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I find it interesting that a commercial truck is 'mass sensitive'. Presumably it's because they need a larger battery capacity due to the work needed to haul th

I find it interesting that a commercial truck is 'mass sensitive'. Presumably it's because they need a larger battery capacity due to the work needed to haul the load?

throwaway0a5e 6y ago
It's mass sensitive because of regulation. Of course you have to haul your battery around and that impacts range, performance, charging, etc. but not wanting to waste money and time while the DOT writes you a ticket is the primary driver. The big problem with electric commercial trucks is that the local delivery stuff that is most readily electrified is also the stuff where weight regulations are your biggest thorn in side (for a variety of reasons). The step van that delivers bread would already be electric if it weren't for the fact that the extra 800lb would push them into a different more expensive regulatory class where they become unprofitable or displace so much cargo they become unprofitable.
- wolfram74 6y ago
  Don't forget road deterioration goes like something between the 3rd and 4th power of mass. If one of your concerns is environmental impact, then minimizing the amount of road being torn up is something you care about. Whether that's on the actual list of reasons is unknowable to us.
  - Robotbeat 6y ago
    Yeah, to the third or fourth power assuming the same width, diameter, and number of wheels. So there are ways around that from an engineering perspective. The Tesla Semi has baselined Super Singles (a single tire as wide as a double tire, more efficient with equivalent or better traction and lower overall weight), I believe, which should help a bit with this. But this is why road regulations limit weight and weight per axle.
    - throwaway0a5e 6y ago
      Super singles are for rolling resistance. For pneumatic tires on highway speed vehicles your ground pressure is approximately your tire pressure. Super singles use pressures in the same ballpark as the duals they replace.
      - Robotbeat 6y ago
        Well yes, reduced road wear is not the primary advantage of super singles. The contact area is slightly larger, which can help slightly (things such as total load and outside dimensions and speed being equal—if you like, it can allow a slightly lower tire pressure). It’s still in the same ballpark, as you say, but it should slightly improve road wear characteristics.
        dotancohen 6y ago
        Why not have a three-wheel axle, with two wheels at the edges like in conventional vehicles, and the third wheel riding in the middle of the lane? That would transfer ~30% of the load to a portion of the road which is not wearing down anyway.
        wcarron 6y ago
        Stability. Roads very often have curvature built into them for rain/runoff/erosion mgmt. If your road surface is an arch, having a wheel at the apex is not gonna go well. You gon' tip over.
        dotancohen 6y ago
        Interesting, thank you. I wonder how well a reduced spring pressure would work for that case, though it would negate much of the advantage of transferring load to the center of the lane.
        wcarron 6y ago
  - throwaway0a5e 6y ago
    Minimizing environmental impact requires considering the vehicle count as well. Having a more light duty trucks zipping around because we've regulated fewer medium duty truck out of profitability for that use case is likely not environmentally efficient. When you're talking about roads expected to last X years with a certain % traffic of semi trucks in the 80k ballpark pretty much nothing you do in the 40k ballpark and below matters. Also, you have to differentiate between wear on the road surface and the road bed. The road surface doesn't care how much weight you have. It just cares about contact pressure. The road bed is going to care more about overall tonnage because by the time the force gets to the road bed it's spread over such an area the contact pressure is low regardless. It's hard to generalize these things because mother nature plays a large role what the depreciation curve of a road looks like and local wealth plays the deciding role in where in the depreciation curve you justify replacing it.
    - myself248 6y ago
      > Having a more light duty trucks zipping around because we've regulated fewer medium duty truck out of profitability for that use case is likely not environmentally efficient. Really? I thought it was personnel-inefficient but pretty much ideal for the roads, for the aforementioned power-law reason. Lighter trucks are gentler on the roads even if there are more of them. Do I misunderstand?
      - throwaway0a5e 6y ago
        There's carbon, particulate and road wear (and noise and traffic). You can prioritize whatever you want in whatever order you want to make whatever state you want seem like the best. If the road has to be built to handle X% semi trucks for 10yr and mother nature will destroy it in 20yr no matter what you do you lose nothing by driving a bunch of medium duty trucks on it.
Robotbeat 6y ago
Yeah. Consider that your whole truck is limited to 80,000 pounds weight and a typical semi tractor might weigh 20,000 pounds (less for a day cab). Anything above that 20,000 pounds eats directly into your payload. Still, Tesla should be able to hit their 500 mile range figure with a full typical load and without exceeding the 80,000 pound total weight limit. Takes a lot of work to improve the efficiency of the drivetrain (low battery internal resistance, low power electronics losses, very high efficiency brushless motors, low gearbox and bearing resistance), improving aerodynamics (surprisingly many tractors still seem to have the aerodynamics of a barn), extremely low rolling resistance tires (while maintaining traction), and reducing weight of the tractor through improved and optimized materials, optimized design, etc. ...and then optimizing the battery to have both high specific energy and long cycle life (even while Megacharging). It’s actually possible to do this, but it requires careful attention to inefficiency and mass throughout the entire vehicle. A lot like designing a reusable orbital rocket.

I find it interesting that a commercial truck is 'mass sensitive'. Presumably it's because they need a larger battery capacity due to the work needed to haul the load?

throwaway0a5e 6y ago

It's mass sensitive because of regulation. Of course you have to haul your battery around and that impacts range, performance, charging, etc. but not wanting to waste money and time while the DOT writes you a ticket is the primary driver. The big problem with electric commercial trucks is that the local delivery stuff that is most readily electrified is also the stuff where weight regulations are your biggest thorn in side (for a variety of reasons). The step van that delivers bread would already be electric if it weren't for the fact that the extra 800lb would push them into a different more expensive regulatory class where they become unprofitable or displace so much cargo they become unprofitable.

wolfram74 6y ago
Don't forget road deterioration goes like something between the 3rd and 4th power of mass. If one of your concerns is environmental impact, then minimizing the amount of road being torn up is something you care about. Whether that's on the actual list of reasons is unknowable to us.
- Robotbeat 6y ago
  Yeah, to the third or fourth power assuming the same width, diameter, and number of wheels. So there are ways around that from an engineering perspective. The Tesla Semi has baselined Super Singles (a single tire as wide as a double tire, more efficient with equivalent or better traction and lower overall weight), I believe, which should help a bit with this. But this is why road regulations limit weight and weight per axle.
  - throwaway0a5e 6y ago
    Super singles are for rolling resistance. For pneumatic tires on highway speed vehicles your ground pressure is approximately your tire pressure. Super singles use pressures in the same ballpark as the duals they replace.
    - Robotbeat 6y ago
      Well yes, reduced road wear is not the primary advantage of super singles. The contact area is slightly larger, which can help slightly (things such as total load and outside dimensions and speed being equal—if you like, it can allow a slightly lower tire pressure). It’s still in the same ballpark, as you say, but it should slightly improve road wear characteristics.
      - dotancohen 6y ago
        Why not have a three-wheel axle, with two wheels at the edges like in conventional vehicles, and the third wheel riding in the middle of the lane? That would transfer ~30% of the load to a portion of the road which is not wearing down anyway.
        wcarron 6y ago
        Stability. Roads very often have curvature built into them for rain/runoff/erosion mgmt. If your road surface is an arch, having a wheel at the apex is not gonna go well. You gon' tip over.
        dotancohen 6y ago
        Interesting, thank you. I wonder how well a reduced spring pressure would work for that case, though it would negate much of the advantage of transferring load to the center of the lane.
        wcarron 6y ago
- throwaway0a5e 6y ago
  Minimizing environmental impact requires considering the vehicle count as well. Having a more light duty trucks zipping around because we've regulated fewer medium duty truck out of profitability for that use case is likely not environmentally efficient. When you're talking about roads expected to last X years with a certain % traffic of semi trucks in the 80k ballpark pretty much nothing you do in the 40k ballpark and below matters. Also, you have to differentiate between wear on the road surface and the road bed. The road surface doesn't care how much weight you have. It just cares about contact pressure. The road bed is going to care more about overall tonnage because by the time the force gets to the road bed it's spread over such an area the contact pressure is low regardless. It's hard to generalize these things because mother nature plays a large role what the depreciation curve of a road looks like and local wealth plays the deciding role in where in the depreciation curve you justify replacing it.
  - myself248 6y ago
    > Having a more light duty trucks zipping around because we've regulated fewer medium duty truck out of profitability for that use case is likely not environmentally efficient. Really? I thought it was personnel-inefficient but pretty much ideal for the roads, for the aforementioned power-law reason. Lighter trucks are gentler on the roads even if there are more of them. Do I misunderstand?
    - throwaway0a5e 6y ago
      There's carbon, particulate and road wear (and noise and traffic). You can prioritize whatever you want in whatever order you want to make whatever state you want seem like the best. If the road has to be built to handle X% semi trucks for 10yr and mother nature will destroy it in 20yr no matter what you do you lose nothing by driving a bunch of medium duty trucks on it.

Robotbeat 6y ago

Yeah. Consider that your whole truck is limited to 80,000 pounds weight and a typical semi tractor might weigh 20,000 pounds (less for a day cab). Anything above that 20,000 pounds eats directly into your payload. Still, Tesla should be able to hit their 500 mile range figure with a full typical load and without exceeding the 80,000 pound total weight limit. Takes a lot of work to improve the efficiency of the drivetrain (low battery internal resistance, low power electronics losses, very high efficiency brushless motors, low gearbox and bearing resistance), improving aerodynamics (surprisingly many tractors still seem to have the aerodynamics of a barn), extremely low rolling resistance tires (while maintaining traction), and reducing weight of the tractor through improved and optimized materials, optimized design, etc. ...and then optimizing the battery to have both high specific energy and long cycle life (even while Megacharging). It’s actually possible to do this, but it requires careful attention to inefficiency and mass throughout the entire vehicle. A lot like designing a reusable orbital rocket.