Conserve Mode Front Wheel Drive, Why?

[lov2krz]

I don’t understand why my quad motor R1S uses front wheel drive in conserve mode instead of rear wheel drive.

As I’ve understood pushing the vehicle is easier on the drive train than pulling the vehicle, but that may only be applicable to ICE vehicles. Also oversteer is terrible in my R1S in conserve mode. If the road is wet oversteer worsens.

Since I have a quad motor vehicle why didn’t Rivian choose rear wheel drive over front wheel drive?

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[carsly]

Probably for the same reason they only run the dual motor in FWD most of the time. That's why I'd never want the dual motor, a 3.5 ton vehicle running FWD? If you thought you had excessive tire wear with the quad in Conserve wait until you see what happens with dual motors, and I don't know if it can be disabled.

At least Polestar changed the single motor to RWD from FWD.

 

[zefram47]

This has been asked and answered several times on the forum. The TL;DR is that weight transfers rearward under acceleration which means the front is lighter yielding less grip/traction. As such, Rivian opted to gear the front motors slightly taller than the rear since under heavy acceleration they were traction limited, not power limited. This means that the front motors will operate more efficiently at highway speeds than the rear.

 

[Electrified Outdoors]

This has been asked and answered several times on the forum. The TL;DR is that weight transfers rearward under acceleration which means the front is lighter yielding less grip/traction. As such, Rivian opted to gear the front motors slightly taller than the rear since under heavy acceleration they were traction limited, not power limited. This means that the front motors will operate more efficiently at highway speeds than the rear.

Excellent explanation. To put it simply it's a front biased drive setup. Both quad and dual operate this way. With the quad the rear motor disconnect is not designed for use under load, hence conserve mode. With dual the disconnect is designed for it so no conserve mode with dual motor. In fault motor rear motors disengage above 20 mph under normal driving conditions. They reengage when traction of acceleration requires.

Tesla uses rear drive but they do it differently. The rear drive units in model 3/Y are more powerful and more efficient then the front drive units. So jn those vehicle the front drive units are disengaged most of the time only coming online when traction or acceleration call for it.

 

[Mathme]

I've only used Conserve 2-3 times in 10k+ miles on my R1T with 20" ATs for a multitude of reasons:

First, there's stories of people who have broken pricy bits back there when the mechanical connection engages/disengages under load. I've even heard mine make loud clunks when I've used it.

Second, having the front tires do all the work is asking a lot of that rubber on a 7k+ lb vehicle. I once drove it on a 150 mile road trip and the thing drove and handles like a marshmallow on a hot griddle. No thanks.

Third, I've decided to ONLY use Conserve when I NEED the miles to get to the next charge stop as the mileage gain really isn't that much. My truck says a 100% charge in AP will get me 284 miles, and Conserve will get me 313 - or 29 miles out of a 100-0% charge. Realistically on road trips, I've drive 85-25% charge which reduces the overall mileage range by 35% - or AP range about 185 miles, conserve 203 miles. In my opinion, the wear and tear on the tires and car generally speaking isn't really worth the extra 18 miles range. These 185 miles on a road trip in AP is still about three hours of constant freeway driving...which is enough for me to want a stretch break

Again, this is just my experience with the Quad Large 20ATs.

 

[shumdit]

The other reason may be that regen on the rear wheels under slick conditions could be dangerous. I experienced this with my Tesla P85+ back in 2013 when it started snowing. Realized it and went right back to work and took a different vehicle home.

 

[R1Tom]

The other reason may be that regen on the rear wheels under slick conditions could be dangerous. I experienced this with my Tesla P85+ back in 2013 when it started snowing. Realized it and went right back to work and took a different vehicle home.

This is strongest reason I have figured too. Rear only with regen could be problematic.

 

[lov2krz]

Thanks for the rational. I admit I’m not into the weeds about this stuff so be gentle with your comments.

I thought having quad motors would give me AWD all the time. If I’m reading this thread correctly the rear motors disengage in AP mode when speed hits 20mph until additional traction is needed like during highway driving. If this is the case is the vehicle in conserve mode more often then not and front tire wear is a fact of life?

I’ve found that in AP I’m getting on average 1.8 miles/kWh and in conserve mode I’m getting about 2.64/miles/kWh. Is the cost of the electricity difference offset some by tire replacement, I pay $0.43/kWh to charge, live in the SF Bay Area under NEM 2 rates.

From talking with a Rivian service advisor yesterday he told me to get AWD all the time I need to be sport mode or off road. I haven’t been off road so in my case it’s moot.

 

[NDIrish]

I've only used Conserve 2-3 times in 10k+ miles on my R1T with 20" ATs for a multitude of reasons:

First, there's stories of people who have broken pricy bits back there when the mechanical connection engages/disengages under load. I've even heard mine make loud clunks when I've used it.

Second, having the front tires do all the work is asking a lot of that rubber on a 7k+ lb vehicle. I once drove it on a 150 mile road trip and the thing drove and handles like a marshmallow on a hot griddle. No thanks.

Third, I've decided to ONLY use Conserve when I NEED the miles to get to the next charge stop as the mileage gain really isn't that much. My truck says a 100% charge in AP will get me 284 miles, and Conserve will get me 313 - or 29 miles out of a 100-0% charge. Realistically on road trips, I've drive 85-25% charge which reduces the overall mileage range by 35% - or AP range about 185 miles, conserve 203 miles. In my opinion, the wear and tear on the tires and car generally speaking isn't really worth the extra 18 miles range. These 185 miles on a road trip in AP is still about three hours of constant freeway driving...which is enough for me to want a stretch break

Again, this is just my experience with the Quad Large 20ATs.

I haven't noticed any difference driving Conserve

I have been doing a ski trip (4x) now and there is a charger 80 miles from home before I start the climb up the mountain and a charger about 80 miles from there that is close to top/ski resort.

Conserve let's me skip the charger at bottom of mtn and reach the one at top with 18% remaining. If I drive in AllPurp math says I would have like 4% remaining... So I would need to charge before the climb

Since I have not noticed any driving feel and I can rotate tires if they wear faster in front, Conserve is a nice option for me on this specific trip.

Also I select Conserve in my garage and return to All Purpose after the trip, so shouldn't really have much effect on the disconnect.

 

[rockandrollray]

I don’t understand why my quad motor R1S uses front wheel drive in conserve mode instead of rear wheel drive.

As I’ve understood pushing the vehicle is easier on the drive train than pulling the vehicle, but that may only be applicable to ICE vehicles. Also oversteer is terrible in my R1S in conserve mode. If the road is wet oversteer worsens.

Since I have a quad motor vehicle why didn’t Rivian choose rear wheel drive over front wheel drive?

JUST FYI: From the Rivian Manual (regarding Wet Road Conserve Handling)
CONSERVE
Conserve mode optimizes the vehicle for maximum range on longer trips. This mode switches to front-wheel drive and lowers the ride height for a more aerodynamic position at higher speeds. Since Conserve mode is front-wheel drive, it's not recommended in rain, snow, or other conditions with reduced traction.

 

[FooF]

Thanks for the rational. I admit I’m not into the weeds about this stuff so be gentle with your comments.

I thought having quad motors would give me AWD all the time. If I’m reading this thread correctly the rear motors disengage in AP mode when speed hits 20mph until additional traction is needed like during highway driving. If this is the case is the vehicle in conserve mode more often then not and front tire wear is a fact of life?

I’ve found that in AP I’m getting on average 1.8 miles/kWh and in conserve mode I’m getting about 2.64/miles/kWh. Is the cost of the electricity difference offset some by tire replacement, I pay $0.43/kWh to charge, live in the SF Bay Area under NEM 2 rates.

From talking with a Rivian service advisor yesterday he told me to get AWD all the time I need to be sport mode or off road. I haven’t been off road so in my case it’s moot.

Quad motor - Conserve Mode is the only mode that is FWD. The rest of the modes are AWD.

 

[Count Orlok]

how many RWD only ICE vehicles are still produced compared to FWD or AWD?

 

[runwithscissors]

Power feels anemic in Conserve. It's a noticeable difference when switching back to AWD and I don't even drive fast.

 

[mkg3]

...Also oversteer is terrible in my R1S in conserve mode. If the road is wet oversteer worsens...

The term can be confusing. Oversteer is when the rear of the vehicle swings outwards. Understeer is when the front pushes and does not turn-in like its supposed to (often referred to as washing out).

I'm sure you mean understeer, given your description. The front of the car wants to keep going straight in the wet when you turn. Try backing off the throttle when you first notice this happening and the vehicle will turn-in as the power is reduced.

There is no way physically possible for any FWD vehicle to have an oversteer, under power. The only time it can is by starting a turn-in and lift throttle and brake heavily so that all the weight is transferred to the front as much as possible.

Also understeer is thought to be safer because the vehicle will not spin out (although if you cannot turn to stay on the road or avoid hitting something, that's just as dangerous).

AWD vehicles drives more like FWD vehicle than RWD vehicle, unless the power is biased to the rear drive wheels. In the case of R1S, I believe only the Sport and Rally modes biases the power to the rear drive unit. You can see it on the Gauge View.

 

[mkg3]

how many RWD only ICE vehicles are still produced compared to FWD or AWD?

Only the real sports car segment, I believe. Even those have AWD option.

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