[Lancelot]

Hi

At highway speeds when driving straight the car is quite sensitive to wind gusts or to the air flow from big trucks when overtaking them; In contrast it's very stable in normal conditions, straight road, light wind, no trucks.
I'd like to know your opinions on the cause;

Background info:
I am running increased negative camber with F80 control arms, stronger H&R anti roll bars and front struts bar, so the chassis is tuned a bit. Tyres are michelin PSS without significant wear.

Last alignment check was 3 days ago and we get front camber -1°50 left -1°20 right, thrust angle 0°01; a bit of cross caster too with 0°30 difference.

Rear is perfectly aligned with -1°50 on both side and thrust angle 0.

Now the car is tracking perfectly straight with no wind, and I'm extremely happy with very stable cornering balance. but the stability under a bit of wind doesn't make me confident for highway trips.

Recently I've got KW coilovers and the car was lowered but that didn't affect the sensitivity to wind much.

Am i running too much camber? Is there a noticeable trade-off where less negative camber would make the car less sensitive to wind when driving straight, but not as stable in corners? I generally note a know tradeoff in tyre wear.

Or would that rather come from cross camber/cross caster?

I'd like to know your thoughts on this, should I spend my efforts in camber/caster adjustment bushings, or reducing negative camber instead?

[Lancelot]

Interesting research paper from 1990 for those who are interested;
Conclusions in a nutshell:

Crosswind senstivity decreases with:
- More mass towards the aft (I lose in this respect with the Hybrid 3 having 300lbs in the trunk)
- Center of lateral air pressure towards the back (I lose again e.g. compared to a Wagon/Touring F31)
- Stiffer suspension (I should gain here thanks to aftermarker coilovers, EDC and stiffer roll bars)

AND interesting comment - trying to control tightly results in poorer results, due to lag in driver response, overcompensation... => so going along with the ride is supposed to be better. I need to relax I guess

https://deepblue.lib.umich.edu/bitst...pdf?sequence=1

[50shadesofhockenheim]

How much of a difference did the F80 control arms make?

[Lancelot]

Just had them removed;
With f80 arms
Camber -1°23' / -1°50'
Caster 7°50'/8°20'

With f30 arms
Camber -0°4'/-0°5'
Caster 6°30'/7°0'

Big difference... and surprisingly less cross caster with f30 arms.

[Lancelot]

FWIW, cross-wind sensitivity is now completely gone after reverting to stock lower control arm/trailing arm. Either the cross camber is to blame, or too much caster.