Traction on hard acceleration

[livingthedream]

If there is no chirp or wheelspin, it is simply by Tesla design. More than enough torque to do the job, but Tesla chooses the "profile" on how that gets to the ground and they appear to be quite conservative. Probably for the greater good, but I still wish a TC-off was offered.

Doesn't slip start turn off TC? Not sure if it also reduces starting TQ tho.

 

[insaneoctane]

Doesn't slip start turn off TC? Not sure if it also reduces starting TQ tho.

Tesla's slip start does not appear to be very helpful and certainly doesn't function like most ice tc disable. I don't think it even increases the likelihood of a chirp.... Any owner's care to comment?

 

[run-the-joules]

Tesla's slip start does not appear to be very helpful and certainly doesn't function like most ice tc disable. I don't think it even increases the likelihood of a chirp.... Any owner's care to comment?

I can get a bit of noise with slip start enabled, but nothing substantial.

One thing I'd like to point out is that I've had an "uncorked" S75 RWD as a service loaner for the last few days (built in December 2017, well after RWD was officially discontinued. See if you can make sense of THAT!!) and I could get it to activate traction control on dry pavement in a straight line under a few circumstances, it has a hell of a lot of torque. The Model 3 doesn't *seem* to be doing the same thing, and based on the feel of the power delivery I have a suspicion that they're artificially limiting the power output at lower speeds (it "surges" a bit once you're on the far side of 20mph or so). I have no realistic way to prove this, just a gut feeling.

 

[Daniel in SD]

You just need a VBOX. Other's have said they felt that the acceleration was limited at low speeds but it doesn't show up in this instrumented testing. My theory is that because the Model 3 torque doesn't taper off like many ICE vehicles it feels stronger in the midrange.
Is there any way to full disable stability / traction control on the Model 3? doing some reading about the Model S it sounds like probably not. Only really relevant for autocross or track use...

 

[run-the-joules]

View attachment 279020
You just need a VBOX. Other's have said they felt that the acceleration was limited at low speeds but it doesn't show up in this instrumented testing. My theory is that because the Model 3 torque doesn't taper off like many ICE vehicles it feels stronger in the midrange.
Is there any way to full disable stability / traction control on the Model 3? doing some reading about the Model S it sounds like probably not. Only really relevant for autocross or track use...

Neat. Disabling ABS will almost certainly take traction control with it, that’s how I’ve always done it in the past. But on this car... who knows.

 

[jelloslug]

My guess would be that the Model 3 does not generate enough torque to the wheels to spin the wheels. This is because it has a flat torque curve almost all the way to 60 mph and a single speed transmission. RWD ice vehicles with similar 0-60 times can spin the wheels because they have faster acceleration (more torque to the wheels) in 1st gear. While the ICE vehicle would beat the Model 3 off the line the Model 3 would catch up after the ICE vehicle shifted into second gear. Obviously this is in drag race type conditions. The ICE vehicle would have to rev the engine and feather the clutch (or load the torque converter in an auto) to achieve "magazine" 0-60 times. All the Tesla driver has to do is push the accelerator to the floor.

That is the exact opposite of what is happening.

 

[Skidmark]

To answer the OPs question, my guess is that the power output is being limited at lower speeds AND there could be a tiny bit of spin that is not as perceptible to the occupants because of how quickly the output can be changed on an electric motor. Electric motors generally have very flat horsepower curves (not torque curves) and it is power, not torque, that determines acceleration, ability to break tires loose, etc..

One good test would be to see how the traction control performs from a stop in the wet and also on ice. If it's very noticeable, then that would give more credibility to the output being limited at lower speeds in general and the traction control not having to activate as frequently in high traction conditions.

 

[Daniel in SD]

To answer the OPs question, my guess is that the power output is being limited at lower speeds AND there could be a tiny bit of spin that is not as perceptible to the occupants because of how quickly the output can be changed on an electric motor. Electric motors generally have very flat horsepower curves (not torque curves) and it is power, not torque, that determines acceleration, ability to break tires loose, etc..

Teslas have flat torque curves that transition to flat power curves. Flat horsepower would mean infinite torque at 0 rpm (HP = Torque x RPM ÷ 5252). Talk about burnouts!

Model 3 measured acceleration data shows a flat torque curve too:

 

[mattack4000]

I don't believe it has to do with the torque output, I still think it is either the traction control or some type of power reduction to start. I have both a B class and RAV4 with a similar Tesla motor, they can spin tires at any launch. How is the Model S or 3 RWD not doing it, I am totally stumped.

 

[Skidmark]

Model 3 measured acceleration data shows a flat torque curve too:View attachment 281121

That acceleration graph is interesting and I'm going to see if I can do a similar test when I get my 3.

I did say generally flat horsepower curves, not absolutely flat. I would consider the HP curve you posted much flatter because it does not steadily head from its peak towards zero as RPMs increase like the torque curve does.

 

[Daniel in SD]

I don't believe it has to do with the torque output, I still think it is either the traction control or some type of power reduction to start. I have both a B class and RAV4 with a similar Tesla motor, they can spin tires at any launch. How is the Model S or 3 RWD not doing it, I am totally stumped.

Both of those cars are front wheel drive cars. It is much easier to spin the tires with FWD vs. RWD because the car's weight transfers to the rear during acceleration.

I did say generally flat horsepower curves, not absolutely flat. I would consider the HP curve you posted much flatter because it does not steadily head from its peak towards zero as RPMs increase like the torque curve does.

I would say that the both the torque curve and the horsepower curve are flat The torque is flat from approximately 0-45mph and the horsepower is flat from 45mph-75mph and then tapers off. Or maybe neither is flat. I guess it's all a matter of perspective. haha

 

[mattack4000]

Both of those cars are front wheel drive cars. It is much easier to spin the tires with FWD vs. RWD because the car's weight transfers to the rear during acceleration.

I would say that the both the torque curve and the horsepower curve are flat The torque is flat from approximately 0-45mph and the horsepower is flat from 45mph-75mph and then tapers off. Or maybe neither is flat. I guess it's all a matter of perspective. haha

Agreed, but to have no chirp at all sounds super strange to me.

Horsepower is basically torque @ different RPM.

 

[insaneoctane]

My Fiat 500e will squeal away at launch without too much effort. @Daniel in SD , while FWD burnouts are aided by weight transfer at launch, EVs with VERY low Cgs do not have anywhere near as much weight transfer as ICE do. Simple trig.

 

[Daniel in SD]

My Fiat 500e will squeal away at launch without too much effort. @Daniel in SD , while FWD burnouts are aided by weight transfer at launch, EVs with VERY low Cgs do not have anywhere near as much weight transfer as ICE do. Simple trig.

Look at the Model 3 brakes. The fronts are dual piston calipers while the rear are single piston because there is much more weight on the front than the rear when decelerating. Acceleration is the opposite of braking. The 60-0 braking distance is 119 feet. That is equivalent to almost exactly 1G. So that's about how much traction all four tires combined have. The acceleration data shows the Model 3 accelerates at 0.6G. I think there's probably enough weight transfer to the rear to get that much extra traction. That's why RWD is superior to FWD.

 

[Zoomit]

The acceleration data shows the Model 3 accelerates at 0.6G. I think there's probably enough weight transfer to the rear to get that much extra traction.

The 3LR rear tire load increases by about 19% during 0.6G acceleration. The load distribution shifts from 52% to 62% [62/52=1.19].

While this load is significant, the other major contributor to traction is tire compound. Credit should be given to the OEM tires and the vehicle design choices that allow low energy consumption without resorting to minimal LRR tires like most EVs.

 

[Daniel in SD]

The 3LR rear tire load increases by about 19% during 0.6G acceleration. The load distribution shifts from 52% to 62% [62/52=1.19].

How do you calculate this? Seem like it would depend on center of gravity, spring rates, etc.

 

[Daniel in SD]

This guy explains it well:

You can see the weight transfer in the video.

 

[mattack4000]

Look at the Model 3 brakes. The fronts are dual piston calipers while the rear are single piston because there is much more weight on the front than the rear when decelerating. Acceleration is the opposite of braking. The 60-0 braking distance is 119 feet. That is equivalent to almost exactly 1G. So that's about how much traction all four tires combined have. The acceleration data shows the Model 3 accelerates at 0.6G. I think there's probably enough weight transfer to the rear to get that much extra traction. That's why RWD is superior to FWD.

The .6G is maximum acceleration, car doesn't sustain that level of acceleration for sure. I don't have my datalogs with me, but what you are saying sounds way off.

 

[Daniel in SD]

The .6G is maximum acceleration, car doesn't sustain that level of acceleration for sure. I don't have my datalogs with me, but what you are saying sounds way off.

Look at the VBOX data above. Accelerates at 0.6G up to about 45mph then motor controller switches from constant torque to constant horsepower. 0.6G all the from 0-60mph would be 4.6 seconds. Model 3 is a little bit slower than that because it can't maintain constant acceleration all the way to 60mph.
Bonus facts 1G = 2.7 second 0-60mph. Ludicrous Model S P100D is accelerates faster than gravity! Must have some sticky tires.

 

[12Pack]

I have not got my Model 3 to get wheel spin from a dead stop. The amount of power it can pull down that low seems limited. However when I am traveling 20-30mph I can get the traction light to come on. It reminds me the difference between a S85 and a P85.

My guess is that the M3 is set up similarly to my first MS - S85. In spite of all the talk about immediate torque, indeed the S 85 did not put out enough kW to the motor from a dead stop and felt stronger once going at 30Mph or so.

That's in start contrast to my new P100D. I understand the "P" comes with higher rated PM (inverters) to allow for full and immediate power delivery.