Adding a second gear for speed above 100mph?

Adding a second gear for speed above 100mph?

I know Tesla must have their reasons for having only one gear on MS, but why not consider adding a second gear for driving above 100 mph or so? Sure no one really drives above 100 mph in normal driving conditions, but all other high end luxury vehicles all have top speed above 160 mph.

I am sure if Tesla would just add a second gear, the MS can easily achieve that top speed without sacrificing too much range while operating above 100 mph.

I am no mechanic, but I can understand the added mechanism for the gear changing will require extra space on the vehicle, and probably causing aerodynamic problems, but I am sure as battery technology improve, the extra space saved from reduced battery size can compensate for that.

And I do believe, by having more than one gear, Tesla can improve power usage rate at higher speed with higher gears.

Do you guys have any opinions regarding this matter?

lph | September 4, 2013

The roadster originally was developed using a two speed grear box. However, they had problems getting it to handle the massive instantaneous torque that the motor could produce, so they went fo a single speed.
I can see tesla using a higher gear ratio on 4 wheel drive cars when the battery tech allows for the extra power and current draw, thereby maintaining acceleration and also a higher top speed. This way it is kept simple.

DTsea | September 5, 2013

There is no clutch, mechanical or fluid. The freewheel state is tied to regen- the motor always turns when the car moves. Adding a transmission instead would be heavy, expensive, and would degrade the instant torque response.

I say NO.

Brian H | September 5, 2013


ian | September 5, 2013

Not going to happen for the S. Maybe for the super car Elon's got in mind for the next generation of Roadster.

Bubba2000 | September 8, 2013

I agree with DTsea. If there is a demand, the battery capacity improves and costs fall, the induction motor can be upgraded with extra stator winding and rotor cage plus inverter.

Energy consumption goes up almost exponentially with speed. Kinetic energy goes up with square of speed. Speed can be a killer.

Timo | September 8, 2013

Kinetic energy stays with zero consumption without losses (think satellites). It's the air resistance that kills the range. Rolling and ancillary losses for slow speeds. Air resistance grows in square of speed, so it is exponential (now some math PhD says something about what exactly is exponential, and how this is not it).

lph | September 8, 2013

Opps my last post seems to say the opposite of what I was trying to say. The second paragraph should had read..... I can see Tesla using a one speed with a higher gear ratio...

Miggy | September 9, 2013

going over 160km/h will end in tears or tickets, with great pick-up to any speed and good range that is all I want in a great e car and this is one great car.

Haeze | September 9, 2013

I am not sure a top speed higher than 130mph is really necessary unless you plan to race it.

Also, the way the torque curve is in the motor, an extra gear will not offer any [appreciable] savings in the form of energy consumption.

In an ICE, a transmission is necessary because the torque curve is exactly that... a curve. As you approach higher RPMs, the engine puts out DRASTICALLY lower Horsepower and Torque. Most of this is attributed to valve float, and to the thermodynamic limits of how much air you can draw in, and how fast the fuel burns, in such a short time. Electric motors do not have this problem.

The AC Induction motor in the Model S has such a flat torque curve that the only theoretical limit to the speed of your car is in the rotor materials' ability to withstand centripetal force causing it to fly apart.

The amount of horsepower and torque that is inherently lost in any transmission will far outweigh any benefit you get of hooking one up to an electric motor. Also, the added complexity, weight, and maintenance of a transmission makes them even more unwanted.

Brian H | September 9, 2013

+1, +1
Hear, hear!

Timo | September 9, 2013

@Haeze The AC Induction motor in the Model S has such a flat torque curve that the only theoretical limit to the speed of your car is in the rotor materials' ability to withstand centripetal force causing it to fly apart.

That's not quite true. Torque is flat only up to some RPM and then starts to gradually decline. There is no sharp drop like in ICE, but there is drop, and because of that at high RPM you don't really have much torque left. Peak HP and top RPM HP are quite different.

Second gear would help, but I rather just have more power and higher gear ratio (or lower, which way you think it: closer to 1:1 ratio anyway). Staying in first and only gear is fun.

carlgo | September 9, 2013

Tires that grow due to centrifugal force, bigger diameter and narrower for less resistance. Dragster tires use this technology as several thousand HP tends to break transmissions in drag race scenarios.

My bold prediction is that this will never happen, nor will a transmission. Perhaps a small motor can spin much faster, so having multiple small motors might allow higher top speeds. At some point there will be motors in the wheels anyway, but see this first on some sort of race car where cost is no object.

risingsun | September 9, 2013

Yes, for the .00001% of the time the average model S driver goes above 100 mph

lph | September 9, 2013

The Tesla is single speed but not a direct drive, so a different gear ratio can be used easily and probably will be when the 4x drive dual motor cars hit the street. In the future, with two motors along with amore powerful battery pack (hopefully) it will be no problem to have the car go faster and still maintain great acceleration. I can see this in Germany where going 150 mph is still legal and is done often.

teslajolt | September 10, 2013

Maybe instead of adding a second gear, they could split the motor windings. at low speed the windings could be setup in series, then at higher speed, dynamically wire the windings in parallel.

nickjhowe | September 15, 2013

The only real use for this would be in a race car - where it would be a necessity. The torque curve is flat to 5000 rpm, or about 50 mph. I'm not a motor engineer so don't know whether you could keep the curve fatter longer by better control software or different mechanical properties (at the expense of $$$)

It is practical to build a gear box that will handle 1000Nm of torque (for $$$$), but gear boxes add drag which affects range. So again, race car yes, road car not necessary.

Brian H | September 15, 2013

Trying to visualize a "fatter curve". Why would it be better? ;)

Timo | September 15, 2013

Well, it is a real curve which you can't say about anorectic curves.

Brian H | September 17, 2013

An oxymoron.

Timo | September 17, 2013

Irrational curve.