Zero-to-60 testing got a lot more interesting when Tesla’s Model S P100D with Ludicrous mode managed to accelerate harder than it could brake. That’s right. While the motors are pulling their hardest—from 10 mph to 50 mph—the car averages 1.14 g of acceleration. From 50 to 10 mph, the antilock system only musters 1.11 g of average deceleration. We were so intrigued by this car’s performance at such around-town speeds that we decided to really dig into the inner workings and find out what’s going on as this car rockets down a drag strip or up a long private driveway, a task made somewhat simpler by the vast amount of data that Tesla cars store to the cloud as you drive them. (Owners can access this info via third-party apps.) So let’s slow the clock down and take a look at the ludicrous things going on inside our P100D during that record-setting 2.28-second 0–60 run.
T≥ -1 minute
The driver activates Ludicrous+ mode by pressing and holding the “Ludicrous” button and accepting the warning screen, after which a battery- and motor-conditioning process takes place (warming the former and cooling the latter). Once the “Ready” message appears:
T≥ -2.00 sec
Driver activates launch mode by holding the brake and quickly flooring and releasing the accelerator pedal. “Launch Mode” message appears on screen. Motor voltage waveforms reach 4 volts @ 3 Hz (that voltage is a root-mean-squared measure, meaning that the AC voltage—alternating at 3 cycles per second—is roughly akin to 4 volts of DC power).
T≥ -1.00 sec
The driver depresses brake hard and floors accelerator. Master cylinder pressure ramps up to 105 bar (1,523 psi). Motor currents are adjusted 20,000 times per second as they ramp to a holding torque of 550 lb-ft combined.
T= -0.26 seconds
The driver releases brake. Front and rear inverter phase currents of 750 amps and 1,430 amps, respectively (again, these are root-mean-squared AC values), flood the motors with magnetic flux within 100 milliseconds. The electromagnetic pressure acting to push the rotor forward across the air gap reaches 10.9 psi in the front motor and 17.8 psi in the rear motor. This results in the production of:
- 791 lb-ft of combined torque at the motor shafts
- 1,119 pounds of force sent to each front tire patch and 2,166 pounds of force sent to each rear tire contact patch
- 0.71g acceleration averaged over the first foot of travel
T= 0.00 sec
The car crosses 1-foot mark and official timing starts. The car is traveling at 5.9 mph, averaging 1.30 g of longitudinal acceleration.
T= 0.40 sec
Longitudinal acceleration peaks at 1.41 g as the car passes through 10.3 mph.
T= 0.87 sec
The car reaches 30 mph after travelling 24 feet 8 inches (1.5 car lengths). The driver is still experiencing 1.14 g’s of acceleration.
T= 1.30 sec
The current flowing out of the battery pack and into the two motors peaks at 1,850 amps.
T= 1.76 sec
Combined motor output power peaks at 680 hp as motor voltage waveforms reach 130 volts at 500 Hz. Again, that’s an AC RMS voltage. Longitudinal acceleration drops to 1.00 g and continues falling from this point. The vehicle is traveling 51.0 mph.
T= 2.28 sec
The car crosses the official 60-mph mark after travelling 120 feet 2 inches (7.4 car lengths). Inside the battery, 25 grams’ worth of lithium ions have migrated from anode to cathode, releasing about 0.33 kW-hrs of battery charge.
T= 10.52 sec
The car crosses the quarter-mile mark, traveling at 125 mph. The front motor is spinning at 14,600 rpm and the rear at 14,200 rpm. That puts the absolute velocity of the outer edges of the front and rear rotors at 391 and 349 mph, respectively. Longitudinal acceleration has dropped to 0.22 g. Inside the battery, 112 grams of lithium ions have migrated from anode to cathode, expending about 1.53 kW-hrs of charge.
Based on that last data point, it’s tempting to imagine that a fully charged 100-kW-hr battery might able to make 64 such passes. Depending on how hot a day it is and how short your shut-down area is, it might be possible to regenerate roughly the energy that will be needed to cool the motors and battery back down to their ideal temperatures before the next run. Just understand that under hard braking, the amount of energy that can be recovered might be as little as one-tenth of the amount recovered during a max-regen coast down. Speaking of which, if your chosen test venue is at least a mile long, you might be able to coast down without using the friction brakes at all. In that case, the max-regen mode should slow the car at a rate of about 0.15 g initially. It will ramp up to a max of 0.20 g in peak regen mode, at the end of which as much as 40 to 45 percent of the 1.53 kW-hrs of energy expended in the acceleration run might be recovered. Conversely, note that little or no energy gets regenerated during a full-force ABS braking event.
Once again, we must express our gob-smacked amazement at the predictive traction management that makes a run like this possible. (The brakes were not used to arrest wheel spin during our acceleration run.) An engineer familiar enough with the traction and stability control systems to have hacked a Model S and disabled them confirms that if Tesla provided a true off button for these systems, standing on the go pedal indiscriminately can indeed provoke a 100-plus-mph speed difference between the tires and the pavement within seconds, melting the treads quickly and rendering the vehicle utterly uncontrollable. It’s a modern engineering miracle that we are never able to detect any torque-reduction intervention from this system. Kind of like a car that can accelerate harder than it can brake.
This graph shows acceleration to and braking from 60 mph for three super-quick cars. Note that the Tesla’s acceleration curve hits the top just slightly ahead of the others, while it’s braking is considerably worse than the others. But the Model S P100D is the only one where both lines terminate at almost the same time. The lighter Ferrari and Porsche; both of which enjoy a braking-optimized rear weight bias, stop notably shorter—95 feet for the 3,495-lb LaFerrari and 97 feet for the 3,557-lb 911 Turbo S, versus 109 feet for the 4,891-lb Model S. Indeed if tuners could somehow tweak those combustion-engine cars to accelerate as hard as they brake, they’d be hitting 60 mph in the 2.20-2.23-second range. If and when that happens, we’ll eagerly strap our gear on them to make the numbers official.
The post A Closer Look at the 2017 Tesla Model S P100D’s Ludicrous Acceleration Run appeared first on Motor Trend.
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