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The first step is to stop pretending AWD and 4WD can sensibly mean different things… unless your number of wheels differ from 4. The naming is truly idiotic. I

The first step is to stop pretending AWD and 4WD can sensibly mean different things… unless your number of wheels differ from 4. The naming is truly idiotic. Instead, be clear about any locking or torque split requirements, so you don’t take your sports SUV with no locking diffs and a 70/30 Torsen center differential on the trail. E.g., “this is an advanced trail that requires three locking differentials or equivalent”, and for lighter trails “this trail requires at least limited slip differentials”.

dotancohen 2y ago
How about the AWD Teslas? They have independent front and rear motors, but I don't know if the rear and/or front diffs limit slip. Even if they don't, the ABS could hold a caliper to prevent wheelslip (Some Mercedes 4WD or AWD had an open differential and used independent brake control to limit slip, it was excellent for mud and sand, I don't know about other conditions).
- gambiting 2y ago
  I was going to say - my Volvo T8 is technically "AWD" but the rear and front axles are completely independent with two different power sources - so there is no need for a locking diff in between them(in fact one isn't possible as there is no driveshaft linking them). Ditto for electric vehicles with modern slip control where one wheel can be locked at any time on any axle.
  - arghwhat 2y ago
    Assuming at least one of the axles is driven by an electric motor, you can lock them in software. That's also what you'd need to do for rock crawling - you don't just want to avoid losing power to a lifted wheel, you want all wheels to rotate with the same steady velocity regardless of conditions so that all wheels remain in static friction (zero slip, which is not possible with e.g. brake-driven soft locking). An electric vehicle with a motor per wheel can do this. Your vehicle would need lockers on front and rear diff, and appropriate software to soft-lock front and rear.
- arghwhat 2y ago
  Electronic Stability Control can sort of mimic a limited slip differential, but I doubt it will work well for rock crawling without at least having been tuned explicitly for it. Even limited slip differentials are not normally suited for this - the engagement of a viscous LSD is proportional to the current slippage, meaning that you only get a notable lock once the other wheels are spinning aggressively. That’s not usable when you want to go slow and steady. In rock-crawling, you want all wheels to spin at the same steady speed regardless of traction, allowing them all to remain in static friction to ensure all wheels provide all available traction regardless of conditions. But, “or equivalent” is important - independent wheel motor setups are superior to lockers - assuming it’s tuned right - so it should be allowed.
- deleted 2y ago
  [deleted]
- b112 2y ago
  One of the terminologies for this is 'ediff', although this is also used for "diff which has its internal clutches electronically controlled'. In "super cheap e-diff with an open diff', only in place to save money, the results are horrid. There are issues where people with an incline cannot get out of their driveway, as the e-diff jockies back and forth, left to right, braking each wheel as it spins. You may say "so?", but with an actual limited slip diff there is no braking, spin happens, and even if it is jockeying left/right, the freakin' car isn't braking whilst you're trying to get out of that driveay. Instead it's shifting power, and wheels are still working at it. You get out. There are many conditions where slip is perfectly normal, and where braking to stop that slip is bonkers. Snow is another example. A great way to have your car spin out of control, is to suddenly auto-brake because it slipped the tiniest bit. Now, that tiny slip has become massive slip. The same holds for ice. ediff tech literally makes cars less safe, less driveable, less stable in snow and ice. This holds true to all current stability and traction control I have tested on gravel, on pavement in rain, on snow, and on ice. I grew up driving on frozen lakes, and can use braking methods to steer, I can drive on snow and then when I turn on traction control? And the result is the worst thing being done at the worst time. Stepping back, we see forums replete with people complaining about auto-drive madness. I've seen people unable to exit their driveway with reverse-impact protection on, because their driveway is angled down to the road, and it detects the road as an object (it isn't... as the car drives down it angles up, but the radar just sees "object"). People complain about their car wildly veering into some turnoffs because it thinks that's how the road goes. People complain about brakes slamming on, when it's a tight turn and there are guardrails, which the radar thinks is an object. The only true answer here is to disable ABS, thus preventing a large aspect of drive control. This is the only safe way to drive. And you make think "WHAT! ABS reduces braking distances!", yet this is misinformation, and absolutely not true. ABS extends braking distances. Its only goal is to allow one to steer while braking hard. That's it. And while in absolutely perfect, and absolutely optimal braking conditions (dry pavement, cool day, lots of grip) ABS is almost as good as a human at distance-to-stop, when it comes to literally every other circumstance ABS is horrid. Most directly, as an example, gravel or deep snow. With gravel you want to lock the brakes up (to a certain degree). With many types of gravel roads, this results in you literally "digging in". Gravel starts to build up in front of the wheel. Braking distances are immensely reduced as a result. Meanwhile, ABS prevents this condition, thus extending braking distances by 2x or even 3x. No, I'm not joking or exaggerating. With deep snow the issue is just as stark. If you're driving in 6" of snow, and you brake hard enough to "dig in", snow just builds up more and more in front of the wheel. And another "trick" to snow driving is to brake VERY HARD, turn the wheel, then release -- and even on ice you often shoot off in the current direction of the wheel. You cannot do either of these things with ABS. Most of the reason for all of this, is that we do not have AGI. Nor do we have AI that is "a good driver". Instead, we have a bunch of algorithmic if/then statements, which do not even remotely match the wildly varying conditions that a drive will reach outside of a lab. One of the worst situations I see with current autodrive, is that California, specifically SV, is one of the most temperate, perfect climates to drive in. Sunny almost all the time, with occasional rain. Developing AI systems, or even just simple driving algos / if+then statements in such conditions is as if driving in a lab. No snow. No ice. You can see the paint on the road (there is no visible paint on roads in the winter in northern climates). Often, in snow storms you cannot even see the road vs the shoulder in a way a car can discern. Yet here we have auto-drive tech being developed in Arizona, California, and sometimes Texas. And it's still wildly imperfect! Not even remotely ready for prime time, and it's only being deployed in absolutely perfect driving conditions! I expect it will be 50+ years before we have autodrive capability that will approach true human driving capability in, for example, a snow storm. Which leads back to using ABS for a diff? It's just auto manufacturers reducing safety to save a few bucks.
- survirtual 2y ago
  I took my Tesla model 3 places that made people's heads spin. The clearance is bad, and I had to replace the bottom coverings a few times (until I installed skid plates), and I scraped more times than I can count, but it always kept going. The only time I got stuck was on a sand dune. I had been through rivers, up rocky mountains, middle of deserts, icy cliffs, but sand managed to stop me. A huge lifted truck saw me and got me out with a tow strap around my front tire. No one would believe or understand the places I went with that car, but I know. Electric drive is just superior, end of story. I will be waiting for someone to make a rugged, utilitarian all-electric truck or jeep-like offroad vehicle. No touch screens, no extras. Just 4 independent motors with adjustable high-low clearance (4 independent hydraulic lifts would be sweet) and at least 500 miles of range -- or more. As much range as possible. This lets you use the battery for other purposes -- running power tools, running climate control all night, even cooking with electricity. My dream is a fully electric off/on road vehicle that can go anywhere, with a foldable 10kw+ solar array for silent charging, totally independent of traditional energy infrastructure.
  - TreeInBuxton 2y ago
    I am keeping an eye on the Ineos Fusilier (https://ineosgrenadier.com/en/gb/news/introducing-the-ineos-fusilier https://ineosgrenadier.com/en/gb/news/introducing-the-ineos-...) for something along those lines - it will have both a full EV and a range-extended hybrid powertrain Maybe one day I will replace my Land Rover...
  - dotancohen 2y ago
    > No one would believe or understand the places I went with that car, but I know. Electric drive is just superior, end of story. Yes, I've taken my Model 3 to some real stupid places. I've always been impressed. Electric drive has 100% torque at 0 RPM and instant throttle response - makes getting unstuck far too easy.
  - arghwhat 2y ago
    I have also been overtaken by old front wheel drive microcars at river crossing. Plenty of lucky idiots out there - it’s all fun and games until it’s not. On and off-road capability are always at odds with each other, because “agile” also means “unstable”. It’s a matter of compromise and expectations.

dotancohen 2y ago

How about the AWD Teslas? They have independent front and rear motors, but I don't know if the rear and/or front diffs limit slip. Even if they don't, the ABS could hold a caliper to prevent wheelslip (Some Mercedes 4WD or AWD had an open differential and used independent brake control to limit slip, it was excellent for mud and sand, I don't know about other conditions).

gambiting 2y ago
I was going to say - my Volvo T8 is technically "AWD" but the rear and front axles are completely independent with two different power sources - so there is no need for a locking diff in between them(in fact one isn't possible as there is no driveshaft linking them). Ditto for electric vehicles with modern slip control where one wheel can be locked at any time on any axle.
- arghwhat 2y ago
  Assuming at least one of the axles is driven by an electric motor, you can lock them in software. That's also what you'd need to do for rock crawling - you don't just want to avoid losing power to a lifted wheel, you want all wheels to rotate with the same steady velocity regardless of conditions so that all wheels remain in static friction (zero slip, which is not possible with e.g. brake-driven soft locking). An electric vehicle with a motor per wheel can do this. Your vehicle would need lockers on front and rear diff, and appropriate software to soft-lock front and rear.
arghwhat 2y ago
Electronic Stability Control can sort of mimic a limited slip differential, but I doubt it will work well for rock crawling without at least having been tuned explicitly for it. Even limited slip differentials are not normally suited for this - the engagement of a viscous LSD is proportional to the current slippage, meaning that you only get a notable lock once the other wheels are spinning aggressively. That’s not usable when you want to go slow and steady. In rock-crawling, you want all wheels to spin at the same steady speed regardless of traction, allowing them all to remain in static friction to ensure all wheels provide all available traction regardless of conditions. But, “or equivalent” is important - independent wheel motor setups are superior to lockers - assuming it’s tuned right - so it should be allowed.
deleted 2y ago
[deleted]
b112 2y ago
One of the terminologies for this is 'ediff', although this is also used for "diff which has its internal clutches electronically controlled'. In "super cheap e-diff with an open diff', only in place to save money, the results are horrid. There are issues where people with an incline cannot get out of their driveway, as the e-diff jockies back and forth, left to right, braking each wheel as it spins. You may say "so?", but with an actual limited slip diff there is no braking, spin happens, and even if it is jockeying left/right, the freakin' car isn't braking whilst you're trying to get out of that driveay. Instead it's shifting power, and wheels are still working at it. You get out. There are many conditions where slip is perfectly normal, and where braking to stop that slip is bonkers. Snow is another example. A great way to have your car spin out of control, is to suddenly auto-brake because it slipped the tiniest bit. Now, that tiny slip has become massive slip. The same holds for ice. ediff tech literally makes cars less safe, less driveable, less stable in snow and ice. This holds true to all current stability and traction control I have tested on gravel, on pavement in rain, on snow, and on ice. I grew up driving on frozen lakes, and can use braking methods to steer, I can drive on snow and then when I turn on traction control? And the result is the worst thing being done at the worst time. Stepping back, we see forums replete with people complaining about auto-drive madness. I've seen people unable to exit their driveway with reverse-impact protection on, because their driveway is angled down to the road, and it detects the road as an object (it isn't... as the car drives down it angles up, but the radar just sees "object"). People complain about their car wildly veering into some turnoffs because it thinks that's how the road goes. People complain about brakes slamming on, when it's a tight turn and there are guardrails, which the radar thinks is an object. The only true answer here is to disable ABS, thus preventing a large aspect of drive control. This is the only safe way to drive. And you make think "WHAT! ABS reduces braking distances!", yet this is misinformation, and absolutely not true. ABS extends braking distances. Its only goal is to allow one to steer while braking hard. That's it. And while in absolutely perfect, and absolutely optimal braking conditions (dry pavement, cool day, lots of grip) ABS is almost as good as a human at distance-to-stop, when it comes to literally every other circumstance ABS is horrid. Most directly, as an example, gravel or deep snow. With gravel you want to lock the brakes up (to a certain degree). With many types of gravel roads, this results in you literally "digging in". Gravel starts to build up in front of the wheel. Braking distances are immensely reduced as a result. Meanwhile, ABS prevents this condition, thus extending braking distances by 2x or even 3x. No, I'm not joking or exaggerating. With deep snow the issue is just as stark. If you're driving in 6" of snow, and you brake hard enough to "dig in", snow just builds up more and more in front of the wheel. And another "trick" to snow driving is to brake VERY HARD, turn the wheel, then release -- and even on ice you often shoot off in the current direction of the wheel. You cannot do either of these things with ABS. Most of the reason for all of this, is that we do not have AGI. Nor do we have AI that is "a good driver". Instead, we have a bunch of algorithmic if/then statements, which do not even remotely match the wildly varying conditions that a drive will reach outside of a lab. One of the worst situations I see with current autodrive, is that California, specifically SV, is one of the most temperate, perfect climates to drive in. Sunny almost all the time, with occasional rain. Developing AI systems, or even just simple driving algos / if+then statements in such conditions is as if driving in a lab. No snow. No ice. You can see the paint on the road (there is no visible paint on roads in the winter in northern climates). Often, in snow storms you cannot even see the road vs the shoulder in a way a car can discern. Yet here we have auto-drive tech being developed in Arizona, California, and sometimes Texas. And it's still wildly imperfect! Not even remotely ready for prime time, and it's only being deployed in absolutely perfect driving conditions! I expect it will be 50+ years before we have autodrive capability that will approach true human driving capability in, for example, a snow storm. Which leads back to using ABS for a diff? It's just auto manufacturers reducing safety to save a few bucks.
survirtual 2y ago
I took my Tesla model 3 places that made people's heads spin. The clearance is bad, and I had to replace the bottom coverings a few times (until I installed skid plates), and I scraped more times than I can count, but it always kept going. The only time I got stuck was on a sand dune. I had been through rivers, up rocky mountains, middle of deserts, icy cliffs, but sand managed to stop me. A huge lifted truck saw me and got me out with a tow strap around my front tire. No one would believe or understand the places I went with that car, but I know. Electric drive is just superior, end of story. I will be waiting for someone to make a rugged, utilitarian all-electric truck or jeep-like offroad vehicle. No touch screens, no extras. Just 4 independent motors with adjustable high-low clearance (4 independent hydraulic lifts would be sweet) and at least 500 miles of range -- or more. As much range as possible. This lets you use the battery for other purposes -- running power tools, running climate control all night, even cooking with electricity. My dream is a fully electric off/on road vehicle that can go anywhere, with a foldable 10kw+ solar array for silent charging, totally independent of traditional energy infrastructure.
- TreeInBuxton 2y ago
  I am keeping an eye on the Ineos Fusilier (https://ineosgrenadier.com/en/gb/news/introducing-the-ineos-fusilier https://ineosgrenadier.com/en/gb/news/introducing-the-ineos-...) for something along those lines - it will have both a full EV and a range-extended hybrid powertrain Maybe one day I will replace my Land Rover...
- dotancohen 2y ago
  > No one would believe or understand the places I went with that car, but I know. Electric drive is just superior, end of story. Yes, I've taken my Model 3 to some real stupid places. I've always been impressed. Electric drive has 100% torque at 0 RPM and instant throttle response - makes getting unstuck far too easy.
- arghwhat 2y ago
  I have also been overtaken by old front wheel drive microcars at river crossing. Plenty of lucky idiots out there - it’s all fun and games until it’s not. On and off-road capability are always at odds with each other, because “agile” also means “unstable”. It’s a matter of compromise and expectations.