Suspension guidelines and changing consequences


Sep 7, 2009
Mesa az
Hey guys,
I obviously don't post too much on RDC but have been a member for a numerous amount of years. Mostly just to check things out and to bookmark good threads that I have found useful over the years. With that being said I have compiled a list of things I have found/learned from numerous threads on suspension design and suspension dynamics throughout RDC. Below is that list so feel free to contest them if they are wrong because I would like to get a few things straight. I am currently building a entire bulkhead from scratch and have a few guidelines that I would like to get cleared up.

One of the things I couldn't find was how the upper and lower mount separation plays into everything. Obviously the closer the mounting points on the lower bulkhead the greater possibility for higher travel numbers. But what happens as you change one or the other? I've played with this a lot and it never seems to be uniform. If you had the lower points fairly close together but spread out your upper mounting points what would that change? Should your upper and lower mounting points be in the same plane? What does making one wider/more narrow than the the other change? Also, what does changing the height of the center line of the upper and lower mounting points do for the suspension?

Without making this any longer than it needs to be I also have another issue that I have seemed to come across. When cycling my suspension I have fairly good camber changes ranging from right around -6.7ish to almost 0 but problem being is that when I get towards the end of my travel I tend to get this "hiccup" where the camber changes from very close to zero to increasingly negative again. No its not going negative and then positive without my knowledge, I checked that. It almost seems that the upper arm runs out of cycle and starts pulling on the top of the spindle. But I have yet to figure out how to fix this without messing everything else up ha. Hence why I think I might need to look into whats wrong with my bulkhead.

any info on the subject would help tremendously. Thanks


24” travel front

(-2.5 deg) camber at ride height

(-6:8 deg) camber bump

as close to 0 deg camber at droop possible

90” outside tire to outside tire.

39” x 13.5 x17” wheel combo 4” backspace.

Scrub Radius:
sand cars: 1/2"-1"
Class 1: 1/2"-3/4"
TT: 1/4"-1/2"

· Scrub Radius: increases with tire diameter.

· Increased wheel travel includes increased angle to control arms and also increased angle to steering linkage

· Anti dive = non parallel arms

· Upper arm roughly 75% of lower to keep from having too much camber gain.

· Possible (-8deg) camber at full bump?

· Craig Hall states 8-12 deg full bump

· Moving inner pivot point of the UCA up or down does two things.

o 1. Moves camber curve up or down.

§ Lowering piv point produces less camber change toward full droop and more toward full bump.

§ Raising the piv point produces more camber change toward full droop and less toward full bump.

o 2. Changes the amount of body roll transferred to the wheel.

§ When arms run parallel, body roll and wheel tilt are the same. When the arms run closer on chassis end the wheel will tilt less than the body. When the arms run closer at the wheel end the wheel will tilt more than the body.

· 26”+ is too much front travel to shoot for.

· Full bump shock and lower should be 90 deg.

· Ex:

o caster: 7deg

o SAI: 9 deg

o Offset: 0

o Camber: -6 full bump, -1 ride height, -6 full droop.

o Lateral tire scrub: LTS< ¼”

o Front travel: 20-21

o Shock angle at bump: 90 deg

o Shocks used: 2.0x12”

o Spindle ¾” heims upper and lower

o Lower arm heims: 7/8”

o Upper to spindle: ¾”

o Ride height: 40% stroke, close to 0 roll center.

· Ackerman: base on center of an imaginary axle between rear wheels.

· As knuckle/upright gets taller it gets heavier and the loads on the upper a arm get lower.

· Knuckle is 100% unsprung mass. While upper is 50% unsprung.

· A Taller knuckle means the UCA will mount on the chassis higher. That spreads the load over a larger area. And can help get the mounts out of the way of steering.