Conserve Mode should only be selected while the vehicle is stopped? (says Rivian Service Center technicians)

[electruck]

Real question is why did Rivian engineering decide to decouple rear motors and not the front? I would have made exactly the opposite decision they made.

Per RJ in the video with Sandy Munro, rear motors got shorter gearing for performance, front got taller gearing for efficiency thus conserve mode disconnects the rears. Doesn't make sense to put the shorter gearing up front because weight transfers to the rear under hard accel thus the fronts don't have the traction to put down the extra power.

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[staytuned]

Per RJ in the video with Sandy Munro, rear motors got shorter gearing for performance, front got taller gearing for efficiency thus conserve mode disconnects the rears. Doesn't make sense to put the shorter gearing up front because weight transfers to the rear under hard accel thus the fronts don't have the traction to put down the extra power.

If we’re playing “how I would have done it”…
I’d have put disconnects on all 4 wheels, and have FWD/RWD/2WD Low like an old twin stick transfer case

and then everyone would curse the additional cost

 

[R1Tom]

Per RJ in the video with Sandy Munro, rear motors got shorter gearing for performance, front got taller gearing for efficiency thus conserve mode disconnects the rears. Doesn't make sense to put the shorter gearing up front because weight transfers to the rear under hard accel thus the fronts don't have the traction to put down the extra power.

That does make sense. I just don't like the compromise of front tire wear. Pulling around a 7000# vehicle with the front steered wheels, seems less than ideal. Granted I only disengage the rears on longer highway drives where I might actually see enough savings or range extension, to make a difference. But if it were rear drive, I might actually use it more.

Basically the way I use conserve, is get to and get on a highway, if that highway travel going to exceed about 30 minutes, and I only planning on light throttle cruising, turn on conserve, and then when on off ramp and down to maybe 35mph, turn it off. So basically all straight travel with speed maintenance throttle intended.

 

[R1Tom]

If we’re playing “how I would have done it”…
I’d have put disconnects on all 4 wheels, and have FWD/RWD/2WD Low like an old twin stick transfer case

and then everyone would curse the additional cost

Just imagine the torque with a low range. It would be mind blowing!

 

[Jack Smoke]

Real question is why did Rivian engineering decide to decouple rear motors and not the front? I would have made exactly the opposite decision they made.

It would be more fun with rear drive, but with aggressive regen, the weight shifts forward. Potentially cause the rear wheels to stop turning. As we learned from driving in snow at low speeds regen is strong enough to stop the wheels from rotating. Imagine going around a wet curve or Corning at low speed and have your rear drive lock up. In essence you’d have to low speed drift every wet curve. Fun, if you know what you’re doing. Scary f you don’t

 

[Mathme]

This sounds like a classic case of one mechanic hearing something somewhere that becomes folk lore.

If it is so bad to switch to/from conserve while moving, it'd say so in the Manual and they'd block it by software. Even my old 1997 Explorer back in the day was limited to switching between 2H and 4WD at 50MPH. Greater than 50MPH, and the light on the dash would just blink at you until you dropped below 50 and it switched.

I'm sure the Rivian in smarter than that 1997 model...

 

[PracticalRivian]

Ludicrous.

If you needed to stop to operate the RADs it'd be in the software...and nobody would use because it'd be inconvenient.

Rears decouple because fronts need to do your braking, regen would lock up the rear wheels.

I've switched from conserve straight to sport while wot (RAM was trying to pass on a ramp). Felt the connection clunk, moments delay, power rolled in smoothly. Did not get passed.

 

[OverZealous]

I can't believe nobody else has pointed this out, but the with the new snow mode update, the truck recommends that you switch out of conserve if it detects low temps and slippage. I can't imagine they'd ask you to pull over and switch while driving in unsafe conditions.

From the horse's mouth here:

The vehicle will automatically nudge you to switch to the new mode if you’re in Conserve and it detects wheel slip and an ambient outdoor temperature of 34 degrees Fahrenheit or lower.

 

[VHRivian]

I am not an engineer, but I can certainly see how the force created when the locking pins acuate and grab the piece connected to the rear drive shaft could create issues. I can see where it should be possible to engineer the part to withstand those forces, but that it also would be a wear point with repeated use while in motion.

It seems clear that this should not be creating any issues for people who make the change on the fly when Rivian has said nothing about restricting its use. Having said that, I'm not really surprised it may be a problem when I look at how that part works:

https://www.meansindustries.com/technology/clutch-systems/dcc

 

[HaveBlue]

There shouldn't be an issue reconnecting out of conserve at any throttle. The rear motors are switched off not providing tons of torque. It's not like an ice car.

 

[Mjl]

Yet another piece of anecdotal advice, but I mentioned this to the service tech in ATL and he mentioned it was fine doing it at speed. Just to be careful I've only done it entering a freeway.

 

[RivianBowerbird]

I know something about this due to my service history. What you don't want to do is switch out of conserve at low speeds (say <15mph). This creates a terrible grinding sound and sensation. At any normal road speed or stopped - it's perfectly smooth. I had the rear disconnects replaced and the truck still did it at said low speeds following the repairs. I noticed it due to switching to conserve to "kneel" the truck rather than using the always kneel option and then switching back out of it as I drove out of my development at low speeds. I took it in for a second replacement and the service techs indicated this time that it's just a quirk of how it operates and that low speed disconnects are very rough. They also stated that I should avoid doing specifically that - which I've done ever since. I think that the service techs who started this thread/said it shouldn't be done while moving really meant not to do it at very low speeds.

 

[OverZealous]

About the only thing I can think that makes sense is you wouldn't want to change in-or-out of it while accelerating or braking. It would be harder to accurately sync the motor and wheel speed at that time (assuming they do sync them).

Generally, I'd get up to speed in whatever mode I'm already in, then only switch into conserve once I'm already cruising, and leave it in that mode for the duration of the trip (including charging stops). But this seems like a no-brainer, anyway, since you shouldn't be messing around with the screen when you are doing something dangerous like merging.

 

[Yellow Buddy]

If we’re playing “how I would have done it”…
I’d have put disconnects on all 4 wheels, and have FWD/RWD/2WD Low like an old twin stick transfer case

and then everyone would curse the additional cost

Just imagine all those posts…”Car pulls to the right when I put it in one wheel drive”

 

[kylealden]

I wouldn't be so shocked. It makes a very unhappy bang if you do the change under hard acceleration. There is no way it could stand up to that abuse long term. I do find it hard to believe that the engineers wouldn't have thought of it, but could have been dismissed as "are people really going to be stupid enough to do that?" by someone in a management position without the same exposure to idiots that the engineers have. At a constant speed, it seems to engage just fine.

My 4WD Sonoma would make a similar grinding to a loud bang if 4WD was engaged during rear wheel spin.

Even this could be governed by software - just wait for the motor torque to ease up before actually disengaging the motors, even after user input.

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