R1T vs. R1S in snow?

[Dark-Fx]

In an effort to make sure the reader does not get the wrong impression here (as 25% sure sounds less than 50%):

Ignoring the fact for a moment that the QM total output is greater than the total output of DM, and just focusing on the percent of power available at each wheel, it is directionally true that the QM can only put down ~25% of the power there. Technically, the motors in front/rear are not identical so it's not exactly 25%, but either way the maximum is equal to what a given motor can give out, which is about 25% of the total.

Now in case of the DM, making similar simplifying assumptions about motors being roughly equal between front/rear, each motor represents ~50% of the available power. However, with an open differential, a brake based differential aid can at most transfer 50% of torque to a wheel, so this would be 50% of the 50%, which gets us right back to 25% of total torque available to single wheel.

So in the end both the QM and DM can each get about 25% of the total available torque to a single wheel.

The observations that a triple locked vehicle can in fact get 100% of the available torque to a single wheel is true.

Isn't it interesting how facts blah blah blah.

I think a lot of the reason specific off-roaders prefer the dual motor is because it drives closer to what they are used to.

My experience with the quad is that it's fully possible to be in the wrong mode for what you are doing. As an example, Rock crawl isn't great for climbing if you don't have good traction, like a steep dirt trail.

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[moosehead]

OP, put a proper set of aggressive snow tires on whichever Rivian you prefer driving through the snow. They will be more effective in snow that the OEM Pirelli Scorpion 20" despite their triple peak ratings.

 

[R.I.P.]

RIP - I wanted to thank you for the information shared in these posts. Very helpful. I'm in Colorado, drive to the mountains regularly, and waiting to lock in. I've been waffling about QM v DM. This is great information. Appreciate it. ?

I'm glad someone could learn from my pain.
??

 

[kylealden]

Yeah, I think there's a lot of hair pulling here over a pretty simple answer:

Just buy the vehicle you want (size/features/price/range) and, most importantly, put serious snow tires on it if you plan to drive it in serious winter conditions. No, the 20s are not serious snow tires. They'll do, but if you're worried about snow, the best decision you can make out of anything in this thread is to buy snow tires. Blizzak LTs are great.

Don't sweat R1T vs. R1S, the differences are likely to be quite small.

Don't sweat QM vs. DM unless you are specifically sensitive to the lateral stability issues raised here.†

† R.I.P. is absolutely right here in the details, but I think it's also reasonable to argue that for most drivers it's likely a niche consideration relative to other factors like price, raw performance, range/efficiency, etc. If you do a lot of wheeling/crawling, or drive on icy off-camber roads, it's something to consider. (If it were me I'd buy a DM for price and efficiency, but the differential performance is a nice perk.)

 

[Technowizzard]

Sure. There are whole threads about it, but a differential offers inherent lateral vehicle stability because of the way it anchors the wheel with the most traction. To do this requires a physical connection between the wheels (the differential), so when the QM removed this, it also removed the inherent lateral stability of the vehicle. To be clear, this is not a Rivian issue, my Hummer EV had the exact same issue (in the rear) in snow, ice, and slippery stuff. The cyber truck (TriMotor) will suffer from the same problem.

Rivian has done much too minimize the problem with snow mode and good tires really help. But at the end of the day, the DM is just going to be much more laterally stable in really slick stuff.

You are all overthinking the issue. The QM uses cross vector technology that solves the “lateral vehicle stability” issue. Above all, don‘t use chains on a QM Rivian vehicle.

 

[Phatman113]

You are all overthinking the issue. The QM uses cross vector technology that solves the “lateral vehicle stability” issue. Above all, don‘t use chains on a QM Rivian vehicle.

Aside from Rivian saying that chains aren't supported, what is your reasoning for the statement about chains?

 

[BCondrey]

So, if the DM is better in the snow why is there no snow-mode on the DM platform? Because we don't need it?

 

[R.I.P.]

So, if the DM is better in the snow why is there no snow-mode on the DM platform? Because we don't need it?

DM does have snow mode. But the DM also handles quite well in the snow/ice in All Purpose and AT mode. The "modes" don't make all that much difference in an Enduro unit, because the more traditional drivetrain is inherently quite stable, and does not need all the special modes to tell the motors how to act. All the motors have to do is provide torque to a traditional differential with traction control; much like any other truck.

More boring for sure, but stable & predictable.

 

[R.I.P.]

Aside from Rivian saying that chains aren't supported, what is your reasoning for the statement about chains?

I know you did not ask me the question, but I can answer it.

The QM depends on sensing micro-slips to try to maintain it's footing on slippery surfaces. Traction devices like chains and cables seem to trigger the algorithm into thinking it is slipping when it is not. The vehicle keeps trying to adjust to a non-existent condition and performs poorly. It feels a bit like it is trying to cross boulders when on a flat road.

I have not tried chains on the DM yet, I will do so.

 

[HaveBlue]

The Rivian has some amazing tech and features but it has some flaws for serious off-roading. The DM vs QM has been beat to death but the article specifically pointed out the issues accurately on that topic.

I'll pick something different to pick on. IFS/IRS is not as good as a straight axle for traction. The reason is because in a crossed up situation, the IFS/IRS drooping wheel progressively looses traction because as it becomes unweighted. The remaining wheel carries all the weight of the vehicle. In a straight axle, weight is transferred to the drooping wheel from the other one by a cantilever effect pushing the drooping wheel into the ground even more than just the spring will do. This multiplication is why unlocked SA trucks do so well. You'll only know that if you've done decades of 4wheeling in both. Ground clearance varies in geometric ways for both but in general IFS is better but often limited for overall travel. IFS wins hands down for unsprung weight, control and ride. SA generally wins for strength unless you are talking about Dana 25s or Landrovers.

Coil springs ride better than leaf springs because there's less friction between the components. Air springs ride better than Coil springs because of the progressive and adjustable nature. However complexity and cost go up as well.

There are a lot of non obvious compromises that occur in the design of any vehicle. I doubt there is a vehicle that performs so well in both on and off road situations. Maybe a new IFS/IRS LandRover but it unlikely handles, accelerates and gets 75mpge.

 

[Nine_One_Six_R1S]

My experience with the quad is that it's fully possible to be in the wrong mode for what you are doing. As an example, Rock crawl isn't great for climbing if you don't have good traction, like a steep dirt trail.

What would be the best Mode for Climbing without good traction? like a steep uphill with loose sand/dirt/rocks.

I've been stalled in such scenario but did not try other modes before getting out of trouble.

Would Changing Traction Control to Reduced or Off help in these cases?

 

[Dark-Fx]

What would be the best Mode for Climbing without good traction? like a steep uphill with loose sand/dirt/rocks.

I've been stalled in such scenario but did not try other modes before getting out of trouble.

Would Changing Traction Control to Reduced or Off help in these cases?

I've had better luck in all terrain for those conditions. Blipping the throttle to get movement started seems more effective than slowly ramping it up. My assumption is Rivian starts dialing back the power request during stall to protect the inverters and that you need to avoid being in stall. My experience is still pretty limited here though.

 

[R1Thor]

I think there are a few people in here getting it.

I don't want to start a debate...again.

But bottom line is that this RIP guy doesn't have all of the facts, despite the fact that he thinks he does, and then insists so, annoyingly, and incessantly.

I caught him at one point on the simple fact that DM has an open differential. I am not here to provide physics lessons, but even WITH a PROPER differential, the MAXIMUM power you can provide to one tire in the drivetrain is 59% (differentials have VERY specific limits due to the physics on how they operate, and different TYPES of differentials will behave differently--be it viscous coupling, quaife, dccd, torsen, haldex, etc).

So, now you have a (performance) DM at 665 HP. (the math absolutely doesn't break down 1:1 per motor, but for the sake of this analysis, we're using it). The MAX you'd get, with an appropriate (not open) differential is 196 to the wheel slipping (665/2 * 0.59). That doesn't account for whatever the other wheel is doing (is it connected to anything? Is it spinning BACKWARDS--because it'll do that; but maybe with torque vectoring, I'll give you a pass and assume the brake clamped down on that corner).

Compare that to the 835/4 = 208.75 hp the quad would have per corner.

So, on the basis alone of "you will get more power to the slipping wheels." False.

The literal only way this 'debate' can be settled is apples to apples. Get different configurations of the same trucks and put them through the same course with the same (professional) driver.

That being said, I have conceded that, depending on how the QM is programmed from a software standpoint, it can absolutely be worse. But it can also absolutely be MUCH better when you can control each wheel discretely and make 100 micro-adjustments per second and control exactly what each wheel is putting to the ground. The best differentials in the world are analog and have zero real-world correction factors. Luckily for us, and the way we've had to develop these to overcome the 'downfalls' of having a single-powerplant ICE vehicle development strategy for the past 100 years, the gearing advantages in differentials tends to allow the distribution of power to where you still have traction. But again, it's limited power, and it's discrete, not intelligent. Even in DCCD cars, that control the differentials electronically, we see power-delivery and slippage limitations.

Source: mechanics and physics.

Here, have fun:

 

[Dark-Fx]

I caught him at one point on the simple fact that DM has an open differential.

He claims to have knowledge of an aftermarket locking differential that's coming soon. Hasn't really elaborated at all but I suppose I can't blame him. Probably a significant amount of testing still needed on that kind of a system before you start marketing it.

 

[R1Thor]

He claims to have knowledge of an aftermarket locking differential that's coming soon. Hasn't really elaborated at all but I suppose I can't blame him. Probably a significant amount of testing still needed on that kind of a system before you start marketing it.

That's cool and all, but same limitations.

I have ZERO issues conceding anyone has a solid case for anything WHEN THEY SHOW UP WITH PROOF.

You know what the lowest level of scientific proof is? "I saw it" or "I have this anecdote."

You need repeatable, actual data.

And the data on paper, I'll stake my Engineering credibility on, is that there is no universe wherein having 4, discrete, deliberate power plants will be superseded by having less and use a mechanism to account for their limitations. That's EXACTLY what a differential is. A SOLUTION to a PROBLEM caused by the SYSTEM. It's a PHENOMENAL solution to a single motor system. It's a phenomenal solution in a dual-motor system. It's a phenomenal solution in a tri-motor system. But having each. individual. wheel. independently. controlled. would be a phenomenal solution to all of the above, *if executed properly.*

Which, in fairness, I'll unabashedly admit that I have zero insider information on the QM and its performance capabilities, but I would continue to posit that if *it is insufficiently capable* compared to the DM, it's a programming issue. OR maybe there's even another piece of data we don't have (like maybe there's a power draw limitation somewhere). But when we're all speaking in theoreticals, you're not convincing me, on paper, of the contrary.

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