Expected torque/speed change with gear swap

[jrstephe]

I saw a post before but now I cannot find it. It told the expected increase in % when changing gear ratios. I've tried the search to no avail. Could the author please repost here. I have tagged this thread to make it easier to find. Thanks, new guy.



2004 36V Elec. EZGO TXT, 6" lift, F/R heavy suspension, Positive rear, currently stock 12:1 gearing, top removed, Mossy Oak Break-up Infinity camo, stock electronics

[jrstephe]

Does anyone remember seeing the post I'm referring to?

[JohnnieB]

Originally Posted by jrstephe

.........It told the expected increase in % when changing gear ratios..................

I'm not familiar with the post you are referring to, but when you change gear ratios, you either increase Speed and decrease Torque or you decrease Speed and increase Torque.

To determine percent of change, subtract original number from new number and divide difference by the original number.

Hope this helps

[jrstephe]

Let me see if I got this right: 15:1 - 12:1= 3
12:1 / 3= 40%
40% increase??

[JohnnieB]

Originally Posted by jrstephe

Let me see if I got this right: 15:1 - 12:1= 3
12:1 / 3= 40%
40% increase??

You've got the math wrong. The difference is divided by the original rather than the original divide by the difference as you did,
Using your numbers, it should be 3/12 = 25%

Also, the original gear ratio might be wrong.
I don't know about Posi-Trak rear-ends, but stock TXT gears are 12.44:1
That would make it a 20.6% increase in Toque with a corresponding 20.6% decrease in Speed.

Looks like you are trying to offset for the loss in torque due to the taller tires.

[jrstephe]

Thanks JohnnieB for your help. And I suppose the taller tires are the contributing factor. The cart has performed well on a full charge on the steepest grades of our hunting property. When I originally contacted Kustom Karts here in Richmond VA, I told them I was only going to need the cart for 5-10 minutes in and out during the hunting season. What I didn't take into consideration was the off-season when I would go in and clear our paths and do some scouting. I ran the cart the first time on the hunting property for about 2-1/2 hours and ran the batteries down to where I couldn't make it up the steep grades. I'm hoping the change to 15:1 will help me conserve some power. ScottyB returned an email question informing me of the option of electrical upgrades, which if needed, I will consider later on. I just bought the cart 6-8 weeks ago and I'm not looking to put another $1K+ in it right now. It's only use is for hunting, as I live in a neighborhood. Loss of speed is not a concern. I want to be able to use the cart intermittently for 4-6 hours and not have to worry about dead batteries.

[Glawrence@gt.rr.com]

I have an 99 ezgo txt with larger tires and rear seat. Hauled it on a seven hour trip to check out a new deer lease. Myself and a buddy got on it and headed out. Couldn't make it up the first hill we came to. Slowed to a crawl and then stopped. Wouldn't do anything for a minute then it might crawl for another 3 or 4 feet and stop. Rolled back down the hill and headed back for the trailer. Any ideas why the lack of power. Doesn't seem right. BTW batteries about a year old

Thanks

[JohnnieB]

Changing tire height effectively changed the final drive ratio. Going to tall tires, you increased Speed and decreased Torque.
Since your goal is Torque, you need to go to a numerically higher set of gears, such as the 15:1 ratio you've mentioned, and/or increase Amps to motor.

If you haven't already guessed it, everything is a compromise.
Allowing motor to draw more Amps, reduces run-time
High Torque gears reduces round trip range. (Run time stays about the same, but speed is less, so less distance can be traveled.)

IIRC, on a good set of T-105 batteries, you can get upwards of about two hours of run-time at a steady speed over relatively flat terrain. Distance traveled in those two hours is determined by your speed.

Basically, you only have about two hours of actual pedal time, but with intermittent use those two hours can be spread out over several hours in the field.

Of course, run-time is akin to gas millage in a car. If you accelerate hard from a stand still or go up inclines without losing any speed, the gas mileage (Run-Time) drops. How heavy your foot is makes a difference.

[JohnnieB]

Originally Posted by Glawrence@gt.rr.com

I have an 99 ezgo txt with larger tires and rear seat. Hauled it on a seven hour trip to check out a new deer lease. Myself and a buddy got on it and headed out. Couldn't make it up the first hill we came to. Slowed to a crawl and then stopped. Wouldn't do anything for a minute then it might crawl for another 3 or 4 feet and stop. Rolled back down the hill and headed back for the trailer. Any ideas why the lack of power. Doesn't seem right. BTW batteries about a year old

Thanks

Sounds like a battery problem.

Charge batteries fully, wait 12 hours and measure individual battery voltages and total pack voltages. (Should be 6.37V per battery and 38.22V for the pack)
(FWIW: I start at right rear battery and work counterclockwise to right front when checking individual battery voltages)

Then run cart until it misbehaves and measure voltages again.

All batteries should be within about 0.1V when fully charged and after they have been discharged some. If not, they might be iffy or bad.

Post what you find.

[Glawrence@gt.rr.com]

Thanks for the reply. I will check batteries. I will have to get cart put back together though. Started out just wanting to put new body on. Now down to frame and axles. Thanks again