Is rear-wheel drive mode possible in OTA update?

[Engi_Nerd]

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.

Pretty sure it's just because you get more regen potential with front wheel drive.

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[electruck]

Or at least document that “frequent use of Conserve Mode may lead to excessive front tire wear”.

You mean the way RWD vehicles document that the rear tires will wear faster than the fronts? Don't believe I've ever seen that in an owner's manual. It is pretty much common knowledge that driven wheels will experience faster tire wear than non-driven wheels. It should thus be obvious that if the front wheels are selected as the primary drive wheels that those tires will wear faster.

 

[onesoil]

You mean the way RWD vehicles document that the rear tires will wear faster than the fronts? Don't believe I've ever seen that in an owner's manual. It is pretty much common knowledge that driven wheels will experience faster tire wear than non-driven wheels. It should thus be obvious that if the front wheels are selected as the primary drive wheels that those tires will wear faster.

I agree that mentioning increased tire wear to the front isn’t necessary, however I do think that it should pop up a message that you are entering a FWD mode when you enter conserve mode. When my dad took delivery of the R1T I’m now driving, he put it in conserve to see what the estimated range max was, left it in conserve while on a drive somewhere, and then proceeded to get “stuck” on a steep, wet, grassy section of his property leading onto a dirt road after he got back from his longer drive. He didn’t know he was in a 2wd mode until he called me to ask if I knew why the truck was spinning fronts tires and seemingly not driving the rears. He had no problem getting sufficient traction once he was back in All-Purpose mode.

I didn’t know Conserve mode was 2WD until I googled it while on the phone with him that first day we had the truck. He’s not an idiot, he’s just used to either AWD or 2H/4H/4L transfer cases, and was on a very slippery surface expecting the truck would have no problem getting from the grass to dirt. The truck should probably be programmed to engage the rear motors (or “shift” into All-Purpose drive mode) when it detects wheel spin in Conserve. At a minimum, it should at least be made clear to the driver that it is in a 2WD mode.

Side not for clarification: my dad decided he preferred his Model S due to the higher seat position in the Rivian exacerbating some sciatic nerve pain he has been experiencing lately when claiming in and out… looks like I’ll probably be buying it off of him, so lucky me

 

[atebit]

You mean the way RWD vehicles document that the rear tires will wear faster than the fronts? Don't believe I've ever seen that in an owner's manual. It is pretty much common knowledge that driven wheels will experience faster tire wear than non-driven wheels. It should thus be obvious that if the front wheels are selected as the primary drive wheels that those tires will wear faster.

Sure, it’s normal for FWD vehicles to wear out the fronts faster which can be mitigated a bit by tire rotation (and luckily all our tires are the same size). But if the mode by design is going to cause abnormally high wear due to wheel slippage (say because of weight distribution or other suspension-specific reasons) on top of normal FWD wear, then yes I think it should be noted. Actually I’d rather just have Rivian adjust CM to try & better avoid the slippage in the first place I’d possible.

 

[cbuckley]

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

The Rivian guy that delivered my vehicle and spent a couple of hours showing me the ropes emphasized this to some extent. He said that using conserve mode was fine for the instances you really need as much range as possible but he strongly discouraged selecting it outside of that use case. Besides the dumbed-down performance making it not as fun to drive, he cited the tire issues.

 

[electruck]

Sure, it’s normal for FWD vehicles to wear out the fronts faster which can be mitigated a bit by tire rotation (and luckily all our tires are the same size). But if the mode by design is going to cause abnormally high wear due to wheel slippage (say because of weight distribution or other suspension-specific reasons) on top of normal FWD wear, then yes I think it should be noted. Actually I’d rather just have Rivian adjust CM to try & better avoid the slippage in the first place I’d possible.

Outside of any potential alignment issues which would be vehicle specific, there is no tire wear associated with Conserve mode that isn't attributable to FWD, especially not for a 400+ hp FWD.

edit: frankly, I think more than a few people will be in for a surprise at how quickly all 4 tires wear on a 7000+ lb, 800+ hp vehicle (even when driven in All Purpose mode).

 

[onesoil]

Outside of any potential alignment issues which would be vehicle specific, there is no tire wear associated with Conserve mode that isn't attributable to FWD, especially not for a 400+ hp FWD.

edit: frankly, I think more than a few people will be in for a surprise at how quickly all 4 tires wear on a 7000+ lb, 800+ hp vehicle (even when driven in All Purpose mode).

Compared to an ICE FWD vehicle I would think there could be accelerated wear due to only two tires handling regen braking (unless rear friction brakes are blended in as well, which I haven’t confirmed), but I assume that would be the case with RWD EVs in reverse.

Then again, I’m not aware of any 7k+ lb, 800+ hp FWD ICE vehicles, so this is sort of a moot point. Tire wear characteristics have everything to do with weight/power/tire compound, and this ticks 2-3 of those boxes for fast wear. My Audi S4 munches on my Michelin Pilot Sport 4S tires at an alarming rate. I justify it by the smiles that car has brought me

I’m honestly a bit surprised that it comes up as a topic for a $75-90k+ vehicle...

 

[Craigins]

Tire wear characteristics have everything to do with weight/power/tire compound,

And driving habbits.

If you're spinning the tires in conserve mode on dry surfaces, let up on the pedal. Sounds like a lot of people with lead feet.

 

[electruck]

Compared to an ICE FWD vehicle I would think there could be accelerated wear due to only two tires handling regen braking (unless rear friction brakes are blended in as well, which I haven’t confirmed), but I assume that would be the case with RWD EVs in reverse.

Then again, I’m not aware of any 7k+ lb, 800+ hp FWD ICE vehicles, so this is sort of a moot point. Tire wear characteristics have everything to do with weight/power/tire compound, and this ticks 2-3 of those boxes for fast wear. My Audi S4 munches on my Michelin Pilot Sport 4S tires at an alarming rate. I justify it by the smiles that car has brought me

I’m honestly a bit surprised that it comes up as a topic for a $75-90k+ vehicle...

About 80% of the braking load on a FWD ICE vehicle is handled by the front tires so not as much difference there as you might expect.

 

[lostpacket]

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/

heck yeah I'm so looking forward to driving through that next spring haha

 

[momo3605]

Pretty sure it's just because you get more regen potential with front wheel drive.

I don’t think this is true. All of teslas 2WD models are RWD and have strong regen to the point of enabling one-pedal driving.

 

[Engi_Nerd]

I don’t think this is true. All of teslas 2WD models are RWD and have strong regen to the point of enabling one-pedal driving.

I never said it was impossible to make a RWD EV, but physics dictates that most of your braking is done by the front wheels due to weight transfer. Likely more of an issue with an 8000 lb truck than a small sedan.

 

[mkg3]

I never said it was impossible to make a RWD EV, but physics dictates that most of your braking is done by the front wheels due to weight transfer. Likely more of an issue with an 8000 lb truck than a small sedan.

In a traditional non-active suspension vehicle this statement is true. In a active suspension vehicle, dynamics are such that it can minimize the weight transfer to the front wheels. I believe Rivian does manage the weight transfer to make sure that all 4 tires and brakes are working optimal to stop 8K lbs vehicle in a shortest distance (for R1).

I understand the OP's desire for RWD but I would recommend learning how to drift with AWD is also worth practicing. The vehicle uses torque vectoring at each wheel such that there is a bias towards the rear wheels.

Last, in conserve mode where its FWD (same with Tycan), the underlying assumption is you are cruising and not maneuvering significant amount. In this state, there really is no difference - except tracking is more efficient than pushing; hence, FWD - which wheel is moving the car. In terms of braking, again weight transfer is managed and all 4 wheels are used to regen as well as mechanical braking.

I like RWD vehicles. Both AWD and FWD vehicles have to be driven using different lines through the corners. While AWD vehicles are technically faster/quicker than RWD, I prefer driving it.

 

[onesoil]

In a traditional non-active suspension vehicle this statement is true. In a active suspension vehicle, dynamics are such that it can minimize the weight transfer to the front wheels. I believe Rivian does manage the weight transfer to make sure that all 4 tires and brakes are working optimal to stop 8K lbs vehicle in a shortest distance (for R1).

I understand the OP's desire for RWD but I would recommend learning how to drift with AWD is also worth practicing. The vehicle uses torque vectoring at each wheel such that there is a bias towards the rear wheels.

Last, in conserve mode where its FWD (same with Tycan), the underlying assumption is you are cruising and not maneuvering significant amount. In this state, there really is no difference - except tracking is more efficient than pushing; hence, FWD - which wheel is moving the car. In terms of braking, again weight transfer is managed and all 4 wheels are used to regen as well as mechanical braking.

I like RWD vehicles. Both AWD and FWD vehicles have to be driven using different lines through the corners. While AWD vehicles are technically faster/quicker than RWD, I prefer driving it.

These are all salient points.

I actually have more experience drifting AWD cars than RWD—starting with 2001 Audi A4 2.8 Quattro in high school, then a Subaru Legacy 2.5GT, and now 2001 Audi S4—all with manual transmissions, which gives the ability to use clutch and e-brake in conjunction to trigger oversteer, rather than strictly power oversteer. These cars were mostly only capable of breaking traction on either snow/ice, mud, or loose dirt. My experience with RWD is limited to midsize trucks (2011 Nissan Frontier and then most recently, a Tacoma). Each have their own dynamics, and I'm sure I will get used to this one. I suppose my desire for a RWD mode was somewhat misguided (using sufficient power to break traction is inherently inefficient, so it wouldn't make all that much sense for conserve mode to be designed with this capability in mind, as much fun as it might be at times).

I haven’t played around much with drift mode since it’s been a very dry and dusty summer, and I try to be respectful of the back roads from a dust raising/gravel throwing perspective. When I have had a chance to drift around one of our compost sites, it was very fun, but this truck grips enough that unless you have a lot of open road/space, it’s hard to get much oversteer angle at any reasonable/legal/safe speeds. One benefit to RWD is having the ability to be in a controlled slide at lower speeds with more extreme vehicle angles. This is certainly not the fast way to go around corners, but it can be the fun way!

I’m sure it will be awesome on lower traction surfaces in the winter/mud season and I’m very excited to let it loose next winter/spring.

On a different note, perhaps they should allow us to set a speed floor below which conserve mode switches to one of the AWD modes. I could imagine two potentially useful scenarios/implementations:

• Being able to set Conserve to automatically activate over 55mph when on a long trip since most of the efficiency gains you are talking about probably happen at highway speeds, while having All-Purpose automatically return for back/side roads, on ramps, etc.
• Setting conserve mode to deactivate under 10mph to help with traction on loose surfaces like gravel driveways, dusty/loose gravely dirt roads, etc.

To your last point: are you saying that even in conserve, regen is achieved with all four motors? So every time you let off the accelerator in CM, the mechanical disconnect is reconnected to achieve full regen? That seems unlikely. I have also noticed less regen feel when in conserve descending steep hills, which led me to believe it was only using two motors.

 

[onesoil]

I never said it was impossible to make a RWD EV, but physics dictates that most of your braking is done by the front wheels due to weight transfer. Likely more of an issue with an 8000 lb truck than a small sedan.

This being the case, do RWD EVs (Tesla single motor cars come to mind) combine rear motor regen with front braking to achieve sufficient deceleration while one pedal driving?

I would imagine it wouldn't be very safe to only regen with rear motor(s) and no front braking, especially on loose or slippery surfaces.

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