Icy Road Accident Possibly Caused By Regen

[Doug_G]

Personally, I find regen to be very helpful during winter driving. Some say to set Regen low but really you just have to be careful with your foot.

In extremely slippery conditions, even in an automatic gas car, lifting off the accelerator can cause you to slide or even spin. Been there, done that, was lucky to escape without damage. If you hit a patch of sheer ice while driving it's best to do nothing if you can; keep the gas pedal neutral, even avoid turning the wheel. But if you are going to hit something, plant the brake pedal and steer. This will engage the ABS which will slow the car somewhat while giving you some steering control.

You say you used the brakes. If you couldn't steer with ABS active then you weren't going to avoid the accident regardless. Regen wasn't the cause; the road was way too slippery.

 

[croman]

I live in the area and was driving a lot between 930am and 1145am when the lake effect was the worst and the conditions were very poor that day. I think OP should be happy it was minor damage (though clearly avoiding it would've been the best, sorry OP).

I have Michelin X-Ice3s on and they make a big impact on traction in difficult winter conditions. This isn't an EV problem or a Tesla regen issue. I suspect that this is a tire problem. You've gotta have winter tires (stock all season are acceptable except for ice/wet snow) and they must be solid ones to deal with Chicago. These cars are HEAVY, so stopping is always more difficult. The roads, on that day, were icy below the snow. Further, since everyone was somehow caught unaware, the roads were not salted. So I think the municipalities' failure to salt was a bigger factor than the regen braking.

I've owned an EV in Chicago for 4 years and other than the Superbowl Blizzard its been fairly smooth sailing (god I miss my Leaf heat pump).

 

[baw]

sorry to hear of the OP's minor bump

this biggest point is - don't forget Model S is 2+ tons.
Physics dictates 2+ tonnes requires more force than a typical ICE <1.5ton car to stop in a given distance
For the same stopping distance this requires more traction from the tires.
With ice + snow only a restricted amount of traction is avaiable.

Leave greater distance for braking because it is a heavy car.
Be less abitious with speed on curves in icy conditions.
Be more inclined to put winter tires on than you would for a smaller lighter car if there is a chance you could encounter even occasional wintry conditions. And yes, regen on low is to be recommended.
Drive safely ... because if nothing else repairing your Tesla is expensive and frequently time consuming.

Thanks for all your suggestions. All make a lot of sense.

Personally, I find regen to be very helpful during winter driving. Some say to set Regen low but really you just have to be careful with your foot.

In extremely slippery conditions, even in an automatic gas car, lifting off the accelerator can cause you to slide or even spin. Been there, done that, was lucky to escape without damage. If you hit a patch of sheer ice while driving it's best to do nothing if you can; keep the gas pedal neutral, even avoid turning the wheel. But if you are going to hit something, plant the brake pedal and steer. This will engage the ABS which will slow the car somewhat while giving you some steering control.

You say you used the brakes. If you couldn't steer with ABS active then you weren't going to avoid the accident regardless. Regen wasn't the cause; the road was way too slippery.

This happened very fast. There is not much time to digest, analyze, react.. It is not clear to me whether this accident was avoidable and whether Regen had a role (thus my post). What I do know though is that Regen (triggered by letting off the accelerator pedal) causes a more sudden deceleration which on an icy road can mean slide and loss of control. At that point its too late for the brakes.

 

[scaesare]

Owning a RWD Model S for 4+ years in an area where we get iced up roads where I have lived, a few comments/observations:

- If you are at the limits of your tire's traction capabilities, then any sudden actions, be it acceleration, braking, or regen have the capability of braking that traction and initiating a slide. Slow and steady are your friend, don't rapidly lift of the pedal in hi-regen any more than you would want to yank your emergency brake

- That having been said, I find the Tesla's traction control on regen to be as effective as ABS on the brakes: that is both are very good at avoiding locking up the tires

- The net result of the above is that you are responsible for safe following distance: If you are going too fast with limited traction and brake/regen too hard one of two results dictated by physics are going to happen - You lock up your tires and slide into the car ahead, or ABS or TSC avoids locking up your tires and you will continue to roll in the car ahead

- Be aware of what your equipment is capable of for your conditions and set/use it appropriately: what type of tires you have, what your regen settings are and how to use them, tractions control settings, slipstart, etc....

 

[baw]

I live in the area and was driving a lot between 930am and 1145am when the lake effect was the worst and the conditions were very poor that day. I think OP should be happy it was minor damage (though clearly avoiding it would've been the best, sorry OP).

I have Michelin X-Ice3s on and they make a big impact on traction in difficult winter conditions. This isn't an EV problem or a Tesla regen issue. I suspect that this is a tire problem. You've gotta have winter tires (stock all season are acceptable except for ice/wet snow) and they must be solid ones to deal with Chicago. These cars are HEAVY, so stopping is always more difficult. The roads, on that day, were icy below the snow. Further, since everyone was somehow caught unaware, the roads were not salted. So I think the municipalities' failure to salt was a bigger factor than the regen braking.

I've owned an EV in Chicago for 4 years and other than the Superbowl Blizzard its been fairly smooth sailing (god I miss my Leaf heat pump).

Thanks for your feedback. Agree 100% on the conditions of the day. I believe you captured it accurately. Just to be clear, I am not trying to slam Tesla or EVs. I love my Tesla and owned a LEAF for 5 years beforehand. At the same time though, trying to better understand the cars behavior or tendencies.

 

[mknox]

I use Nokian Hakka R2 winter tires (which are quite good) on my RWD S85. I too have experienced the sudden loss of control when quickly lifting off the accelerator. Sure, some folks say ease on and off the pedal, but that's not so easy to do when, for instance, someone darts in front of you and you have no choice but to get off the "go" pedal. I have had no serious consequences other than the rear end kicking out, but the car's traction and stability control seemed to correct things pretty quickly. I would be in the camp of those who set re-gen to "low" in slippery conditions.

 

[ChrML]

As a Norwegian who drives on icey roads half a year every year:
- This is not regens fault
- This is not Teslas fault

If you applied your brakes and still skid into the car infront, that's how physics work when traction is low.

Next time you drive on a potential slippery surface:
- Keep a longer distance to the vehicle in front
- Decellerate earlier
- Maybe consider better tires

If in doubt if you can manage to modulate the throttle in slippery conditions, turn regen to Low instead of Standard.

 

[animorph]

I thought reports from last winter were indicating that the dual motor Teslas were pretty good with traction control during regen, while RWD Teslas were trickier. That made sense to me, since RWD regen will be braking only the rear wheels. If RWD regen is enough to break traction, adding additional braking is probably not going to restore traction. I think we should be clear in this thread about D/RWD and regen setting to get the most out of it.

 

[The Duke]

Anyone have a link to anti-skid with regen? I can verify anti-skid works very with fair to good traction using the brakes and regen. But no idea if anti-skid works with just regen.

 

[Doug_G]

Traction control does work with regen. It was excellent in the old Rodaster, maybe not quite as good in Model S but still very good. (Though on the other hand, the Roadster tended to overdo it and drop regen entirely if you hit a bad bump, which was alarming.)

I found with my old RWD Model S the regen tended to stabilize the car, by putting down an anchor in the rear (with a light lift!). It would swim a little if you overdid the regen, but the TC would limit the wiggle. I would just ease back on the pedal slightly and the wiggling would stop.

I haven't driven my new AWD car in winter yet, but I did have a "moment" in an AWD loaner last year. The fool thing had all seasons - bad idea but what can you do when it's a loaner? I was a little tired, and it was dark, and I didn't realize there was black ice on the right side of the lane. When a light turned red ahead of me I lifted - too abruptly. That was a dumb move and the car started to spin. That probably would have happened to an ICE car too. (As I realized later... there certainly were enough of them in the ditch that night.)

Given that I was approaching a now-red light and cross-traffic was starting to move, I elected to hit the brakes hard to engage the ABS and then steer. The car responded beautifully and it took all of a second to get the car straight in the lane again.

It really pays to understand how your car responds when it's sliding, regardless of whether it's electric or not.

 

[SomeJoe7777]

TI do not have winter tires and have never needed them with any of my previous vehicles.

Keep in mind that in all likelihood, your previous vehicles were 1000-1500+ pounds lighter than the Model S. More weight = more need for traction = winter tires are needed to maintain the same safety margin.

The Model S will easily fool you in this regard. Because it's so powerful and so responsive, it doesn't drive or feel heavy at all. It makes you think you're driving around a light sports car. Until the traction breaks loose, then you realize that it's 5000 lbs that's going to go wherever it wants to ...

 

[Olle]

On Friday I had my first accident with my MS. Icy conditions in Chicagoland. Was driving around 15-20mph behind a car that came to a stop at a stop sign. When I took my foot off the accelerator to slow down, I believe the regen kicked in and may have caused the vehicle to slide (instead of coast/deaccelrate smoothly). Applying the brakes did nothing at that point and I slid into the car ahead of me. Very minor accident, but damage to front bumper will require repairs.

I am not suggesting that I know with 100% certainty that this was caused by regen, but I would like to share this experience with someone at Tesla. Does anyone have any suggestions as to who a good contact would be for something like this?

Thanks in advance!

Having done 1000s of miles of severe winter driving with Model S in icy and snowy conditions I can with confidence say that regen, if anything, lessened your impact by starting to brake the fraction of a second it took to move your foot between the pedals.

Model S is a better winter driving car than any car I've driven, owing to the precise control of the drive wheels. And yes, anti spin works inversed on regen, at least on the Tesla's I have tried. Much, much better than ICE cars where engine braking doesn't care about the road surface

 

[evp]

How does this info jibe with the theory that regen is a sort of descent control (on hills) in icy weather?

Does it still work that way to a point? And perhaps the speed here was too great?

My experience (with a 2WD Model S) is that the traction control doesn't do as good a job in regen as it does in acceleration. I've often felt that the back end is getting very loose when coming down an icy hill. If I'm coming down a snow-packed mountain pass, I'll set regen on low so that I get ABS braking working for me instead of traction control. It works better, and it's using all four tires.

I don't know whether the same is true in the AWD Model S.

 

[CalBlue 85D]

Speed for conditions.....

 

[Shock-On-T]

I do not have winter tires and have never needed them with any of my previous vehicles. The roads around me are well plowed/salted and ice is actually rare.

Sorry to hear about your accident.
With EV "one pedal driving", releasing the throttle is as much of a control input as is pushing the throttle.
Makes it a bit touchy on a slippery road. Probably could use winter tires, although living in Australia I'm hardly an expert.

 

[David.85D]

FWIW, they made a point of discussing this issue in the truck announcement a couple of days ago, saying regen is modulated to detect and prevent jack knifing. Makes me wonder if that’s also in the model X software.

 

[Dax279]

While not overly icy here, I thought I would try my regen in few different scenarios and my car handled as I remember from last winter, which was pretty good.

 

[Tam]

...prevent jack knifing...

It's possible that the statement is conditional which is only applicable for non-slippery roads.

 

[David_Cary]

I have a habit that started with manual cars as a teen. I always popped into neutral (or clutched) on cold wet bridges and whenever braking was needed in similar circumstances.

I started life on LI with a VW bug. So RWD in a mild climate so no snows. Spun out as a teen in Tahoe with a RWD Volvo. College in upstate NY with RWD, no snows. Moved all around and lived in Buffalo for 4 winters, with an RX-7 (Blizzaks). Have slid off several roads at speed.

Tesla was the first with AWD and I am not sure I have had occasion to go into neutral. AWD seems to change things a lot. I have mostly had RWD but some FWD. Regen on AWD at least is all 4 wheels and they of course can't lock.

But in the end, every car has throttle off properties that are not neutral in force. These must be anticipated in icy conditions. I personally think my D is great in this regard but I suspect it depends what you are used to.

 

[Chris_G]

You should watch this video from AutoExpress, compairing normal tires with winter tires. There really is a huge difference. I use low regen mode in winter to keep the rear from sliding out in slippery corners. But in the case described here I don't think regen settings would matter as the friction was to low. Using winter tires would probably save the situation.