Sprocket ratio for fuel economy

[Beemeridian]

7564

[CycleRob]

yellowjacket,
I have some experience with taller gearing on two different guy's 500 Nija's. I rode both bikes on the street after the 17T front sprocket (plus 1 tooth) changes and thought the ratios were what the factory should have done in the first place. The 2nd bike also also installed a 2 tooth smaller rear sprocket and a larger cross section rear tire that had a larger circumference. That bike seemed sluggish and barely able to handle any kind of headwind with the little hamster motor turning so slow. Then again, I was repeatedly spoiled by my R1150R's consderable low RPM torque . . . so the 500 Ninja's sluggishness may not be that bad.

Since your aim is a max fuel economy commuter bike, you need to find the point where the engine is turning slower at cruise speed, but not at a throttle opening that is too large. My guess is go another 3 teeth smaller on the rear. Any more than that and you may not be as efficient because of the large throttle opening necessary at the too low engine rpm's where you are too low on the engine's torque curve. The acceleration won't be that bad, but maintaining cruising speed up hills or against headwinds may make 5th gear a better choice. Bear in mind that 5th gear with the taller 17/40 gearing is still lower RPM's at 60MPH than 6th gear with stock 16/43 gearing. You'll still be ahead overall efficiency wise, even though you are over geared (too tall) for certain adverse conditions like hilly country and headwinds. In any case, you should keep the 17T sprocket because of the lower chain friction inherent with the larger diameter's less chain bending and the larger front sprocket also provides less moving chain contact with the top of the swingarm pivot's hard rubber rubbing strip.

After you've settled on the gearing, there may be small gains by leaning out the idle mixture screws. The carbs may still have the factory tamper plugs in place that'll sour those attempts. I always set them for the leanest smooth idle on a cold engine that has been running for 2 minutes at the start of adjustment. You should set them for the leanest smooth idle on a hot motor. Do not adjust them on rainy days or if the engine is very hot. That'll require some experience to compensate.

Tire pressures of 36F/40R, lower handlebars and an always juicy chain will also help the MPG's.

[DJ Downunder]

What's a sprocket????..............

DJ

[Beemeridian]

545

[CycleRob]

Here's what I was talking about. It's a dyno chart for a Honda weed wacker 4-stroke engine. See the under load, RPM/fuel consumption curve? It shows there is an optimal RPM for the load.

[Beemeridian]

564

[machew01]

A weed wacker on a dyno. That had to be interesting.

mac