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How does FWD vs RWD matter for energy recapture in regen breaking? As long as you're not losing traction on your rear wheels during breaking, there's no differe

How does FWD vs RWD matter for energy recapture in regen breaking? As long as you're not losing traction on your rear wheels during breaking, there's no difference in terms of energy captured in FWD vs RWD.

lowbloodsugar 4y ago
The front brakes do most of the work. It is not the case, as you assume, that both front and rear contribute equally to braking. If you didn't use the front brakes, or even if you tried to have them apply the same force, the rear wheels would absolutely skid. If you want an extreme visual example, check out stunt cyclists who brake so hard the rear wheel comes off the ground. Pretty easy to see that the rear wheel isn't contributing to braking when it's in the air.
- Kirby64 4y ago
  In cars that only have rear motors, unless you apply the brakes (or they have some blended braking setup) then ALL regen is via the rear motor. Obviously, front brakes are capable of more braking, but the limit at the end of the day is the regen of the battery itself and how much the inverter can handle regen. RWD-only EVs are already capable of ~75kW of regen. Moving to FWD to try to gain regen is only marginally going to give you better efficiency, if anything. It only matters for harder braking.
- gnicholas 4y ago
  Bingo. When I was a kid, I once flipped my bike because I was only braking with the front. I learned not to do that, but to an extreme — I then braked almost always with just the back. It wasn't until I got older and faster that I realized that braking just in the back is not as effective, since the braking action makes your nose dive and puts more weight over your front tire. I now brake with both sides, but always first in the back.
  - skeeter2020 4y ago
    My commuter bike only has a front brake. You can shift body position to make it pretty much impossible to go OTB. Meanwhile my DJ bike only has a rear brake, which at best "strongly suggests" you slow down.
    - gnicholas 4y ago
      Why would a commuter bike (or any bike) have only a front brake?
      - eimrine 4y ago
        Having only front brake is almost common for fixed gear bikes because they can break rear by retention and fixie counts as a commuter bike. Also it might be a decent config for learning some BMX tricks because if you want to be able to do a barspin you can not have both brakes. And if you have a bicycle with a coaster hub and a front brake and your chain is off than you are effectively having only front brakes.
    - alephxyz 4y ago
      Ironically the law pretty much everywhere in north America mandates that bikes have at least a rear brake.
  - deleted 4y ago
    [deleted]
  - thomastjeffery 4y ago
    The trick is to lean your body backward while braking. Unless you are in a big rush to stop, you can keep the balance pretty even between wheels.
kenhwang 4y ago
"As long as you're not losing traction on your rear wheels" is the key part. The more you brake, the more weight shifts forward, which results in less traction available to use to recapture. People vastly overestimate how much traction is available at the rear during braking, and running out of traction at the rear typically results in the car spinning (especially in an EV with low rotational inertia with most of the weight between the axles) so regen tends to be very conservatively tuned to not cause rear lock up, thus using even less of the little traction available.
- frosted-flakes 4y ago
  This is obvious to anyone who's changed the brakes on their car. Front brakes are massive compared to the rear.
  - scottyah 4y ago
    Also people who ride dirt bikes- the back will slide out fairly easily compared to the front (but using the front exclusively comes with some pretty big tradeoffs)
  - skeeter2020 4y ago
    Or used any vehicle with independent front/rear braking like a motorcycle or bike. The rear is for fine tuning while the front is for actually stopping.
    - adrianmonk 4y ago
      Also anyone who has ridden a bicycle.
      - thomastjeffery 4y ago
        In that case, leaning back makes a surprising amount of difference.
    - akira2501 4y ago

lowbloodsugar 4y ago

The front brakes do most of the work. It is not the case, as you assume, that both front and rear contribute equally to braking. If you didn't use the front brakes, or even if you tried to have them apply the same force, the rear wheels would absolutely skid. If you want an extreme visual example, check out stunt cyclists who brake so hard the rear wheel comes off the ground. Pretty easy to see that the rear wheel isn't contributing to braking when it's in the air.

Kirby64 4y ago
In cars that only have rear motors, unless you apply the brakes (or they have some blended braking setup) then ALL regen is via the rear motor. Obviously, front brakes are capable of more braking, but the limit at the end of the day is the regen of the battery itself and how much the inverter can handle regen. RWD-only EVs are already capable of ~75kW of regen. Moving to FWD to try to gain regen is only marginally going to give you better efficiency, if anything. It only matters for harder braking.
gnicholas 4y ago
Bingo. When I was a kid, I once flipped my bike because I was only braking with the front. I learned not to do that, but to an extreme — I then braked almost always with just the back. It wasn't until I got older and faster that I realized that braking just in the back is not as effective, since the braking action makes your nose dive and puts more weight over your front tire. I now brake with both sides, but always first in the back.
- skeeter2020 4y ago
  My commuter bike only has a front brake. You can shift body position to make it pretty much impossible to go OTB. Meanwhile my DJ bike only has a rear brake, which at best "strongly suggests" you slow down.
  - gnicholas 4y ago
    Why would a commuter bike (or any bike) have only a front brake?
    - eimrine 4y ago
      Having only front brake is almost common for fixed gear bikes because they can break rear by retention and fixie counts as a commuter bike. Also it might be a decent config for learning some BMX tricks because if you want to be able to do a barspin you can not have both brakes. And if you have a bicycle with a coaster hub and a front brake and your chain is off than you are effectively having only front brakes.
  - alephxyz 4y ago
    Ironically the law pretty much everywhere in north America mandates that bikes have at least a rear brake.
- deleted 4y ago
  [deleted]
- thomastjeffery 4y ago
  The trick is to lean your body backward while braking. Unless you are in a big rush to stop, you can keep the balance pretty even between wheels.

kenhwang 4y ago

"As long as you're not losing traction on your rear wheels" is the key part. The more you brake, the more weight shifts forward, which results in less traction available to use to recapture. People vastly overestimate how much traction is available at the rear during braking, and running out of traction at the rear typically results in the car spinning (especially in an EV with low rotational inertia with most of the weight between the axles) so regen tends to be very conservatively tuned to not cause rear lock up, thus using even less of the little traction available.

frosted-flakes 4y ago
This is obvious to anyone who's changed the brakes on their car. Front brakes are massive compared to the rear.
- scottyah 4y ago
  Also people who ride dirt bikes- the back will slide out fairly easily compared to the front (but using the front exclusively comes with some pretty big tradeoffs)
- skeeter2020 4y ago
  Or used any vehicle with independent front/rear braking like a motorcycle or bike. The rear is for fine tuning while the front is for actually stopping.
  - adrianmonk 4y ago
    Also anyone who has ridden a bicycle.
    - thomastjeffery 4y ago
      In that case, leaning back makes a surprising amount of difference.
  - akira2501 4y ago