Gauge view and front motor bias

[R.I.P.]

This isn't possible. The computer can't know the point at which you lose traction without crossing it. There's no way to proactively go right up to the point of traction loss without crossing it. Car can sense traction loss and respond, it can't predict it.

What you don't want is to cause wheel slip every time people are stopping. On slick roads etc you'd be asking for people's rear ends to slip out all the time. Imagine the complaints if every rivian lost rear traction and fishtailed a bit every time you let off the gas on wet roads....

Ugg.

Yep.

This.

People have a gross misconception that the QM can sense traction. It cannot, and this is the cause of most of it's woes. It is good to see another voice of reason chiming in on this terribly misunderstood topic.

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[Arnie1]

Gauge view is very interesting. Has anyone else noticed a front motor bias on acceleration?

Clearly there is front motor bias on regen, which is fine, but I also see the rear motors used less on straight line acceleration. I have always felt this and now is I see apparently confirmed. I am always down for more RWD blend; is there any drive mode that will get me there? Is this merely a traction control or tire wear oddity? Would I get more RWD with more weight in the back?

Are you guaging the bias by the amount of blue fill in each wheel on the display image?
From Rivian site
Looks like the rear setup has slightly more hp but with torque vectoring the output to each wheel will vary depending on surface,steering angle etc..
Rivian Quad-Motor AWD delivers instant power and independently adjusts torque at all four wheels for precise wheel control in virtually all conditions. Proactively adjusting power at each individual wheel enables 4-wheel torque vectoring — the ability for each wheel to independently help accelerate, decelerate and even turn the vehicle — providing the highest levels of on-road performance and off-road capability.

This system is comprised of two drive units — one for the front axle, and another for the rear — with an independent motor for each wheel. Powering the front axle is a compact 415 hp unit with 413 lb-ft of torque. In the rear, a higher torque derivative delivers 420 hp and 495 lb-ft of torque. Together, they deliver 835 hp and 908 lb-ft of torque for a 0–60 mph time as quick as 3.0 seconds, while providing exceptional efficiency and instant adjustability for any condition.

 

[s4wrxttcs]

As others have mentioned, the front bias on regen is normal and expected - basically all cars are designed with brake bias toward the front. Whether or not this is related to the "tock" is probably a moot point, since changing brake bias rearward is unlikely to be a desirable fix for that issue.

It tocks on acceleration as well so it wouldn't fix the issue anyways.

There are people that have had their tock fixed, but Rivian is being stubborn about fixing mine.

I was simply surprised that ALL the regen was on the front wheels towards the end.

 

[NineElectrics]

This isn't possible. The computer can't know the point at which you lose traction without crossing it. There's no way to proactively go right up to the point of traction loss without crossing it. Car can sense traction loss and respond, it can't predict it.

Sure, but Rivian engineers already made predictions when they biased towards the front. Front wheels can slip, too, it’s just less likely. So my question is, is there room to safely apply more rear regen, at least when initially braking?

I would much prefer less of a bias towards front regen in snow mode, since I really, really don’t want the front wheels sliding. The recovery is difficult. Maybe they already do that.

 

[NineElectrics]

Looks like the rear setup has slightly more hp but with torque vectoring the output to each wheel will vary depending on surface,steering angle etc..

Just as an aside, I have never felt (or seen on gauge view) any signs of torque vectoring in my R1S quad when steering. If they do it, it must be subtle. I suspect this is more aspirational Rivian marketing.

At best, I think the car can sense the slip of each wheel, and back off on torque independently at each motor. I suppose you could call that “vectoring”, but to me that’s just “traction control without having to use the brakes.”

 

[jimmyb2]

This isn't possible. The computer can't know the point at which you lose traction without crossing it. There's no way to proactively go right up to the point of traction loss without crossing it. Car can sense traction loss and respond, it can't predict it.

What you don't want is to cause wheel slip every time people are stopping. On slick roads etc you'd be asking for people's rear ends to slip out all the time. Imagine the complaints if every rivian lost rear traction and fishtailed a bit every time you let off the gas on wet roads....

Oh ye of little faith! I am not talking about faith in God, but faith in human beings and progress.

Firstly, nowhere did I say it is possible with our current collective knowledge to control the wheels in the manner I suggested. What I actually said was that I would LIKE to see this done. If you would NOT like to see this done that’s fine. I am okay with that.

It was not that long ago that we didn’t have smart phones, ABS, reusable rockets, 3D printed rockets, vehicles able to parallel park themselves, EVs that could sometimes come to you when called via your phone, etc., etc.

So in the future one of the things I envision relative to EVs is just what I said I would like to see … the individual wheels able to be independently controlled such that they could each be used to their fullest, just short of losing traction, in all driving scenarios for braking, regeneration, and acceleration.

I believe that there are Rivian engineers actually working towards this end. Someday some engineer will have a completely new idea of how to sense and control the wheels. Just because you or I are unable to visualize how that might work does not mean it cannot be done. There exist many other things that you and I did not foresee.


Please don’t try to “read between the lines” of what I write. Please read my actual words, and I will thank you for that.

 

[racekarl]

So in the future one of the things I envision relative to EVs is just what I said I would like to see … the individual wheels able to be independently controlled such that they could each be used to their fullest, just short of losing traction, in all driving scenarios for braking, regeneration, and acceleration.

OK, but why? There already exists a very cheap and easy fix for the problem you seem to perceive, which is rotating your tires. What would be the justification for diverting potentially millions of dollars in R&D, software development, etc. to solve what is essentially a non-issue?

 

[jimmyb2]

I suppose you are free to think that, but unless you are an automotive engineer who worked on the Rivian I don't think you can state as a fact that it does cause additional front tire wear.

I am not an automotive engineer; however …

It seems plain to me that when you apply additional force/use to one tire that tire will wear more quickly than another with less use.

For example, my spare tire which has not been used clearly has less wear than any of the tires mounted on my R1S that have been used.

 

[racekarl]

I would much prefer less of a bias towards front regen in snow mode, since I really, really don’t want the front wheels sliding. The recovery is difficult. Maybe they already do that.

Disagree strongly. You would much rather have your front tires sliding than your rear tires sliding. Recovering from understeer (front tire sliding) is easy and intuitive: just slow down. As you decelerate, weight will transfer from the rear tires to the front, increasing their traction to the point where you can eventually recover grip. Recovering from oversteer (rear tire sliding) is much more complex and involves counter steering and sometimes counterintuitively NOT braking to shift weight to the rear tires.

 

[jimmyb2]

OK, but why? There already exists a very cheap and easy fix for the problem you seem to perceive, which is rotating your tires. What would be the justification for diverting potentially millions of dollars in R&D, software development, etc. to solve what is essentially a non-issue?

Why … it will result in the best overall performance. My concern is not about tire wear. That is kind of a side issue in my mind.

I am simply after the ultimate best vehicle performance. But each to their own.

 

[Nuclianba]

Oh ye of little faith! I am not talking about faith in God, but faith in human beings and progress.

If we're making up non existent tech then I want my flying car and hoverboard

 

[jimmyb2]

If we're making up non existent tech then I want my flying car and hoverboard

That’s fine. As I said earlier, each to their own.

 

[NineElectrics]

Disagree strongly. You would much rather have your front tires sliding than your rear tires sliding. Recovering from understeer (front tire sliding) is easy and intuitive: just slow down. As you decelerate, weight will transfer from the rear tires to the front, increasing their traction to the point where you can eventually recover grip. Recovering from oversteer (rear tire sliding) is much more complex and involves counter steering and sometimes counterintuitively NOT braking to shift weight to the rear tires.

Let me tell you my tale, and perhaps you can advise on how best to prevent it.

In 5° temps, in the middle of storm, I found my R1S sliding uncontrollably down a highway off ramp and though a stop sign. The ramp was probably -2.5° and covered in ice. This slide was triggered by regen. I tried the brakes, but they did nothing; the wheels were already stopped. I believe the appropriate response is to touch the throttle, but I find that non-intuitive, and I’m not sure that regen wouldn’t have triggered the slide again soon afterwards.

Better tires would have helped, but if snow mode regen used all four wheels, I don’t think I would have slid in the first place. That’s what I mean by less forward bias in snow mode: using all wheels to regen on ice. Change my view.

 

[R.I.P.]

Let me tell you my tale, and perhaps you can advise on how best to prevent it.

In 5° temps, in the middle of storm, I found my R1S sliding uncontrollably down a highway off ramp and though a stop sign. The ramp was probably -2.5° and covered in ice. This slide was triggered by regen. I tried the brakes, but they did nothing; the wheels were already stopped. I believe the appropriate response is to touch the throttle, but I find that non-intuitive, and I’m not sure that regen wouldn’t have triggered the slide again soon afterwards.

Better tires would have helped, but if snow mode regen used all four wheels, I don’t think I would have slid in the first place. That’s what I mean by less forward bias in snow mode: using all wheels to regen on ice. Change my view.

... Which is exactly why I sold my QM & bought the DM. Seriously, it is a world of difference when you put the lateral stability of a differential back into the vehicle.

 

[zefram47]

Just as an aside, I have never felt (or seen on gauge view) any signs of torque vectoring in my R1S quad when steering. If they do it, it must be subtle. I suspect this is more aspirational Rivian marketing.

It absolutely does torque vectoring. The fact that you haven't experienced it (at least noticeably) just means you're staying inside the traditional traction envelope...i.e., being a safe and responsible driver. On a fun canyon blast I can definitely feel the truck pulling out of corners in a way that it couldn't without the QM torque vectoring in action. I also recently had the opportunity to play on a skid pad. Short of going full-ham with the throttle the truck just wanted to stay on the radius circle I asked of it. To get it to really get out of sorts you needed to use Rally or Drift mode and give some liberal throttle. The folks watching were suitably impressed.

Better tires would have helped, but if snow mode regen used all four wheels, I don’t think I would have slid in the first place. That’s what I mean by less forward bias in snow mode: using all wheels to regen on ice. Change my view.

Better tires *are* the correct answer. If the goal is to prevent exceeding the amount of grip available, then you first need to know how much grip there is. The short version is that if all 4 wheels are turning at the same speed (or stopped), the truck can't know there is anything wrong. Essentially speed or torque differential between any of the wheels indicates that there's a change in grip (mu / friction) at one of the corners. Without some information to bias that estimate it can only assume the surface is uniform and all wheels stopped means you are in fact stopped. It's likely that the accelerometers might be able to tell you're sliding, but if you're not accelerating or decelerating in the slide that's debatable.

This is neglecting the fact that physics says most of the weight transfers to the front wheels under braking, so you get most of your braking from the front. If you add too much rear bias you will spin the vehicle. Anyone that has a racing simulator (computer or console) that can change brake bias will tell you this. Whether or not it's the physics explanation or the control-law explanation for why it's so heavily front-biased for regen none of us non-Rivian engineers could say.

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