Brakes suddenly stop working

[harv]

Hello, I'm wondering if anyone else is having this issue.
When braking a bit aggressively, the brakes stop working for a split second (the car continues to roll with little brake pressure).

I took it to the service centre and they said it's because of the size of the new winter tires. Since it doesn't happen frequently I let it go, but I just realized that the winter tires are the exact same size 255/45 r19 just like the tempest wheels (not staggered though). The tech mentioned that the regen-braking gives out because it can't calculate the rotation with the new wheels. The regen-braking indicator on the screen drops suddenly when this happens as well. But this doesn't seem normal... any ideas?

 

[GtiMart]

You are mixing a few things here. Your title says "brakes suddenly stop working" which would indicate that the brake pedal doesn't work. If that is the case, it's a serious problem that you should get checked asap.

Braking on a slippery surface might activate the ABS, which might feel like you are losing the brakes as the car doesn't stop as quickly. But I'll presume you know what ABS is and how it affects your driving.

Regen is the car using the motors to slow down the car and recharge the battery. That is not the only system to stop the car, you have real brakes too, and a brake pedal. First, when the battery is really cold, there is no regen at all. Clearly you cannot rely on just regen. Second, just like the ABS system, regen will lower or even cut completely when the car feels the wheels are blocking/slipping. That's normal, you wouldn't want the car to lock the tires as it's trying to regen. This automatically adjusts to the road conditions, much like ABS adjusts and starts/stops as needed.

Using winter tires means you are more mushy/supple rubber. That's great for driving on snow and ice but it means the car might sometimes think that wheels have blocked whereas it's really just the rubber giving away a bit. It's possible that the regen system temporarily acts weird if you just changed tires. I've heard that around here, especially on ice tires (they are even more supple, more sipes). It will adjust eventually.

 

[harv]

Thanks for the reply. Sorry I didn't articulate the issue really well. I understand that the regen-brakes and standard calipers+rotors work together when you hit the brake pedal. Also, this happens on dry pavements and it's definitely not the ABS.

If I'm stopping from 100Kph to 0 quickly, I press the brake peddle. After a second of the car slowing down the brake peddle is no longer effective and the car will continue to roll and I'll have to press it again, harder. In that time, I notice the regen-brake green bar on the screen reduces very quickly as well. It's a very strange behaviour but I'm certain it can't be the tires. I've made another appointment with the service centre but was curious if anyone else has this problem.

 

[krsgio]

Might help to give the model/year of your car. I can't understand if you're having problems with the regen or the braking. Your title makes it sound like brake failure but you describe something that sounds similar to brake fade but also talking about regen so I have no clue where to start.

 

[GtiMart]

When you brake with the pedal, initially there is also good regen. If the car thinks the wheels lock and it reduces regen, it can feel like you're losing your brakes but you're not. Look at it this way.: in a normal situation you might have half your braking power that's done in regen and the other half from friction brakes. In most cases regen is more like 80%. If regen goes away, you're losing 50-80% just like that.
Make sure this is not what's happening first.

 

[harv]

@krsgio it's a 2021 Model S Long Range (picked up in October 2021). Wheels replaced in mid-December.

@GtiMart "If the car thinks the wheels lock and it reduces regen" - the problem is the regen shuts off instantly making you think the brakes have stopped working. When this happens, the car is on dry surface, the wheels are not slipping nor locked, it's not ABS.

I've scheduled an appointment with the service centre, they'll have to take another look at it. This is definitely not normal behaviour in any car.

 

[JADCa]

It sounds like you went with the same size tires front and rear, which is far from what Tesla did. The computer is setup to analyze the wheel speed of 255/45 front and 285/40 tires rear. You have changed that ratio which will completely confuse the ABS system of any car, especially near the limits. See this issue at the track a lot with after market wheels and tires.

 

[harv]

You're right @JADCa. I thought it was only the width of the staggered wheels that's different - but the aspect ratio is different (40 vs 45). I called the shop from where I got the wheels - they reported no one else has this issue and they put the same wheels as mine on a lot of Tesla's. The shop is pretty popular and was recommended to me by a Tesla service tech.

Thanks everyone!

 

[Destiny1701]

Are these tires a good brand or?
I had this same issue on my car and was told to inflate the tires more to make them less soft/slushy. It actually worked for me.
Issue never came back.

 

[harv]

@Destiny1701 it's nice to know someone else had the same issue! I got Michelin X-Ice Snow. I've used the x-ice on every car I've ever had and love them.

 

[Berlant57]

Had my two front tires changed this morning and suddenly experienced braking issues. Seemed as if regenerative was turned off but it wasn't. It was weird - sometimes it acted normal, but then all of a sudden it seemed as if my foot was on the accelerator. Checked all other settings I could think of. Drove back to the tire store, and they realized they had left it in jack mode. Maybe this gets reset when you do a console reboot, and that could explain why that fixes it for some people.

 

[Big Earl]

Had my two front tires changed this morning and suddenly experienced braking issues. Seemed as if regenerative was turned off but it wasn't. It was weird - sometimes it acted normal, but then all of a sudden it seemed as if my foot was on the accelerator. Checked all other settings I could think of. Drove back to the tire store, and they realized they had left it in jack mode. Maybe this gets reset when you do a console reboot, and that could explain why that fixes it for some people.

The car is probably disabling regenerative braking because of different rotational speeds on the front and rear axles (traction control thinks there is a slipping wheel). This can happen when the tires aren’t the same diameter due to not being replaced as a set. I’d try doing a front-to-rear tire rotation and see if that makes a difference.

The best way to avoid this is to rotate your tires regularly so you can replace them as a full set.

 

[Hebby]

You're right @JADCa. I thought it was only the width of the staggered wheels that's different - but the aspect ratio is different (40 vs 45). I called the shop from where I got the wheels - they reported no one else has this issue and they put the same wheels as mine on a lot of Tesla's. The shop is pretty popular and was recommended to me by a Tesla service tech.

Thanks everyone!

This is happening to me right now. Factory installed tires on my 2022 model 3. I’ve had it almost a year with 28,000kms on it and within the last month the brake pedal doesn’t work the first time you push it. Just when you think you’re going crazy and push it again it works fine… I’m taking it in to have it serviced on Monday.

 

[Midnightsun]

It sounds like you went with the same size tires front and rear, which is far from what Tesla did. The computer is setup to analyze the wheel speed of 255/45 front and 285/40 tires rear. You have changed that ratio which will completely confuse the ABS system of any car, especially near the limits. See this issue at the track a lot with after market wheels and tires.

Only thing that matters is the tire diameter which by the way are both the same on those sizes. Going square will not affect anything. I have had 255/45 19 tires on appropriate wheels all around all last winter and the same now this winter, no issue.

here is a link so you can verify.