It seems like dual motor EVs have significantly less range. Can’t dual motor EVs run in single motor mode to save range and only use the 2nd motor when absolutely necessary? The motor can’t weigh that much that it contributes to often 50mi difference in range.
In: Technology
A lot of answers here but the biggest way to lose a ton of range in the US is this:
EPA test weight classes. If you add another motor which pushes you into a higher weight class, your EPA range testing needs to be ballasted up to the middle of that higher weight class. Ie: if your RWD version weights 4999 lbs you remove weight to get to the middle of the weight class and do your range testing with that lower mass. If your AWD version weighs 5000 lbs you do your EPA range testing ballasted up. The worst case would be if the additional motor and structure pushes you up two weight classes
The motor definitely can weigh that much.
The motor alone weighs about 100 lbs, plus about another 100-150 lbs for the extra drivetrain. 200 lbs is nothing to scoff at, and will affect the range/efficiency of any vehicle.
Weight has two main impacts:
1. Rolling resistance. More weight means the tires deform more under the weight, and resist rolling more. It takes more energy to make the vehicle move. There are other rolling resistances, but they’re pretty minor compared to the tires.
2. Kinetic energy is proportional to mass, which means more kinetic energy required to achieve the same speed. This only really affects the energy required during acceleration, but range estimates include typical starts and stops, which means weight affects it. Regenerative braking helps return some of this energy, but not all.
In addition to that, it’s possible that there are other factors at play that may be specific to each EV.
You mention you should be able to disable a motor, but that doesn’t mean it doesn’t spin, it just means it doesn’t get pushed.
EVs (to my knowledge) don’t contain clutches to mechanically disengage a motor from the driveshaft. If you want the tires to spin, the motor has to spin too. So in order to accelerate a vehicle, you also have to get the weight of the motor’s rotor spinning as well. That’s energy that doesn’t get converted to forward kinetic energy, and dual motor EVs have to do that for two motors instead of just one, regardless of whether the second motor is “on” or not.
It also means that any of the motor’s resistances to turning have to be considered as well.
Some EV models might have other factors that differ between the single and dual motor trims. E.g. the dual motor trim might have other features like wider tires that improve traction but increase air resistance.
The more I think about it, the more I’m thinking there’s another large factor that’s not related to weight.
A battery’s efficiency depends on how quickly it’s discharged. The faster energy is drawn from the battery, the more heat is generated from inefficiency that needs to be dissipated.
A dual motor EV is capable of drawing energy from the battery in much faster spikes. Typical driving of a dual motor is going to naturally include faster accelerations and power draws from the battery, which means more energy loss to heat.
The same is true for turbocharged ICEs. Turbos increase the efficiency of engines by reclaiming waste energy from exhaust gas and using it to compress intake air. However they also increase power, making the car more “peppy” and powerful. This results in a behavioral change in drivers where they accelerate harder, drive more aggressively, and offset any efficiency gains.
It’s the battery that will increase range, not more motors.
You can actually compare them directly to regular gas cars in this instance. Imagine two cars with the same 10 gallon fuel tank (in an EV this would be a battery). If one of those was an inline 4 ( think single motor EV), and the other was a V8 (think dual motor), while still having that same fuel capacity, the V8 using significantly more power, will burn though it faster.
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