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Toe in/ toe out influence on off camber roads

Joined
20 January 2008
Messages
705
Location
France
This might come as an evidence to most of you but let me relate my experience with respect to the subject above.
Last year, I upgraded my suspension to KW V3 clubsport shocks.
I tried to replicate the ride height I had with my Bilstein/Zanardi combo but I must have ended up a little lower...
At first, with this whole new setup, I didn't realize that the car was sensitive to off camber roads.
It happens while passing cars on a normal road.
In fact as the car moves from the right to the left side of the road, I have to correct my steering to keep going straight?
As I ride bikes a lot it reminded me of having the rear wheel not perfectly aligned in the frame except that here the wheel alignment issue changes as the road camber changes!
Given that my car was too low, I decided to raise it slightly by 1 full turn upfront and 1 and 1/4 turn in the rear.
I knew that this would also affect the toe in ( less at the rear) and toe out ( less at the front).
Well it worked!
The car is now almost unsensitive to the road camber and is far more relaxing to drive.
The explanation is quite obvious I suppose: with more weight on one side of the car it follows the direction the wheels on that side want to go.
Toe out in front and toe in at the rear will drive the car off the road as if you were on a bicycle.
I need to check during my next alignment by how much these parameters were changed by raising the car.
 
I've given further thought to this off camber issue.
Is it the rear wheels that drive the car off the road or the front or is it the combinaison of both?
In fact the camber seems to play an important role also when it comes to keep the car in a straight line.
I read that radial tires produce a toe-in effect that's equivalent to one tenth of the camber value.
This means that a camber of 1° produces a toe-in effect of .1°.
If the rear camber is at 3° this means .3° of toe to be added to the typical 3 mm of toe ( equivalent to .3°) that gives a total toe of .6° or roughly 4.8 mm for an 18" wheel.
For the front wheel, the camber induced toe opposes the toe out setting making it negligeable.
So it's clearly the rear wheels that steer the car on an off camber road.
No wonder the feeling is so unpleasant!
 
Hi John!

Thanks very much for sharing your experience! very valuable as always!

I'm also on KW (not clubsport but V3), and i would like to know your ride height at the moment, also tire sizes to compare with my actual values (maybe on your jack points to be easier to measure and compare).

my actual values measured to the lower face of the jack points are:

Front: 95 mm
Rear: 100 mm

I'm on 205/40/17 (F) and 255/35/28 (R)

Thanks
Bruno
 
Hi Bruno,

I'll check as soon as I can get the car on a really flat surface.
As far as I remember my ride height was very similar to yours but my tires are slightly different with 215/40*17 and 265/35*18.
Do you have your camber and toe settings?
Have you noticed any off camber issue?

Bonne journée!

John

I did a quick measurement on ground soil that comes out to FR: 100 , Rear: 105
They must have been previously at around 95 mm
 
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Hi John

Well since your tires are a bit wider, and side tire wall height is a percentage of the tire wideness... theoretically your tires increase height by 4 mm Front and 3,5 mm Rear, so our suspension geometry should be very very close (1-1,5 mm difference). I haven't noticed any off camber issue... but my NSX has never been lower in the past...

IIRC my camber is at ~2,5º (R) and ~1,2º (F). Front Toe out is close to original values, but in the rear, since i have non complience toe arms and bushings i reduced toe in from 3mm to 2mm.

Thanks
Bruno
 
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Hi Bruno,
I sent you an email did you get it?
Thanks
John
 
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