Taycan 4s parked on snow rolling forward - how why and wtf??

Dave T

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But people are claiming that their cars rolled, not slid. Having summer tires would not explain that.





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jetbox

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See pic, also my connect app only shows car locked and no parking brake...
A440DD55-E6D5-4611-B7CA-68301F528D7C.png
 

manitou202

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As a side note, driving summer tires in temperatures below 40F (5C) can cause the tires to crack. The Michelin Pilot Sport tire from Porsche come with this specific warning. Here in Colorado many dealerships make you sign a liability form when taking delivery of a vehicle with summer tires saying that you are aware of the risks of driving in freezing temperatures.
 

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But people are claiming that their cars rolled, not slid. Having summer tires would not explain that.
rolling is explained by car not having a park brake on. On Ice I would never use that as the P mode would be pretty much the same. So assuming P would be similar state whilst it actually isn’t - spectacularly bad UX example by Porsche :/

on a side note, it is always adviced to turn the front wheels when parking on an incline, to use sidewalk as additional anti roll measure.
 

svp6

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I would imagine not engaging the parking brake is uncommon. Whenever I stop the car, if I do not get our of gear by pushing P (which engages the parking brake too) I cannot take my foot of the brake - hence I always use the P. What am I missing?

I suppose you could switch off from the dash button before disengaging, but after using Tesla's without a start / stop switch that possibility is not on my mind.
 

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I dont buy that. Plenty of cars not on winter tyres in the U.K. not rolling down hills. Winter tyres are not as common in the U.K. as other countries. Something’s a miss with this!
Not saying this is the issue, but there is a big difference between summer tires in snow and having regular or all season tires. Its not about having special winter tires, rather how summer tires in snow will become very hard and brittle and may slide. In fact summer tires in snow will probably damage the tires.

I am always amazed when I see Lambo owners park their cars in snow in London...
 

Docjonday

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Hi All

Just had a rather scary near miss and felt the need to warn people. Im a UK 4s owner, loving the car which Ive had for 6 weeks (pre cool issues aside).

We have had a classic UK snow fall overnight around a few cm's which is enough to decimate the town!! Drove my Taycan to the office and parked on a very slight incline, handbrake engaged. One foot out of the car and on the ground and the rolling starts!! A 2 ton car rolling on 3-4 cm of snow. Managed to get back in and pulled up a few feet away from a wall.

How the hell has this happened? Imagine this occurring on a sharp incline in a town centre?

Is there no anti-roll safety feature? My wheels were turning so I was told by a witness, meaning they werent locked or fixed by the handbrake.

I would definitely avoid parking this car on an incline in snow. Of more concern is the question as to how the car would behave in traffic facing downhill when stationary in these conditions?

Any thoughts welcome particularly from any UK dealers who may be aware of this issue.
If I may add some holistic science to this debate, the modulus of rubber, which can be conveyed in more layman’s terms as it’s softness, is the key point of difference between summer and winter tyres. Softer compounds of rubber have fewer cross links of sulphur between the polyisoprene chains of rubber that make up its structure. This means they can flex and move more easily at a molecular level; an analogy being that of being able to rub your hands together to generate heat and being less able to do so with sticky hands while wearing handcuffs. However, in both scenarios, when there is no movement, there is no heat generation. Things only start to change beyond this within the latex rubber structure below zero, when more hydrogen bonds between water trapped within the latex structure start to form, making it a lot more rigid. It’s why winter tyres are often mandatory in climates regularly sub zero vs those that aren’t, like the UK.

The key factors at work in these sliding vehicle scenarios are force, mass and coefficient of friction. The latter concerns both the friction between the tyre and the road surface, and the friction between the brake caliper surface and the disc surface. The vehicle is on a negative incline and is subject to a gravitational force, multiplied by the weight of the car; it’s mass. But these two factors are constant and unchanged in the case of the car being parked in the same place both in normal and cold conditions.

My point is this. If you take the latter point, UK trucks don’t run on winter tyres. At 40,000 kgs, the sum of that equation even taking into account the more tyres of such a vehicle and greater contact patch area, is higher for the truck than the Taycan. Trucks don’t roll down inclines typically when parked on summer tyres in winter in the UK. Hence, the most likely factor at play if rolling is proven is the coefficient of friction between the calliper and the disc and this being reduced at lower temperatures. If the disc glazes with ice deposits due to lack of heat input related to regen rather than friction braking dominating before parking, there will be a lower coefficient of friction between the calliper and the disc surface. This would explain potentially why the wheels of the Taycans in question were spotted rolling and not sliding if proven. There is still no evidence the cars rolled rather than slid - in fairness to Porsche, this must be emphasised!

I’m going to guess that both vehicles affected have the same brakes - would be interesting to know if these were either PSCB or PCCB v standard. This could be key.

If this theory is proven right and the vehicles were found to have rolled, Porsche could potentially solve this with a software update via a recall, disengaging regen for periods of use during low temp driving to avoid glazing with ice prior to the calliper surface locking in place with the disc on parking. The analogy would be how modern braking systems see the shoes kiss the discs during wet weather driving.

DISCLAIMER- One should point out these are just theories based on inadequate data to reach conclusions. Other issues may have been at play here, nothing to do with the vehicle. One would also expect this to be a global issue and there to be far more occurrences already, which isn’t the case and points to these cases being no fault of the car. However, UK roads can often be poorly treated for ice - a lack of salt residue on the discs would make the risk of slip between the calliper and the disc more likely - this perhaps being a consideration. Or it could be an electronics issue, or that the brake callipers are not being anchored on to the disc at sufficient pressure for some reason on the vehicles concerned, if it is proven that they rolled rather than slid. I’d expect Porsche to investigate this matter and quickly discount a fault with the Taycan in these cases by trying to replicate the scenarios at their research centre in Weissach. If an issue is identified, this is potentially no different to countless other issues seen across all car manufacturers when bringing new tech to market. No amount of pre launch testing data is full-proof evidence of perfection, with real-world use often identifying issues requiring recall updates. Rest assured, Porsche either already have looked into this or will be doing so, I’m sure of that.
 
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Incredible post! Thank you for your thoughts and scientific analysis.

So much excellent feedback on this thread

To add more to the mix, the brakes on my car were standard fit. This car was garaged overnight prior to driving to the office. Relevant? Not sure but it hadnt been sitting in snow like a block of ice all night. Nice 10 min drive to the office, not long enough to get the car components fired maybe?

I have considered whether this incident happened due to my own errors (weve all seen the Taycan wall climbing incident...terrifying!). I dont think it did because my muscle memory and actions when I park are well etched *but* I cant rule this out 100%

I have read the manual and the section on engaging handbrake before switching off the power. Did I get this wrong on the day...few seconds out? I dont believe I did. Is this mechanism normal on EVs where the handbrake doesnt operate once the power is off? Curious to know.

Im going to switch tyres. However I will not be parking on any inclines on snow again in this car. Something isnt right.

Lets hope there are no more incidents. :please:
 

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Incredible post! Thank you for your thoughts and scientific analysis.

So much excellent feedback on this thread

To add more to the mix, the brakes on my car were standard fit. This car was garaged overnight prior to driving to the office. Relevant? Not sure but it hadnt been sitting in snow like a block of ice all night. Nice 10 min drive to the office, not long enough to get the car components fired maybe?

I have considered whether this incident happened due to my own errors (weve all seen the Taycan wall climbing incident...terrifying!). I dont think it did because my muscle memory and actions when I park are well etched *but* I cant rule this out 100%

I have read the manual and the section on engaging handbrake before switching off the power. Did I get this wrong on the day...few seconds out? I dont believe I did. Is this mechanism normal on EVs where the handbrake doesnt operate once the power is off? Curious to know.

Im going to switch tyres. However I will not be parking on any inclines on snow again in this car. Something isnt right.

Lets hope there are no more incidents. :please:
Looking at https://www.taycanforum.com/forum/t...on-snow-bad-day-at-the-office-pt2.3394/page-2 and examining the posted picture, it seems that they key could be here:

31F712FF-75A0-49F1-B708-B5458107AF5B.jpeg

If the incline was less that 8%, still enough to cause a slide in a snow and no auto parking brake.
 

Fawad

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Hi All

Just had a rather scary near miss and felt the need to warn people. Im a UK 4s owner, loving the car which Ive had for 6 weeks (pre cool issues aside).

We have had a classic UK snow fall overnight around a few cm's which is enough to decimate the town!! Drove my Taycan to the office and parked on a very slight incline, handbrake engaged. One foot out of the car and on the ground and the rolling starts!! A 2 ton car rolling on 3-4 cm of snow. Managed to get back in and pulled up a few feet away from a wall.

How the hell has this happened? Imagine this occurring on a sharp incline in a town centre?

Is there no anti-roll safety feature? My wheels were turning so I was told by a witness, meaning they werent locked or fixed by the handbrake.

I would definitely avoid parking this car on an incline in snow. Of more concern is the question as to how the car would behave in traffic facing downhill when stationary in these conditions?

Any thoughts welcome particularly from any UK dealers who may be aware of this issue.
I’m with you on this one - my experience was slightly different but the concern was just as worrying. Driving at slow speed on some hail and the brakes couldn’t cope. The car didn’t stop at the giveaway and carried on. Fortunately there was no oncoming traffic. A serious issue that I’ll be bringing up with my OPC on Monday. I suggest this is also raised with the HQ
 

evanevery

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Handbrake? We have a handbrake?

Seriously... I haven't used a handbrake in years!
 

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I drove the whole day on snow with my Taycan. I had no special issues other than those known for cold cerlamic brakes. But I will really pay attention to this parking brake issue in future.
Thank you
 

evanevery

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I’m with you on this one - my experience was slightly different but the concern was just as worrying. Driving at slow speed on some hail and the brakes couldn’t cope. The car didn’t stop at the giveaway and carried on. Fortunately there was no oncoming traffic. A serious issue that I’ll be bringing up with my OPC on Monday. I suggest this is also raised with the HQ
Driving on hail? Are you sure this wasn't the ABS doing what exactly it was designed to do? Just because the car isn't stopping as quickly as you'ld like, doesn't mean it necessarily could stop any quicker. The ABS may very well kept the wheels rolling (so you had some steering) rather than locking them all up and sliding without ANY control.

Just because you'ld like to have stopped sooner, doesn't mean it was possible given the situation.

Physics always wins.

I was out doing laps around my office building in unplowed snow yesterday (with ceramic brakes) and never had any indication that the brakes weren't doing exactly what they were supposed to do. (Even when you turn Stability Control Completely Off for Maximum Fun on snow/ice, ABS will still intervene while braking).
 

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Driving on hail? Are you sure this wasn't the ABS doing what exactly it was designed to do? Just because the car isn't stopping as quickly as you'ld like, doesn't mean it necessarily could stop any quicker. The ABS may very well kept the wheels rolling (so you had some steering) rather than locking them all up and sliding without ANY control.

Just because you'ld like to have stopped sooner, doesn't mean it was possible given the situation.

Physics always wins.

I was out doing laps around my office building in unplowed snow yesterday (with ceramic brakes) and never had any indication that the brakes weren't doing exactly what they were supposed to do. (Even when you turn Stability Control Completely Off for Maximum Fun on snow/ice, ABS will still intervene while braking).
I was doing no more than a max of 10mph and brakes in plenty of time (with only a slight pressure on the brake)
 

Dave T

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I was doing no more than a max of 10mph and brakes in plenty of time (with only a slight pressure on the brake)
Did you not feel the ABS kicking in? What kind of tires do you have?
 

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