How to make plaid accelerate faster ?

[ramirj2]

Cybertruck's 800V architecture and the 4680 cells, would reduce our loss of power as battery % decreases and unleashed the 932KW potential from the 3 motors (1242 hp).
We are limited by the battery and 400V more than anything else as the required amperage to reach the target power is very high.
Also, the ability to do a burnout to improve 60' on sticky tires would be welcome.

 

[BowserP3D]

Cybertruck's 800V architecture and the 4680 cells, would reduce our loss of power as battery % decreases and unleashed the 932KW potential from the 3 motors (1242 hp).
We are limited by the battery and 400V more than anything else as the required amperage to reach the target power is very high.
Also, the ability to do a burnout to improve 60' on sticky tires would be welcome.

Do you think that’s what the 2024 or perhaps 2025 plaids will have? 4680s at 800v and 1242hp?

 

[BowserP3D]

As I mentioned in the other post, there's nothing that's swappable currently. Maybe the CT gears will be, but that setup is for torque not HP. The plaid simply needs to be able to stick more power to the pavement on launch, or it needs more HP on the top end.

Every racer always wants faster and faster, but there's limitations on EVs when we can't get into the computer and modify power delivery...and rightfully so, because people having no clue what they're doing can change one setting, stall current, and fry all three motors in 1 second.

Any idea how much would it cost to have custom gears made for the plaid?

 

[ramirj2]

Do you think that’s what the 2024 or perhaps 2025 plaids will have? 4680s at 800v and 1242hp?

For sure I see the next evolution of all Tesla platforms, not just the Plaid would be 800v high current and 48v low current.
They will make it standard.
Less copper, weigh and cheaper with faster charging speeds.
For performance, Plaid or else, the competition will decide if a 1200 hp platform will make sense (I think they will).
As the car charge speed increases with 800v, so will the discharge rate allowing higher HP with less amperage.
Model S is not doing that well in sales so that’s my doubt, if it will be in a refresh of our cars or in another car….

 

[Bouba]

If the S and the X get 48v steer by wire....then it’s possible that they could reintroduce it back to the UK market because conversion to right hand drive will be easier ??

 

[ramirj2]

If the S and the X get 48v steer by wire....then it’s possible that they could reintroduce it back to the UK market because conversion to right hand drive will be easier ??

For sure!
There are no physical connections to the steering wheel.
You can have the steering wheel on the rear seat if you want to

 

[Sam1]

Any idea how much would it cost to have custom gears made for the plaid?

No clue, on one of my old race cars a quick change diff gear set was $1500. I don't know how the gearboxes inside the tesla is set up, but that $1500 was just for two gears. If it's some sort of standardized set, you can get the quick swaps for under $500 depending on the manufacturer and what level of processing you want done to them.

I'd say all in for 3 gear swaps you're probably looking $7500-$10000 without knowing if it will work.

 

[terranx]

I imagine the software would throw all sorts of errors of the n/v ratio doesn’t match what it’s expecting. Without the ability to tune these things ourselves, I wouldn’t count on a gear swap working well.

 

[Sam1]

I imagine the software would throw all sorts of errors of the n/v ratio doesn’t match what it’s expecting. Without the ability to tune these things ourselves, I wouldn’t count on a gear swap working well.

Agree completely. Gear swaps are something I would consider on a custom retrofit of an EV system in a different chassis. Not in a stock Tesla. Reward vs cost risk doesn't even come close.

 

[TIppy]

Tesla has a pre-programmed torque curve for launch that's designed for 19" summer tires on asphalt. Or at least it was on the Raven. This torque curve keeps the tires on the edge of their traction limit, until the torque is limited by horsepower and speed. For small amounts of tire slip, the torque is adjusted slightly downward to allow the tires to re-attach. Once there is appreciable tire slip, the torque is drop drastically and takes a while to build back up to the pre-programmed torque. So decreasing the weight of the car by a large amount doesn't really help acceleration. The car is constantly cutting the torque deeply and slowly returning to the pre-programmed torque curve where the tires break loose again. The average torque-to-weight ratio is substantially less. Of course at the drag strip, the tires have more grip than on asphalt so you can get away with some weight reduction. But eventually with enough weight reduction you overwhelm this additional traction.

Shorter gearing would have a similar effect. There would be more torque to the wheels than what was being called for by the pre-programmed torque curve so the torque would go through the same drastic cycling. Also, Andrew from the Tesla Plaid Channel had major computer problems in going from 45 to a 35 sidewalls on 19" tires on his Raven. That's no much of a gear change.

Anything you can do to reduce rotational mass would help. The mass of a wheel increases the effective mass of the car by 1.5 times the actual mass of the wheel. Since the tires are farther out from the center of the wheel, their effective mass is twice their actual mass. So the smallest wheel you can fit over the brakes, and the lightest tire is most effective. The narrowest tire that still has traction is preferable.

If you could run the quarter mile in a vacuum, therefore with zero aerodynamic drag, you would go from 9.23s @ 154.6mph to 9.15s @ 158.2mph. At sea level the aerodynamic drag at 154.6 mph is 1400 newtons. The car is still accelerating at 0.38Gs, so the rearward force due the effective mass of the car is 9249 newtons. There is also a rolling resistance of 219 newtons. So even at 155mph, the majority of the rearward force is still from accelerating the effective mass of the car.

 

[WilliamG]

I can't imagine street legal fan car, tbh. All the pebbles flying up from it...

Also, I wouldn't want to drive one - large enough bump during high G turn and all the traction is gone.

Pothole or speed bump in the road and your spine is gone, too.

 

[Mash]

Pothole or speed bump in the road and your spine is gone, too.

That can be solved by seat cushion.

But, yeah, there were cases people were braking back in rally cars just by rolling out in the bumpy field without any crash.

 

[flyingfish28]

This torque curve keeps the tires on the edge of their traction limit, until the torque is limited by horsepower and speed.

The average torque-to-weight ratio is substantially less.

Why would torque be limited by horsepower ? I can accept that torque is affected by motor RPM - is this what you mean?
Also: are you suggesting that traction loss resulting from lower weight will be large enough to negate the benefit of reduced weight in F=m*a?
Wouldn't that imply that Model S should be slower than Model X?

 

[TIppy]

Why would torque be limited by horsepower ? I can accept that torque is affected by motor RPM - is this what you mean?
Also: are you suggesting that traction loss resulting from lower weight will be large enough to negate the benefit of reduced weight in F=m*a?
Wouldn't that imply that Model S should be slower than Model X?

Horsepower is the product of torque and rpm. That is, torque is Horsepower divided by rpm, so both horsepower and rpm affect torque. Below a certain rpm for a given horsepower the torque becomes greater than the traction the tires can provide. At this point the pre-programmed torque is just below what would cause the tires to break free. The torque is more or less constant as the rpms decrease further, so the required horsepower steadily decreases as the rpms tend to zero. Going in the other direction as rpms increase, the torque must decrease because for the plaid the horsepower remains almost constant out to 200 mph. Once the constant torque times the rpms reaches the maximum horsepower available from the motor, the torque begins to linearly decrease as the rpms increase. The horsepower is limited by battery voltage, so as the battery gets to a low state of charge the maxium horsepower is decreased. This means there is less torque at a given speed. Since maximum horsepower isn't reached during a zero to sixty, it is less affected by battery voltage. You see the effect sooner in the quater mile.

As you decrease the mass, the traction decreases proportionately, and so the tires will lose traction at a lower torque. The decreased mass also means that you can achieve the same amount of acceleration with this lower torque. But the pre-programmed torque curve doesn't adjust for the decreased weight and supplies a torque greater than the tires can handle. The tires immediately begin to spin, and the torque is drastically cut. When the tires finally regain their grip, the torque is ramped back up to the pre-programmed value. But again the tires begin to spin. You can feel this surging in the car. The average value of this cycling torque is less than a constant torque that would be just below the traction limit of the tires. Also since the tires are repeatedly breaking free, the average coefficient of friction is less. So it's not the traction loss due to lower mass, it's the torque control algorithm. This algorithm works better than active control as long as the conditions are as they were at the factor when then tuned it.

I haven't seen a horsepower vs speed plot for the Model X Plaid, but apparently it's the same as the Model S Plaid since its zero to sixty takes longer due to its greater mass. That would also means the tires on the Model X aren't as close to the traction limit as on the Model S, unless they are not as sticky. That increased mass would decrease the acceleration for the entire quarter mile. The Model X get the same torque as the Model S at all speeds.

 

[terranx]

Model X tires are also nearly 2" larger in diameter than the Model S tires, so they will spin at about 7% less RPM at a given road speed and generate 7% less force

 

[flyingfish28]

Thank you for taking the time. I understand this and the following makes me raise an eyebrow at Tesla:

You say that the pre-programmed torque limiting algorithm is unable to adapt to vehicle loading and/or to different / tyre characteristics and that this is left to the traction control system which is much more crude.

Have you just pointed us to a big theoretical area of improvement?
I am not saying it is easy, but: hack into that system and adjust the torque limiting algorithm...

Shall we further discuss this: how does the lower acceleration of the Model X fit in the above logic?

 

[terranx]

Shall we further discuss this: how does the lower acceleration of the Model X fit in the above logic?

More weight, more drag, less force (due to the wheel diameter difference effectively changing gear ratio)

 

[BowserP3D]

More weight, more drag, less force (due to the wheel diameter difference effectively changing gear ratio)

I thought a larger diameter tire would help acceleration because for every revolution you are going a farther distance. So if you were to keep the weight the same by getting lighter wheels, then you’d accelerate quicker, no?

Anyone checked what the largest tire that can fit under the chassis?

 

[Sam1]

I thought a larger diameter tire would help acceleration because for every revolution you are going a farther distance. So if you were to keep the weight the same by getting lighter wheels, then you’d accelerate quicker, no?

Anyone checked what the largest tire that can fit under the chassis?

My personal experience is that the 295 OEM PS4S rear topped out at 174.16 and a 305 Goodyear nao f1 topped out at 175.94 on dragy with the times being almost identical.

Not sure how much taller you can go without interfering with the computer. I know some people are running 315's, but it's not something I'm interested in. Would guess 1/2" taller is fine, but when you get closer to the 1" mark you're going to see issues.

 

[terranx]

I thought a larger diameter tire would help acceleration because for every revolution you are going a farther distance. So if you were to keep the weight the same by getting lighter wheels, then you’d accelerate quicker, no?

Anyone checked what the largest tire that can fit under the chassis?

No, it would effectively reduce linear force. Torque = force*distance. If you increase distance per revolution, then you're reducing force and therefore acceleration. Basically same end result as using a taller gear ratio.