Can too much negative camber cause instability in a straight line under load?

[CTSV]

I recently had another wheel alignment done on my Detroit Speed converted Mustang.

prior my negative camber was .9 -.1 degree and my caster was 6 degree positive

my toe was toed in a touch


Now we adjusted my camber to -1.4 both sides, caster is now 7.8 + and my toe was set to ZERO

i notice now under load the front end seems to wander in a straight line and i am considering switching my camber back the way it was.

can anyone comment on this?

[andrewb70]

I recently had another wheel alignment done on my Detroit Speed converted Mustang.

prior my negative camber was .9 -.1 degree and my caster was 6 degree positive

my toe was toed in a touch


Now we adjusted my camber to -1.4 both sides, caster is now 7.8 + and my toe was set to ZERO

i notice now under load the front end seems to wander in a straight line and i am considering switching my camber back the way it was.

can anyone comment on this?

My guess is that it is the zero toe that is making it seem less stable. I run zero toe and on my set-up it is OK, but obviously you have a different set-up and it will react differently. I had a Miata that when I got it was set-up to autocross. It actually had some toe out in the alignment. It tuned in super fast, but I could hardly drive it in a straight line.

I am no expert, but that is my best assessment...

Andrew

[SSLance]

Yep I agree, put just a touch of toe in back on it and it'll be good.

[wendell]

Your terminology is ambiguous. Straight line with the front tires loaded (decelerating)or the engine loaded (accelerating)? Either way, camber won't effect straight line stability. BUT, what will definitely effect straight line stability is toe. Static toe out can be very squirrely and so can zero toe. With zero toe during braking, compliance in the front end bushings frequently results in dynamic toe out. Another problem with zero toe is that any positive or negative bump steer is translated into toe out and in through the range of suspension travel. Not confidence inspiring.
Put 1/16" of toe in into the car and see if its more predictable.

[83hurstguy]

EDIT: what I originally typed wasn't making sense... The toe (especially dynamic) is certainly something to look at as described above, and what I would change first.

[RobNoLimit]

On a perfect road, the static camber will have only a little effect on stability. Unfortunately, we don't get perfect roads too often, so, the increase in -camber can make the car a little less predictable. Anytime you increase the + caster, you are also making changes to the dynamic camber curves in a turn. Meaning, as you add + caster, in a turn you get increased - camber on the outside tire, and a shift towards + camber on the inside tire. Almost as if to 'lean' the car, like a bicycle. When + caster is increased, the need for static - camber is less. With caster in the +8 to +9 range, I almost never (only on ultra tight and slick course) run more than -1* camber. Usually I start at -.8*. As for toe, I agree that '0' is a no win. Straight line cruisers and drag cars go 'in'. But, for a sports/cornering car, I would try a slight toe out. With a front steer rack, this will keep the tie rod slack initially tight on what will become the outside wheel, which will react first when entering a corner. Also, a slight toe out will aid in acremen effect in the entry and roll-zone of the corner. I agree that with compliant OE rubber bushings and low caster numbers, toe out will make the car a little darty, but with modern suspension parts and concepts, this is not the case. - This is IMHO, I'm not here to argue. , But, if you try a set up like, -.8 camber, +8.5 caster, (or the +7.8 that you have) and 3/16" total toe out, you may learn something about the car's ability and the value of the IFS under it.

[79-TA]

I recently had another wheel alignment done on my Detroit Speed converted Mustang.

prior my negative camber was .9 -.1 degree and my caster was 6 degree positive

my toe was toed in a touch


Now we adjusted my camber to -1.4 both sides, caster is now 7.8 + and my toe was set to ZERO

i notice now under load the front end seems to wander in a straight line and i am considering switching my camber back the way it was.

can anyone comment on this?

Short answer: yes, a bit.

A tire running at an angle experiences camber thrust.

http://en.wikipedia.org/wiki/Camber_thrust

This translates to each tire creating a bit of turning force when rolling straight. If one tire is unloaded more than the other due to a slight bump or other road imperfection, there is a difference between the magnitude of that turning force from tire to tire. This creates a net imbalance and the more loaded tire turns the car a bit.

Also, the narrower inside contact patch of the more aggressively cambered tire is more susceptible to falling into ruts and dips on the road.

Going from toe in to neutral toe or toe out is a noticeable change for how the car tracks. You could experiment and just see how the car felt with different toe settings leaving the other settings alone.

[CTSV]

guys i got the car at a another shop today for once again another alignment.

what they found is my 4 link was slightly off causing one rear wheel to be toe out and one toe in, since the other 2 shops i used were using the rear as the baseline for the front this seemed to make sense to why my car wandered s

well now my wheelbase is perfect, ride height is perfect all 4 sides

my settings now are
Front Left -1.3 camber
Front Right -.9 camber
Caster left+8.3
Caster right +7.3

slight variance now between both sides but im not sure its enough to cause a pull?



they toe the car in this time to 0.06 per side

the car feels much better however the car still has a pull to the right side and i cant understand why. I swapped tires let to right and it still does it. My front tires are 295 and quite large and im not sure where to go now to change this set up to alleviate the drift to the right.

any suggestions on the right side pull?

[83hurstguy]

guys i got the car at a another shop today for once again another alignment.

what they found is my 4 link was slightly off causing one rear wheel to be toe out and one toe in, since the other 2 shops i used were using the rear as the baseline for the front this seemed to make sense to why my car wandered s

well now my wheelbase is perfect, ride height is perfect all 4 sides

my settings now are
Front Left -1.3 camber
Front Right -.9 camber
Caster left+8.3
Caster right +7.3

slight variance now between both sides but im not sure its enough to cause a pull?

they toe the car in this time to 0.06 per side

the car feels much better however the car still has a pull to the right side and i cant understand why. I swapped tires let to right and it still does it. My front tires are 295 and quite large and im not sure where to go now to change this set up to alleviate the drift to the right.

any suggestions on the right side pull?

Your cross camber is biased slightly to force the car right, and the cross caster is setup to really pull the car to the right. Get the side to side values evened out more. Usually street cars want a little left pull bias with the caster to account for road crown, but for a performance car, equal is better. With 1 degree cross caster set the wrong way, coupled with some road crown, it will definitely drift to the right. I would try to keep the bias to 1/4 degree or so if possible. I once accidentally set the cross caster at 0.5 degree the wrong way (similar to yours) and it noticeably pulled right.

[mmosley]

Your cross camber is biased slightly to force the car right, and the cross caster is setup to really pull the car to the right. Get the side to side values evened out more. Usually street cars want a little left pull bias with the caster to account for road crown, but for a performance car, equal is better. With 1 degree cross caster set the wrong way, coupled with some road crown, it will definitely drift to the right. I would try to keep the bias to 1/4 degree or so if possible. I once accidentally set the cross caster at 0.5 degree the wrong way (similar to yours) and it noticeably pulled right.

Yes... I did alignments for about ten years, the olds dude is spot on, both your camber and caster are "leaning" to the right. You probably do not have a lot of country roads in your parts, so a bias to the left is probably not needed. If they had a fancy enough machine to see your rear toe thrust angle they should be able to see this.

[CTSV]

guys attached is the print out from today.

thanks for the suggestions but how is cross caster adjusted specifically?

maybe something is more obvious so i took a photo of the actual settings.

the drift to the right is annoying and in the NYC area we have horrible roads and it exaggerates this.

[CTSV]

since my car has the DSE speed lign system changing caster and camber is very easy. I just took 1/16 of negative camber off the drivers front and it has made a huge difference in the drift. I also will do the same with the caster on that wheel and then drive it again to see if it is pretty much gone. ZI am hoping these 1/16 increments might make both sides relatively equal in regards to camber and caster.

[mmosley]

since my car has the DSE speed lign system changing caster and camber is very easy. I just took 1/16 of negative camber off the drivers front and it has made a huge difference in the drift. I also will do the same with the caster on that wheel and then drive it again to see if it is pretty much gone. ZI am hoping these 1/16 increments might make both sides relatively equal in regards to camber and caster.

Essentially your driver's side upper ball joint is too far back relative to the lower ball joint, that is the caster part. So, to address just caster you want to move the front adjustment in a very small amount, then move the rear out about that same distance. Unfortunately this may move the toe a little. You can also try to split the difference: since you still have too much camber on the drivers side, just adjust the rear out a little, that will decrease the caster and give you a little less negative camber at the same time. This is best done on the alignment rack, watching the numbers, jouncing the car between adjustments, and with you sitting in the drivers seat. I always try to get the caster numbers close, preferably with a hair more on the passenger side. I would also want your total camber to be less than -1 for your street car, in other words your passenger side is perfect...