How much impact does tire diameter have on...

[Lees23]

.... power?

I currently have a cart that has 20.5” tires and I am considering moving them to 18”’tires to give the cart extra power to get up hills. Will this make a significant difference?

[JohnnieB]

My spreadsheets were set up to calculate power loss and speed gain caused by increasing the tire height, but they ought to do it the other way around also.

Looks like you'll gain 13.9% in torque and lose 12.2% in speed.

[Lees23]

Originally Posted by JohnnieB

My spreadsheets were set up to calculate power loss and speed gain caused by increasing the tire height, but they ought to do it the other way around also.

Looks like you'll gain 13.9% in torque and lose 12.2% in speed.

Thanks!

[JohnnieB]

I did some number crunching and it looks like my spread sheet works going up or going down.

With 20.5" tires, the gear ratio from motor shaft to tire tread is 14.56:1 and with 18" tires it is 16.59:1 and 16.59 divided by 14.56 is 1.139423, so the torque gain is 13.95%

That will be a noticeable torque gain, but there are other things that can cause a cart to slow excessively on upgrades.

Bad high current cables and bad batteries are at the top of the list.

All carts slow going uphill, but series drives slow the most.
Which drive system do you have?

[jclark138]

When Lees23 first posted, I was gonna through out an answer. Glad I didn’t. JohnnyB’s is SO much better than what I woulda offered ! X2

[Lees23]

Thanks all. Took off the the rear 20.5” and put on 18”, noticeable difference. One of my biggest issues is actually stopping, which has be helped as well. The tires I used for testing at standard golf cart tires, I’ll have to shop for a set of 10”/12” wheels with 18” diameter tires.

[Lees23]

Originally Posted by JohnnieB

I did some number crunching and it looks like my spread sheet works going up or going down.

With 20.5" tires, the gear ratio from motor shaft to tire tread is 14.56:1 and with 18" tires it is 16.59:1 and 16.59 divided by 14.56 is 1.139423, so the torque gain is 13.95%

That will be a noticeable torque gain, but there are other things that can cause a cart to slow excessively on upgrades.

Bad high current cables and bad batteries are at the top of the list.

All carts slow going uphill, but series drives slow the most.
Which drive system do you have?

It’s a 2017 RXV. There are HUGE hill in our complex. I am just trying to give the cart the best chance to power up the hills. The smaller tires led to a significant difference. Now trying to decide between 10” wheels with tires that have a little more side wall and 12” wheels with very low profile tires.

[JohnnieB]

Originally Posted by Lees23

It’s a 2017 RXV. There are HUGE hill in our complex. I am just trying to give the cart the best chance to power up the hills. The smaller tires led to a significant difference. Now trying to decide between 10” wheels with tires that have a little more side wall and 12” wheels with very low profile tires.

The AC drive of an RXV slows the least on hills of the three drive types found in electric carts (Series, Sepex and AC).
Bob Boyce might be able to crank up the torque for better uphill performance, I'm pretty sure you can contact him via "usgcollector" (or something like that - anyone that knows for sure, please correct.)

As I understand it, the lower the profile the harder the ride, so I'd go with the 10" rims, or stick with 8". Of course, there may be something that can be done with the suspension to soften the ride if hard riding tires are installed.

[PingEye3]

Originally Posted by Lees23

It’s a 2017 RXV. There are HUGE hill in our complex. I am just trying to give the cart the best chance to power up the hills. The smaller tires led to a significant difference. Now trying to decide between 10” wheels with tires that have a little more side wall and 12” wheels with very low profile tires.

Like JohnnieB says, contact USGICollector to make arrangements for you to send your controller to our resident RXV guru, Bob Boyce and let him perform magic on it for you. Then stick with 12" wheels and 215-50/12 road tires. You will end up with more speed and lots of torque when he unleashes the hidden power in the controller.

[kgsc]

Originally Posted by PingEye3

Like JohnnieB says, contact USGICollector to make arrangements for you to send your controller to our resident RXV guru, Bob Boyce and let him perform magic on it for you. Then stick with 12" wheels and 215-50/12 road tires. You will end up with more speed and lots of torque when he unleashes the hidden power in the controller.

Agreed. You will need to upgrade the battery wires if you haven’t done so already and I suggest a bigger better solenoid. That “stock” controller will put a smile on your face once it is tweaked.