Separate names with a comma.
Discussion in 'Model S: Driving Dynamics' started by Boatguy, Apr 7, 2016.
If you have the air suspension, at what speed do you set it to automatically lower?
i do it at 70 mph
I have it set at 55
95km/hr, about 55mph
115 km or 71 mph. Just in time for motorway cruising speed at 120+
50 mph. Note that once lowered, it stays lowered until around 30 mph.
Lowering your car at modest highway speeds seems to be kind of pointless - you might gain a very slight efficiency boost, but it's at the expense of your camber and tire wear.
Just curious why you guys are lowering at such low speeds? I can understand at 90+ mph, but 55 mph is just silly.
Mine is at 95+, as I like to keep the ride softer at high speeds. Also, I heard that by lowering it the inside tire wear takes a heavier toll, at least with my staggered 21' setup.
100 mph for the same and correct reasons given by the previous 2 posters.
I have even tire wear in the rear and set it at 50+ which was the original Tesla setting before they changed it. It does help handling. I don't see any reason to have it set higher.
A couple of questions for the group:
First, can someone explain to me why there should be more wear on tires with the suspension lowered? I have seen illustrations of the MS suspension, and it looks like it maintains the wheels at the same angle to the road regardless of suspension height.
Has anyone with a lower-speed auto-height-reduction actually experienced uneven tire wear? I mean, is this concern based on facts?
Initially, there was very bad wear, my initial set only last 13K miles. This was actually due to the toe-out in the rear, not camber. You can read this thread at your leisure. After the skid plate and it's accompanying software the Model S didn't lower as far as it did previously. Also they fixed the incorrect settings on the alignment machines, and some of us got eccentric bolts to help reduce the camber.
Note that camber amplifies any errors in toe, it doesn't do much on its own to wear tires (this is not zero, but it's fairly close). Think of camber like speed. Speed in and of itself doesn't cause accidents, but it does shorten the time--or lengthen the distance depending upon how you look at it--you have to mitigate a potential problem, and if you have an accident the more speed there is going into it, the more damage will be done.
The Model S uses a double-wishbone suspension in the front with unequal length control arms -- the upper control arm is shorter than the lower control arm. This configuration intentionally causes camber to become more negative as the wheel moves upward. The intent of this design is keep the maximum tire contact patch in contact with the road during hard turns.
In a hard turn, the body of the car rolls towards the outside of the turn, pushing the outside tires towards positive camber. If unchecked, the tire will lose contact with the road on the inside edge of the contact patch as the tire rubber that is in contact with the road rolls towards the outside sidewall. By designing the suspension as above, the body weight on the outside turn side of the car causes the wheels on that side to move upward within their suspension travel, and the suspension will then pull the tire back towards negative camber, restoring the contact patch.
The rear suspension is not double wishbone, it is independent multilink, but is designed to work similarly.
See the following videos for a more detailed graphical explanation (not my videos):
Lowering the car at speed causes the air suspension to move upward, increasing negative camber as if you're in a turn, but you're not. This causes the contact patch to be biased more towards the inside edge of the tires instead of evenly across the tires, and can accelerate tire wear on the inside edges. This is already a problem with the Model S, as the factory settings for negative camber are pretty aggressive, even at normal suspension heights.
Now, having said that, I use 65 MPH as my auto-lowering speed. I'm running the 19" stock Michelin Primacy MXM4 tires, which originally came with 7.9 mm of tread. I have about 8,500 miles on them, and the tread is at about 5.8 mm on average now. I routinely rotate my tires every 2500 miles in a rear-cross pattern and measure the inner, center, and outer tread depths. (I rotate more often than recommended because I believe it helps keep the tires quieter, even later in their life). I have not noticed any excessive wear overall, nor have I noticed more wear on the inner edges.
Inner edge tire wear appears to be more of a problem with the 21" tires than the 19"s, especially those vehicles that are using staggered tires since the rears cannot rotate to the front positions. However, I believe this has a lot more to do with the lack of rotation and soft rubber compounds of the 21" summer tires rather than the air suspension settings.
Great explanation - thank you.
To answer the OP, I have mine set at 80, and have been thinking about raising it to 85. I may reconsider after reading your post. One thing I noticed that I don't like, which was causing me to consider raising the threshold, is that once the lowering is triggered, it stays low even if the speed drops below the threshold. It stays at Low, until the car is turned off and then on again. I didn't like that because of the potential tire wear. I wanted the benefit of better handling on the highway at high speed, but I didn't want it to trigger when I'm in "bursty" type traffic, like during a commute on an interstate or beltway. By "bursty," I mean very fast, then slow, then medium, then very fast,...etc. I want it to trigger when I'm on a highway at continuous high speed.
I've never had it do that. I've watched a few times and it raises to standard at about 30 mph. Tire wear is not a problem if the other alignment angles are correct--particularly toe. You absolutely don't want any toe-out in the rear.