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4WD drive means all tires spin at the exact same speed, no matter what. AWD drive means each tire can rotate at a different speed. Tires with less grip will spi

4WD drive means all tires spin at the exact same speed, no matter what. AWD drive means each tire can rotate at a different speed. Tires with less grip will spin faster. Notably, if a tire on an AWD car is in the air, only that tire will spin. You won’t move anywhere because all of the force is expelled through the free wheeling tire. 4WD solves this issue by essentially locking everything together. Great for unsticking yourself, but terrible for every day driving. Things like turning into a parking spot can cause binding since wheels on the outside of the turn need to travel a longer distance than those on the inside of a turn

olliej 2y ago
Ah, so AWD vs 4WD is _definitionally_ the presence or lack of some form of locking differential? e.g if I were to take an AWD and weld the diff it would be 4WD (and not be too fun for daily driving)?
- SkyPuncher 2y ago
  Practically speaking, yes. The whole conversation is a bit tough because there are a LOT of blurred lines. Some 4WD systems can act like AWD systems. Some AWD systems can act like 4WD systems.
aranchelk 2y ago
> 4WD drive means all tires spin at the exact same speed, no matter what. Make sure you only drive in a straight line.
- SkyPuncher 2y ago
  Yes! You end up with binding when you turn. At best, the wheels either slip or "crow hop". At worse, you can destroy the transmission.
dingaling 2y ago
> Notably, if a tire on an AWD car is in the air, only that tire will spin On the contrary, here's a demonstration of the opposite. Subaru AWD, three wheels without grip, power goes to the wheel with grip. https://m.youtube.com/watch?v=mryGnENTsoI https://m.youtube.com/watch?v=mryGnENTsoI
- SkyPuncher 2y ago
  That's because Subaru does torque vectoring. Most of these use the brakes to fight the natural tendencies of AWD systems.
  - aeonik 2y ago
    And yet a Subaru was the car cited in the article as not being compliant with their regulations... it's just clear that the National Park Service doesn't understand how cars work.
    - SkyPuncher 2y ago
      I'm not sure there's anything wrong with the rule. It's easy to understand by everyone and doesn't require any additional level of testing of certification. Realistically, people who regularly drive on these types of trails want a proper 4WD system. Not just for the "locking diff", but for the other capabilities that tend to come with a "proper" 4WD car. Beyond "hard" capabilities, AWD torque vectoring tears roads up. The torque vectoring essentially requires the tires to spin before it will kick in. That doesn't happen in a "locked" 4wd system.
      - aeonik 2y ago
        Please just stop. Where are you getting your information? Maybe some crappy AWD systems have damaged roads at some point, I will give you the benefit of the doubt, but most do not. I've honestly never even heard of this. 4WD absolutely loses traction on roads if you leave the differential locked, and I'm sure if you amortized the extra weight and clueless drivers, 4WD does more damage then AWD. I got rid of my 4WD truck for an AWD system specifically because the performance was better. It wasn't even close. Trucks suck compared to a Subaru in traction, and off roading for obvious reasons: 1. Trucks have no weight in the back most of the time. 2. Trucks have poor clearance. 3. Subaru's AWD is pretty danged good. (I really didn't want to like Subarus, trust me, I looked at all the data though, and test drove everything) Of course, none these vehicles compare to purpose built and custom off-road vehicles, but that's not what we are talking about here... And yes, I have seen people fix the deficiencies of a truck, and have a nice cargo vehicle that climb cliffs, it's bad ass, but expensive and rare. Those trucks cost as much as a Ferrari. And again, advanced AWD systems are more advanced and better than 4WD in every single way, and there is even more room for improvement with AWD systems. Why waste sending power down a shaft that has no traction? Why wouldn't you want more control over more control surfaces of your vehicle?

olliej 2y ago

Ah, so AWD vs 4WD is _definitionally_ the presence or lack of some form of locking differential? e.g if I were to take an AWD and weld the diff it would be 4WD (and not be too fun for daily driving)?

SkyPuncher 2y ago
Practically speaking, yes. The whole conversation is a bit tough because there are a LOT of blurred lines. Some 4WD systems can act like AWD systems. Some AWD systems can act like 4WD systems.

aranchelk 2y ago

> 4WD drive means all tires spin at the exact same speed, no matter what. Make sure you only drive in a straight line.

SkyPuncher 2y ago
Yes! You end up with binding when you turn. At best, the wheels either slip or "crow hop". At worse, you can destroy the transmission.

dingaling 2y ago

> Notably, if a tire on an AWD car is in the air, only that tire will spin On the contrary, here's a demonstration of the opposite. Subaru AWD, three wheels without grip, power goes to the wheel with grip. https://m.youtube.com/watch?v=mryGnENTsoI https://m.youtube.com/watch?v=mryGnENTsoI

SkyPuncher 2y ago
That's because Subaru does torque vectoring. Most of these use the brakes to fight the natural tendencies of AWD systems.
- aeonik 2y ago
  And yet a Subaru was the car cited in the article as not being compliant with their regulations... it's just clear that the National Park Service doesn't understand how cars work.
  - SkyPuncher 2y ago
    I'm not sure there's anything wrong with the rule. It's easy to understand by everyone and doesn't require any additional level of testing of certification. Realistically, people who regularly drive on these types of trails want a proper 4WD system. Not just for the "locking diff", but for the other capabilities that tend to come with a "proper" 4WD car. Beyond "hard" capabilities, AWD torque vectoring tears roads up. The torque vectoring essentially requires the tires to spin before it will kick in. That doesn't happen in a "locked" 4wd system.
    - aeonik 2y ago
      Please just stop. Where are you getting your information? Maybe some crappy AWD systems have damaged roads at some point, I will give you the benefit of the doubt, but most do not. I've honestly never even heard of this. 4WD absolutely loses traction on roads if you leave the differential locked, and I'm sure if you amortized the extra weight and clueless drivers, 4WD does more damage then AWD. I got rid of my 4WD truck for an AWD system specifically because the performance was better. It wasn't even close. Trucks suck compared to a Subaru in traction, and off roading for obvious reasons: 1. Trucks have no weight in the back most of the time. 2. Trucks have poor clearance. 3. Subaru's AWD is pretty danged good. (I really didn't want to like Subarus, trust me, I looked at all the data though, and test drove everything) Of course, none these vehicles compare to purpose built and custom off-road vehicles, but that's not what we are talking about here... And yes, I have seen people fix the deficiencies of a truck, and have a nice cargo vehicle that climb cliffs, it's bad ass, but expensive and rare. Those trucks cost as much as a Ferrari. And again, advanced AWD systems are more advanced and better than 4WD in every single way, and there is even more room for improvement with AWD systems. Why waste sending power down a shaft that has no traction? Why wouldn't you want more control over more control surfaces of your vehicle?