I am crossposting this from the MSP vs M5 forum. Feel free to scroll down to the portion I marked as "Relevant to this thread"
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Been super busy lately with the election and with work, so haven't been able to keep fully abrest of the info stream.
Current summary -
Cottonwood had a bad day, and couldn't get a single valid lap in. That's an issue, which is either particular to Cottonwood, or a limitation with the car itself.
Personally I think it was Cottonwood centric, but that is pure opinion, based on the following - MSP has now been extensively track tested, by multiple publications and independant writers as a part of the review process. Lap times have not been released, but nobody has reported a problem with the car being unable to complete laps. Automobile Magazine reported the following -
For all its high-tech novelty, the Model S does an exceptional job at the things we expect any high-priced sport sedan to do well. The electric power steering is nuanced and well-weighted, with natural buildup just off-center. Through corners, the Model S exhibits impressive body control and vacuumlike grip despite weighing more than 4500 pounds. Editors also raved about the suspension's ability to soak up bumps that tortured other test cars. It was just as impressive on the racetrack -- yes, we took it on the track. "All that speed, along with powerful braking, superflat handling, and sharp steering, gives you the sense that you're invincible," marvels Jennings.
You'd think that at some point they'd mention that the car failed to complete a lap. For background, I've met Jean Jennings. She is not a professional race car driver, but she came up through Chrysler where she was a professional test driver and mechanic at their test facility. She is very experienced at pushing a car to it's limits. Among her testers at Automobile Magazine are also drivers with professional racing experience.
MotorTrend does extensive track testing with SCCA certified testers. Sports Car Club of America sanctions road racing, rallying and autocross, for both amateur and professional racers, and I would presume that their certified testers are accustomed to measuring performance at the edge of the envelope.
Neither magazine reported problems with the car being unable to complete a lap. Both raved about it's track performance (but did not publish lap times). Both publications voted it Car of the Year
because of it's performance.
Edmunds Inside Line *DID* report a falloff in straight line 0-60 performance over multiple tests, with a best of ~4.3 and eventually falling off to ~4.6. This was on a hot day, and we speculated that it might be due to heat buildup. Nobody else has reported this, but the other publications only report best times.
Edmunds itself speculated it might be because of a falling battery charge, but seemed unconvinced. Every car made has a couple of tics variation on any given run. While this is not usually a linear decrease (or increase), in any limited set of runs (in this case 3) there is a significant chance you will have what appears to be a linear decrease in performance. More testing is required before we know there is an issue, let alone determining a cause.
At the 2012 Refuel races, a pre production Model S did a 1:51. At the time I posted that M5 does 1:40's and that a 1:51 is disappointing. But based on data from Inside line I was (and still am) convinced that MSP should be able to do 1:40's at Laguna Seca. We now have more test data which points to substantially faster times than 1:51's, but that and $8 will buy you a $6 burger combo at Carl's Jr (time to change the name of that burger IMHO).
RELEVANT TO THIS THREAD
Regardless, Cottonwood *DID* have a problem. Suggested reasons are -
A low state of charge causing excessive heat.
A malfunction in the cooling system.
A design limitation that prevents the car from being operated at maximum performance for even a single lap (I'll take odds against that).
?
I'll go out on a limb and propose another possibility pulled directly from my nether regions. It's known (or assumed) that Model S will cut power when it encounters heat issues, just like the Roadster. But it has been reported by Cinergi that the Model S will cut power output in the way described when its predicted range gets down to ~30 miles.
Under track conditions ~100 ideal miles might have briefly dipped under this limit as the car looked at actual usage and predicted that it could only make it ~30 miles under those conditions, causing it to cut power. Of course, once you stop pushing it the predicted range starts moving back up to the ideal range and suddenly you get your performance back until you try pushing again.
Call it the Top Gear rule. A 200+ mile Roadster predicts it can only go ~50 miles under load. If control software shuts you down at 30 miles predicted that might be an issue when you are racing with only 100 ideal miles left in the tank. Keep in mind, if you start with a full SOC you can race for dozens of real miles before this issue crops up.
Here is the link to Cinergi's report -
Behavior when getting low on range
Personally, I'd bet on any hypothesis not relying on a design limitation which causes the more advanced liquid cooled power electronics to shut down before the air cooled Roadster does. On a cool day.
I think that the firmware reigning in the car as reported by Cinergi (which I guess *IS* a design issue, albiet software related), or a simple mechanical malfunction in the cooling system are the most likely possibilities in the absense of additional data.
Edit:
Note Post #5 on Cinergi's report about the dotted yellow line at 160kWh (normally 320kWh) starting at 30 miles projected range.
Also note Cottonwoods report of the car being limited to 160kWh in post #1
Model S vs Roadster on the Track
With its liquid-cooled PEM, batteries, and motor, I had high hopes for the MSP to hold power. Unfortunately, my hopes were dashed. In 1/2 to 2/3 of the 1.83 mile lap, the little dashed limit line came on the power display, usually reducing power from 320 kW to a little more than 160kW. This shows up in the MSP having a better maximum speed (at the end of the south straight away) before the power was limited, but having worse lap times because of the reduced power in the last 1/3 of the lap. The Roadster tells you the PEM hot is the limiting factor. The MSP just lets you know the power is limited. We don't know if it was the PEM, batteries, or the motor. We did do this at the end of the day with the MSP charge at 100 miles or so rated range.
The lowest I've gone now is 20 miles left. The battery goes yellow around 30 and power is limited. I know others have had less. Would love to document what happens as you get to 0 ... can you keep driving all the way to 0? Past 0? Does power get limited even more as you get closer to 0? Details / pics please! Here's one to start:
View attachment 11616
The only thing unusual in those pics is the yellow dotted line near the 160kW power mark. That appeared with around 30 miles left.