Vulnerable to crosswinds on highway? NOT!

[bluetinc]

I have also noticed that I feel the crosswinds quite a bit. I also noticed that when I took the steering setting off of sport, it was harder to notice the cross winds. It was almost as if the electronic steering system picked up the push of the wind and tried to push that feedback into the wheel for me to feel (as it should for a tight turn). Anyway detuning the setting helped a lot in my mind. I'm curious if others have noticed the same thing?

Peter

 

[Jason S]

I dislike the Sport steering as too sensitive. Jiggle the driver a little, jiggle the car.

 

[wycolo]

> I have also noticed that I feel the crosswinds quite a bit. [bluetinc]

Been on STD steering since mile one. NO sensitivity whatsoever, non issue. Steering is tight, too tight for them that steers with their pinky!
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[kinddog]

quality discussion people.

killer contribution, Bearman.

i still don't get how/why an aerodynamic car from the front would all of a sudden turn non-aerodynamic from the side. looking at a profile of the Model S, it looks sleek that way too.

 

[Discoducky]

My experience is that it the primary variable is the steering setting. No crosswind issues on standard setting and some on sport.

 

[ckessel]

I use standard steering. I've noticed the cross wind effect is stronger than in my Mazda RX8, but about the same as my wife's Acura RDX. On gut feel, that seems odd since the RX8 is a light car and thus wind should blow it around more, but if I think of the profile in the wind it makes more sense. The RDX and Model S have much larger side profiles to catch the wind than my RX8 had.

Either way, it's not a big deal, just something to be aware of. My RX8 got moved around a lot more by the tire grooves in the asphalt, so every car has it's quirks.

 

[SuperCoug]

From what I understand it can be pretty difficult to know what exactly makes different cars feel more sensitive to crosswinds than others so take any general ideas with a grain of salt. There seems to be some truth to the idea that the type of steering can influence negative dynamics of the car in crosswinds, in one research article[1] those drivers who just went along and didn't over-correct ended up moving the car around less. So electrical power steering might be too direct for some drivers and increase the cars movements to the sides especially since the crosswinds usually come in unpredictable short bursts. This could be tested by changing the steering response in the Model S to a less sensitive setting on the touchscreen. The general consensus is that cars with low coefficients of drag are more sensitive to crosswinds because of their asymmetric side surface area but apparently a "Kamm rear end" (Prius) mitigates this.

View attachment 17800

However why a car is more or less stable in heavy crosswinds is answered by the fundamental properties of the car: Center of mass, Center of steering forces, Aerodynamic center of pressure, Tires, etc.
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Here is the link to the full [1]article.

Damn, talk about an A++ post! That is some fine work, sir. Bonus points for references to research done in the 1930's! Well done.

 

[Bearman]

i still don't get how/why an aerodynamic car from the front would all of a sudden turn non-aerodynamic from the side. looking at a profile of the Model S, it looks sleek that way too.

I think the best explanation is what I got from this paper "Numerical investigation of unsteady crosswind aerodynamics for ground vehicles" and ill just post the relevant pieces for your question here:

"Crosswind characteristics of a vehicle are usually described by two aerodynamic quantities, the side force and the yaw moment. The side force originate from the difference in pressure in the windward and leeward sides of the vehicle. High velocities around the leeward leading edge of the vehicle produces large negative pressure and hence is mainly responsible for the side force.

Negative pressure is also observed at the rear, mainly depending of the design, and the unbalance in pressure between the front and the rear leads to a yaw moment tending to turn the vehicle front away from the crosswind."

Fig 1.2

"According to Hucho (1998), the side force is not as important as the yaw moment in influencing the crosswind sensitivity. Figure 1.2 shows the side force and yaw moment for three traditional car designs. Despite its larger side force, a squareback, with its lower yaw moment, is a more favourable design than fast or notchbacks. The strength of C-pillar vortices in the rearslant of the two latter designs are responsible for this higher yaw moment values, Cairns (1994).
In addition, the well rounded rear surfaces is found to increase the yaw moment, Howell (1993)."

In short: A low drag design isn't pushed to the side more in fact it is pushed less, but it is turned (away) around its vertical axis more because of the higher difference in pressure between the front and the rear.

 

[Duckjybe]

I have also noticed that I feel the crosswinds quite a bit. I also noticed that when I took the steering setting off of sport, it was harder to notice the cross winds. It was almost as if the electronic steering system picked up the push of the wind and tried to push that feedback into the wheel for me to feel (as it should for a tight turn). Anyway detuning the setting helped a lot in my mind. I'm curious if others have noticed the same thing?

Peter

I have definitely noticed the instability in cross winds especially when in Sport steering mode. Changing the setting to Comfort seems to help a little by making it easier to make small steering corrections. I do have Nokian Hakkapalita R snow tires on which probably does not help matters. However, I have snows on my BMW and it is steadier on the highway than the S. I made sure the tires were the right PSI. I wonder if it could be an issue with alignment coming from the factory? My steering wheel is slightly off centre but the car doesn't pull at all.

 

[wycolo]

Yesterday: serious sidewinds (or oblique) on 100% dry good pavement. With STD setting there was NO feedback to steering wheel; the car just moved over an amount corresponding to strength of wind gust. All predictable and comfortable. No YAW (fishtailing) or other instabilities detected. On I-80 did some serious blasting past semis @~90 mph (who wants to meander past a sashaying rig?). My first outing (120 miles rt) in non-winter conditions. I think I could detect a slight bit of 'snow tread slop'. Overall: very happy camper.
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[Al Sherman]

Yesterday: serious sidewinds (or oblique) on 100% dry good pavement. With STD setting there was NO feedback to steering wheel; the car just moved over an amount corresponding to strength of wind gust. All predictable and comfortable. No YAW (fishtailing) or other instabilities detected. On I-80 did some serious blasting past semis @~90 mph (who wants to meander past a sashaying rig?). My first outing (120 miles rt) in non-winter conditions. I think I could detect a slight bit of 'snow tread slop'. Overall: very happy camper.
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Nice wycolo. Way to really put her through the paces! Good stuff. Be careful.:wink:

 

[Electric1]

Al, if anyone knows about crosswinds it should be you!

 

[Al Sherman]

Al, if anyone knows about crosswinds it should be you!

LOL. Oh the stories I could tell! However we can't crab the MS and maintain a constant course. YET.:smile:

 

[Plug Me In]

I would think the solution would be to drive much faster. That way your relative wind becomes more of a headwind and the awesome aerodynamics of the S take over. This, I think, is a good solution to many of the problems on these forums. Just drive faster!

 

[Al Sherman]

I would think the solution would be to drive much faster. That way your relative wind becomes more of a headwind and the awesome aerodynamics of the S take over. This, I think, is a good solution to many of the problems on these forums. Just drive faster!

Way too much science involved and probably over my head. I don't think speed will have any affect on the effect of a direct cross.

 

[jerry33]

Well, yet again Citroen had some good ideas with the DS series. It had active hydraulically augmented steering set up so that at higher speeed there was a small range of steering which was less sensitive so you could make precise corrections with less tendency to over correct. At lower speed and outside that range it was normal. The effect was that staying within a lane at highway speed used the less sensitive area. I never noticed any particular cross wind sensitivity but the car was also quite aerodynamic and the weight distribution was strongly front biased.

Not to mention the distance between the front wheels was about 12" wider than the distance between the back wheels.

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If the tire pressures are not correct (in particular if they don't have the same balance front to rear as on the vehicle placard--and assuming no mistakes in the placard recommendation) a crosswind will push one axle more than the other causing the car to turn. Because wind is seldom steady, this causes the car to wander. So if your having a problem, first check the tire pressures. Second try one finger steering. If there is still a problem check the alignment--in particular unequal camber from side to side can cause this. If both these are okay, experiment with a bit more pressure in the rear than in the front.

 

[brianman]

Get a room.

/deepbellylaugh

 

[neroden]

Ok, maybe I'm jumping into the fire here, BUT, the car is pushed around a-lot by cross winds.

Hmm. I thought it was pushed around less by crosswinds than my old Toyota Echo. Maybe it's all to do with what you're used to. :wink:

 

[mrcool1122]

I think you're probably on to it. My S and my last car, a Mini, both have electric steering. The Mini is not a big car, and had an excellent chassis with great feedback and sharp responses. But it, like the S, always seemed a little bit more affected by freeway crosswind than other cars I've owned. It may be because there's a little bit of a dead zone in the center of the steering in electric steerers.

 

[Quibbs]

Good news. I finally have my car. Yesterday, the first day I drove it to work, we had high winds for most of the day. My route to work takes me through many areas (back roads, then highway). I put the car in standard mode and drove through the crazy winds crossing the highway at various speeds. The car was rock solid for the most part. I was greatly concerned about this aspect, but no longer fear it after the drive.

The only real movements I felt from the wind were when I was at a stop light. I could feel a little movement in the higher part of the cabin. Outside of that, nothing really.