# Running a leaf motor with different gear reduction



## CanadaLT28 (Oct 15, 2011)

We know the stock gear reducer is roughly 9:1 but I would like to understand the issues behind running the stock motor through a diff with a 5:1 reduction. What would be the pros and cons? One of the reasons, I decided to redo the whole rear end on the pickup was that there was limited slip available for my diff. That has changed and one is available to me. Now I am trying to sort out the options.


----------



## Electric Land Cruiser (Dec 30, 2020)

Pros: Faster theoretical top speed

Cons: worse efficiency, bad torque, slow acceleration, possibly overheat motor


----------



## brian_ (Feb 7, 2017)

In the motor speed range in which the motor is torque-limited, for any given road speed you will be limited to about half as much torque to the wheels.
The road speed at which you reach full motor power will be twice as high. 
Above that torque-limited range (about 0-2800 RPM for the Leaf motor), the ratio difference won't matter to performance, but the motor will be running at half the speed and twice the load as it would be with usual gearing, and that will shift it to a different point in its efficiency map. The most efficient operating point for the Leaf motor and controller system is in the top half of its speed range, which you'll never see in use with the tall gearing.


----------



## brian_ (Feb 7, 2017)

To compound this further, the LT will presumably use taller tires than Leaf - sorry, I can't remember if the specific size for this project was discussed, but a stock LT28 apparently used various sizes such as 185/75R14, which is 13% taller than the sizes (such as 215/50R15) used on a Leaf, so the gearing should be 13% shorter (close to 9:1, versus the stock 7.937:1 for 2011-2012 and 8.193:1 for 2013-2017), rather than taller.

A roughly 2:1 reduction gearbox between the Leaf motor and the traditional final drive unit would be good combination, but those gearboxes (such as the ev-TorqueBox) are not cheap.


----------



## CanadaLT28 (Oct 15, 2011)

I suppose this would not result in better power consumption either. I was hoping for at most, a moderate reduction in torque. Not as bad as stated. The current tires I'm running are 215/75-15


----------



## brian_ (Feb 7, 2017)

CanadaLT28 said:


> I suppose this would not result in better power consumption either.


No, worse, due to lower motor efficiency at lower speed and higher torque.



CanadaLT28 said:


> I was hoping for at most, a moderate reduction in torque. Not as bad as stated.


To be fair, I used "half" and "double" as a really rough approximation of the ratio of the ratios.
If you have 8.193:1 Leaf gearing and are considering a 5:1 final drive (which won't be exactly 5:1), it would be 5/8.193 or 61% of the torque, in the torque-limited speed range.



CanadaLT28 said:


> The current tires I'm running are 215/75-15


That's nominally (215 x 0.75 x 2 + 15 x 25.4) = 704 mm tall (TireRack shows one example at 722 revolutions per mile).
Stock Leaf tires vary by year and trim, but include 215/50R17, which are (215 x 0.50 x 2 + 17 x 25.4) = 647 mm tall (TireRack shows one example at 815 revolutions per mile).
So even with the same gearing, the motor in the LT will turn at about 90% of the stock speed (for the same road speed) and will get 90% of the drive force to the tires (with the same gearing, so the same torque, in the torque-limited speed range).


----------



## CanadaLT28 (Oct 15, 2011)

brian_ said:


> No, worse, due to lower motor efficiency at lower speed and higher torque.
> 
> 
> To be fair, I used "half" and "double" as a really rough approximation of the ratio of the ratios.
> ...


And that's with the stock Leaf gears. It really looks like I need to maintain 9:1 or better yet 10:1. At $3500US, the planetary reducer is difficult to swallow. Best I just get this beastie on the road with the VW T4 subframe (full leaf motor and gear reducer) I already have made up. Just waiting for the body to get media blasted so I can finish the bodywork. I was hoping this would save time. Oh well.


----------



## Electric Land Cruiser (Dec 30, 2020)

I am in the same boat. Been looking at industrial reduction gearboxes and boat reduction gearboxes. There are tons available but trying to find one rated to 10,000 RPM and 300-400Nm that isn't absolutely massive has been a challenge. The boat gearboxes are very intriguing but I don't know how long it would last in a car.


----------



## CanadaLT28 (Oct 15, 2011)

Electric Land Cruiser said:


> I am in the same boat. Been looking at industrial reduction gearboxes and boat reduction gearboxes. There are tons available but trying to find one rated to 10,000 RPM and 300-400Nm that isn't absolutely massive has been a challenge. The boat gearboxes are very intriguing but I don't know how long it would last in a car.


In your case, if you still have the gear box in the truck, and the drivetrain is not in the way of batteries, I would use that. Many of the people doing landrovers that I talk to are taking that approach. At least you have some gears you can pic from.


----------

