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Tell me if this is a bug... After driving a new car to work for 2 years, the traction control started kicking in on certain curves. I take a windy road to work

Tell me if this is a bug... After driving a new car to work for 2 years, the traction control started kicking in on certain curves. I take a windy road to work and had never had traction control activate. When it kicked in, it pulsed the right front brake and slowed the car quickly, likely unnerving the guy tailgating me. This happened several times, both going to and from work. The road was perfectly dry, no snow or rain. Same turns at the same speed as always. The clues are was that my rear tires had worn and I replaced them a few days before. And, I drive a Tesla Model 3. It's a rear-wheel drive version and the front tires still had good tread so I didn't replace them. Why the right front tire? What I finally brained out, which you may have quickly realized, is that the diameters of the worn front and new rear tires were then slightly different. The front had a lower diameter than the rear and therefore turned at a slightly faster rate when driving. When I took a hard bank, the outside wheels also turned faster than the inside as they do in any turn. That increased the delta in spin rate the most between the outside worn front tire and the inside new rear tire. The traction control determined that the right front must be slipping and pulsed the brake on it. I replaced the front tires and everything went back to normal.

cowsandmilk 6y ago
Why not just move the tires from the front wheels to the back?
- bbddg 6y ago
  Yeah isn't this why you should rotate your tires regularly?
  - jhoechtl 6y ago
    You get downvoted but yes, that's the reason for swapping front to back and vice versa.
- crazyjncsu 6y ago
  Just so the laymen here don’t think this is some kind of hack, this is what is referred to as “rotating your tires”, which should sound familiar. The problem is that tires are often not rotatable due to staggered setups where the front and back tires are different sizes (very common) or due to directionality of tires (less common).
  - ComputerGuru 6y ago
    Different sizes means you can swap left to right and right to left. Directionality means you can swap front to back and back to front. Directional tires of different sizes means you can’t swap a damn thing (as drivers of Porsche and some BMW configurations find out quickly enough.)
- Cactus2018 6y ago
  Might have different tire size front and back - https://tiresize.com/tires/Tesla/Model-3/2020/ https://tiresize.com/tires/Tesla/Model-3/2020/
- jhayward 6y ago
  In commercial tire shops in the US the tires with the most tread always go on the back regardless of any other consideration. This is because losing traction in front causes understeer, which is usually easily managed by typical drivers. On the other hand losing traction in back causes oversteer, which is often very rapid in attack and severe in extent. For some vehicles it is essentially impossible for a non-professional driver to maneuver out of an oversteer event. So for safety sake the best tread always goes on the back. Most shops will refuse to do anything else.
  - treeman79 6y ago
    Then there is my eldest daughter. “Dad, car has been a little bumpy for the past month” I hop in go down to road. Experience is best described as driving on square tires. https://youtu.be/QF7odK55gkI https://youtu.be/QF7odK55gkI Both front tires had massive bulges sticking out. She had been driving like that for a month.
    - pengaru 6y ago
      She's your daughter...
      - treeman79 6y ago
        Oh I have my own stories of being completely oblivious, or not wanting to bother others. However she was a special needs adoption due to age. Only had her ~4 years at that point.
  - throwaway0a5e 6y ago
    This is one of those myths that just needs to die. "Put the good tires on the back" is a terribly inaccurate rule of thumb. Whether you want the good tires on the rear or the front is gonna depend on how the vehicle handles. Most modern mom-mobile type crossover are so biased toward under-steer (usually from a combination of rear weight and stiff front sway bar) that they need all the help they can get up front and putting the better two tires on the rear is just wasting traction because that end was never going to break traction anyway. Also, Firestone happily puts fronts only on my junk.
yholio 6y ago
Sounds like a safety critical bug. Rotating tires and replacing them asymmetrically (for example, after a tire explosion for me) is regular practice. If a small difference in wear disables critical safety systems and engages them in inappropriate circumstances, this can lead to deaths. It seems simple enough to detect that, on a straight road with the steering wheel balanced, one of the wheels makes more rotations on average; then you calibrate the algorithm based on that. Sounds like a bug in this very algorithm, or maybe some hardware defect on your specific vehicle (i.e a sensor) that interferes with it.
- aidenn0 6y ago
  Many AWD cars require replacing tires in sets in the manual
  - ComputerGuru 6y ago
    As a long-time owner of AWD performance vehicles (Midwest for you, possible snow eight months of the year!) I can assure that whether or not you replace your tires four, two, or even just one at a time, there are absolutely zero visible/immediately tangible repercussions and the issue described with the Tesla is absolutely not normal even under those circumstances. As for the long term ramifications, you’ll definitely see increased wear/camber on the opposing tire(a) and I’ve read it could theoretically cause issues with the diff, but I find that extremely hard to believe at least for the cats I’ve driven, because the front:back power ratio is dynamically recalculated and changed continuously depending on driving conditions. If it were 4WD rather than AWD, that might be the case though.
    - o-__-o 6y ago
      Okay here is anecdotal experience. I had a set of treads on my rear tire at 15/32 while the fronts where at 9/32. Viscous coupled AWD with traction control via four-wheel braking. I first noticed something was up when the car would launch rather quickly. I added an odb-2 reader and saw my AWD clutch was engaging a lot. Thought this was by design due to my heavy foot. Then the clunking started. The AWD would rather stay engaged which puts strain on the transmission to shift harder. Over time this showed up as increased transmission temperatures. My transmission is sensitive to heat but has a poor design which makes any heat a very big deal. At about the same time I was researching new wheels and determined I could fit 9” wide tires in the rear vs 8.5” in the front. A staggered wheel set would give me more rear wheel power bias, but the closest I could get in tire size was still almost .5% larger in diameter. In all my research it turns out you need tires of the same size within 3/16 wear of each other to avoid non-full time AWD transmissions from doing dumb things like my car does. You see, the AWD clutch simply engages a power transfer unit and then depends on ABS to control power sent by the differential to individual wheels. That system needs to recalibrate itself regularly and it does this when the clutch disengages. When it doesn’t, all sorts of warnings are tripped (in my car I went down 6 floors of a spiraling parking garage exit at 15-20mph and at the 2nd floor a “service stabili-trak” icon appeared on my dashboard) In cars with a well designed AWD system this will not happen.. but most cars are not designed to engage in AWD for prolonged periods of time and are really there as a beefed up version of traction control. For instance my Torsen Quattro AWD Audi had full time AWD and never had this problem nor would a Nissan GT-R. But for that fancy Lexus or Hyundai AWD, you may want to make sure you stick to the recommended tire rotation schedule To end my story, I was at the service center and they mentioned I should get my transmission checked out by the bigger repair bay because of the clunking. I suggested it may be the wear of the tires and they agreed to see if that solved the problem. New set of tires and the clunking, extra AWD engagement, and transmission temps went away.
londons_explore 6y ago
This is a bug... The system should learn the tyre diameters after driving a half mile or so on a new set.
- jhoechtl 6y ago
  Are you a car safety expert or is this your assumption how a car should behave? I doubt it is a road safety requirement for a car to learn tire diameters.
  - throwaway0a5e 6y ago
    >I doubt it is a road safety requirement for a car to learn tire diameters. If you want to have hair trigger traction control systems then it kind of is.
  - BoorishBears 6y ago
    They do learn tire diameters, they can even detect a flat using this information.
    - lultimouomo 6y ago
      And to be clear, flat detection using slippage, dynamically calibrating to the actual tire diameter, is the cheapest way of doing it. Since flat detection is required by law, at least in the EU, every 10k€ new car sold in the last 5 years does it. Tesla does some marvelous stuff, but they also have some unbelievable inability to provide functionality that is nowadays just expected from a car.
      - BoorishBears 6y ago
        In one of my cars (124 Spider) the method used to detect tire pressure actually depends on the trim chosen for that reason I chose one that comes with performance oriented changes and interestingly enough that includes using a direct TPMS sensor in each wheel Meanwhile the base trim uses an indirect system designed around the ABS sensors
mrgordon 6y ago
Many cars like 4WD require all tires to be replaced at the same time to avoid weird issues like this with the automated systems
- riverdroid 6y ago
  There might be some software issues at play with some modern AWD systems that I am not aware of, but it's traditionally a mechanical issue with 4WD and AWD. 4WD has a physical link, so having two different diameters linked stresses the links and tears the rubber. With AWD there is a differential, and different diameters cause mechanical stress and wear in a mechanical diff.
  - jakear 6y ago
    My understanding is that AWD has computer controlled power distribution and 4WD has a diff. My 4WD has a (lockable) center diff.
    - centimeter 6y ago
      Not quite: AWD has diffs between each of (FR,FL), (RR,RL), (F,R). 4WD has diffs between (FR,FL) and (RR,RL), but it has a transfer case (like a permanently locked center diff) between F and R. So you’re not supposed to use 4WD on dry asphalt roads because the natural slippage between front and rear has no easy way to release itself. Modern diffs are usually limited slip, which helps prevent spinning tires. LSD can either be mechanical or computer controlled. Computer controlled LSD can apply brakes to individual tires.
      - jakear 6y ago
        Interesting. So I think I technically have AWD, but I do have a transfer case with a 2X reduction available and a locking center diff.
- rasz 6y ago
  That would be probably most cars with some form of electronic differential lock (EDL), similar system to the one described here.
autotech 6y ago
Not a bug. This is a weird but documented phenomenon. There are multiple published technical bulletins on similar issues caused by uneven tire wear/replacement. I must admit that I never came across traction control false activation due to 2 new tires. I have seen burnt transfer cases on AWD with this though. Were you advised by a shop to change just 2 or was it your independent decision?
simonebrunozzi 6y ago
It's a terrible bug, but at least Tesla should be able to fix it quickly. Just need to add a check that calculates the average of these values over the past few hours or days, and decides to modify the tipping points for traction control accordingly. Did you consider contacting Tesla and submitting a bug report?
- pfranz 6y ago
  Isn't individual rotation speed how most cars detect underinflated tires? I imagine this problem would also happen if the tires had different tire pressures.
  - kart23 6y ago
    I believe some older cars used this method. Nowadays, all the monitoring systems use little sensors mounted on the wheel to transmit pressure information.
centimeter 6y ago
That sounds unreasonable to me. The (virtual, on a Tesla?) differential should allow at least the amount of slip induced by a new tire.

cowsandmilk 6y ago

Why not just move the tires from the front wheels to the back?

bbddg 6y ago
Yeah isn't this why you should rotate your tires regularly?
- jhoechtl 6y ago
  You get downvoted but yes, that's the reason for swapping front to back and vice versa.
crazyjncsu 6y ago
Just so the laymen here don’t think this is some kind of hack, this is what is referred to as “rotating your tires”, which should sound familiar. The problem is that tires are often not rotatable due to staggered setups where the front and back tires are different sizes (very common) or due to directionality of tires (less common).
- ComputerGuru 6y ago
  Different sizes means you can swap left to right and right to left. Directionality means you can swap front to back and back to front. Directional tires of different sizes means you can’t swap a damn thing (as drivers of Porsche and some BMW configurations find out quickly enough.)
Cactus2018 6y ago
Might have different tire size front and back - https://tiresize.com/tires/Tesla/Model-3/2020/ https://tiresize.com/tires/Tesla/Model-3/2020/
jhayward 6y ago
In commercial tire shops in the US the tires with the most tread always go on the back regardless of any other consideration. This is because losing traction in front causes understeer, which is usually easily managed by typical drivers. On the other hand losing traction in back causes oversteer, which is often very rapid in attack and severe in extent. For some vehicles it is essentially impossible for a non-professional driver to maneuver out of an oversteer event. So for safety sake the best tread always goes on the back. Most shops will refuse to do anything else.
- treeman79 6y ago
  Then there is my eldest daughter. “Dad, car has been a little bumpy for the past month” I hop in go down to road. Experience is best described as driving on square tires. https://youtu.be/QF7odK55gkI https://youtu.be/QF7odK55gkI Both front tires had massive bulges sticking out. She had been driving like that for a month.
  - pengaru 6y ago
    She's your daughter...
    - treeman79 6y ago
      Oh I have my own stories of being completely oblivious, or not wanting to bother others. However she was a special needs adoption due to age. Only had her ~4 years at that point.
- throwaway0a5e 6y ago
  This is one of those myths that just needs to die. "Put the good tires on the back" is a terribly inaccurate rule of thumb. Whether you want the good tires on the rear or the front is gonna depend on how the vehicle handles. Most modern mom-mobile type crossover are so biased toward under-steer (usually from a combination of rear weight and stiff front sway bar) that they need all the help they can get up front and putting the better two tires on the rear is just wasting traction because that end was never going to break traction anyway. Also, Firestone happily puts fronts only on my junk.

yholio 6y ago

Sounds like a safety critical bug. Rotating tires and replacing them asymmetrically (for example, after a tire explosion for me) is regular practice. If a small difference in wear disables critical safety systems and engages them in inappropriate circumstances, this can lead to deaths. It seems simple enough to detect that, on a straight road with the steering wheel balanced, one of the wheels makes more rotations on average; then you calibrate the algorithm based on that. Sounds like a bug in this very algorithm, or maybe some hardware defect on your specific vehicle (i.e a sensor) that interferes with it.

aidenn0 6y ago
Many AWD cars require replacing tires in sets in the manual
- ComputerGuru 6y ago
  As a long-time owner of AWD performance vehicles (Midwest for you, possible snow eight months of the year!) I can assure that whether or not you replace your tires four, two, or even just one at a time, there are absolutely zero visible/immediately tangible repercussions and the issue described with the Tesla is absolutely not normal even under those circumstances. As for the long term ramifications, you’ll definitely see increased wear/camber on the opposing tire(a) and I’ve read it could theoretically cause issues with the diff, but I find that extremely hard to believe at least for the cats I’ve driven, because the front:back power ratio is dynamically recalculated and changed continuously depending on driving conditions. If it were 4WD rather than AWD, that might be the case though.
  - o-__-o 6y ago
    Okay here is anecdotal experience. I had a set of treads on my rear tire at 15/32 while the fronts where at 9/32. Viscous coupled AWD with traction control via four-wheel braking. I first noticed something was up when the car would launch rather quickly. I added an odb-2 reader and saw my AWD clutch was engaging a lot. Thought this was by design due to my heavy foot. Then the clunking started. The AWD would rather stay engaged which puts strain on the transmission to shift harder. Over time this showed up as increased transmission temperatures. My transmission is sensitive to heat but has a poor design which makes any heat a very big deal. At about the same time I was researching new wheels and determined I could fit 9” wide tires in the rear vs 8.5” in the front. A staggered wheel set would give me more rear wheel power bias, but the closest I could get in tire size was still almost .5% larger in diameter. In all my research it turns out you need tires of the same size within 3/16 wear of each other to avoid non-full time AWD transmissions from doing dumb things like my car does. You see, the AWD clutch simply engages a power transfer unit and then depends on ABS to control power sent by the differential to individual wheels. That system needs to recalibrate itself regularly and it does this when the clutch disengages. When it doesn’t, all sorts of warnings are tripped (in my car I went down 6 floors of a spiraling parking garage exit at 15-20mph and at the 2nd floor a “service stabili-trak” icon appeared on my dashboard) In cars with a well designed AWD system this will not happen.. but most cars are not designed to engage in AWD for prolonged periods of time and are really there as a beefed up version of traction control. For instance my Torsen Quattro AWD Audi had full time AWD and never had this problem nor would a Nissan GT-R. But for that fancy Lexus or Hyundai AWD, you may want to make sure you stick to the recommended tire rotation schedule To end my story, I was at the service center and they mentioned I should get my transmission checked out by the bigger repair bay because of the clunking. I suggested it may be the wear of the tires and they agreed to see if that solved the problem. New set of tires and the clunking, extra AWD engagement, and transmission temps went away.

londons_explore 6y ago

This is a bug... The system should learn the tyre diameters after driving a half mile or so on a new set.

jhoechtl 6y ago
Are you a car safety expert or is this your assumption how a car should behave? I doubt it is a road safety requirement for a car to learn tire diameters.
- throwaway0a5e 6y ago
  >I doubt it is a road safety requirement for a car to learn tire diameters. If you want to have hair trigger traction control systems then it kind of is.
- BoorishBears 6y ago
  They do learn tire diameters, they can even detect a flat using this information.
  - lultimouomo 6y ago
    And to be clear, flat detection using slippage, dynamically calibrating to the actual tire diameter, is the cheapest way of doing it. Since flat detection is required by law, at least in the EU, every 10k€ new car sold in the last 5 years does it. Tesla does some marvelous stuff, but they also have some unbelievable inability to provide functionality that is nowadays just expected from a car.
    - BoorishBears 6y ago
      In one of my cars (124 Spider) the method used to detect tire pressure actually depends on the trim chosen for that reason I chose one that comes with performance oriented changes and interestingly enough that includes using a direct TPMS sensor in each wheel Meanwhile the base trim uses an indirect system designed around the ABS sensors

mrgordon 6y ago

Many cars like 4WD require all tires to be replaced at the same time to avoid weird issues like this with the automated systems

riverdroid 6y ago
There might be some software issues at play with some modern AWD systems that I am not aware of, but it's traditionally a mechanical issue with 4WD and AWD. 4WD has a physical link, so having two different diameters linked stresses the links and tears the rubber. With AWD there is a differential, and different diameters cause mechanical stress and wear in a mechanical diff.
- jakear 6y ago
  My understanding is that AWD has computer controlled power distribution and 4WD has a diff. My 4WD has a (lockable) center diff.
  - centimeter 6y ago
    Not quite: AWD has diffs between each of (FR,FL), (RR,RL), (F,R). 4WD has diffs between (FR,FL) and (RR,RL), but it has a transfer case (like a permanently locked center diff) between F and R. So you’re not supposed to use 4WD on dry asphalt roads because the natural slippage between front and rear has no easy way to release itself. Modern diffs are usually limited slip, which helps prevent spinning tires. LSD can either be mechanical or computer controlled. Computer controlled LSD can apply brakes to individual tires.
    - jakear 6y ago
      Interesting. So I think I technically have AWD, but I do have a transfer case with a 2X reduction available and a locking center diff.
rasz 6y ago
That would be probably most cars with some form of electronic differential lock (EDL), similar system to the one described here.

autotech 6y ago

Not a bug. This is a weird but documented phenomenon. There are multiple published technical bulletins on similar issues caused by uneven tire wear/replacement. I must admit that I never came across traction control false activation due to 2 new tires. I have seen burnt transfer cases on AWD with this though. Were you advised by a shop to change just 2 or was it your independent decision?

simonebrunozzi 6y ago

It's a terrible bug, but at least Tesla should be able to fix it quickly. Just need to add a check that calculates the average of these values over the past few hours or days, and decides to modify the tipping points for traction control accordingly. Did you consider contacting Tesla and submitting a bug report?

pfranz 6y ago
Isn't individual rotation speed how most cars detect underinflated tires? I imagine this problem would also happen if the tires had different tire pressures.
- kart23 6y ago
  I believe some older cars used this method. Nowadays, all the monitoring systems use little sensors mounted on the wheel to transmit pressure information.

centimeter 6y ago

That sounds unreasonable to me. The (virtual, on a Tesla?) differential should allow at least the amount of slip induced by a new tire.