Gear Ratio Question

[xj11yamaha]

Ok as some of you know i am doing a XJ11 Engine into 1992 Ezgo Golf Cart Project. Well anyways in exploring the Driveline and Diff Issue i came across the idea for reusing the golf cart diff. I opened it up and its OVERBUILT. Its a Dana/Spicer H12 Diff. So on to the question. Does any one know the gear ratio at the rear of the bike (the diffs gear ratio) Also this may be hard to answer but ill ask anyways, If the bikes rear wheel is spinning at about 30 MPH how many RPMS is the rear diff outputting. Thanks you guys are always so helpful.

[xj11yamaha]

Maybe a Repair or Factory Service Manual might have this info. Too bad i dont have one. Could anyone that has one take a peek for me. Thanks

[DiverRay]

I don't have that handy, but if you have the old diff from the bike, just rotate the input side and count the revelutions for one on the wheel. It will get you close. I will try and look up on the Yamaha site, as the final drive specs should be listed.
The middle gear is 1:1, so the final ratio is in the Yamaha diff.

[DiverRay]

Just did a quick look, and the final drive is 3.30:1 on the '78. I believe all the models are the same.

[xj11yamaha]

Thanks... I got another question!

Thanks DiverRay, so the driveshaft is spinning at the speed coming off of the transmission... DiverRay do you happen to know where i could find transmission ratios too. Thanks, this is going to be a big help!

[DiverRay]

Look at the left of your screen. The Specifications should give you all you need. That's how I found the final drive ratio so quickly!
I realize that the small tires on the cart will gear it down a lot, but it should still be able to hit 45 to 60, if you can keep it steady!

[pggg]

On a similar subject - I've always wondered what those hand-engraved numbers on the middle drive unit mean. Looking at my 2 spare units, one has 9/28, 7?9.95, and 24.96 on it. The other (which looks identical) has 9/26, 96.64, and 84.96 engraved. Whoever engraved the numbers had sloppy handwriting. Do any geniuses out there know what the hell those numbers mean?

[xj11yamaha]

Because I am having the golf cart made road legal (yes its possible, according to secretary of state) its going to have slightly bigger than normal DOT approved golf cart tires, probably going to have them mounted on 12" Tires if i cant find some a bit bigger.

[xj11yamaha]

Ok maybe someone can firgure this out for me if the golf carts rearend has approximately 12.5: 1 which would be mated to the yamaha xs rear end which outputs 3.30: 1 so what speeds can i expect from this configuration. I can buy different gear sets for the Golf Carts Dana Rear End.

[TopCatGr58]

Hey JR,

I had done some fartin' around with rear wheel ratio calculations for 16" vs. 17" wheels, this is what I came up with:

Overall diameter of Dunlop 140/90-16 is 25.72", times 3.1416(Pi) gives 80.8 divided by 12" gives 6.73ft. One mile of 5280ft divided by 6.73ft/1-wheel rpm= 785 rpms=60MPH.

4000 crankshaft rpm, reduced at clutch to 2414, increased thru 5th gear to 2735, reduced thru final drive to 829 wheel rpm, roughly about 64MPH, which is about what I read on my Special!

So...with an average of 800 rpms of the final drive shaft, bolted to your 12.5:1 rear end should yeild appx. 64 rpms, now depending on the size of your tire, you said about a 12"...that's only about 2.25(YES THAT's 2 and 1/4) mph in 5th around 4krpm!

Was wondering if your design requires you to keep and use the XS11 final drive vs. connecting directly to the driveshaft? Guess it depends on how you position the engine in the chassis, cause the direction of rotation is the same!

So...either you'll need much larger tires, or a steeper lower ratio in the Differential!? Hope this helps!?
T.C.

[TopCatGr58]

Okay, just calculated running directly from the driveshaft to your 12.5:1 DIff, with 12" wheel, gets you about 8mph at 4k engine rpm.

IF you ran a 1:1 DIFF, you'd get about 97 mph with the 12" wheels at 4k engine rpm!
T.C.

[Ken Talbot]

Transmission ratios

From the January 1978 issue of "Cycle":

[xj11yamaha]

Ok from all the input you guys have given me so far is that using the golf cart diff is not going to be an option. I have another diff that i bought to use as a second option, its out of a yamaha 250 four wheeler, i asked here on the board a few months or so ago and was told that i would most likely handle the XJs power. I think its going to be my best option, mostly because its shaft driven and will be a much easier setup. I'll have to check on the gear ratio though. With the golf cart the input shaft face the side of the cart. So my theory was that i could have gotten a guy that i know who owns a machine shop make me an adapter to use the XJs rear diff to mate up with the golf carts. But I know i am going to have to go with the Yamaha ATV diff to avoid anymore of this confusion. Thanks Guys for all the input, I Really appreciate it .

Also would i want the rear end that i end up installing to have a lower gear ratio or higher. I'm thinkin lower...

[DiverRay]

If you read back through, you will see that the tire size will "gear down" the cart. Just the rolling diameter of 12" wheels will cut the top speed in half, or less. That would be with the same gearing as the bike.
Off the driveshaft, the Yamaha turned 3.26 times for 1 turn on the rear wheel. If the wheels you are putting on the cart are 1/2 the rolling diameter, that will change to 6.52 turns on the driveshaft to 1 on the rear wheel.
I know you probably don't want to go 100mph in the cart, but you will need to keep an eye on the over all gear reduction. You could alway's put in a jack shaft to gear it up if needed, and if you have the room.

[xj11yamaha]

I went out and check the ratio for the rear end that i bought. It has a 4: 1 Ratio so its not like way away from the XS/XJ gearing.

Only thing thats still got me is where i can get a set of big DOT Approved Tire for 10 or 12" Golf Cart Wheels.

Again, Thanks for all of the help.