acceptable camber change....

[UndercoverFab]

i`m wondering what everyones opinion on acceptable camber change from positive at full droop to negative at full bump, thanks in advance.

[ntsqd]

Ideally you want the tire to stay flat to the surface it is rolling on. So optimum camber change will depend on your roll center and the roll angularity limit of the design. Then what ever camber you pre-set to offset tire carcass squirm will remain constant thru the range of motion. If you are running a light tire or a heavy vehicle you may want a little camber gain from the above ideal to help with excessive carcass squirm.

[BA_DirtDriver]

positive camber is not good. You should be gaining negative camber up to full bump. The appropriate amount depends on the anticipated body roll per steering/ turning input. As most off road trucks/vehicles run low spirng rates at the wheel the anticipated body roll might be quite high. This would generally require more neg camber gain. Most designs that I have seen let the vehicles take 5-7 degrees of "set" with considerably less neg camber gain. This stems from much more important striaght line bump characteristics than then turning performance. Watch any off road video most of the vehicles roll pretty far on asphault turns. This attached pics shows not nearly enough negative camber gain, but the truck wins so obviously there has been some compromise.

FWIW

Bret

[UndercoverFab]

almost every truck i`ve seen with beams has some amount of positive camber at full droop, i`m building a set for a fullsize chevy now and the minimum amount of positive camber i have gotten so far is 2 1/2 degrees at full droop while having 3 1/2 at full bump, i still live on the east coast and i cant just run to a local shop to shoot the breeze about suspension design.

[Brian Mapes]

With beams there is going to be positive camber while drooping but with arms you dont want to have positive camber at all. Positive is =\ / Negative is = / \ It is always going to be different with every truck because there are so many variables. I wouldnt have any more than six at full bump and about 4 at full droop.

[UndercoverFab]

my main concern is what the front ends gonna do when it comes down off a jump or skipping along a whoop section with an excessive amount of positive camber when its at or close to full droop, with the arms i have planned now i`d only be at 2 1/2 maxed out and i have no problem with 22 inchs of usable travel, thanks for the help guys, it`d be alot easier if their was a desert on the east coast http://www.race-dezert.com/vb3/attachments/old/images/graemlins/grin.gif

[Brian Mapes]

Wait so you are building a chevy right? With a arms or I beams? With a arms you want no positive camber at all. I think that if you had positive camber on a armed truck that it would try to cause excess body roll. As well as putting more stress on your suspension and steering components.

[UndercoverFab]

yeah you got it right, chevy with beams. i thought i mentioned that in the first post but i guess i forgot, my bad.

[Brian Mapes]

Well since it is beams then you are going to have a pretty good deal of camber change. Are they equal length beams or not. If you are only gong to be getting 2 1/2 degrees of positive camber at full droop then I would say that is pretty good as most i beam trucks are getting much more than that. But if you are going to be getting that minimal amount of camber at full droop then what are you getting at full bump because it seems like you will get enourmous negative camber. Search for "any one have more pics of this truck?" and there is some pics of a class 8 with some crazy beams take a look at them. Solo motorsports is also doing a chevy with beams. Solo (http://solomotorsports.com/home.html) You cant see any beam pics but you can see the rest of the truck.

[UndercoverFab]

the ones i drew up with 2 1/2 positive at full droop had 5 degrees negative at full bump, the ones with 3 1/2 negative at full bump had 4 positive at full droop, i`m pretty set on the first design right now except for that fact that i have more up travel from ride height then i do down travel, i don`t know which would be better more up travel or more down travel, basically living on the east coast i`m shootin from the hip at what i think will work good, theres only so much i test out on mx tracks and fire roads out here.

[curt]

My thought is look at the pic above, the left front tire is doing very little to help with traction and a little positive camber might be very helpful in getting more front end grip for vehicles that turn frequently like in shortcourse or stadium racing. Curt

[ntsqd]

My thots exactly, Curt.
Way up there I said the most ideal is for the tire to be FLAT to the ground all of the time. If it isn't flat then you're giving away traction. Usually getting a camber curve somewhat like that of a beam with A-arms isn't really possible. So it isn't that staying negative is desirable and that's why the big name built trucks/buggies are like that. It's that with a-Arms it can't be easily done.

[curt]

I was agreeing with your post about maintaining flat contact patch. Can't be easily done is definately true but some can be done. I'd start working with the upper a-arm first, at full compression it should be at about 45% to the frame like - |_|/, then I'd work the down travel to about 90% to the frame |_|_ and see how the travel is. If you can get the desired amount of travel within those parameters the upper arm would be at it's longest point when at extension and should stick out further than the lower creating a bit of positive camber. See atatchment, as a starting point it would be about 15" based on a pivot points about 14-1/2" on the upper arm...Curt

[UndercoverFab]

again this is beamed chevy not a arms but i appreciate everyones input, i know in a perfect world the tire would stay flat to the ground throughout its whole range of motion, my concern was mostly the positive camber when the beams were at or near full droop.

[ntsqd]

Just as an SOP starting point, I would limit inside droop at the point that the outside tire ceases being flat (i.e. starts to pick up the inside corner of the tire) in roll. That the outside tire be flat on the ground is far more important than the inside tire being flat on the ground.

Curt, I knew you were agreeing with me. I was trying to acknowledge that. Think my wording failed.

[curt]

Out of curiosity, how much travel are you pushing for? A beam truck could get hugantic travel but I would think after the novelty wore off you'd probably be strapping it to around 16-18" or so which might not be an excessive amount of positive camber. I'd ask around to see what everyone is getting from their beam trucks if they limited it and why they did...I would assume the limiting factor is probably the steering more than anything else...Curt

[UndercoverFab]

21-22 inchs, i`ve only built two trucks previously, the first was a chevy with beams that was strapped at 18 and i wanted to try more but sold the truck, so this is bastardized chevy #2 http://www.race-dezert.com/vb3/attachments/old/images/graemlins/smirk.gif

[geoff]

from what i have found, a bit of negative camber at full bump and slight neg at full droop seems to be the setup of choice.

ntsqd definately is on point