Hello all, I am sure this has been answered somewhere in this forum, but...do any of you know if I can put a 15-tooth front sprocket on my '09 KLX250SF without modifying the case, or anything else? The reason I am doing this is that there are more aftermarket rear sprockets available in the 42+ tooth range, and using a larger front sprocket will allow me to keep gearing pretty close to stock.
thanks in advance,
Will

 

Yes, a 15T sprocket will fit. I had one on my 09 KLX250. If you run a 45/15 it is equal to a 42/14.I ran a 39/15 for a bit on my 250 just to see how it did. Too high to be practical. I found you couldn't carry enough momentum/power to pull 6th until around 60 mph and even then it was pushing a lot of air. I found even smaller rises on the road would require a downshift, but it would cruise at 70 on the flats.

When I require another chain I will be going to the 45/15, because that's about the best general gearing for what do now, but allows a drop if I go with a 14 or a 13.

 

To KLX 678,
Thanks for your reply and the gearing chart, all very helpful! I currently have the stock (I believe) 14:39 set-up on the "09 KLX250SF. I'm planning on a another run down the MABDR this summer/fall, will probably go with the 15:42 to give me decent mileage for the 500+ mile run down to the Tennessee/Virginia border. I have to admit the 14:42 set-up would be more desirable for the trails. I'm having a great time with this bike so far on my local trails here in Bucks County, PA. By the way, the current setup lets me get up to around 80, and I'm no where near redline. Like you, I recognize that gearing this bike any taller is asking a lot from the little motor.

 

The trick is to learn to let the engine rev. Riders are so afraid to let them run up around 6000 rpm and higher. I rode a Honda 250 scooter that had a tachometer and like all scooters it was well muffled. I found that when you cranked it open as one would normally, the drive would allow the engine to be reving around 6000-6500 rpm and be doing the same at around 50-55 mph. But for whatever reason it doesn't bother the scooter riders and I know of Honda 250 scooters doing upward of 50,000 miles with no engine issues. So don't be afraid to rev the engine, the small light parts aren't that highly stressed.