I have a 1998 Kawasaki Ninja Zx6r. The engine is rebuilt n runs great. My issue is...

[Dave]

...with the chain n sprocket? I am not really going to be racing I am going to be doing more highway driving. So is it better to have a small sprocket in the rear or larger sprocket. I ideally would like to have better gas mileage and not really lose too much in speed. What is the difference between a 42 tooth rear sprocket and a 48 tooth rear sprocket?

[Marc C]

Going up in the number of teeth on the rear sprocket is done to allow the bike to get to top speed faster (better acceleration). It will also lower the bike's top speed somewhat. And at 55 mph the engine will now be turning more rpms than it was with the smaller sprocket. Obviously, more rpms means more gas consumed.

I don't think that is what you want.

If you go with a smaller rear sprocket, you will accelerate a little more slowly, you should gain a little on top speed and you engine will be turning fewer rpms at 55 mph (or what ever speed). I think that is what you want.

Instead of messing with rear sprocket though, you can change the front cheaper and easier (usually).

The rules I just gave you are just the opposite though, if you change the front instead if the rear. Smaller front, less top end, more acceleration, worse mpg, Bigger front, more top speed, less acceleration.......you get the idea.

[Marc C]

Going up in the number of teeth on the rear sprocket is done to allow the bike to get to top speed faster (better acceleration). It will also lower the bike's top speed somewhat. And at 55 mph the engine will now be turning more rpms than it was with the smaller sprocket. Obviously, more rpms means more gas consumed.

I don't think that is what you want.

If you go with a smaller rear sprocket, you will accelerate a little more slowly, you should gain a little on top speed and you engine will be turning fewer rpms at 55 mph (or what ever speed). I think that is what you want.

Instead of messing with rear sprocket though, you can change the front cheaper and easier (usually).

The rules I just gave you are just the opposite though, if you change the front instead if the rear. Smaller front, less top end, more acceleration, worse mpg, Bigger front, more top speed, less acceleration.......you get the idea.

[Dani G]

A larger rear sprocket will give you better acceleration by lowering the gearing. The disadvantages will be that the engine will spin at a higher rpm for any given road speed thereby increasing both wear and fuel consumption. Your top speed will also diminish a little bit.

A smaller rear sprocket will result in taller gearing. This will give your bike "longer legs" for the highway. In other words, the engine will spin more slowly at any given road speed resulting in less wear and less fuel consumption. The disadvantages are that you might have to downshift one or two gears to get maximum acceleration such as when trying to pass a line of cars. It also won't wheelie as easily, if that matters to you.

If it was my bike I would choose the taller gearing.