Lets Talk Gear Change On A RXV

[Bigchief803]

I want to hear you guys sets ups with pros and cons I just ordered a 10:1 gear set for a 16 RXV

[cgtech]

You are gonna hate how it rolls backward about a foot when you come to a stop. It's not good at all..... I I dont do gears on rxvs ever anymore, since the curtis controller change in 2012.5.

[Bigchief803]

Why does this happen? I don’t understand it’s a gear change notting to do with controller

[JohnnieB]

Maybe Bob Boyce will come along and explain what can and cannot be done with a RXV controller.

All I know is there is a tire height limit of about 20" without some very high level re-programming of the controller and even with the needed tools and knowledge, 23" is about the tallest tire that can be ran. Going from the stock 16.99:1 gears to 10:1 gears is effectively the same as replacing the stock 18" tall tires with 30.5" tall tires.

[BobBoyce]

Originally Posted by Bigchief803

Why does this happen? I don’t understand it’s a gear change notting to do with controller

As JohnnieB mentioned, changing the rear end gear ratio is the same as putting much larger tires on the cart. It changes the EFFECTIVE gear ratio, which alters the speed the electric motor turns as compared to the tire rotational speed. Electric motors lose efficiency as RPM reduces and torque demand increases. This means they require more current and waste much more of that applied energy as heat. The motor runs hotter and cooks internally, controllers run hotter and cook. The damage caused is cumulative. Top speed actually drops because the motor cannot develop enough torque at a lower speed to push the cart. You lose on hill climbing ability, and you lose on top speed ability.

Sepex and AC motors have maps that determine how much field current is applied over particular RPM blocks. The stock Curtis 235 Amp RXV controller has motor maps written to support up to 20.5" tires. If you exceed that tire size, the motor begins to suffer. I have rewritten the motor maps (not downloadable or uploadable) and made 21" tires supportable with a reprogrammed 235 Amp controller. That is a custom thing that must be reprogrammed live to the controller while it is on the vehicle. These new maps can be reprogrammed into a replacement controller however, once they have been written and tuned to match the configuration. The upgrade Curtis 350 Amp RXV controller has the same maps, but has the current to push the torque to support up to 23" tires. It still requires reprogramming to do this, as the default (Factory) programming of all Curtis AC controllers limit maximum current to about 70% of its rated power.

I hope this explains why gear ratio changes are frowned upon, in a way that is understandable to non-engineers.

Bob