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From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air

From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air kind of builds up in the front. It also looks like truck in EU are limited to 55mph. When I tow our trailer (just with a normal vehicle), there's minimal difference between fuel economy between 45 and 60. Significant drops come into play at higher speeds.

colechristensen 5y ago
Drag is proportional to the square of speed
- SkyPuncher 5y ago
  Ah. Yes! I forget about this! In vehicles, there's a lot of additional, interesting factors at play - like engine efficiency.
  - colechristensen 5y ago
    Yes there will be many nonlinear factors which combine to a maximum efficiency speed, which can, to an extent, be chosen by design.
reaperducer 5y ago
From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air kind of builds up in the front. A lot of long-distance American tractor trailers deploy fold-out cones on their back doors to improve their aerodynamics while driving. They fold up for low speed driving and loading. Also, fold-out flaps under the trailer for the same reason.
- mindslight 5y ago
  I've always wondered the reasons behind the regional difference in popularity of these. Trucks in the middle of the country seem to have them, trucks on the coasts seem to not. And you'd think longer haul trucks would be the most likely to have them, and so you'd end up seeing some on the coasts regardless. Is it something with state by state safety regulations, like prohibitions on protruding structures that aren't part of the main body? Or differently-defined overall length restrictions? Does a given long haul truck have them deployed in the middle of the country, but then they're removed before getting to the coastal states?
  - SkyPuncher 5y ago
    > I've always wondered the reasons behind the regional difference in popularity of these. There's an interesting mis-alignment of incentives. It comes down to who owns the truck vs the trailer. * Truck owner pays for fuel. * Trailer owner pays for the flaps. So, unless you own both the truck and trailer, there's little incentive for trailer owners to install them.
    - mindslight 5y ago
      That by itself isn't enough to explain the stark discrepancy though. Surely in the regions where tail flaps are extremely rare, there are still some operators that own both trucks and trailers.

colechristensen 5y ago

Drag is proportional to the square of speed

SkyPuncher 5y ago
Ah. Yes! I forget about this! In vehicles, there's a lot of additional, interesting factors at play - like engine efficiency.
- colechristensen 5y ago
  Yes there will be many nonlinear factors which combine to a maximum efficiency speed, which can, to an extent, be chosen by design.

reaperducer 5y ago

From my understanding, the drag caused by the flat back of the trailer causing a vacuum is much more impactful than the front shape. I believe a "pillow" of air kind of builds up in the front. A lot of long-distance American tractor trailers deploy fold-out cones on their back doors to improve their aerodynamics while driving. They fold up for low speed driving and loading. Also, fold-out flaps under the trailer for the same reason.

mindslight 5y ago
I've always wondered the reasons behind the regional difference in popularity of these. Trucks in the middle of the country seem to have them, trucks on the coasts seem to not. And you'd think longer haul trucks would be the most likely to have them, and so you'd end up seeing some on the coasts regardless. Is it something with state by state safety regulations, like prohibitions on protruding structures that aren't part of the main body? Or differently-defined overall length restrictions? Does a given long haul truck have them deployed in the middle of the country, but then they're removed before getting to the coastal states?
- SkyPuncher 5y ago
  > I've always wondered the reasons behind the regional difference in popularity of these. There's an interesting mis-alignment of incentives. It comes down to who owns the truck vs the trailer. * Truck owner pays for fuel. * Trailer owner pays for the flaps. So, unless you own both the truck and trailer, there's little incentive for trailer owners to install them.
  - mindslight 5y ago
    That by itself isn't enough to explain the stark discrepancy though. Surely in the regions where tail flaps are extremely rare, there are still some operators that own both trucks and trailers.