04-20-2017, 02:13 AM | #1 |
Major
568
Rep 1,292
Posts |
Sensitivity to wing gusts?
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?
__________________
2017 M550i | Sophistograu
Previous cars: 2014 F30 ActiveHybrid 3 | 2012 f20 M135i |
04-26-2017, 07:18 AM | #2 |
Major
568
Rep 1,292
Posts |
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
__________________
2017 M550i | Sophistograu
Previous cars: 2014 F30 ActiveHybrid 3 | 2012 f20 M135i |
Appreciate
0
|
04-28-2017, 12:27 AM | #4 |
Major
568
Rep 1,292
Posts |
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. Last edited by Lancelot; 04-28-2017 at 01:27 AM.. |
Appreciate
0
|
05-08-2017, 10:31 AM | #5 |
Major
568
Rep 1,292
Posts |
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.
__________________
2017 M550i | Sophistograu
Previous cars: 2014 F30 ActiveHybrid 3 | 2012 f20 M135i |
Appreciate
0
|
Post Reply |
Bookmarks |
|
|