Have the brakes on the P85D been upgraded to match the power?

[marchyman]

1. more braking power, since at point B you're carrying more speed than in a P85/S85/S60, OR
2. to start braking EARLIER than point B, if your brakes are the same as a P85/S85/S60

Assume for the sake of argument that you can lock the brakes in zero time. The car with more speed will still take longer to stop. Bigger brakes don't help in that situation. If you are going faster you will have to brake earlier or miss the turn. If (and I don't know this... I won't get my car until next month) you can lock the current brakes adding extra braking doesn't help stop you any faster. It might help in shedding excess heat, brake system longevity, amount of force needed on the brake pedal, and a bunch of other things -- but once the wheel is stopped extra braking power can't stop it any more

 

[lolachampcar]

Sticky tires........

 

[jerry33]

Sticky tires........

^ This. Beat me to it. Braking distance is ultimately how sticky the tires are. Almost all braking systems can overpower the traction of the tires. Put on some "R" compound tires and you'll see a tremendous difference in stopping ability (and tread life).

 

[basvk]

Huh? Braking is about traction. Can the current brakes trigger the ABS system? If so you've got enough braking power. More won't help.

But can the brakes do this multiple times in short succession without overheating? That is the question. So when talking about brake upgrades, it's really about heat management more than it is about braking power per se.

 

[Firewired]

What impact do you think the number of pistons have not the braking strength? I had an Audi RS4 and it likewise was a heavier car with large brakes, but also 8 pistons and the brakes were one of the best I had experienced. Afterwards I had a E92 M3 and I believe the brakes were single piston and somewhat dissapointing for the level of potential performance. I believe the Model S has 4 piston brakes.

 

[MarcG]

Assume for the sake of argument that you can lock the brakes in zero time. The car with more speed will still take longer to stop.

Agreed, but I wasn't talking about locking the brakes or assuming there is more braking power than tire traction.

Bigger brakes don't help in that situation. If you are going faster you will have to brake earlier or miss the turn.

Correct, but in the situation that I was describing where there is enough traction from tires to decelerate more quickly with better (not necessarily bigger) brakes, your statement is false. You CAN brake at the same point with higher speed AND better brakes.

Anyway, I'm still unclear as to whether any improvements have been made to the braking mechanics, including heat dispersion as some have suggested. I guess we'll find out when customer cars start to ship next week!

 

[mspohr]

Ok, I'll try to explain it a little differently. Let's suppose the following points exist on a road or track:

A = Apex of the first corner/turn/bend in the road
B = Braking point ahead of second corner/turn/bend

The theory is that you start accelerating at point A and keep your foot in the accelerator pedal until point B, at which point you break to get ready for the next corner.
In a P85D, you would reach point B with HIGHER speed than if you were in a P85/S85/S60. So to turn into corner 2 safely, you'll need either:

1. more braking power, since at point B you're carrying more speed than in a P85/S85/S60, OR
2. to start braking EARLIER than point B, if your brakes are the same as a P85/S85/S60

It still comes down to the top speed and mass of the car. It doesn't matter how fast you accelerate. Brakes are about deceleration so brakes have to be designed to stop the car mass from the top speed. The mass and top speed of the S and the PS are the same so they need the same brakes.

 

[EarlyAdopter]

Agreed, but I wasn't talking about locking the brakes or assuming there is more braking power than tire traction.



Correct, but in the situation that I was describing where there is enough traction from tires to decelerate more quickly with better (not necessarily bigger) brakes, your statement is false. You CAN brake at the same point with higher speed AND better brakes.

Anyway, I'm still unclear as to whether any improvements have been made to the braking mechanics, including heat dispersion as some have suggested. I guess we'll find out when customer cars start to ship next week!

The tires are currently the limiting factor in braking distance on the Model S. Bigger brakes will not reduce stopping distances, unless you've switched to R comp tires or are experiencing significant brake fade from track driving - a situation that is unlikely to occur given the power limiting that kicks in all to early on the Model S.

The new and improved electromechanical brakes on autopilot equipped cars appear to have the same calipers and rotors. What has changed is the actuation mechanism and brake boost system. System reaction time and foot pedal feel have both been reportedly improved.

I'm excited about this. While my older P85 has great stopping distance and power, even on heavy track driving, the pedal feel has always been a bit mushy. Doesn't compare well to Audis and BMWs I've had. Looking forward to this being improved on my P85D. Will report back when I get the car end of next week or week after.

 

[basvk]

It still comes down to the top speed and mass of the car. It doesn't matter how fast you accelerate. Brakes are about deceleration so brakes have to be designed to stop the car mass from the top speed. The mass and top speed of the S and the PS are the same so they need the same brakes.

The thing that is not the same between a P and an S is the theoretical amount of heat dissipated by the brake system:

I can bring the P from 0 to 60 mph and back more often than the S in the same amount of time (say ten minutes), so I will use the brakes of the P more in that same amount of time. This means that in such a case the brakes of the P will have to dissipate more heat in the same time period than the brakes on the S. So while the stopping power needed for both P and S is the same, the amount of heat these brakes have to handle at maximum repeated usage in the same time period will be higher on a P, hence the TS's legitimate concern.

- - - Updated - - -

So bigger brakes, more pistons etc. help to dissipate the buildup of heat faster, postponing fading.

 

[breser]

It still comes down to the top speed and mass of the car. It doesn't matter how fast you accelerate. Brakes are about deceleration so brakes have to be designed to stop the car mass from the top speed. The mass and top speed of the S and the PS are the same so they need the same brakes.

That's not strictly true. The S60 and S85 have lower top speeds. The 85D and P85D have higher top speeds. The D vehicles are also heavier and the 60 should be lighter than an 85. If the differences are significant in terms of braking I have no idea. But these are not identical cars as far as mass and speed.

 

[randompersonx]

The thing that is not the same between a P and an S is the theoretical amount of heat dissipated by the brake system:

I can bring the P from 0 to 60 mph and back more often than the S in the same amount of time (say ten minutes), so I will use the brakes of the P more in that same amount of time. This means that in such a case the brakes of the P will have to dissipate more heat in the same time period than the brakes on the S. So while the stopping power needed for both P and S is the same, the amount of heat these brakes have to handle at maximum repeated usage in the same time period will be higher on a P, hence the TS's legitimate concern.

- - - Updated - - -

So bigger brakes, more pistons etc. help to dissipate the buildup of heat faster, postponing fading.

I agree completely as far as a car with faster acceleration requiring better brakes.

Has anyone done any comparison on Turbine 21" wheels (which should add a large amount of airflow) to either the 19's or aftermarket wheels which are not in a turbine configuration? I would assume this airflow makes a significant difference on brake temps as long as you spend a fair amount of time at high speed.

 

[Zextraterrestrial]

^ This. Beat me to it. Braking distance is ultimately how sticky the tires are. Almost all braking systems can overpower the traction of the tires. Put on some "R" compound tires and you'll see a tremendous difference in stopping ability (and tread life).

and brake fade!

 

[jerry33]

and brake fade!

That's certainly true, but the OP's question--the way I read it--concerned on-road safety, rather than track use. If you have to do two heavy braking in a row during regular driving, there's likely a problem with your driving style

 

[tezco]

That's certainly true, but the OP's question--the way I read it--concerned on-road safety, rather than track use. If you have to do two heavy braking in a row during regular driving, there's likely a problem with your driving style

But you would like the ability to do that so that you have some reserve in the event of a partial failure of the system.

 

[David_Cary]

Just my $.02 - any brake can engage ABS. My understanding is a better brake can get you right before ABS. Right before ABS engages is the best braking distance but it takes really good control at that limit. You can also gain some distance (shortening?) with pre-priming brakes as many german cars do because you get to max braking a millisecond or two earlier.

There are also many cars where the second fast braking in a row creates some increased pressure which could make a difference in time to engage ABS in even a panic stop (depending on the strength of the driver). And right - maybe a problem with driving style...

So it isn't entirely about the tires and COG.

 

[jerry33]

But you would like the ability to do that so that you have some reserve in the event of a partial failure of the system.

Given that most of the braking is done by the motor, the disk brake system is the reserve. Has anyone had brake fade on the second or even third 80-0 stop?

 

[AWDtsla]

You're all missing it.

Brake capacity is only directly related to inverter/battery capacity. First law of thermodynamics. No one knows when the P85D will go into reduced power mode relative to a P85, so no one can answer this question.

Oh and while we're here - higher top speed means that less brake sink capacity is needed, since you're using up that energy in drag.