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I just bought an 18tooth sprocket to adjust the gearing on my Ninja 500R for greater FE. Cruising RPMs should drop by more than 500rpms and thrust at the wheel will be reduced by about 10%. You can see more details of my planned modification on my Live Video account: http://www.livevideo.com/video/lessdeth69/319D527A70CC48CDA2C69F27F50E7CEB/2007-08-01-why-i-chose-an-18to.aspx

and http://www.livevideo.com/video/lessdeth69/0119483AE94F42BD83C21B793B7010BA/2007-08-02-analysis-of-thrust-.aspx

I'll start reporting out tanks next week with this mod installed :Banane04:

Great. It will be intersting to see what the final results are.

I just input my first full tank with my revised gearing. There seems to be an FE improvement with the revised gearing of about 5-10% This tank was a bit atypical for several reasons, some days were less FE friendly than usual others more friendly, so more tanks will have to be input before a final conclusion can be arrived at.

antrey, any further results on the revised gearing?
Reducing rpms seems like a no-brainer good idea; I wish it were as easy to do in a car.

You can see a video of my analysis of 12 tanks, 6 before the gearing change and 6 after, on my live video page: http://www.livevideo.com/video/lessdeth69/608B0300E81D4890A39CDED71B758975/fuel-economy-with-18tooth-spro.aspx Basically, I've seen about a 14% improvement with my gearing change. I went from averaging mid 50s MPG to Low 60s MPG. The final drive ratio can be modified on many cars but typically only shorter gearing for faster accel is available.

wow i didn't think a 500 rpm change at cruise would make such a difference i might try this!

I would expect about a 5% improvement for a 10% drop in RPMs.Was the original countershaft sprocket a 16T?
What were the RPMs at 60 mph originally-maybe 4500? A nice smooth power twin like that could probably not lug at as low as 3500 RPMs-maybe lower.
I have 2 bikes-A 1978 SR500 that I geared for better accel(15/46 originally 16/44-) it turns 4800 rpms at 60(originally about 4300) and a VT500 Ascot about 4300 at 60 mph.I'm going to regear the SR500 to 17/42 and drop it to 3800.I can't regear the driveshaft VT500 unfortunately.
Let us know the rpms etc you are/were turning,and how close it "feels" to lugging at 60mph with constant throttle position.
Boy, it sure seems that we should be able to "beat" a 2950 lb Prius, but in fact my bikes might nose it on the hy, but not in the city(all about 40-45 mpg).Originally the SR500 would get close to 60 mpg in city driving with lots of city interstate mixed in(I used it during the 79-83 gasoline crunch).
Luck,
Charlie.

My Ninja 500 is quite comfortable running at RPMs as low as 2000RPM so the revised gearing does not make it feel like it's lugging at highway speeds at all. You can see a video where I analyze the RPM and Thrust force changes in great detail using a Labview program I wrote: http://www.livevideo.com/video/0119483AE94F42BD83C21B793B7010BA/2007-08-02-analysis-of-thrust-.aspx?lastvcid=315340 As you can see at 60mph I dropped 575RPMs going from stock 4825 to 4250 by going from 16teeth up to 18teeth, and at 70mph the drop is 650rpms from stock 5650 down to 5000.

Long ago I went to an 18 tooth countersprocket from a 16 tooth & changed the wheel sprocket too. My 1980 450 Suzuki's rpms dropped 15% & my mileage went from 66MPG to 74MPG on flat highways. Even on an 8200mile western U.S. cycle vacation the Suzuki only used 120 gallons of gas which included numerous 10,000+ foot Rocky Mountain passes.

That is really impressive, Litesong! It sounds as though you guys have found a very worthwhile modification for your bikes.

Now if I could just get a Civic HX's transmission gear ratios into my Elantra... ;)

Antry 4250 rpms at 60 mph-pretty good.Let us know how it goes-mpg- over time.You could probably drop the RPMs even more, but maybe you would have to go to a smaller sprocket since you might be running out of space where the countershaft sproket slides on.
litesong,I always liked the 450 Suzuki- it was the quickest of the 2 cyl 400/450-about 13.6 1/4 according to the mags,and obviously fuel efficient.I have a XS400 Yamaha that gotten decent-55 mpg or so-mpg but it was a lot slower than the Suzuki. I wonder how its grandson-the 500-does mpg wise? A fair # of folks were racing it in some box stock type class.
Right lane cruiser-you could put taller tires on your Elantra, but this sorta' increases the frontal area(taller profile-the air that goes underneath is all"bad"),so it might hurt hy mpg.
Going up one notch in tire profile-say 70 from 65-usually makes the tire about 18mm(3/4") taller-so the RPMs drop about 3%-not much-maybe 100 rpms at 60 mph-not worth the effort.
Luck,
Charlie

You should make your program from the video, available to the public :) I am particularly interested in getting a sv650 or something similar (v-twin), with a torque advantage, and gearing it for better FE.

Also, gearing your ninja like that should allow you a higher max speed, right?

P.S. How do you guys survive driving/riding 60mph on the freeway? I will get run over if I even attempt this.

I'm curious, what size rear sprocket do you have, and what size was the original front sprocket?

I bought a '79 KZ650 last summer to use as an economical daily rider. It's taken FOREVER to get the running issues sorted out. As soon as I did, the chain broke, which I took as an opportunity to go to more fuel-efficient gearing.

Stock, the bike had a 16 tooth front sprocket and a 42 tooth rear for a ratio of 2.63:1.

Someone had swapped to a 41 tooth rear sprocket on mine, for a ratio of 2.56:1.

I went with an 18 tooth front and a 40 tooth rear for a ratio of 2.22:1. I hated it. It lowered my highway cruising rpms by over 800, but, in 5th gear at 60 mph, the slightes uphill caused it to lug terribly. I also had to slip the clutch like crazy to get it to take off.

I swapped to a 17 tooth front sprocket, keeping the 40 tooth rear, for a ratio of 2.35:1 and like it a lot better. I've had the gauges off being restored since I got it on the road with the 17 tooth front sprocket, so I don't have any hard data on rpms, mileage, etc., but the 2.35:1 ratio seems a much better compromise to me.