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Overdrive

As I understand Model S is planed to have a one speed gearbox ( like the roadster has ).

Wouldn't it be nice if it would have a one speed gearbox with an overdrive ( this little switch on some oldtimer cars )?
It would diminish the RPM of the motor on the Autobahn, might have some advatages on engieneering ( the motor would not have to sustsain high RPM's ), noise and may be even energy.
Plus such a gearbox could be made simple and lightweight as it does not have to switch when accerating and it does not have to switch fast!

There is no need for any gearbox; the motor itself is almost silent and friction free at any RPM. There would probably be more noise from the gearbox!

Greg.

Which brings in my mind some old interview of someone in Tesla when Roadster was still in beta. He said that they have managed to get emotor RPM higher than 20kRPM in the test-labs. Roadster does 200km/h with 14k, so 20k it would be 285km/h.

Lets see when we get a real supercar from Tesla. Roadster has acceleration but not speed. As it stands now it is just high performance sport car.

Timo,

going 285kph might be only slightly above what roadster could do today. I calculate 240kW motor power output for that (with some guesswork).
To compete with other supercars regarding acceleration beyond 200kph and top speed would require some drive train in the >=300kW area. That's a complete redesign of PEM, ESS, motor and gearbox.
I figure that speed alone does not justify that.

My suggestion is to tune a Roadster to excel at TopGear's track test. Replace the 450kg ESS with a 70kg high power pack that delivers 220kW for just 90 seconds. Then beat all the other quarter million USD supercars! Would make the petrol heads gawk.

The final EV breakthrough would be of course, different speed limits for ICE and EV. 120kph for BMW, Porsche, Audi, Ferrari, Lamborghini on German autobahn. No limits for TESLA, Nissan Esflow, Rolls Royce 102EX, Venturi Fetish and the like. That would boost EV supercar development!

again the speed issue: I used JB Straubels spread sheet and did an order 3 fit to the power/speed curve. Some figures to quote from that: going
180mph (=285kph) takes 230kW,
200mph (=321kph) takes 307kW, and
220mph (=353kph) takes 400kW.

Conclusion for me: top speed is an ICE domain for the time being. Doing the same with an EV drivetrain will result in massively over-dimensioned components for everyday speeds.

One of the representatives from Tesla told me that they could raise the top speed of the roadster quite a bit, but they're afraid that heat would become a major issue.

400kW is piece of cake for electric drivetrain. You only need a bit more power-friendly batteries and a bit more engine power. Roadster engine is just tiny 70kg lump of metal and it gives 215kW. Double that size and you have that 400kW and it still is tiny compared to ICE that gives same power. Batteries give no restriction other than price. PEM is a bit more tricky, but it too isn't too hard to do.

You could sacrifice acceleration for speed. That is what transmissions do. Higher gear gives less torque, but higher speeds. With engine that can deliver 400kW power torque at lower speeds would be enormous, so you can actually use higher gear ratio and still have same acceleration.


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