degrees and one last question is it better to go for more up travel or more down travel.
 

UndercoverFab

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ok part of that got screwed up that one sentence is supposed to say that the beams i built for the chevy put the track width at 87 inchs.
 
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