I will never again make a post as long as this one, I promise.

I thought it would be interesting to take all the data we now have and see what can be made of it. That includes what’s in the newest MS owners manual and elsewhere.

In the manual (p 161) it says overall final drive ratio is 9.73:1, apparently for both motors (and I thought the front was geared differently). Tires are 245/35R21 on my non-staggered P85D. That’s 727 revolutions per mile (calculated and checked against tire manuf data). So 727*9.73 = 7074 motor revolutions/mile = 7074 motor RPM @ 1 mile/minute (60 MPH), so divide by 60 to get 118 motor RPM/MPH.

Max combined motor torque is 713 lb-ft from Tesla website, presumably from 0 RPM up. P85D battery-limited horsepower is 463. RPM = 5250*HP/Torque. Output hits 463HP at 5250*463/713 = 3409 RPM: that’s at 3409/(118 motor RPM/MPH) = 29 MPH, so max acceleration is limited by rated torque up to ~30MPH, as we know by experience. How much acceleration? Tire radius = 1.16 feet (calculated from tire specs). Combined axle torque = 713*9.73 final drive ratio = 6937 lb-ft. Torque = force*radius, so force = torque/radius. So force = 6937/1.16 = 5980 pounds of force. The manual says curb weight (weight ex-driver) = 4963 lbs. Adding 160 lb driver gives 5123. Acceleration (in G-forces in these units) = force/mass = 5980/5123 = 1.17 Gs. So 1.17Gs maximum acceleration from 0 to 29MPH, Vbox measurements yield 1.10Gs from 0 to 30MPH, where I assume the difference is traction, very small air resistance and surprisingly small frictional losses – apparently much smaller than in ICE car drivelines, which is one reason Teslas go so fast on less HP than we thought. Note that max torque and thus max acceleration is apparently the same for P85D and P90DL (or so the website implies) so the difference between them is their torque in the battery-power-limited region over 29MPH (33 MPH for the P90DL), where the P90DL has 532/463 = 15% more.

What's the significance? In the dispute over the horsepower of the P85D, the most accurate statement is that BOTH the 762 motor HP and the 463 battery-limited HP are significant, and subjectively I think they are about equally significant. From 0 - 30 MPH the car performs like a 762 HP car because its limiting factor is rated engine torque. That's why it has hypercar acceleration off the line. Above 30 it behaves like a 463 HP car, and from 30 - 60 like a 463 HP car with short gearing and multiple gears that keep it right at the peak of its power band. Then at high speeds it falls out of its power band and performs like a less-than-463 HP car. Subjectively, I think we P85D owners have experienced hypercar enjoyment off the line and a bit of frustration at more typical passing power in about equal measure. But I think it's as misleading to say it is only a 463 HP car as it is to say it's a 762 HP car.

In this way, when Elon said the P85D has 1 1/2 times the power of the 85D, that is true below 30MPH where power at a given MPH is proportional to speed and max torque, so 713 lb-ft (P85D & P90DL) /485 lb-ft (85D) = 1.47.

Also interesting is that the manual says max rear motor RPM is 16000, and max front motor is 18000. If the final drive for both is 9.73:1 (as the manual implies) and with non-staggered tires, then 16000RPM/(118 RPM/MPH) = 136MPH, while 18000RPM gives 153MPH. From which I conclude 1) power for you autobahn-driving Europeans is entirely out of the front motor, the rear must be deadheading unpowered above its max RPMs, and 2) the reason Tesla has taken a while to raise the MS from a 135MPH max speed to a 155MPH max speed is because they have to overspeed the rear motor in this way.

Next, the manual says the max ‘net power’ for the ‘performance’ rear motor is 350Kw @ 5950RPM (divide by .7457 to get 469HP), and the front ‘performance’ motor is 193Kw @ 6100RPM (259HP). This disagrees with the 503HP for the rear now on the website, but DOES agree with the 259HP for the front. Discrepancy unexplained. Note that the ~6000RPM for peak powers in each = 51MPH. It sounds like the MS, with its single gear, begins to fall out of its power band over 51MPH, but how this interacts with max battery power is unclear.

Finally, Dragtimes has the P85D running 11.6 @ 116MPH. Motor Trend has the P90DL running 10.9 @ 122.7MPH. If you put these and 5123 lbs into Dragtimes’ HP calculator you get 634 and 760 HP respectively. Obviously the calculator is designed for the characteristics of ICE car engines and transmissions, but the the ratio might be meaningful: 760/634 = 20% more. This is more than the 15% difference in battery-limited power between the two. What I infer from this is that software in the Motor Trend car controls the motors in an improved way, so the motors fall our of their power band more slowly and are able to apply max battery power across a greater range of RPM. Hopefully this will work for the ludicrous-upgraded P85D too.

I thought it would be interesting to take all the data we now have and see what can be made of it. That includes what’s in the newest MS owners manual and elsewhere.

In the manual (p 161) it says overall final drive ratio is 9.73:1, apparently for both motors (and I thought the front was geared differently). Tires are 245/35R21 on my non-staggered P85D. That’s 727 revolutions per mile (calculated and checked against tire manuf data). So 727*9.73 = 7074 motor revolutions/mile = 7074 motor RPM @ 1 mile/minute (60 MPH), so divide by 60 to get 118 motor RPM/MPH.

Max combined motor torque is 713 lb-ft from Tesla website, presumably from 0 RPM up. P85D battery-limited horsepower is 463. RPM = 5250*HP/Torque. Output hits 463HP at 5250*463/713 = 3409 RPM: that’s at 3409/(118 motor RPM/MPH) = 29 MPH, so max acceleration is limited by rated torque up to ~30MPH, as we know by experience. How much acceleration? Tire radius = 1.16 feet (calculated from tire specs). Combined axle torque = 713*9.73 final drive ratio = 6937 lb-ft. Torque = force*radius, so force = torque/radius. So force = 6937/1.16 = 5980 pounds of force. The manual says curb weight (weight ex-driver) = 4963 lbs. Adding 160 lb driver gives 5123. Acceleration (in G-forces in these units) = force/mass = 5980/5123 = 1.17 Gs. So 1.17Gs maximum acceleration from 0 to 29MPH, Vbox measurements yield 1.10Gs from 0 to 30MPH, where I assume the difference is traction, very small air resistance and surprisingly small frictional losses – apparently much smaller than in ICE car drivelines, which is one reason Teslas go so fast on less HP than we thought. Note that max torque and thus max acceleration is apparently the same for P85D and P90DL (or so the website implies) so the difference between them is their torque in the battery-power-limited region over 29MPH (33 MPH for the P90DL), where the P90DL has 532/463 = 15% more.

What's the significance? In the dispute over the horsepower of the P85D, the most accurate statement is that BOTH the 762 motor HP and the 463 battery-limited HP are significant, and subjectively I think they are about equally significant. From 0 - 30 MPH the car performs like a 762 HP car because its limiting factor is rated engine torque. That's why it has hypercar acceleration off the line. Above 30 it behaves like a 463 HP car, and from 30 - 60 like a 463 HP car with short gearing and multiple gears that keep it right at the peak of its power band. Then at high speeds it falls out of its power band and performs like a less-than-463 HP car. Subjectively, I think we P85D owners have experienced hypercar enjoyment off the line and a bit of frustration at more typical passing power in about equal measure. But I think it's as misleading to say it is only a 463 HP car as it is to say it's a 762 HP car.

In this way, when Elon said the P85D has 1 1/2 times the power of the 85D, that is true below 30MPH where power at a given MPH is proportional to speed and max torque, so 713 lb-ft (P85D & P90DL) /485 lb-ft (85D) = 1.47.

Also interesting is that the manual says max rear motor RPM is 16000, and max front motor is 18000. If the final drive for both is 9.73:1 (as the manual implies) and with non-staggered tires, then 16000RPM/(118 RPM/MPH) = 136MPH, while 18000RPM gives 153MPH. From which I conclude 1) power for you autobahn-driving Europeans is entirely out of the front motor, the rear must be deadheading unpowered above its max RPMs, and 2) the reason Tesla has taken a while to raise the MS from a 135MPH max speed to a 155MPH max speed is because they have to overspeed the rear motor in this way.

Next, the manual says the max ‘net power’ for the ‘performance’ rear motor is 350Kw @ 5950RPM (divide by .7457 to get 469HP), and the front ‘performance’ motor is 193Kw @ 6100RPM (259HP). This disagrees with the 503HP for the rear now on the website, but DOES agree with the 259HP for the front. Discrepancy unexplained. Note that the ~6000RPM for peak powers in each = 51MPH. It sounds like the MS, with its single gear, begins to fall out of its power band over 51MPH, but how this interacts with max battery power is unclear.

Finally, Dragtimes has the P85D running 11.6 @ 116MPH. Motor Trend has the P90DL running 10.9 @ 122.7MPH. If you put these and 5123 lbs into Dragtimes’ HP calculator you get 634 and 760 HP respectively. Obviously the calculator is designed for the characteristics of ICE car engines and transmissions, but the the ratio might be meaningful: 760/634 = 20% more. This is more than the 15% difference in battery-limited power between the two. What I infer from this is that software in the Motor Trend car controls the motors in an improved way, so the motors fall our of their power band more slowly and are able to apply max battery power across a greater range of RPM. Hopefully this will work for the ludicrous-upgraded P85D too.

Last edited: Nov 1, 2015