DIY- Sprocket Swap

[toku]

One more DIY just for the fun of it

Since I was changing both the front and rear sprocket I started with the rear and kept the wheel loose to get enough chain slack for the front sprocket. Changing the rear sprocket will require stands of some sort to drop the rear wheel out, just changing the front sprocket could be done without stands.


Start by removing the cotter pin and loosening the axle nut on the rear wheel.

I then loosened the adjusting nuts and pushed the wheel forward as far as it would go. Then to drop the wheel all you have to do is pull out the rear axle and then remove the chain. After the wheel is out it's a good idea to make sure that no one messes with your rear brake, getting the pads to spread out can be a pain.

After taking the wheel out I placed it on some 4x4's to keep the brake disc from touching the ground.


At this point you need to unscrew the six nuts to take the sprocket off. I ended up having to kneel on the 4x4's with the wheel between my knees and putting pressure down on the center of the wheel to keep it from sliding while trying loosen these nuts. I was fairly surprised by how tight those nuts were on there.
Now you have the wheel with no sprocket


Now just place the new sprocket on and tighten up the nuts. I tightened mine in sets of 2 going to opposite sides of the wheel to avoid warping anything by over tightening one side. I tightened the nuts according to the service manual at 44 ft-lbs each.


At this point it's time for the wheel to go back on. Since the axle is already out it's a good idea to clean and lube it. As I mentioned earlier I only put the wheel back on I didn't tighten the axle nut or adjust the chain yet since I wasn't sure how much slack would be needed for the front sprocket.

Next we'll swap out the front sprocket.

[toku]

Now to change the front sprocket. To start off unscrew the bolt holding the rod to the crankcase and slip it off so that the lever hangs freely.


Next you need to unscrew the three bolts circled in red below that hold the cover. These bolts are not the same length, to help remember how they go I put them through a piece of cardboard marking which direction is up.


Now you can pull the cover off and you have access to the sprocket. Before you can take the nut off the crankshaft you need to straighten out the washer that is bent over the nut.


Once the washer is straight you can begin to attempt to unscrew this nut. That sucker is on there tight. With the bike in first gear and my dad holding the rear brake the wheel still kept spinning and the nut wouldn't unscrew. To stop this I took off the chain guard and placed a 2x4 over the swingarm through the tire.


After that it was fairly easy to get the nut loose. It is now possible to pull the sprocket off and to place the new one on. When swapping the crank sprocket the service manual says to lubricate the new sprocket and crankshaft with molybdenum disulfide. I used some moly grease and put the sprocket on.


After that I placed the washer I took off earlier back on the crankshaft and tightened the nut. To keep the wheel from spinning while tightening I used the 2x4 again but this time I placed it under the swingarm. I tightened the nut 94 ft-lbs, according to the service manual.

At this point you're pretty much done. All that's left is to put the cover and gear lever back on. Then you need to adjust your chain and tighten the rear axle.

I haven't gotten any significant saddle time with this set up and probably won't still spring time but the short test run I took had me wishing I've done this earlier and these bikes should definitely come from the factory with a 15 tooth sprocket up front.

With this set up my rpms dropped by about 1000, a little less I'd say but I was able to travel on some of the roads I've taken before pretty much a gear lower. Setting up for corners I was able to stay in the same gear and have enough power to drive through the corner. Before I was either getting close to redlining driving through corners or I'd have to grab a gear up to drive out of the corner.

EDIT: Since this DIY was published, a number of folks have come to the conclusion that the spacer side of the front sprocket should be facing in, not outwards as shown in the last picture

[kkim]

thank you, sir!

[Alex]

So the new sprockets you put on are 15/44. What are the stock sprockets? (I'm pretty sure it's 14 in front, but not sure on the rear)

[VeX]

Originally Posted by Alex

So the new sprockets you put on are 15/44. What are the stock sprockets? (I'm pretty sure it's 14 in front, but not sure on the rear)

Stock for the '08+ is 14/45

[Alex]

Makes sense. That is a difference in overall gearing (14/45 to 15/44) of just a little under 10%, so if it was turning 10k rpm at a certain speed before, it would now be a little over 9K rpm.

[Trozza]

Do the numbers represent how many teeth the sprocket has?

What would be a good setup for a more fuel efficient run?

[kazam58]

Originally Posted by Trozza

Do the numbers represent how many teeth the sprocket has?

Yes

Originally Posted by Trozza

What would be a good setup for a more fuel efficient run?

The setup that he uses in the DIY would be more fuel efficient. Any setup that has a front sprocket with more teeth than stock and a rear sprocket with less teeth than stock will offer better fuel mileage. If your bike has the power to pull then this will also give you a higher top speed (and less acceleration), so you can only change the gearing so much.
So the closer the ratio between the front and rear sprocket is 1:1 then the better mileage and top speed the bike will have. And vice versa.

[Alex]

Originally Posted by kazam58

Any setup that has a front sprocket with more teeth than stock and a rear sprocket with less teeth than stock will offer better fuel mileage. If your bike has the power to pull then this will also give you a higher top speed (and less acceleration), so you can only change the gearing so much.
So the closer the ratio between the front and rear sprocket is 1:1 then the better mileage and top speed the bike will have. And vice versa.

Neither of these statements are true. The only thing that is guaranteed with a sprocket swap for one with a taller gear (larger front and/or smaller rear) is that for a given road speed, engine revs will be lower.

At that same given road speed, the bike needs to produce the exact same thrust at the rear wheel (often measured as rear-wheel horsepower). If the engine is turning less revs, that often means the rider must use more throttle at that lower engine speed. Whether or not using more throttle at a lower engine speed uses more or less fuel than a higher engine speed with less throttle, well, the answer is it depends. And in many cases, there is actually very little difference at the end (for all reasonable changes in gearing). Depends on the particular engine's power curve, and fuel usage along that power curve. There's no free lunch. To push a certain bike a certain speed through the air takes a fixed amount of horsepower.

As for a taller gear ratio allowing a higher top speed, that's also B.S. for almost all production motorcycles. The only way that would be true is if the motorcycle could pull to the engine redline in top gear, so a taller gear ratio would allow the bike to go faster at the same redline. The ninjette can't pull to redline in top gear, so the point is moot. And any sportbike on the market today is geared such that it can't redline in top gear either; even the hyperbikes are hitting their 186 mph limiter at significantly below their engine's redlines.

[kazam58]

Originally Posted by Alex

Neither of these statements are true. The only thing that is guaranteed with a sprocket swap for one with a taller gear (larger front and/or smaller rear) is that for a given road speed, engine revs will be lower.

Then shouldn't this give better mileage? If you are traveling at a constant speed with 1K less revs then your mileage should be better in theory. I realize that if you're cruising at 5K then it's hard to go down to 4K because of the lack of power on the bike. But when you're talking the difference between 9K and 8K then the power becomes irrelevant and you can use less throttle (and so fuel) to go the same speed. Or am I missing something completely? yes, i did read your explanation in the middle, and it makes sense, but only if you're in a situation where there is a pretty big difference of power between that 1K of engine rpms
Also, for the top speed thing, I realize I should have inserted the word theoretically. A taller gear ratio theoretically gives you more top speed. Of course the ninjette can never reach redline at top speed to begin with, so it won't actually improve top speed.
I don't wish to argue, as you of course know more than I do, but if there is absolutely no gain (in any aspect) with a taller gear ratio, then why on earth would people swap sprockets? going down for the track makes sense so they can get the punch out of corners, but then why don't we all just gear down then if there's no difference in mileage?
Now I'd actually be interested if someone did a "before and after" for mileage and a sprocket swap.

[Alex]

I did a sprocket swap and saw zero change in mileage. The reason 99% of motorcyclists who swap sprockets do so, is for quicker acceleration. Which works. Using a shorter gear ratio allows higher revs sooner, and higher revs for just about all sportbike motors mean higher power, as they make most power not far off redline. And by going to a shorter gear ratio, many of them do lose ultimate top-speed, but gain acceleration. A great example of this would be an AMA superbike. 215+ hp at the rear wheel, but is geared to top out at 175 mph or so at most tracks, even less at some of the tighter tracks. Geared differently they'd likely reach 205 mph or more, but that wouldn't get them around the racetrack any faster. (The 2nd reason I believe sportbike riders swap out sprockets is they love to see the perceived increase in performance since their speedos are now showing faster speeds much quicker, as most bike speedos are run off the countershaft. If the dash is telling you you're accelerating faster, sure feels like you are, even if the actual performance change isn't really as drastic.)

Ninjettes are a special case. We have such a small high-revving motor already, that going to taller gearing makes the bike better behaved on the freeway. It is more comfortable for some people to be going 9.2K rpm instead of 10K pm. Or 8.3K rpm instead of 9K rpm. Less vibration, less noise, motor just feels a little better behaved. But the bike still needs to produce the same amount of hp at the rear wheel to maintain the same speed on the highway, even at those new rpm levels. And there just isn't much difference in fuel economy from 8.3k to 9k rpm, when the bike is making the same power.

If people are really interested just in better mileage, the way to manage that is riding style. A stock ninjette can range from mid-30's mpg up to high 60's mpg, with zero mechanical changes to the bike. Just a matter of how that control on the right handlebar is used.

[kazam58]

alright, well I guess I'll just go sit this one out then...

[Alex]

No need to sit anything out! This board is for all of us to learn more about our bikes. I'm certainly not the be-all and end-all authority by any means, and I learn things from this board and others every day.

One thing that I do know though, is that motorcyclists put way too much faith in sprocket changes as some magical elixir that will give much better performance and fuel economy. When it's just math.

[toku]

As Alex mentioned sprockets don't change power, this change wasn't done for more speed or less fuel. Honestly the way I ride maybe about 20% of the time I'll truly take advantage of the ninjas gas mileage.
Again as Alex said it's really all about changing the behavior of the bike, the taller gearing ratio helps me get the power I want at rpms that I feel are healthier for the engine. Rarely will I take the bike to redline anyway so not having the power to pull to redline in the taller gears isn't something that's going to bother me.

[Viper-Byte]

I am considering swapping the sprockets, not for fuel economy, or accelleration. Just to reduce the RPMs at highway speeds, though I will see what it is like after I have finished the mods that are in the mail (AreaP CF full system and Dynojet jet kit )

[Sailariel]

I find these discussions on sprocket swaps informative. I am constantly doing this on bicycles--except that on a bicycle you are dealing with a 10 sprocket cluster in the rear and a 2 or 3 chainring cluster in the front. It gets quite complicated because in the end, you are the engine. Like Alex, I plan to leave things alone. I like the quiet exhaust, so that will stay stock. I also have no complaints about the performance. I do think that the Kawa engineers did their homework--after all, you have to have done something right to be the top 250 since 1986. My only gripe with Kawa is that their factory Shop Manual leaves a lot to be desired. It very briefly describes procedures and only mentions special tools. It could, for example mention that the rear axle requires a 24mm socket. The DIYs on this forum make the manual look sick. This sprocker DIY is great for those wishing to replace worn sprockets.

[voodoomaster]

Lot of opinions about sprocket teeth, power, and gear engineering. Don't need to bring out the calculus book on this one my fellow engineers. Empirical data collection works better for this. On my little Yamaha Virago 250 I dropped my rear sprocket down 4 teeth from a 45 to a 41. Not a surprise that my overall fuel economy bumped up from the original configuration (from about 80 MPG to well over 90 MPG). I commute 26 miles to the office at a max speed of about 60 MPH. It's a cruizer for gawd sake so one might expect that kind of gas mileage. Anyway. my tach tells me that I dropped around 800 - 900 RPM at that 60 MPH speed. My available acceleration dropped at the seat of my pants, and I can feel that. But at that 60 MPH cruising speed the tach is singing to me, in 800 RPM alto less. So, lets see. My RPMs dropped, my V-Twin is smoother and is happier, my fuel economy improved rather well, and I can STILL go as fast as I want. Don't need no stinkin' math to tell me that dropping the gear drive ratio from 2.81 to 2.56 was the ticket to less fuel use. My + I will raise you 1 tooth

[voodoomaster]

By the way. Has anybody dropped their rear sprocket on their 2008/2009 model to 43 teeth? If so, can you feel the loss of acceleration much in any gear?

[Broom]

some locktight on the bolts that hold your rear sprocket on would be nice too

[inbox526]

Hmmm.... about the sprockets..

taking what I know, if you have a matched gear ration, 1:1, that means that the rear wheel should spin at the same speed as what your engine/front sprocket is right? So for arguments sake, lets say the engines spinning at your 10k rpms, then at a 1:1 sprocket ratio, your rear wheels will be spinning at 10k rpms, which in the end means a REALLY REALLY HIGH top speed. So we can naturally assume there is zilch torque.

At the other end of the spectrum, we start separating the ratio, putting more and more teeth on the back sprocket, which means what, that for every tooth the front sprocket pulls, 1 will be pulled on the back. Which in turn means that the rear wheel does NOT spin as fast as the front sprocket. Which means... lower top speed, but a gain in torque right?

So, out of pure common sense, a closer (1:1) ratio means less torque, more top speed, and a higher (1:15) ratio means less top speed, lots more torque. In proportionality of course.

However there's the thing about saving gas..

I've got the whole idea worked in my head, but I don't know which concept I need to share first.. so bear with me please.

Power is defined as energy over time. More clearly defined here as "work" over time. Work per second you could say.

Work in a very physical sense here is basically your rpms. Each revolution of the engine/front sprocket requires a certain amount of gasoline. That gasoline gives the same amount of work every time its burned up. When you establish that, its so much more natural to make the assumption that "less rpms, is less gas, is gas saved" Thus we have the integral of the puzzle, any decrease in overall rpms needed to do anything, will save us gas.

The reason this works, is that the force you need to maintain a certain speed is yes, a certain "rear-wheel horsepower," how much of this rear-wheel horsepower is actually given by the engine is very different, and dependent on your sprocket ratio. Alex, i believe you were mistaken in assuming that rear wheel horsepower is the same as engine horsepower. If you need x amount of rear-wheel horsepower, you must ask y amount of power from the engine. But y does NOT equal x at all times. Its dependent on your sprocket set up. What happens is if you're using a 1:1 ratio, (or defined as 1/1, which is 1) you are using 100% of your y into pushing out x, giving your top physical speed from your engine. But lets say you use a 2:3, or a 1.5 sprocket ratio, then you are using 1.5 of y to push out the same amount of x, which means you have that much less maximum y to push out the same amount of x. Now, you can do this indefinitely to get more and more acceleration, but we'll run out of top speed. Where as if you went the other way and sprocket the ratio closer, you'll get more top speed. However the limiting factor is not really how much engine output there is, but rather, how fast your rear wheel can spin before it destroys itself. Wheels simply CANT spin at 14k rpm. So we take all that extra energy we can't exactly use yet, and put it into straight acceleration (with a transmission. A sprocket ratio is just a more permanent thing).

As I was writing this post, I found the best way to think about it was literally, to think about your gear box. You know the lowest gear has the most torque, the most acceleration. When you finally use up all of your horses into accelerating, you shift up, to a bigger gear, a gear with more teeth you could say.

[Alex]

Nope.

Pushing a bike down the road at a certain speed is always going to require the same amount of power from the engine. And the same amount of work from the engine. The rear wheel is turning at the same speed. And all of the forces trying to keep the rear wheel from turning at the same speed are exactly the same (wind resistance, rolling resistance, and every other class of friction).

The engine can certainly be turning different speeds to push the rear wheel at the same speed, that's what a transmission does, and changing the sprockets in any way will do the same thing by adjusting the effective ratio from crankshaft rotation to rear wheel rotation. But running the engine twice as fast does not use twice the fuel, and running the engine half as fast does not use half the fuel. Think about what happens when you are revving an engine with very little load on it. Notice how at 1/8th throttle, it still goes all the way to redline? Then think about when there is close to max load on it, going up a steep hill, and when you apply even full throttle, the engine in many vehicles struggles to reach redline very slowly, if it ever gets there. Amount of throttle alone does not equal amount of revs an engine produces. Amount of throttle, combined with the current load on the engine equals the amount of revs an engine produces. At a higher (taller) gear ratio (engine spinning slower), there is more load on the engine, which requires more throttle (more gas per revolution) to produce the same amount of revs. At a lower (shorter) gear ratio (engine spinning faster), there is less load on the engine, which requires less throttle to produce the same amount of revs.

All that said, the slower an engine turns to produce the same power, usually that does mean that it is using the minimum amount of fuel that it can. This is primarily due to less frictional losses in the engine at a lower engine speed, even though it needs to use somewhat more fuel per revolution to make the same amount of necessary power. Yes, bikes get better fuel mileage in 6th gear than 5th gear at a certain speed. Yes, they get better mileage in 5th gear than 4th gear, at a certain speed. But they don't get 6/5ths better mileage. And they don't get 5/4ths better mileage. Doing the math the other way: lowering the revs from 9000 to 8000 does not change the fuel consumption to 8/9ths what it was. More throttle is necessary at 8000 to make the same power that was being made at 9000 rpm. So the actual fuel consumption is a heck of a lot closer to 17/18ths what it was. Or even 35/36ths. Theoretically lower, but a small enough difference that it may not be enough to even notice. A 10% gearing change does not (and can not) result in a 10% increase in fuel efficiency, if the vehicle is driven in the exact same manner at the exact same speeds as prior.

[lavid2002]

When swapping the crank sprocket the service manual says to lubricate the new sprocket and crankshaft with molybdenum disulfide. I used some moly grease and put the sprocket on.

Thats cool that you guys use this! I dont own a motorcycle but im trying! I am however a very avid marksman. I reload my own ammunition and some of the reloads I make use Molybdenum disulfide covered bullets (I just call em moly) They yeild higher velocities, cleaner bores, and dirty fingers. :P

[Rawr]

Originally Posted by voodoomaster

By the way. Has anybody dropped their rear sprocket on their 2008/2009 model to 43 teeth? If so, can you feel the loss of acceleration much in any gear?

BUMP

im also curious about this...i was actually planning on droping mine down to 41, giving me nearly the same ratio as 15/44...i know i will lose acceleration...but i feel this will be overcome by my installation of dynojet 98s and a full area p

soooo yea....anyone out there feel a very noticable loss in acceleration?

[Broom]

Yes, you're going to notice a difference. Even with the pipe and jet kit. If fun acceleration isn't important to you, then it'll be fine
Posted via Mobile Device

[Buffalony]

So uhh. I want a 20T front and uhh 30t rear how much extra gas is that gonna use?


Kidding kidding

So essentially changing out the front and rear come down to rider needs/preferences, theres a trade off either way because the same amount of energy is needed to achieve and maintain a given speed!

How does engine efficiency plays a role here?

The ability of a motor to run at higher revolutions can hinder its ability to harness energy in an efficient manner((see first attachment. m=motor)). Generally speaking about sportsbikes they are higher RPM, Higher HP to torque machines.
Demonstrated here:
http://www.sportrider.com/performanc.../kawasaki.html

Generally speaking about the amount of bang your getting for your buck. With the absense of fuel injection and computer engine management systems and a fuel return line it's pretty easy to determine anyway you gear our little ninjette it will use the same amount of fuel.
demonstrated here:
http://upload.wikimedia.org/wikipedi...oke-Engine.gif

a 14t/45t stock setup going x mph at y RPM needs the same amount of energy as a 15T/44T going the same road speed but with a different engine speed((see second attachment.P=power V=velocity)). Another way to put it..>At the same road speed: The engine rotating more is doing a greater number of smaller burns, the engine rotating less is doing a lesser amount of burns harder. Also demonstrated above.

One critical factor left out of our pointless dispute is tire size. Demonstrated here:
http://en.wikipedia.org/wiki/Gear_ratio

And in the end to really be the fastest most fuel efficient bastard out there... wait until you get home to eat instead of showing your bike off at the local Micky Ds like I do.

Well hope you guys understand my point. I wasn't serious.

[voodoomaster]

Originally Posted by Buffalony

So uhh. I want a 20T front and uhh 30t rear how much extra gas is that gonna use?


Kidding kidding

So essentially changing out the front and rear come down to rider needs/preferences, theres a trade off either way because the same amount of energy is needed to achieve and maintain a given speed!

How does engine efficiency plays a role here?

The ability of a motor to run at higher revolutions can hinder its ability to harness energy in an efficient manner((see first attachment. m=motor)). Generally speaking about sportsbikes they are higher RPM, Higher HP to torque machines.
Demonstrated here:
http://www.sportrider.com/performanc.../kawasaki.html

Generally speaking about the amount of bang your getting for your buck. With the absense of fuel injection and computer engine management systems and a fuel return line it's pretty easy to determine anyway you gear our little ninjette it will use the same amount of fuel.
demonstrated here:
http://upload.wikimedia.org/wikipedi...oke-Engine.gif

a 14t/45t stock setup going x mph at y RPM needs the same amount of energy as a 15T/44T going the same road speed but with a different engine speed((see second attachment.P=power V=velocity)). Another way to put it..>At the same road speed: The engine rotating more is doing a greater number of smaller burns, the engine rotating less is doing a lesser amount of burns harder. Also demonstrated above.

One critical factor left out of our pointless dispute is tire size. Demonstrated here:
http://en.wikipedia.org/wiki/Gear_ratio

And in the end to really be the fastest most fuel efficient bastard out there... wait until you get home to eat instead of showing your bike off at the local Micky Ds like I do.

Well hope you guys understand my point. I was'nt serious.

[almost40]

Was gona post but then decided not to Ive posted way too many times on this topic. Find my other post if your looking for some insight.

[hzrnbgy]

what metric size do you guys need to loosen the front sprocket?

[Buffalony]

Originally Posted by hzrnbgy

what metric size do you guys need to loosen the front sprocket?

27mm. Search?

[hzrnbgy]

i have a 17/16 SAE size but its kinda loose

i guess i should stick with the metric sizes

[kkim]

Originally Posted by hzrnbgy

i guess i should stick with the metric sizes

yes, most definately. this is not a nut you want to have any "looseness" on the socket seeing as it's so tight on there.

[voodoomaster]

Originally Posted by kkim

yes, most definately. this is not a nut you want to have any "looseness" on the socket seeing as it's so tight on there.

Only a "nut" would use a non-metric socket on a Cowsooki nut

[Buffalony]

Originally Posted by voodoomaster

Only a "nut" would use a non-metric socket on a Cowsooki nut

Sounds nuts.
While your picking up a random 27mm socket. Grab a 17mm and a 24mm to save yourself a trip or two. 17mm right rear axle 24mm left rear.

[voodoomaster]

Originally Posted by Buffalony

Sounds nuts.
While your picking up a random 27mm socket. Grab a 17mm and a 24mm to save yourself a trip or two. 17mm right rear axle 24mm left rear.

HeLL! Buy a complete metric set...and get the best you can afford while U R at it.

[hzrnbgy]

after three attempts at unscrewing the sprocket nut, im still unable to take that damn nut off the sprocket.

i have a 27mm socket and a 22" drive wrench. what am i missing still? that sucker is driving me crazy. do i need to heat it up or something? melt the black rubber to loosen it? should i get a longer wrench? im running out of options already...

pleaseeeeee help.........

[Broom]

you need a 3 foot piece of pipe to use as a breaker bar

[Buffalony]

Flaten the bent washer, put a 2x4 through the rear rim, Get a long pipe to put over the wrench handle for extra leverage, crack it off

[hzrnbgy]

three foot? thats from the socket to bar end right? i got a 22" so i need more. dang!

gotta run to City mill

thanks man

[Buffalony]

Originally Posted by hzrnbgy

three foot? thats from the socket to bar end right? i got a 22" so i need more. dang!

gotta run to City mill

thanks man

It doesnt matter as long as your getting more leverage. 2ft may even work. Longer the better. Dont go all 10 footer an sh!t
A good sized Dead Blow hammer might work ok aswell.

[voodoomaster]

Originally Posted by Buffalony

It doesnt matter as long as your getting more leverage. 2ft may even work. Longer the better. Dont go all 10 footer an sh!t
A good sized Dead Blow hammer might work ok aswell.

I agree. Your socket wrench can be extended with the pipe from a pipe-clamp (wood working tool) or any medium to heavy wall pipe. 2 feet will be fine if you employ the aid of a 3 pound mini-sledge hammer. Give the set-up a good whack. The longer the pipe, the better leverage. The 2x4 jammed thru the rear wheel will keep the engine from turning while you work. Don't forget to flatten the washer first. Have a torque wrench to re-install???