Gear ratios

[Chavannigans]

Lets have a discussion about gear ratios.

I come from the rock crawling/overland world.

Gearing is a make or break for slow speed control, as well as efficiency.

I had a 100 Series Land Cruiser that I could get up just about anything I pointed it at.

When I installed 35"s I wanted as much gear reduction as I could get, so I installed 3:11:1 low range transfer case gears, and found a way to get 5.29 gears to work with the factory e-locker rear diff using a hybrid carrier from an 80 series with the side gears of the 100 series. It was a goat. My fuel range per tank also INCREASED going from factory 4.30 gears to 5.29s. While the tire size ratio is roughly 14% larger, they also weighed more so the engine wasnt working as hard to spin those big meats. The gearing difference was approximately 23%, which is a lot more than the 14% difference in tire size but it felt right, if that makes any sense.

I was thinking about this scenario today.

Lets say you are a prudent and savvy shopper, and buy a base model Scout with coilovers with the intent of adding a premium lift kit from Icon or Carli down the road. There really isnt a point to buying factory lifted vehicles if you intend on ripping all of those components out and replacing them anyways.

Scout has already said they will design the vehicle to accommodate larger tires and aftermarket suspension.

Someone here said you can fit 37"s by removing the fender liners so clearly Scout is thinking about people modding these vehicles.

So lets assume base models will come with 32"s

If you add a modest lift and 35"s to be a menace at your local Trader Joe's parking lot, you will suffer range loss not only from the mass of the tires, but a less than optimal gear ratio designed for a 32" tire. (Your speedometer would also be off if its not GPS based)

So a big question is will Scout will be offering multiple ratios when you spec your vehicle?

If not, will they allow 3rd party aftermarket companies to have access to the geartrain in order to design aftermarket ratios?
American companies like Nitro Gear already have a big presence and could be really helpful to gain traction in the offroad world.

Will we be able to correct for different size tires in settings if we have a larger set for offroading?
(A GPS based speedo would negate this being an issue since onboard computers could figure out wheels speed to actual speeds)

Going up in tire size over 2" can cause a significant loss in range and offroad performance on gas vehicles without regearing.

This could also impact the second hand market down the road if you are stuck with the same ratio and are holding onto a lower tier model years from now.

Lets discuss how we would like Scout to navigate this.

 

[R1TVT]

I'm guessing with the Rivian partnership in place we might see similar functionality to this. I use it in my truck to swap between AT's and dedicated Snows in winter:

 

[SpaceEVDriver]

Your Land Cruiser's maximum torque from the factory was about 315 ft-lb, somewhere in the mid range RPM (3400 RPM). With your improved gear ratio, you were able to bump that up by about 3.8x to get around 1100-1200 ft-lb of torque at just the right rpm. Likely you wouldn't always be at that perfect RPM while crawling. My guess for the best numbers for your torque at low speeds was closer to 800 or so ft-lb.

The Rivian tri motor (11.7:1 rear and front) lays down more than 1100 ft-lb of torque at 0 RPM, and it doesn't drop much until you're at cruising speeds.

And with electric motors, Rivian can adjust torque to go exactly where it's needed several thousand times a second, compared with your pedal feathering a few times a second.

Scout will probably be dual motors. Those motors will be integrated into the axles and you will not be able to change the gear ratio in the axles (at least not without replacing the entire assembly). But you'll be getting 600-1000 ft-lb of torque from the factory. And if Scout includes intelligent off-road anti-slip, the torque will be applied much more accurately.

 

[R1TVT]

Yeah, I didn't want to go down the rabbit hole of the 4-motors, which is pretty unique...

These ZF systems seem to be targeted toward off-roaders. Don't know much about them and I'm not an engineer.

 

[Cranky Canuck]

Lets have a discussion about gear ratios.

I come from the rock crawling/overland world.

Gearing is a make or break for slow speed control, as well as efficiency.

I had a 100 Series Land Cruiser that I could get up just about anything I pointed it at.

When I installed 35"s I wanted as much gear reduction as I could get, so I installed 3:11:1 low range transfer case gears, and found a way to get 5.29 gears to work with the factory e-locker rear diff using a hybrid carrier from an 80 series with the side gears of the 100 series. It was a goat. My fuel range per tank also INCREASED going from factory 4.30 gears to 5.29s. While the tire size ratio is roughly 14% larger, they also weighed more so the engine wasnt working as hard to spin those big meats. The gearing difference was approximately 23%, which is a lot more than the 14% difference in tire size but it felt right, if that makes any sense.View attachment 6081
I was thinking about this scenario today.

Lets say you are a prudent and savvy shopper, and buy a base model Scout with coilovers with the intent of adding a premium lift kit from Icon or Carli down the road. There really isnt a point to buying factory lifted vehicles if you intend on ripping all of those components out and replacing them anyways.

Scout has already said they will design the vehicle to accommodate larger tires and aftermarket suspension.

Someone here said you can fit 37"s by removing the fender liners so clearly Scout is thinking about people modding these vehicles.

So lets assume base models will come with 32"s

If you add a modest lift and 35"s to be a menace at your local Trader Joe's parking lot, you will suffer range loss not only from the mass of the tires, but a less than optimal gear ratio designed for a 32" tire. (Your speedometer would also be off if its not GPS based)

So a big question is will Scout will be offering multiple ratios when you spec your vehicle?

If not, will they allow 3rd party aftermarket companies to have access to the geartrain in order to design aftermarket ratios?
American companies like Nitro Gear already have a big presence and could be really helpful to gain traction in the offroad world.

Will we be able to correct for different size tires in settings if we have a larger set for offroading?
(A GPS based speedo would negate this being an issue since onboard computers could figure out wheels speed to actual speeds)

Going up in tire size over 2" can cause a significant loss in range and offroad performance on gas vehicles without regearing.

This could also impact the second hand market down the road if you are stuck with the same ratio and are holding onto a lower tier model years from now.

Lets discuss how we would like Scout to navigate this.

I think a very important thing to understand first is that electric drivetrains don't really have gears as most people understand them. EVs tend to have a single reduction gear and that's it. This is because unlike combustion engines that have very narrow power bands, electric motors have 100% available torque at 0 rpm and their power band is so wide that needing to change gears isn't really necessary.

There area couple of EVs out there that have an added gear for high speed cruising efficiency like the Porsche Taycane and Formula E cars (making them 2-speed gearboxes) but that added gear is to make them more efficient at the top end of the power curve.

As far as physical low-speed gears go, that's not really a thing EVs need. Those gears were designed to get around the limitations of combustion engines. EVs don't have those limitations.

 

[Chavannigans]

I think a very important thing to understand first is that electric drivetrains don't really have gears as most people understand them. EVs tend to have a single reduction gear and that's it. This is because unlike combustion engines that have very narrow power bands, electric motors have 100% available torque at 0 rpm and their power band is so wide that needing to change gears isn't really necessary.

There area couple of EVs out there that have an added gear for high speed cruising efficiency like the Porsche Taycane and Formula E cars (making them 2-speed gearboxes) but that added gear is to make them more efficient at the top end of the power curve.

As far as physical low-speed gears go, that's not really a thing EVs need. Those gears were designed to get around the limitations of combustion engines. EVs don't have those limitations.

I guess I cant wrap my head around it yet. In my mind, the final drive ratio is being altered by the circumference of the larger tire so it will be slower to accelerate with the larger tires, and have less available torque in low speed crawling.

F250s with 1,200ft-lb at low RPM needs it final drive ratio corrected with differential gears when going from 33" tires to 37" tires to restore performance and efficiency.

My RC rock crawlers have replaceable gears. A larger gear on the motor will give you a higher top speed, and a smaller gear will give you finer control for low speed crawling. Even with brushless motors it makes a noticeable difference.

Something like portal axles could still be an option.

 

[R1TVT]

You also need to consider more than 1 motor!~

 

[Chavannigans]

You also need to consider more than 1 motor!~

Portal axles replace the wheel hubs so that is probably not a factor unless they are direct drive, which I highly doubt.

 

[J Alynn]

It was made pretty clear at the reveal that portal axles would not be used. Could always change but it was asked and clearly stated NO

 

[SpaceEVDriver]

Going from 33" (likely stock on the Scouts) to 37" means an increase in diameter of ~4", a radius of ~2", or a radius increase of 2/16.5 = 12%. That's a decrease in output torque of 12%; 0.88 * 1100 = 968.

You get a much quicker decrease in torque by changing the rpm of an ICE (whether diesel or gas). The top-end on the F-250 Powerstroke is at about 1500 RPM (1032 ft-lb). If you're down at, say 1250 RPM (885 ft-lb), you've lost 14% of your torque just by nature of not being in the perfect part of the power band. If you go over 1500 RPM, you also lose torque, though not quite as quickly. Add in the increase in tire size, and you're looking at an additional 12% loss (885 * 0.88 = 779 ft-lb) for a total of around 25% loss.

The AC permanent magnet motors used by Rivian (and Scout will likely use similar ones) have a nearly flat torque curve from 0 RPM to about 5,000 RPM. They will provide the same torque (100%) at any low speed.

And with multiple drivetrains (multiple motors), you don't lose torque in the rear just because the front slips. Even with all the mechanical and ABS tricks that can be played to try to reduce this, in the end two drive motors are better than one.

As far as which drive assemblies are going to be used, as far as I know Scout has been pretty close-to-the-chest about this. We can speculate, and some have speculated that they will use a ZF E-Beam solid axle drive assembly. At least for the rear. This is a very tightly-integrated motor assembly and to me doesn't appear end-user modifiable. ZF does also offer a specialized gear reduction add-on that appears to be a sort of portal axle, but I'm unfamiliar with it, and it's not obvious how one would fit it into the system. I don't even know if that's an aftermarket or OEM option.

 

[Chavannigans]

It was made pretty clear at the reveal that portal axles would not be used. Could always change but it was asked and clearly stated NO

I wasnt implying Scout would offer them. Thats why giving access to aftermarket companies for product development before launch would be key

 

[Chavannigans]

Your Land Cruiser's maximum torque from the factory was about 315 ft-lb, somewhere in the mid range RPM (3400 RPM). With your improved gear ratio, you were able to bump that up by about 3.8x to get around 1100-1200 ft-lb of torque at just the right rpm. Likely you wouldn't always be at that perfect RPM while crawling. My guess for the best numbers for your torque at low speeds was closer to 800 or so ft-lb.

The Rivian tri motor (11.7:1 rear and front) lays down more than 1100 ft-lb of torque at 0 RPM, and it doesn't drop much until you're at cruising speeds.

And with electric motors, Rivian can adjust torque to go exactly where it's needed several thousand times a second, compared with your pedal feathering a few times a second.

Scout will probably be dual motors. Those motors will be integrated into the axles and you will not be able to change the gear ratio in the axles (at least not without replacing the entire assembly). But you'll be getting 600-1000 ft-lb of torque from the factory. And if Scout includes intelligent off-road anti-slip, the torque will be applied much more accurately.

In this comment you mentioned Rivians 11.7:1 ratio. So there are gear ratios involved right?

Is the 1,100ft-lbs raw motor power? If so that would mean you are multiplying the 1,100ft-lbs X 11.7:1 which would yield 12,870ft-lbs to the ground. Right?

 

[SpaceEVDriver]

In this comment you mentioned Rivians 11.7:1 ratio. So there are gear ratios involved right?

Is the 1,100ft-lbs raw motor power? If so that would mean you are multiplying the 1,100ft-lbs X 11.7:1 which would yield 12,870ft-lbs to the ground. Right?

There's a single reduction gear within each motor assembly to drop it to 11.7:1.
The total output from the three motor assemblies, through the wheels+tires to the ground is 1100 ft-lbs.

 

[SpaceEVDriver]

I might be wrong about my statement above. I had assumed it was grounded torque, but ... While digging into the GMC Hummer EV's claim of 11.5k ft-lb of torque, I found this quote from Rivian:

"Richard Farquhar: That’s correct – we have four identical motors, left and right, front and rear. Every wheel has the exact same amount of torque and power available to it to maximize performance. We achieve over 14,000 Newton-meters [10.3k ft-lb] of grounded torque at the wheels combined and 125 miles per hour maximum speed. With the fixed-ratio single-speed gearbox there is no need to change gears, no need for twin speeds. This maximizes efficiency in terms of losses from gear meshing while achieving all of our performance targets."

So, that 1100 ft-lb may be the torque output at the motors for the tri-motor setup, which would mean, yes, 12.9k ft-lb at the wheels. I find that number difficult to accept, but now I don't know...

-----

My hope and expectation is that Scout Motors will be in the ballpark of Rivian performance. Even the lowest trim dual-motor AWD vehicles outperform similar-cost offroader-ideal vehicles like the $105k Jeep Rubicon 392, which produces 470 ft-lb of torque.

The overall specs for each of the configurations of Rivian:

Gen 2 vehicles

• (2025) Quad-Motor AWD vehicles produce 1,025 horsepower and 1,198 ft lbs of torque.
• Tri-Motor AWD vehicles produce 850 horsepower and 1,103 ft lbs of torque.
• Performance Dual-Motor AWD vehicles produce 665 horsepower and 829 ft lbs of torque.
• Dual-Motor AWD vehicles produce 533 horsepower and 610 ft lbs of torque.

Gen 1 vehicles

• Quad-Motor AWD vehicles produce 835 horsepower and 908 ft lbs of torque.
• Performance Dual-Motor AWD vehicles produce 665 horsepower and 829 ft lbs of torque.
• Dual-Motor AWD vehicles produce 533 horsepower and 610 ft lbs of torque.

 

[cyure]

I might be wrong about my statement above. I had assumed it was grounded torque, but ... While digging into the GMC Hummer EV's claim of 11.5k ft-lb of torque, I found this quote from Rivian:

"Richard Farquhar: That’s correct – we have four identical motors, left and right, front and rear. Every wheel has the exact same amount of torque and power available to it to maximize performance. We achieve over 14,000 Newton-meters [10.3k ft-lb] of grounded torque at the wheels combined and 125 miles per hour maximum speed. With the fixed-ratio single-speed gearbox there is no need to change gears, no need for twin speeds. This maximizes efficiency in terms of losses from gear meshing while achieving all of our performance targets."

So, that 1100 ft-lb may be the torque output at the motors for the tri-motor setup, which would mean, yes, 12.9k ft-lb at the wheels. I find that number difficult to accept, but now I don't know...

-----

My hope and expectation is that Scout Motors will be in the ballpark of Rivian performance. Even the lowest trim dual-motor AWD vehicles outperform similar-cost offroader-ideal vehicles like the $105k Jeep Rubicon 392, which produces 470 ft-lb of torque.

The overall specs for each of the configurations of Rivian:

Gen 2 vehicles

• (2025) Quad-Motor AWD vehicles produce 1,025 horsepower and 1,198 ft lbs of torque.
• Tri-Motor AWD vehicles produce 850 horsepower and 1,103 ft lbs of torque.
• Performance Dual-Motor AWD vehicles produce 665 horsepower and 829 ft lbs of torque.
• Dual-Motor AWD vehicles produce 533 horsepower and 610 ft lbs of torque.

Gen 1 vehicles

• Quad-Motor AWD vehicles produce 835 horsepower and 908 ft lbs of torque.
• Performance Dual-Motor AWD vehicles produce 665 horsepower and 829 ft lbs of torque.
• Dual-Motor AWD vehicles produce 533 horsepower and 610 ft lbs of torque.

WOW

 

[Chavannigans]

https://www.rivianforums.com/forum/threads/torque-multiplication.1779/

I came across this thread while I was trying to understand these ratings.

In that thread someone shared this video. Its a.... a little unorthodox but he goes over the ratings and real world applications.
He also goes off on a tangent about environmentalism at the end but the math checks out about the gearing.

He compared the Rivian torque vs his custom Jeep with an NV4500 trans, stock ford V8, aftermarket t-case, and aftermarket diff gears, as well as the numbers for a Jeep Rubicon.

When engaged in low range they outperform the Rivian single speed final drive.

When we look at my Land Cruiser with the Toyota A343F trans with a terrible 2.80 1st gear, with the 3.11:1 t low range t-case gear, and my 5.29 differential gears turning 315/75R16 tires (deep inhale) my final drive ratio was 46.07

If we take my final drive ratio of 46.07 and multiply it by the weak 331 ft-lbs of peak torque from my non-VVT 4.7 V8 we get roughly 15,249 ft-lbs of realized torque at the wheels, which is still better than the Rivian when crawling offroad.


I was able to drive a few Land Cruisers with 4.56 gears and 4.88 gears. The 5.29s with the 3.11:1 gears felt like a massive leap when climbing uphill compared to those.

I hope this can help clarify what I am getting at now.

 

[SpaceEVDriver]

I suspect the math does check out, for the most part, other than his outdated (and average) information about EVs. I'm also not a fan of his assumptions that lead him to convert from RPM to speed in the graph. Engine RPMs are far more important than speed for torque considerations. Speed isn't directly related to RPM when rock crawling.

For me, the last time I modified a vehicle for crawling was something like 20 years ago. Since then, I've just stayed with stock plus new tires, so I'll stick with a vehicle I don't need to modify (also, I have no intention of ever going back to gas).

All of that said, I can understand someone wanting to be able to regear. Even a 2:1 would bump something like the tri-motor torque of 12.9k up to 25.8k. I know both ZF and Dana have gear boxes that might be able to be slipped into the drivetrain of a vehicle with the engineering setup. A full solid axle like the ZF ebeam is probably not one that will allow inserting new gearing between the motor and the wheels. I haven't seen the inside of the ZF ebeam, so I don't know how possible it would be to switch out the internal gearing for a different one.

But something like the Rivian configuration with independent suspension and the drive assembly connection to the wheels via CV axles may allow you to shorten those axles and slip something like the Dana e-gearbox in. The Dana gearbox is a 2-speed, but I don't know what the gearing ratio is. And you'd have to put such a gearbox everywhere you wanted the additional gearing, so probably on each of the four wheels.

I will say that I would find an offroad-capable EV to play with before going too deep into spending any money on the idea of regearing. I find the low-speed control on our Lightning is far superior to any gas vehicle I've driven offroad, including the ones I've regeared.