How do I change my gearing?
For about $60 you can get some new sprockets for the Ninja 250 that will lower the rpm at highway speeds (which equates to better mileage). On a stock Ninja the front sprocket has 14 teeth and the rear sprocket has 45 teeth.
The first mod done by many people is replacing the front with a 15-tooth sprocket. If that doesn't drop your rpm enough for you, you can try a 44-tooth or a 42-tooth rear.
There are a couple other options. The JT catalog lists a 16-tooth front. Don't Do It. It will cause clearance issues. It's better to step down in the rear than go any bigger than a 15 up front. You can use a 41-tooth in the rear if you do a lot of commuting and don't have to worry about going up hills. Several members on the board have a 15/41 combo, but they are shooting for gas mileage and live in flat places like North Texas.
See the chain & sprockets page for information on available products.
Gearing for the highway
Duke: The F-model 250 (88-07) runs best on the interstate between 8000 and 9500. You can play around with the gearing until you get this rpm and your desired speed to match. Personally, I like 70 mph at 8000, which allows enough torque in reserve to pick up the speed if necessary.
Does installing a new front sprocket make a significant difference?
Changing the countershaft gear from a 14 to 15-tooth sprocket is the most common gearing mod, and it does make quite a difference. At first the bike might seem sluggish after the change; the torque you were used to isn't really there. As you ride around town for awhile, it may seem that the bike isn't revving as quickly as it used to. This of course is to be expected, since the countershaft is now working harder. But the change in acceleration is really marginal; though the bike now takes longer to rev through the gears, each gear is putting out 7% more travel per revolution.
So, the twist on throttle has to be a little greater now to get a satisfying 0-60 run, but the high-speed cruising is noticeably improved. Until you get used to it, you may think you're in sixth at times when you're really still in fifth. This mod also makes first gear seem more useful.
It isn't too difficult a task: loosen the rear wheel, remove the countershaft housing, remove the 14-tooth sprocket, put the new sprocket in, torque the retainer bolts, replace housing, set correct tension to chain, torque rear wheel, and clean/wax the chain. The sprocket switch takes about an hour overall. Popping the old sprocket off is a snap; putting the new one on takes a bit because the countershaft teeth are cut to very close tolerances. Cost = $15-20.
Is there any advantage to installing a smaller front sprocket?
Some track racers have used a 13-tooth front for a little while. It makes it harder to keep lube on the chain because the chain is turning a tighter corner. Also, the chain eats into the keeper, even if you file it waaaay back.
The only advantage is it puts the gear ratios closer together. Aside from that, it's all the same because you end up in 3rd when you would normally be in 2nd... etc.
What drive ratios are attainable?
The most common non-stock sprocket combinations are:
15/45 Replacing the stock 14-tooth front.
15/44 Running a smaller rear reduces rpm at a given speed.
15/42 Reduces rpm even further.
15/41 For flatlanders only, although you can always kick it down into fifth if you have to.
Gear ratio Chart for most motorcycle sprocket ratios.
Opinions on some gearing combinations
You can check the speed calculator for more information on speed, rpm, and gearing.
15/44 vs 15/45
- I find the 15x44 is a good compromise, and it's perfect for 70-80mph riding. I have 2 bikes - One is 15x45 and the other 15x44. The 15x45 is (very marginally) quicker through the gears, pulls harder in top gear at terminal speed / has a higher top speed, but the trade-off is higher rpm on the highway. Either works just fine for me. I run the higher gear on the bike which I use for touring. However, I've also done local club rides (all 600cc+) in the twisties using the 15x44 bike and had no problems whatsoever (the trick to club rides on an underpowered bike is to stay as close to the front as possible to avoid the inchworm effect).
- This works fine in twisties and on a track, although I do prefer 15/45 for that kind of riding. 15/42 can handle performance riding, too. You just have to keep the revs up. I'd imagine 15/41 is almost the same, but to me, 15/42 is enough. I wouldn't go any lower on the back.
- I had changed my front sprocket to a 15, then about a month later changed the back to a 42. For me it was not good. I'm not sure if it is mostly my weight (~210) plus the weight and wind resistance of my loaded bike and touring windshield, but when I traveled long distance, loaded for camping and tools and pushing the bike for speed, I was running WOT all day and getting mpg in the 40's. That was the reason I missed on my Iron Butt Bun Burner Gold attempt: too many gas stops!
- I later changed my rear sprocket back to the original, so I am now running 15/45. Maybe if you weigh less, don't load down so heavily, keep it a bit slower (less than 75-80) and miss the Midwestern high winds and hills, it will work better. Others have sworn by the 15/41-42. Definitely YMMV.
- 15/42 works great for me, but I'm only 150 lbs plus or minus. Commuting mpg (65-70) didn't go up noticeably from the 15/45, although it did go up noticeably when I went to the 15T front sprocket first.
- The 15-41 results roughly in 1000 rpm per 10 mph in 6th. The engine is doing about 5750 rpm at an indicated 60 mph and spinning at about 6900 at an indicated 70 mph.
- The 250 engine has plenty of power, but is a small “peaky” engine that has a narrow powerband compared to a big V-twin or an automobile engine. You just may need to spend a little more time in 5th than a stock bike if you live in hilly country or are battling a stiff headwind at highway speeds. Passing can be done comfortably in 4th or 5th. I would look at the 6th gear as an "overdrive".
- When riding single I only felt the need to leave 6th if I was on a steep incline and traveling at less than 50 mph. When taking one of my offspring for a ride, 5th is sometimes needed to maintain highway speeds if heading into a stiff headwind or going up an incline. In 4th the bike will accelerate smartly up steep inclines. Just keep in mind that close ratio transmissions are meant to be shifted.
- In short: You don't need a 39T; consider a 41 as the smallest option.
- I had the 39 tooth rear on for a while and enjoyed "seventh gear" and 8000 rpm freeway cruising. However, this came at the expense of a serious lack of torque from a dead stop. If you lane split through traffic, then end up at a red light, when the light turns green you might find that the cars you just passed can make up all that ground while you're trying to get moving. It's both unsafe and humiliating at the same time.
- Another drawback is that if you run 14/39 you'll run out of chain adjustment - the rear wheel is as far back as it can go and there is still a lot of chain slack. Installing the bigger 15T front to reduce the chain slack will make the gear ratio even taller. And my gas mileage did not go up significantly when on a 15/39 combo compare to the 15/45.