Series TXT Motor vs Input Shaft Tooth Count

[preston8705]

Cart: ‘97 36v series txt with 24” tires. Curtis 500A controller, HD F&R, MZJ 400A solenoid. Looking to replace the stock with an AMD 7126 motor and thought I’d replace the input shaft while I was at it.

Use: The cart is used on fairly flat streets with Max 30 mph to bring people and boards the half mile or so to the beach and back. Speed is more of a concern for me than torque (planning to upgrade to 48v when the batteries go in about 4 years).


First brain boggler: All the series motors specifically say 19 tooth, but all input shafts say 21 tooth. I’m assuming the listed 21 tooth is the differential side spirally ones and not the motor side teeth. Just want to confirm.

Second question: apologies if this ones been answered all over the place. The input shaft I’m looking at is a 12.44 ratio. Is this a good ratio for my intended use and tire size? I’ve heard of people going down to 8 but don’t know if going down is better for torque or speed.

Any help is much appreciated. Thanks for taking a look.

[scottyb]

19 splines is the motor side of the shaft (all ezgo motors 1988 and up) and either 21 or 22 is the differential side. For 1990s era it is best to remove and count splines before ordering.
A lower ratio like 8:1 is a taller gear compared to 12:1 by about 33%. The result is 33% higher top speed and 33% less torque or power. Taller gear sets sound like a good way to get speed but they power loss creates more problems than they solve.
1st of all you have to to have 33% too much power to throw away... not many carts fall into this category.
2nd you have to have a cart that is safe at 33% higher speeds ... not many carts fit this category either.

Remember the 24" tires you mentioned already constitute a 33% increase in size. Essentially they do what the 8:1 gear set is designed to do for stock tire carts

When increasing speed always keep safety in mind.

[JohnnieB]

The 19 and 21 tooth references are for two separate items.
The motor output shaft has 19 splines and the differential input shaft has a 19 tooth spline and they are connected together with a 19 spline coupler.
The gear inside the differential on the input shaft has either 21 or 22 teeth.

The differential (transaxle) is a torque multiplier, which is to say the input shaft (motor) spins more times than the output shaft (rear axle). Therefore, when the motor is spinning at 3,000 RPM the rear axle is spinning at 241 RPM with 12.44:1 gears and 375 RPM with 8:1 gears.

When you say: "The cart is used on fairly flat streets with Max 30 mph" Do you mean the road has a 30 MPH speed limit or do you mean the cart will currently do 30 MPH and you want to go faster?

[preston8705]

Thank you to “The B’s” for the quick response. Exactly what I needed.

In response to JohnnyB’s follow up, the area (Bird Rock La Jolla, CA) is mainly residential 25 mph streets with a few main roads that are 30mph. The cart only does approx. 22 mph now. Would like to get up close to 30 so I get less honks behind me but I know that’s unrealistic at 36v.

[JohnnieB]

If you are getting 22MPH at 36V on 24" tall tires, going to 48V will up both speed and torque by 33.3%, taking you to 29.3MPH. There will be some increase in wind resistance, so the cart probably won't fully reach that speed, but it should eliminate most of the honkers.

On the other hand, you gotta remember the cart's rear wheel only mechanical brakes were designed for stopping vehicles with a gross weight (Cart + cargo + people) of about 1500 pounds from golf course speeds, or about 15 MPH or less. To safely stop a cart from 30 MPH, you might consider going to 4-wheel disk brakes, especially if the passengers are paying customers.