Is rear-wheel drive mode possible in OTA update?

[onesoil]

I am wondering if it’s mechanically possible to have a rear-wheel drive mode. I would like to be able to choose a rear-wheel drive conserve mode, and possibly the choice of a rear wheel drift mode. Having the truck for only a month, I have only had it during dry conditions here in VT, where I really don’t need all-wheel drive modes a lot of the time, and find myself in conserve mode a lot when on normal roads under normal driving (especially when my 8-month pregnant partner is in the passenger seat, since any sudden acceleration/braking is currently very uncomfortable for her).

I just wish I could have a rear-wheel drive conserve option, since I have found myself spinning the front tires on driveways and other slightly steep uphill inclines with loose gravel/silty soil we get after heavy rains followed by dry weather if I forget to put it in other modes when I get to wherever I’m going. I’m really not even sure why they chose front wheel drive for conserve, but think it should be an option to choose front or rear drive when using two motors.

Does anyone know if this is possible? Is it a hardware disconnect, or just a software thing?

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[godfodder0901]

I am wondering if it’s mechanically possible to have a rear-wheel drive mode. I would like to be able to choose a rear-wheel drive conserve mode, and possibly the choice of a rear wheel drift mode. Having the truck for only a month, I have only had it during dry conditions here in VT, where I really don’t need all-wheel drive modes a lot of the time, and find myself in conserve mode a lot when on normal roads under normal driving (especially when my 8-month pregnant partner is in the passenger seat, since any sudden acceleration/braking is currently very uncomfortable for her).

I just wish I could have a rear-wheel drive conserve option, since I have found myself spinning the front tires on driveways and other slightly steep uphill inclines with loose gravel/silty soil we get after heavy rains followed by dry weather if I forget to put it in other modes when I get to wherever I’m going. I’m really not even sure why they chose front wheel drive for conserve, but think it should be an option to choose front or rear drive when using two motors.

Does anyone know if this is possible? Is it a hardware disconnect, or just a software thing?

The current implementation is hardware based. They could, theoretically, allow the front wheels to spin without adding drive power and only using the rear motors. That said, I think it's unlikely to happen.

 

[AxelR]

Whenever I get mine I would love RWD as well.

 

[onesoil]

The current implementation is hardware based. They could, theoretically, allow the front wheels to spin without adding drive power and only using the rear motors. That said, I think it's unlikely to happen.

That’s what I suspected, which seems like an unfortunate decision. Most people coming from trucks are used to RWD, and many EVs are as well. Why would they choose FWD only for the two-wheel drive mode? It seems like an odd decision.

Would there be any added friction/drag on the system or anything if they did allow you to just send power to the rear? I assume if there’s a mechanical disconnect, there’s a reason why it’s there. I think this is something they should be more clear about in their vehicle information/marketing, since the vehicle gets much better range in conserve mode, but having it be FWD only is a turn-off for some (myself anyways, but I’m sure I’m not alone). RWD just performs better many situations in my experience—better traction on loose/slippery uphill surfaces, safer in a lot of situations if you are an experienced driver, better for towing due to weight over rear axle—and honestly is just more fun a lot of the time. This seems like a missed opportunity to me, but I guess it is what it is.

 

[atebit]

I have found myself spinning the front tires on driveways and other slightly steep uphill inclines

I’ve had the same issue since Day 0 driving home from my delivery. Though my superpower is apparently being able to spin on dry & level pavement too in Conserve Mode.

 

[CommodoreAmiga]

I think people are over-using conserve mode. Leave it in all-purpose — that’s the point of that mode.

 

[ajdelange]

The rear wheels can be disconnected via mechanical clutches thus enabling conserve mode. The front wheels cannot so in that sense the answer is "no" but if you ever get into a situation where you need rwd the control system will implement rwd for as long as it is needed and then revert to 4wd as soon as that becomes the better mode. This is 'torque vectoring" at which the Rivian, with its 4 motors, is very good. It does not send torque to wheels that slip. Torque always goes to wheels that can accept it.

 

[Dark-Fx]

I think people are over-using conserve mode. Leave it in all-purpose — that’s the point of that mode.

You're probably right. My front tires are wearing out much quicker. Any energy cost savings are likely lost to accelerated tire wear.

 

[ajdelange]

My front tires are wearing out much quicker. Any energy cost savings are likely lost to accelerated tire wear.

That (wear) is the main complaint. As for energy savings I am frankly still in disbelief as to what the trip OD is telling me about the general-purpose mode and am quite happy about that. Plus i paid a lot of bucks for two motors that are never used? Nosir.

 

[atebit]

I think people are over-using conserve mode. Leave it in all-purpose — that’s the point of that mode.

Perhaps. But in the world of Agile development, a mode that’s rarely used is rarely tested, which could be why all we have are anecdotal reports. Even little-used modes oughta work without detrimental side effects. Or at least document that “frequent use of Conserve Mode may lead to excessive front tire wear”.

 

[onesoil]

The rear wheels can be disconnected via mechanical clutches thus enabling conserve mode. The front wheels cannot so in that sense the answer is "no" but if you ever get into a situation where you need rwd the control system will implement rwd for as long as it is needed and then revert to 4wd as soon as that becomes the better mode. This is 'torque vectoring" at which the Rivian, with its 4 motors, is very good. It does not send torque to wheels that slip. Torque always goes to wheels that can accept it.

Has anyone seen if Rivian gives a reason for selecting FWD instead of RWD for that clutch disconnect? It just seems like an odd choice to me… RWD provides better traction under acceleration and going up hills than FWD (hence why they give more torque to the rear motors in all the AWD modes), so it just seems counter intuitive to then only use the front motors for the only 2WD mode. The reduced traction potential also probably contributes to more wear than it would if it were RWD (assuming no hooning around in conserve mode, which I couldn’t promise not doing if it were RWD).

I would think most of their customer base is familiar enough with RWD cars (either coming from trucks, sport s cars, other RWD EVs, or all of the above) that any “safety” argument wouldn’t carry much weight. I mean the thing has a drift mode… so at least some of the engineers understand the need/want for intentional oversteer and opposite lock when the going gets rough (or just for fun when it’s snowy, muddy, etc). Maybe they didn’t want a bunch of burnout videos upon release of the truck forbad PR reasons?

I guess I’ll limit my use of it to the Highway.

 

[domoplaytime]

It's a shame Rivian doesn't offer coast mode (no regen breaking) at least when using Conserve. The front tires are certainly going to wear faster if the back don't get to participate in slowing the vehicle down. That said, I won't be using coast or Conserve much, lest I regret my choice of 20" ATs.

 

[onesoil]

It's a shame Rivian doesn't offer coast mode (no regen breaking) at least when using Conserve. The front tires are certainly going to wear faster if the back don't get to participate in slowing the vehicle down. That said, I won't be using coast or Conserve much, lest I regret my choice of 20" ATs.

Thats a good point. I have noticed the reduced regen in conserve, and it finally occurred to me weeks in why (kind of a “well duh!” moment). It just occurred to me that this is likely why they went with FWD! RWD regen alone probably wouldn’t provide ample stopping power without blended in front friction brakes.

I think they should at least use some rear brake when one pedal braking in conserve mode (if they don’t already, but it doesn’t feel like they do) to balance the braking load across the four tires. Also not safe if you hit anything slippery while in conserve and regen braking.

On a different note, I wish you could enable a “coast mode under x mph” for parking. I find parallel parking with one pedal much less smooth/quick. I’m sure I’ll get used to it, but it’s the one time I really miss being able to coast and/or feather a clutch.

 

[onesoil]

The rear wheels can be disconnected via mechanical clutches thus enabling conserve mode. The front wheels cannot so in that sense the answer is "no" but if you ever get into a situation where you need rwd the control system will implement rwd for as long as it is needed and then revert to 4wd as soon as that becomes the better mode. This is 'torque vectoring" at which the Rivian, with its 4 motors, is very good. It does not send torque to wheels that slip. Torque always goes to wheels that can accept it.

So I suppose drift mode intentionally keeps sending torque to slipping rear wheels to allow oversteer angle manipulation with throttle input? I’m excited to try drift mode on snow and mud. In VT we have a 5th season we call “mud season,” and this year was as bad as it has gotten in decades. This year many people were stranded from their homes due to the insanely deep frost heaves and ruts, but it’s quite fun if you have the right vehicle for it… I would play the game of “how far can I make it in RWD” with my Tacoma with many tail out moments along the way.

https://vtdigger.org/2022/03/23/its...h-mud-season-unlike-any-in-recent-memory/amp/

 

[electruck]

Has anyone seen if Rivian gives a reason for selecting FWD instead of RWD for that clutch disconnect? It just seems like an odd choice to me… RWD provides better traction under acceleration and going up hills than FWD (hence why they give more torque to the rear motors in all the AWD modes), so it just seems counter intuitive to then only use the front motors for the only 2WD mode. The reduced traction potential also probably contributes to more wear than it would if it were RWD (assuming no hooning around in conserve mode, which I couldn’t promise not doing if it were RWD).
...
I guess I’ll limit my use of it to the Highway.

Brace yourself here, Conserve mode is for... conservation. It was intended as a way to extract an extra bit of range in a pinch, not as a normal driving mode. Traction when accelerating is not much of an issue under slow acceleration when one is driving conservatively. Compromised traction on inclined gravel driveways is an acceptable compromise when trying to squeeze as much range as possible out of the remaining battery to ensure you reach the next charging stop. The R1 is first and foremost an AWD vehicle. Conserve mode is offered as a compromise when the extra range it offers makes a difference between reaching your next charging destination or being stuck on the side of the road. As CommodoreAmiga has noted, people seem to be using Conserve mode as a primary driving mode which I don't believe is what Rivian had in mind.

As has been stated, the axle disconnects are at the rear. Why the rear instead of the front? That goes back to the tradeoffs made between normal driving and range extender mode (perhaps Rivian should have called it Range Extender mode instead of Conserve mode). Rivian has used different gear ratios front and rear, with the rear getting shorter ratios and the front taller. For normal and spirited driving, they wanted the extra torque on the rear axle for the very reasons you have stated. In order for Conserve mode to offer maximum range, that forced the use of the front wheels as the drive wheels because that's where it makes the most sense to have the taller gearing. Hopefully this clears up why Conserve mode is FWD and not RWD.

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