Quad vs Dual - snow performance?

[Dark-Fx]

Personally I enjoy that my Rivian has no issues breaking all four of my snow tires free around corners when I want to. Wee!

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[endress14]

I spent a ton of time in the snow last winter in the Rockies. Mountain pass snow when freezing, wet snow, deep snow, snow on trails, city streets full of snow, etc. I had no issues whatsoever with traction or lateral movement with my QM on 20” AT. It has plenty of power to break them free when desired, but I never had an issue when I wanted to maintain traction

 

[kylealden]

So now that we're done with motors... can someone point me in the direction for the best/consensus take on tires/wheels... TIA

I've been very happy with the Bridgestone Blizzak LTs (275/65/R20), which fit on the 20s, are rated for the weight of the truck, and are available at most tire shops. They're a proper LT tire arguably better suited to the Rivian's size and weight than the OEM tires.

(Edit: And you can fit five of them in the bed for when you wander down to Discount Tire for your seasonal changeover ? Just be sure to take the metal rod and other tire change equipment out of the spare compartment before letting the staff at it, or they'll scratch the hell out of your spare rim.)

 

[R.I.P.]

FWIW I think the problems R.I.P. is calling out are most apparent in offroading or other situations where you're on a side slope - essentially the issue is that the quad motor is guessing at wheel traction until it actually applies torque to a given wheel; this can result in undesirable wheel spin and lateral slipping if you're on a low traction surface, which is potentially a big problem in a side slope, especially at low speed and starting from a stop.

Bingo. Out of Spec Kyle has documented this as well, as have others. Being that the OP lives in Tahoe, sloped slippery surfaces are the norm there... as they are here, which is why unless you _enjoy_ the sideways action the quad can give you in this scenario (some do, granted), the dual seems a no-brainer.

 

[endress14]

Bingo. Out of Spec Kyle has documented this as well, as have others. Being that the OP lives in Tahoe, sloped slippery surfaces are the norm there... as they are here, which is why unless you _enjoy_ the sideways action the quad can give you in this scenario (some do, granted), the dual seems a no-brainer.

IDK man, it's as slopey? here as it is in Tahoe and i haven't heard any complaints about sideways drifting in normal or even light off road driving conditions. If rock crawling in snow, sure the dual probably has an advantage, but for general purpose driving i'm sure it is a wash.

 

[edk]

I am very skeptical about claims that dual motors with locking differentials will always be better than quad motors. I do not believe that a tiny amount of slippage before a quad motor reduces torque will have an effect on overall stability. ABS systems reduce braking force only after detecting slippage and the effect on stability is neglible. I think that a good quad motor implementation should be able to accurately emulate a dual motor locked differential situation if it is advantageous. At other times, when not tracking a straight line on an even road surface, it will be more advantageous to vary the RPMs of the four wheels.

 

[WSea]

FWIW I think the problems R.I.P. is calling out are most apparent in offroading or other situations where you're on a side slope - essentially the issue is that the quad motor is guessing at wheel traction until it actually applies torque to a given wheel; this can result in undesirable wheel spin and lateral slipping if you're on a low traction surface, which is potentially a big problem in a side slope, especially at low speed and starting from a stop.

For most drivers and most circumstances this is an edge case, and I wouldn't lose sleep over it if you're otherwise committed to the quad motors. It's going to a non-issue on roads at any speed, where the computers can continuously evaluate traction to meter torque (just as they would to apply brake vectoring), and where some of the advantages of a quad motor can stretch their legs.

All that said - traction control with brake vectoring and a differential is a well understood problem space, and I'd be very confident with dual motors. While I'm skeptical that the disadvantages of quad will be a big deal for most drivers under most conditions (including light offroading), likewise the advantages of quad are for pretty narrow and niche cases (beyond "gotta go fast" and "$100k burning a hole in my pocket). The dual motor is lighter, cheaper, and gets better range.

I drive in snow a lot. If I was shopping today I'd buy a non-performance dual motor for the above reasons, and don't think I'd miss anything from my LE quad. (Except the 12V ports ?)

And the new gauge screen apparently

 

[Dark-Fx]

I am very skeptical about claims that dual motors with locking differentials will always be better than quad motors. I do not believe that a tiny amount of slippage before a quad motor reduces torque will have an effect on overall stability. ABS systems reduce braking force only after detecting slippage and the effect on stability is neglible. I think that a good quad motor implementation should be able to accurately emulate a dual motor locked differential situation if it is advantageous. At other times, when not tracking a straight line on an even road surface, it will be more advantageous to vary the RPMs of the four wheels.

The primary issue is on an off-camber surface. Once the vehicle starts sliding sideways, you don't have control over the slide. Dual motor being an open differential means you're much less likely to break all four wheels loose at the same time from overpowering the available traction.

Really a non-issue outside of this particular extreme circumstance IMO.

 

[kylealden]

And the new gauge screen apparently

There's a whole thread on this but I'm 99% sure that's a bug or short-term limitation. All the evidence points that way.

 

[WSea]

There's a whole thread on this but I'm 99% sure that's a bug or short-term limitation. All the evidence points that way.

I hope you are right. IMO all flavors of R1s should have it.

 

[R.I.P.]

IDK man, it's as slopey? here as it is in Tahoe and i haven't heard any complaints about sideways drifting in normal or even light off road driving conditions. If rock crawling in snow, sure the dual probably has an advantage, but for general purpose driving i'm sure it is a wash.

Ok... Kyle goes into this, and is probably better at explaining it, but I will present you with a scenario that both he and I have been in a number of times:

It is slick, ice, mud, what have you. You are on an off-camber surface in a heavy vehicle, with a cliff on the downhill side (describing my driveway BTW). In a vehicle like my F250, or the Enduro Rivian, when power is applied the tires with the most traction do not spin, the tires with the least traction do. This is critically important, because since the tires with the most traction do not spin, they maintain lateral traction, holding the vehicle from moving sideways while the other side tries to get you moving. Worst case is that you don't move, but at least you did not slide sideways over the edge or into the ditch.

With no differential and no way to physically vector torque, the quad motor tries to apply torque to both wheels in this scenario. The computer has no way of knowing the the mu under each wheel until it actually slips; and then it is too late, you are moving sideways toward the ditch/cliff.

It is simple physics.

The differential can overcome the traction problem using LS or locking, but the lack of a differential can never overcome the absence of the physical link between the wheels to actually vector torque and maintain the best lateral traction.

There are those that simply do not want to believe this super simple law of physics, early Kyle is an example. He learned, now he knows, I learned, now I know. For anybody out there that has not learned and would like to, bring your truck to my driveway this winter... I'll show ya.

 

[R.I.P.]

I am very skeptical about claims that dual motors with locking differentials will always be better than quad motors. I do not believe that a tiny amount of slippage before a quad motor reduces torque will have an effect on overall stability. ABS systems reduce braking force only after detecting slippage and the effect on stability is neglible. I think that a good quad motor implementation should be able to accurately emulate a dual motor locked differential situation if it is advantageous. At other times, when not tracking a straight line on an even road surface, it will be more advantageous to vary the RPMs of the four wheels.

The piece that you are missing is that with a differential, laws of physics dictates that slippage will always occur on the side with the least traction; making the vehicle inherently laterally stable (side with the most traction does not slip).

Once both wheels on the axle are slipping, the vehicle is inherently laterally unstable, and they are trying to correct that with software. Granted, it is a lot better than when we first started testing the quads, but the problem can never be completely eliminated... you know, physics & all.

 

[endress14]

Ok... Kyle goes into this, and is probably better at explaining it, but I will present you with a scenario that both he and I have been in a number of times:

It is slick, ice, mud, what have you. You are on an off-camber surface in a heavy vehicle, with a cliff on the downhill side (describing my driveway BTW). In a vehicle like my F250, or the Enduro Rivian, when power is applied the tires with the most traction do not spin, the tires with the least traction do. This is critically important, because since the tires with the most traction do not spin, they maintain lateral traction, holding the vehicle from moving sideways while the other side tries to get you moving. Worst case is that you don't move, but at least you did not slide sideways over the edge or into the ditch.

With no differential and no way to physically vector torque, the quad motor tries to apply torque to both wheels in this scenario. The computer has no way of knowing the the mu under each wheel until it actually slips; and then it is too late, you are moving sideways toward the ditch/cliff.

It is simple physics.

The differential can overcome the traction problem using LS or locking, but the lack of a differential can never overcome the absence of the physical link between the wheels to actually vector torque and maintain the best lateral traction.

There are those that simply do not want to believe this super simple law of physics, early Kyle is an example. He learned, now he knows, I learned, now I know. For anybody out there that has not learned and would like to, bring your truck to my driveway this winter... I'll show ya.

Dude, nobody is disagreeing about the situation you describe. We are saying that in normal driving in snow (which is what the OP asked about, not about off camber cliffside situations) there is likely no difference at all. You may encounter these situations regularly and the DM is a better buy for you, but that doesn't mean it will out perform the quad for a vast majority of other buyers.

 

[kylealden]

Once both wheels on the axle are slipping, the vehicle is inherently laterally unstable, and they are trying to correct that with software. Granted, it is a lot better than when we first started testing the quads, but the problem can never be completely eliminated... you know, physics & all.

Totally understand the case you're describing and I don't disagree with the intrinsic limitation. I'm just skeptical that it comes up that often.

As a principle I like to avoid situations where once a side slip starts, it will continue until I'm doomed. The exact same thing would happen if you had lockers engaged, or braked to a stop on a downward slope, etc. It's a somewhat unique failure mode in a very specific circumstance for quad motor, but also a situation that most people would simply be better off avoiding regardless of equipment.

I can't help you with your driveway, except to politely decline your invitation to come visit while it's icy ?

I'm still on team dual motor for the better day-to-day usability and my general skepticism that the quad motor brings meaningful real world advantages. I'm glad I got my quad motor because it got me an extra 18 months in a truck I love, and for $73k and <2% interest rates; but I'd trade across the board for comparably equipped dual motor without blinking. With a max pack? I'll be there in 5.

(The one place Quad should win decisively, rock crawling with wheels in the air, it loses because the motors fail at 0-RPM torque application under load, where again a differential and brake-driven torque vectoring wins, and lockers win even more. Better motors may fix this someday.)

 

[R.I.P.]

I am very skeptical about claims that dual motors with locking differentials will always be better than quad motors. I do not believe that a tiny amount of slippage before a quad motor reduces torque will have an effect on overall stability. ABS systems reduce braking force only after detecting slippage and the effect on stability is neglible. I think that a good quad motor implementation should be able to accurately emulate a dual motor locked differential situation if it is advantageous. At other times, when not tracking a straight line on an even road surface, it will be more advantageous to vary the RPMs of the four wheels.

The piece that you are missing is that with a differential, laws of physics dictates that slippage will always occur on the side with the least traction; making the vehicle inherently laterally stable (side with the most traction does not slip).

Once both wheels on the axle are slipping, the vehicle is inherently laterally unstable, and they are trying to correct that with software. Granted, it is a lot better than when we first started testing the quads, but the problem can never be completely eliminated... you know, physics & all.

Dude, nobody is disagreeing about the situation you describe. We are saying that in normal driving in snow (which is what the OP asked about, not about off camber cliffside situations) there is likely no difference at all. You may encounter these situations regularly and the DM is a better buy for you, but that doesn't mean it will out perform the quad for a vast majority of other buyers.

I completely agree that quad outperforms in a number of areas. Quad is faster, hands down. Quad wins when it comes to desert racing, when you are trying to get every last bit of forward motion out of each wheel. Quad wins on the fun meter when in rally mode for sure.

I am just trying to point out an area, which I would argue applies to the OP, where dual actually feels much more secure, and I would be far more comfortable letting my wife drive it on icy and snowy roads.
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