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2021 M3 SR+ & 82 kw battery
- Thread starter thformula1
- Start date
willow_hiller
Well-Known Member
It's actually an advantage for the SR+. Fewer physical cells means the SR+ is much lighter; I regularly achieve around 200 wh/mi at reasonable highway speeds.
Weight means basically nothing at highway speeds. The advantage is during acceleration and braking.
AlanSubie4Life
Efficiency Obsessed Member
Definitely not the SR+! May not even get the denser cells (but that is TBD).
As understood at the moment, the Performance is the one getting the denser cells. The AWD is not, apparently. (The 353-mile range is accomplished with less energy than the 322-mile range of the 2020 vehicle.)
I expect that sometime in 2021, when volumes allow, all vehicles using 2170 cells (Y and 3) will get the higher density cells. They are unlikely to remove cells, so this will result in higher capacity packs, and longer range vehicles across the line (except for Performance which already has the boost). That range increase will not be retroactive to early 2021 vehicles without the denser cells.
The forward-looking stuff is speculative, but we will see!
SageBrush
REJECT Fascism
m*g*ƒ
~ 8 - 9 Newtons per 100 Kg, so 2.2 - 2.5 Wh per Km.
At EPA type speeds, ~ a 1.0 - 1.5% difference in fuel economy per 100 Kg
willow_hiller
Well-Known Member
So a difference in curb weight of about 200 kg would account for 2% increased fuel economy. Looks like the SR+ is about 14% more efficient than the LR AWD according to the EPA. Is the rest due to the lack of a second motor, and the efficiency gained during acceleration/deceleration?
SageBrush
REJECT Fascism
I would expect the acceleration/deceleration weight penalty to show up in the city MPGe but not the highway MPGe.
Look at the Model 3 LR AWD over time
There are efficiency improvements that appear in the models at different times so any one snapshot in time is difficult to figure out. If we think that both models are even as of 2021 then there is a ~ 4% diff in the highway MPGe. Close enough for government work
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AlanSubie4Life
Efficiency Obsessed Member
Can you define f? And show how you came up with your number out of your formula?
Can you explain how rolling resistance scales this way? In general, rolling resistance is affected by weight, because it impacts the amount of deformation of the tires, some of which is non-recoverable energy.
It’s possible that your formula is close to correct, but I am not really following the calculation. Even if the formula is correct, you might be able to make it wrong if you inflate the tires more when the car is more heavily loaded (or just heavier), for example.
In any case most of the efficiency improvement of the SR is due to the lack of an extra motor which has to be turned even when it is not being used. Much more significant than the weight difference (which may be able to be mostly nullified by inflating the tires more, assuming no acceleration/deceleration).
JBHemlock
Member
There's more to it than just weight, too. Mountain Pass Performance did some dyno testing of the SR+ versus AWD models, and the power/torque curves are pretty different. They speculate that Tesla flattened the power/torque curve for the SR+ in order to make it feel peppy despite the lower power, but that once both cars hit field weakening (where current is traded for additional motor speed) they end up with very similar power curves.
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