Tesla Braking Power?

[Ulmo]

I decided to test braking power on the following pictured wet driveway on a hill in my Model S 60D with ~1,150 miles on it.

It seemed to slide a long way for twice the time and distance as my 2005 Mercedes E500 W211 with SBC. It also gave me much less physical pain from stopping force. The MB would stop so fast and precise that I would be in physical pain from it. The Tesla slithered along. I don't know if my MB would have slid further than I'm used to due to the downhill, but MB has been king of stopping from my experience, and that unusual MB SBC system actually worked pretty well while they made it (they've since replaced it), so this isn't necessarily a slam on Tesla.

 

[Pezpunk]

uh maybe try it on a road that's not covered in debris and also not downhill? am i missing something?

 

[McRat]

Tire selection and PSI.
The 650lb though? No way to fix that.

 

[ecarfan]

uh maybe try it on a road that's not covered in debris and also not downhill? am i missing something?

@Ulmo are you saying that your Mercedes stopped in a much shorter distance on the same road, the one shown in the photo? In other words, are you comparing the Tesla braking to the Mercedes braking on the same road in the same conditions?

 

[Ulmo]

No. This is a case of me posting subjective information, hoping people post useful responses. So far, I like both responses. I'll have to consider it more fully. If you don't like the thread, you can delete it.

 

[McRat]

Tire age, PSI, treadwear rating (stickiness), pattern, and footprint all contribution to good stopping distances.

However, many of the same things that give a car low rolling resistance give it poor braking distances. It's a trade-off.

For now, lower down to 36 PSI or so and try it again.

Note: Wet leaves are like ice. No tire without super aggressive tread or studs is going to save you from hydroplaning on the them. Motorcycles fall down just by looking at a wet leaf.

 

[McRat]

Way off topic.

One of the most fun things you can do with your clothes on is to sign up for a professional track school.
My first one required a week to take the grin off my face. But they teach you what to do after you've run out of traction.

Money well spent, and kicks Vegas + Disney World in the nuts. I recommend either Bondurant in AZ or Spring Mountain north of Vegas.

With modern cars able to exceed 100 mph in just seconds, it's also an investment in your lifespan duration if you love to drive.

Stupid Video of Bondurant in older Corvettes:

Gen 2 CTS-V on wet track:

Loved the Lambo AWD:

 

[EarlyAdopter]

Thanks for the subjective info, but it's completely useless.

How about some objective measurements?

Edmunds test of the Model S:
2015 Tesla Model S P85D Road Test Specs | Edmunds
Braking comments Fantastically sticky summer performance tires are on display here, but give credit to the brake system as well. Even though the pedal exhibited the kind of "dead" feel we usually associate with electric vehicles, and a longish amount of pedal travel, the distances stayed consistently short. The first run was 104 feet, the fifth run was the shortest at 102 feet and the sixth and final stop was 104 feet with zero pedal fade and minimal brake odor. Each stop was drama-free, without any side-to-side squirming.

Edmunds test of your E500 with SBC:
2003 Mercedes-Benz E500 Road Test Specs | Edmunds
Braking comments The electronic brakes being fitted to new Mercedes-Benz products are undeniably effective in terms of stopping distances. Our test car stopped in 120 feet on its first braking attempt and 124 feet on its third and final run, so fade was nearly non-existent. However, braking feel remains an issue with this system. When pressed into maximum service the pedal gave minimal resistance for most of its travel, and then got "squishy" as it neared the floorboard and stopped moving. The upside is that there was absolutely no ABS vibration in the pedal, and the only noise to be heard was a slight whine that continued for a second or two after the car came to a stop (the whine was completely inaudible as the car slowed). Bottom line: these brakes are great in terms of outright function, but they need work in the "feel" department, even if improving them involves fabricating the sensations normally associated with hydraulic brakes.

Consumer reports test of the Model S:
Tesla Model S P85D Test Results - Consumer Reports
Braking
No track testing is done before the vehicle hits 2,000 miles, and we perform a brake seating procedure the day before we take measurements. The test procedure is done on special areas of our test track that are monitored for consistent friction and involves over a dozen stops, with cool-down laps in between to ensure accurate results. We begin measurement as soon as the driver hits the pedal, and the distances are adjusted for temperature. The P85D stopping distances were very short, like a high-performance sports car at 118 feet in the dry and 129 feet in the wet with the optional 21-inch wheel and tire package.
Braking
Excellent
60 mph Dry
118 ft.
60 mph Wet
129 ft.

Consumer reports test of Mercedes latest and greatest 2017 E-Class:
2017 Mercedes-Benz E-Class | Reviews and Ratings from Consumer Reports
Braking
Excellent
60 mph Dry
128 ft.
60 mph Wet
143 ft.

So, the Model S is better under all tested conditions than all tested Mercedes E-Class.

Also, worth noting that Mercedes ditched the SBC system and went back to traditional hydraulic brakes after recalling over a million cars with SBC for pump failures. Sensotronic Brake Control - Wikipedia

Good luck with that though.

You're far better off in your Model S.

 

[Ulmo]

Thank you. From 2014 Tesla Model S 60 - Instrumented Test I see:

Stopping distance from 70 mph, however, increased from 160 feet in the P85 to 174 in the 60.

That's a ratio of 160:174::118:x, so x=128 for mine (not exact since there's nonlinear action involved), 8 more feet in my Tesla than the discontinued MB SBC one I'm accustomed to. So, you're probably right -- 6% seems like a false amount for me to notice. It must have been conditions. At least I know that they are comparable -- that I didn't downgrade.

 

[artsci]

No. This is a case of me posting subjective information, hoping people post useful responses. So far, I like both responses. I'll have to consider it more fully. If you don't like the thread, you can delete it.

Objective tests of the Tesla brakes rate them quite high, among the best (see EarlyAdopter's post above). Tests have be done under controlled conditions (same weather, same surface/road, same application points, same measuring devices, etc). Otherwise they are not to be trusted.

 

[oktane]

Braking power could be better for the P100DL. I've owned other high performance ice cars, and in general with more HP you get bigger brakes. With the crazy acceleration of the Tesla, it's possible to run out of brake performance unless you plan ahead. I like the car and would rate suspension and brakes as "not bad" and acceleration as "awesome."

 

[Bangor Bob]

If you can engage ABS on all 4 wheels in a panic stop, the brakes are big enough. Additional clamping force won't stop you any faster.

Corollary: If you can engage ABS in a panic stop, your tires aren't sticky enough.

 

[Ulmo]

New information:

I just took a drive in Yosemite, and there was frozen water and partially melted frozen water on the roads in many sections (temperatures from 31º to 35º with some snow left on the roads in plowed and salted sections are what I'm discussing; anything above 36º I didn't have these experiences). For sure, there is suboptimal braking power compared to my old SBC system. When the road is dry, Model S 60D has a glorious stopping distance. When the road is icy, the Model S 60D decides to go into a mode in which it will not use the maximum traction at all, instead being totally paranoid, as if it is attempting to go a braking traction speed in which it will never lose even the tiniest amount of traction (despite tires always sliding on every surface to some degree), rather than finding the point at which maximum traction is available by backing off as soon as it loses it, as I thought it was able to do (and as the SBC system was able to do extremely well). This mode is persistent throughout a braking application. Thus, if the car enters this wimpy braking mode and I hit a patch of totally dry road, I can continue to drive at basically full speed with a minimal slowdown by holding the brakes down, or totally release the brakes and re-apply them and get full traction full braking power, with a difference in stopping distance of about 20 times.

In other words, the Tesla will decide to remove braking power that is available to the driver, I guess in the fear that the driver is unable to calculate how to regain control of a sliding or partially sliding car, and also in the Tesla's inability to calculate this itself (despite many other manufacturers able to figure this out very well). This is highly dangerous, because the stopping distance is artificially made to be about 20 times as long as it would normally be compared to advanced traction control systems if the brakes were applied to the fullest braking power it would be able given the amount of traction available, and about 10 times as long as an expert driver could wrest from the roads.

Is this an error in the way just my car operates, or does everyone's Tesla have wimpy braking power on marginal traction roads?

It resulted in one scary moment when I saw a plow coming, and the car decided it didn't want to slow down at all after I pressed the brakes, despite me having about 20 seconds reaction time. My old Mercedes would have stopped within 1/10th the distance for sure if not sooner. I know this Tesla could stop even sooner than my Mercedes if it applied more traction (especially if it did it smartly); instead, it just removes this ability from the driver and car.

Also, I'd like to know if there are adjustments or a way to turn it off.

Also, there is a loud clunking noise from the front right wheel area during aggressive test stops I did in similar situations, but not in half braking power in same conditions (same as I could muster); is that normal?

The below pictures aren't that good, so I'll try to get better ones later. (A photo from a dash mount phone usually doesn't come out well, and it's one button press, so I'm not going to try harder than that while driving.)

 

[jerry33]

Tires make the difference. On the dirt/mud road pictured (way) above, the stock tires are going to have very little traction. Tread depth is important as well. (Some tires have indicators that tell when the tire should no longer be used for winter conditions.) Tire pressure plays an important part, but depending upon the circumstances, either lower or higher could be better. For on road driving, higher is better for most, but not all, winter conditions. For off-pavement conditions, lower is almost always better, but be sure to lower the speed both for traction and to help prevent tire and wheel damage from potholes.

 

[JHuberman]

I passed a guy on the highway. Then a few minutes later, as we were both exiting on a 2-lane exit at about 60 mph he passed me, cut very close in front of me and slammed on his brakes. I reacted in time, slammed on my brakes, and my MS60 slowed much more quickly than he did. I really appreciated the brakes. I can't understand why he would want to cause an accident?

 

[wesley888]

He could claim you ramp into him and sue you for money. Hope you have a dash cam, in case for the future...

 

[Pezpunk]

Braking power could be better for the P100DL. I've owned other high performance ice cars, and in general with more HP you get bigger brakes. With the crazy acceleration of the Tesla, it's possible to run out of brake performance unless you plan ahead. I like the car and would rate suspension and brakes as "not bad" and acceleration as "awesome."

part of the problem is physics. no other performance car with this level of acceleration weighs over 5,000 pounds.

the brakes on the Tesla are pretty beefy, but there's only so much that can be done to stop a 5,000 pound car. as someone else mentioned, if you can engage ABS, then additional clamping power is irrelevant.

 

[oktane]

A valid point. Good ol' 1/2mv^2. But KE increases linearly with mass, so if we assume ICE performance cars weigh 4,000 lbs instead of 5,000 lbs, they need 20% more stopping power. I do not know what technical limitations exist to achieve this. I'm sure there are a lot of equations to figure this out.