5 ms·

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

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
        Likewise, an interesting potential solution to the problem. I hadn't thought of a lower spring rate. It would certainly reduce the braking distance. A lot more complexity, cost, and weight, though.
- usrusr 6y ago
  When you are all-in on electric, I wonder if it could make sense for a truck to accept the unsprung weight penalty of wheel motors and go for uniform, independently steerable, suspended, self-monitoring and motored wheel-units that are simply repeated under the vehicle as often as needed for the load/power requirements and controlled with clever software that takes care of driving dynamics etc. Like a lazy copy/paste design, like all post-Tesla EV batteries are designed. It would be terrible for center of gravity because all the room between where conventional designs have their wheels would be filled with more wheels (and the accompanying suspension) but it would be a one size fits all design that I'm sure could have many benefits beyond just reducing per wheel load if the controlling software is smart.
  - Robotbeat 6y ago
    Tesla’s Semi prototypes do use 4 BLDC motors (well, more complicated than straight BLDC) from the Model 3. But I think optimization is really key for making it economically viable for mass cargo transport. Lazy copy-paste is great for prototypes and really shows how awesome electric is for making new vehicle configurations, but you really HAVE to optimize to be competitive at scale. Tesla has succeeded over the last 9 years against all comers BECAUSE they’ve optimized. Of course, manufacturability is one of the optimization constraints...
- adgjlsfhk1 6y ago
  How do Super Singles deal with punctured tires? I'd think one advantage of dual tires is that if one pops, there's a higher likelihood of the truck remaining drivable?
  - throwaway0a5e 6y ago
    >How do Super Singles deal with punctured tires? You sit on the side of the road waiting for the tire service to show up. >there's a higher likelihood of the truck remaining drivable? "DOT would like to know your location" You're technically not supposed to be operating with a blown tire. That said, driving to the nearest place you can reasonably get or wait for a replacement is the correct course of action.
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, 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
        Likewise, an interesting potential solution to the problem. I hadn't thought of a lower spring rate. It would certainly reduce the braking distance. A lot more complexity, cost, and weight, though.
usrusr 6y ago
When you are all-in on electric, I wonder if it could make sense for a truck to accept the unsprung weight penalty of wheel motors and go for uniform, independently steerable, suspended, self-monitoring and motored wheel-units that are simply repeated under the vehicle as often as needed for the load/power requirements and controlled with clever software that takes care of driving dynamics etc. Like a lazy copy/paste design, like all post-Tesla EV batteries are designed. It would be terrible for center of gravity because all the room between where conventional designs have their wheels would be filled with more wheels (and the accompanying suspension) but it would be a one size fits all design that I'm sure could have many benefits beyond just reducing per wheel load if the controlling software is smart.
- Robotbeat 6y ago
  Tesla’s Semi prototypes do use 4 BLDC motors (well, more complicated than straight BLDC) from the Model 3. But I think optimization is really key for making it economically viable for mass cargo transport. Lazy copy-paste is great for prototypes and really shows how awesome electric is for making new vehicle configurations, but you really HAVE to optimize to be competitive at scale. Tesla has succeeded over the last 9 years against all comers BECAUSE they’ve optimized. Of course, manufacturability is one of the optimization constraints...
adgjlsfhk1 6y ago
How do Super Singles deal with punctured tires? I'd think one advantage of dual tires is that if one pops, there's a higher likelihood of the truck remaining drivable?
- throwaway0a5e 6y ago
  >How do Super Singles deal with punctured tires? You sit on the side of the road waiting for the tire service to show up. >there's a higher likelihood of the truck remaining drivable? "DOT would like to know your location" You're technically not supposed to be operating with a blown tire. That said, driving to the nearest place you can reasonably get or wait for a replacement is the correct course of action.

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.