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Discussion Starter · #1 ·
I just bought a 2004 Kawasaki Ninja 250R and was wanting to increase the top speed. Can anyone tell me what the best sprocket setup would be to increase my top speed?
 

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15/43 offers the best balance of acceleration and top speed provided you are maxing out rpms in every gear. Your rpm speed will decrease about 750 rpm in any given gear, but you will see an increase in top speed.

stock gearing 14/45 @ 11000 rpm, 6th gear = 89.3 mph
custom gearing 15/43 @ 11000 rpm, 6th gear = 100.2 mph
 

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Discussion Starter · #4 ·
Thanks. I was needing to get it closer to about 110mph but that will work great.

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Discussion Starter · #5 ·
Would i have to get a different chain with a 15/42 setup? I cant find a 42T.

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I have had my 04 250 at 110 and all I did was straight pipes and tuned the carb. Stock sprocket and chain. She is loud but then at least cars here me at 110.

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DaBlue1, thanks for the quick response to my question. Before I bought my bike, I read numerous road tests. They stated 60 mph = 7,500 rpm's. I was shocked that mine was 9,000 rpm's. Because it's linear (gearing, not exponential) that computes to 12,000 rpm's = 80 mph, and redline (13K rpms) = about 87 mph. I created a spreadsheet with all the math in it according to the owners manual, of rpms/primary gearing/gearbox gear ratio/final drive, tire circumference, etc and the only way I mathmatically get 60 mph = 9,000 rpms is with a 20 inch diameter rear tire (but it's really 23). I wonder if they changed some gearing and didn't update the owners manual? I'm going to do what you suggest and change to 15/43 gearing to hopefully get the best of both worlds (reduced rpm's and still have some power). Thanks also for the tip about the fuel gauge undertank wiring, I'll check that out.
 

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@zx9r; You should be going about 73 mph in 6th gear @ 9k rpms. 65 mph in 5th gear (actual speed). The speedos are known to be off a little, but not by so much. They are usually about 5 mph faster than the actual speed.
 

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I agree with what you're saying (according to the magazine articles I've read) but that's not what I'm seeing. I'm making sure I'm in 6th gear (counting the shifts and even when I'm in 6th pulling in the clutch and trying to shift up again to no avail), but 7,500 is 50 mph (I also agree with you on speedo error - my 73 XLCH indicated 60 mph at a radar timed 49 mph) and 9,000 is 60 and yes the engine is screeming. That calculates to 87 mph at 13,000. I counted the teeth on both the countershaft (14) and rear wheel (45). I don't get it? On "Motorcycle Superstore.com" I noticed they sell TJ sprockets from 45 down to 38 for the rear wheel and even have 15 & 16 teeth countershaft sprockets? I'm thinking of going to a 15/39 combination and see what happens? If I don't look at the tach (and my other bike is a 1600 cc Nomad) and shift at what seems a "normal" shift point, I find I'm in 6th gear at about 30 mph and it "pulls" just fine. 30 mph is 4,500 rpm's. Stay tuned....
 

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@zx9r, if your tach is reading correctly at low rpms but you suspect an error at higher rpms, you may have a tach problem or IC Igniter problem. see this thread- http://www.250r.net/forum/showthread.php?goto=newpost&t=1449

Lately, I've been seeing a lot of riders with improperly adjusted clutches, having rpm issues as well. One has had to replace the clutch within a year of having the bike. A properly adjusted clutch lever makes a the difference in the world. The clutch lever needs a little bit of slack in it.

If you do a 15/39 combo you will have to shorten the chain. The stock chain is way too long. Also you will have to at least shim the needles and remove the snorkel for a little more low rpm umph. The smallest rear you should do with the stock chain is 15/41. Keep in mind that the bike will have a hard time reaching red line in 6th with these combos unless you re-jet or put on a full exhaust. Even then the gains maybe minimal.
 

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Update: I took my new 2012 250r for another test ride. I road out my driveway in 4th gear at 4,000 rpm's at 20 mph. When I got to the street (my driveway is dirt and 1/2 mile long) I got in 5th gear at a steady 4,000 rpm's. It indicated 25 mph. I then shifted into 6th to see if the rpm's dropped. They did, but not much. In 6th at 4,000 rpm's I was going 28 mph. At 30, 4,500 rpm's. Again at 60 mph I was turning somewhere between 9,000 and 9,100 rpm's. I don't get it??? It IS in 6th and it IS stock gearing (14/45). I just ordered a 15/39 set up. This will reduce my gearing 19.1%. That should equal 7,281 (or rounded to 7,300) rpm's at 60 mph. That also equals 107 mph at the 13,000 rpm redline, which I doubt it will "pull." Maybe down hill. Anyway I'll find out about the 60 mph = 7,281 rpm's as soon as the new gears arrive. I'll let you know what happens.
 

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DaBlue1, I want you to know I really appreciate your responses, read every word, and think about what you say. My bike acts perfectly normal (but it's new and I'm not used to what "normal" is yet?). You may have hit the nail on the head about the tach and the I/C ignitor. I assumed the tach and ignition where OK, since it only has 30 miles on it, but remember, the fuel gauge isn't working either (I checked the wires under the tank and under the left side cover and everything seemed connected OK, and I did push and pull on each connector to doublecheck). If the tach or I/C Ignitor are bad, I wouldn't know because I'm believing what's indicated, but it really violates all the road tests I've read. I'll take the bike back to the dealer Tuesday when they open back up, and have them check it out. I adjusted the clutch and throttle cable before I road the bike home. I'm sure the clutch isn't slipping. I've never worn out a clutch on a bike (I've owned 20). My Ford Escort has 360,000 miles on it, and I replaced the clutch on it at 305,000, but the only thing wrong with it was the needle bearing was shot. The plate was fine. But I'll watch to see if there is any slippage. As for the 39 rear sprocket, that's what I suspected. I know the 15 will take up some slack, and the swing arm adjustment will too, but if it's not enough I'll buy another chain or a 41 sprocket. Thanks again.
 

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Actually a 15 in front versus a 14 will decrease your rpm's and hopefully will increase your gas mileage at the same given speed (for example 60 mph).
 

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Actually a 15 in front versus a 14 will decrease your rpm's and hopefully will increase your gas mileage at the same given speed (for example 60 mph).
correct. Combined with replacing the rear sprocket with one with even less teeth, such as 15-41, will lower rpm's even more than just changing the front sprocket. That setup isn't widely encouraged, especially to those living and riding in hilly areas. I live in a very flat area of Texas and don't do any hill riding, due to lack of hills lol. So that will be my setup pretty soon hopefully. For sure I'll be changing my front sprocket, which is something I think everyone should do.



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@zx9r, There is a way to check your rpms externally. You can use an inductive pickup clip accessory on a digital multimeter. The clip attaches to the spark plug wire. If the multimeter is good, it can be set up to convert electrical pulses into a rpm format. With this I believe you will be able to tell if there is a different reading between the tach and actual spark output. The trick would come in trying to mount the multimeter and take a reading while riding at speed.

This is what the dealer should do as well, however since the bike is new and stuff isn't working 100%, the dealer needs to fix it all and a free oil change!
 

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DaBlue1, thanks. I have a multimeter, but it's a cheap Wal-Mart one. I agree the dealer should fix the rpm issue and the fuel gauge. (and I bought the 5 year warrenty!). But, I really think you are correct about either the tach being wrong or the I/C or both. Why? Because of my spreadsheet. I know all the math to convert rpm's to mph and can apply it to any gear. All I need is a baseline. I measure the diameter of the rear tire. It's at least 23 inches (I did this with a measuring tape, which isn't exactly perfect with the axle nut in the way etc.). On my spreadsheet I can only calculate 9,000 rpms at 60 mph with a 20 inch rear tire. It's impossible with a 23 inch. I should have figured that out, and you "tach I/C" email got me thinking about it, thanks! I think the tach's been wrong all along. Oh, thought I'd let you know, even though I did order that 39 tooth sprocket, I just got back on M/C Superstore and ordered a 42 (along with the 15 countershaft). So either way I'm covered. BTW, with the 39/15 combo "if" it would pull redline in 6th (I'm sure it won't) it would be 130 mph! Tomorrow the dealers open, bike goes back...
 

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The bike will not pull a 15/39 combo to redline in 6th with out some serious mods;
Racing carbs
Shaved heads
Polished valves and seats
High compression pistons
Advanced timing
and
Nitrous

That should get you a little past 121.854 mph and a new Official Land Speed Record for a Modified Ninja 250.
 
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