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Dual motor efficiency
- Thread starter LectrikPower
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- Model 3
mspohr
Well-Known Member
Can't do that since I throw all my fast food trash there.
dgpcolorado
high altitude member
Well, yes. I rather like the extra frunk space and on long trips I will be using it to carry a spare tire, since I prefer to be able to self-rescue when I am very far from home or a city.
Garlan Garner
Banned
Garlan Garner
Banned
yes, you can. The Model S allows you to software select different versions. For example if you have a P90D you can select the 70D, or just the 70. The car will then limit the performance so that it drives like that lower model. Unfortunately it does not work the other way around ;-)
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Garlan Garner
Banned
That's interesting. I would never have thought that Tesla would do something like that. Hmmmm
Why would someone pay all that money for extras....and then downgrade through software?
I think it's mostly intended for the sales people so they can simulate different versions you're considering. However, the ability to switch between RWD and AWD would be nice for the reasons posted in the original question.
timk225
Active Member
On the S, with single motor, what was the 0-60 difference between the 60 and 85 batteries, before the performance and D and Ludicrous options became available?
Thanks for pointing this out.
I was trying to take the purist approach and save the weight of an extra motor (and bigger batteries), however front re-gen is too good of a thing to miss-out on.
Not just because of the added charge recovery, but because it will minimize using friction brakes in front.
All the other advantages of AWD usually do outweigh the weight increase.
Now you convinced me that AWD is a must-have option.
I just hope under-steer is not an issue.
Seems like a manipulative sales tactic.
I imagine the real 70, which is 500lb lighter than a 90D, would represent itself better than a software neutered 90D would.
Although, for non-up-sell purposes, it is cool to have the choice to select RWD mode.
I think teslabj0rn was using a RWD tesla in Norway and didn't complain about it.
To be frank... I'm torn on the awd myself and largely due to price. I want the same upgrades you do, but I'm concerned that if I add all wheel drive, the 35 base turns more into 44, then doc and delivery brings it to 45, and then sales tax can bring it up to 48-49. That's an expensive car! If the full federal tax credit is still there, great, it'll come down a little to 41 or so.
Without AWD, I'm thinking it might be closer to 38-39k.
For me, I won't get this car without a range upgrade or autopilot. The winter package is minor in cost so I'm not concerned about that. I'm hoping the price of awd, autopilot, and range upgrade is significantly less than the premiums they charge on the S.
If it's not, there's a chance I'll cancel my order. The 215 miles of range just won't cut it for me. I need 300+.
To be frank... I'm torn on the awd myself and largely due to price. I want the same upgrades you do, but I'm concerned that if I add all wheel drive, the 35 base turns more into 44, then doc and delivery brings it to 45, and then sales tax can bring it up to 48-49. That's an expensive car! If the full federal tax credit is still there, great, it'll come down a little to 41 or so.
Without AWD, I'm thinking it might be closer to 38-39k.
For me, I won't get this car without a range upgrade or autopilot. The winter package is minor in cost so I'm not concerned about that. I'm hoping the price of awd, autopilot, and range upgrade is significantly less than the premiums they charge on the S.
If it's not, there's a chance I'll cancel my order. The 215 miles of range just won't cut it for me. I need 300+.
But...that first statement is not true. An EV with RWD-only will regen with the back axle until the desired braking effectiveness is insufficient and you need to use the friction brakes. Regen maxes out well below the deceleration possible with only the rear tires, under most conditions. Besides the Model S, the i3, smart ED and i-MiEV have all used RWD regen. For any given deceleration rate and under most conditions, a RWD will regen with the same efficiency as a FWD and AWD.
It is definitely true that dual axle regen will be more stable and consistent. I've read that i3's will reduce regen in wet conditions to keep the rear tires from skidding as part of stability control.
S 60 4323 lb from 2014 Tesla Model S 60 - Instrumented Test
S 70D 4608 lb from 2015 Tesla Model S 70D - Instrumented Test
I'm not sure how much the 70kWh battery added, but that difference is 285 lb. If it is ~200 lbs in the Model 3, that will make a difference in how it handles. (as will the AWD: possibly good, possibly bad.) The 3 xxD will be more efficient however.
JeffK
Well-Known Member
Zoomit are you sure about the RWD regen thing... last time I checked there's much higher torque at the front during braking as the weight of the car shifts forward... Also with a smaller motor up front, this increases the efficiency of the regen due to higher load. A large motor on the back can't get the same regen efficiencies due to far less load.
It's the same reason older traditional cars had disc brakes in the front and drum brakes in the back.
Here's an article on the matter as well BMW i3 versus Tesla Model S 70D
It's the same reason older traditional cars had disc brakes in the front and drum brakes in the back.
Here's an article on the matter as well BMW i3 versus Tesla Model S 70D
Sure? Yes. Think about it this way, if you lost your front brakes in an ICE vehicle, could you stop? It would no problem in most cases. Max braking deceleration is typically over 1g eyeballs out. Max regen peaks only around 0.3g. Can only the rear tires create that deceleration? Absolutely. With the relatively light braking forces created by regen, a rear motor can extract the kinetic energy just like a front motor.
This is true as long as the rear tire can create ~0.3g, for example. As that article said, "[the 70D] should be less prone than the i3 to traction loss during difficult braking conditions."
While I don't know how the efficiencies change when the braking load is split between two motors, I don't think it's significant. Remember, most EVs are FWD and have very efficient regen. Of course the most efficient car, the i3, has RWD regen.
Creating maximum brake force is completely different and that's where the ~70% number come in for front brakes. This is due to the vehicle's inertia creating a moment on the front wheels and a higher vertical force. That higher vertical force creates greater tire friction and allows greater braking force to be applied to the tire before it starts skidding. Hence bigger, more capable brakes are on the front axle.
So regen efficiency should not be a discriminator when choosing between RWD and AWD. Regen braking feel and stability are something to consider, especially in marginal traction conditions.
In an ICE vehicle, AWD only accelerates you quicker. It does not slow you down any better. (Arguably it slows you down worse due to the additional weight of AWD.)
In an EV, AWD accelerates you quicker and also provides more stable regen braking than RWD.
