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[br]Since I did this conversion, alot of people have been asking me about where to buy the sprockets, how much, is it worth doing.. etc etc. So I thought I'd do a write up which can answer all the questions people might have in reguards to it, and include a walkthrough into how it may be done.

[red]Background info[/size=6][/red]
The cbr250rr's stock sprocket setup consists of a 52 tooth rear sprocket and a 17 tooth front sprocket. From memory the chain is 136 link, however im not sure of the pitch. This is the regular setup any stock cbr250rr will come with.
So, why would we want to change the size of the sprockets? Well.. the less teeth we have on the front sprocket, and the more teeth we have on the rear sprocket will determine how much faster the chain will run along the sprockets and rotate the rear wheel. The higher the rate of which the rear wheel rotates in a set amount of time, the more acceleration we have. There is ofcourse downsides to doing this, but that will be discussed later.
Why 14/53? why not any other combination of sizes? well the stock sprockets of the cbr250rr are only sold with either 52 teeth, or 54 teeth from most bike stores. You can ofcourse use the 54t rear sprocket with the stock 17t front, however that will only grant you 4% increase in acceleration (gay). The 14/53 sources sprockets from other bikes, and a different chain to give you a very nice increase of acceleration without losing too much top end speed (will be discussed later) so we could say it would be the optimum sprocket conversion to go for, with the parts which are available to us, and will fit on the cbr250. In saying this, none of the new sprockets, or chain, are designed for the cbr250. The front sprocket is off the VTR250, and the rear sprocket is off some old dirt bike, however they do fit the cbr250 perfectly, so don't worry too much about this.

[red]Purchasing[/size=6][/red]
I bought my sprockets and chain from MCA in Auburn and the city. Most other bike stores should sell them, however they might have to order the rear sprocket in, which could take time. They are usually more expensive aswell. I would suggest to buy from MCA.
Firstly, give them a call and see if the sprockets and chain are in stock. Dont mention that they are for a cbr250 otherwise it will confuse them, and they will start blabbering on about how the sprockets you are inquiring about won't fit your bike (they don't know about this uber sprocket mod).
Instead tell them to look up in the link international book (this is the book they use to source and track down all the parts in store) for the sprocket codes:
31-kvo 14 tooth - This is the front sprocket. It is from the VTR250
32-428 53 tooth - This is the rear sprocket. It is from a dirt bike, so tell them to look it up in the dirt bike section of the book, otherwise they will tell you they don't have it.
Lastly ask for a 120 link, 520 pitch chain. They have a few of these, they vary in quality and price, so it is up to you with which one you go for. I went for the cheapest which was the RK 520S0 O-Ring chain.
The prices you should be paying for these are:
Front sprocket - $17? (cant remember for sure though)
Rear sprocket - $55
Chain - $136 (for the cheapest)
If they dont have something in stock, ring other MCA stores and see if they have them. I got my front sprocket and chain from Auburn and rear sprocket from the city store. If no one has them, ask them to order one in. They will do it.
Here are some pictures of what everything looks like, dont be alarmed at the size of the rear sprocket. I almost shat my pants when I saw how big it was.


Rear Sprocket^[/size=3]

Front Sprocket^[/size=3]

Chain^[/size=3]

[red]Converting the sprockets[/size=6][/red]
What you will need:
- Rear Stand
- Your trusty tool kit. wont go into too much info
- Breaker bar will be very useful
- Angle Grinder or chain breaker tool.
- your new sprockets and chain.

Start by removing your LHS fairing. Once it is off, move down to your front sprocket cover. Remove the speedo drive, and then the sprocket cover. If you got alot of gunk and shit in here, I suggest you give it a good cleaning. When your front sprocket is exposed, you will need to loosen the bolt holding it on (the big one right in the centre). This has been a very annoying task for most and it will be the part where a breaker bar will save your life. You will also need to make sure your bike is in gear when you try and remove this bolt. I did it in one go with a long breaker bar.Proceed by removing the front sprocket, and just let the chain hang down.
Raise your bike on the rear stand and remove the rear wheel and put it aside. Now if go get your angle grinder/chain breaker tool and cut through your old chain and take it off and throw it in the bin.
Pull the rear sprocket off the back wheel and replace it with your new sprocket, put it back into the cush drive housing, and put your rear wheel back on.
So now you should have both your new front and new rear sprocket on, with no chain.
Now you will need to get your new chain and cut 3 links off it. Do this with an angle grinder or chain breaker tool, and install it.
Put everything back on, and your ready to go!

[red]Pro's and Con's[/size=6][/red]
Here is a review which I wrote about the mod, and what I thought on my very first ride. I mounted a camera for my ride to try to give you a better idea of how the acceleration is, although it turned out very shakey: http://www.youtube.com/watch?v=PxJsLROT_as

Review:
I was at first hesitant to go with this setup, as the size of the rear sprocket kinda threw me off when I bought it. Nevertheless, After some convincing from Fatty, I went ahead and bought the sprockets and chain and took them home to be fitted.
I was aiming to do the whole thing in a few hours, although that few hours stretched to a few days, and then became a full week (stupid work) and the suspense of trying her out was getting to me. But FINALLY.. everything is back on the bike, and she was ready this morning to go on her maiden voyage with the new 14/53 sprocket setup.
She glided out the garage like a pushbike, no resistance whatsoever.. mmm.. the feeling of new sprockets. I fired her up, and she awakened with a deafening roar, much to the dislike of sleeping neighbors.

I didn't thrash her all that much to start, I went around for 5 minutes getting everything warmed up, but even so, I could feel her pulling away like a whole different bike. I came around the block, stopped outside my house and waited for a clear road to let her rip.
I jumped on the throttle, opened it all the way up, and within 2 seconds (quite literally) I was at redline in first gear, and going WTF!! where did my revs go!?! The front wheel nearly lifted off while I was in sitting position, I guess the 115 sized jets and unifilter played a part in that aswell.
Pushed her into second, and the same thing. 2 seconds and I was at redline again. At this point, I hadn't noticed a loss in speed, it felt like I was still traveling at however many km/h it was, but the acceleration took me there much, much quicker. To be honest, I felt like I had a brand new bike.
It was once I got up into 5th gear that I noticed.. shit, my left foot is going nuts with shifting. This was the first downside I noticed. You are shifting like crazy, to a point where it felt weird. From memory I had to take it into 4th or 5th gear just to ride down my street without sounding like a F1 car on steroids.
At this point I was still pretty excited at the new acceleration, but was bummed out at the rate of gear switches I had to do, I wasn't expecting it to eat through gears that fast.

By the time I got home after a short half hour ride, I was happy with the sprocket conversion, but if I had the choice again I think I would go with the 17/54 to be honest. The reason why this conversion works pretty nicely on the mc22 is that it revs to 20k (from memory). So it is quite nice that you can take it to redline and still be putting out a decent speed, unlike other learner bikes I have ridden.
I would like to try get a camera mounted to the bike and take a video to show you just what its like. I'll try to do this by the end of the day.
All in all, I don't think I could ever go back to the stock 17/52 after I have tried out the 14/53, but if I still have my bike by the next time I need a change of sprockets and chain, I think I will go with 17/54. Although I am still VERY pleased with it, and the acceleration which it puts out is nuts! (definitely doesn't feel like you're on a 250 anymore)


Here are the actual pro's and cons:
Pro's[/size=3][/size=3]
- crazy acceleration
- its cheap to do the conversion
- It will beat any other cbr250rr you race
- its fucking crazy, just take my word for it, and do it

Con's[/size=3][/size=3]
- Reduced top speed. Some say that your top speed is reduced to 160hm/h, however I have broken that and taken my bike to somewhere close to 180km/h I believe. But when are you gonna go that fast on a aussie road (legally) anyway.
- your speedo will show that you are going faster then you actually are
- Your engine and gearbox will have approximately 18% less life.
- You will be shifting gears much more, however you will get used to this


I ride a CBR250RRR...The extra R is for Red.
 

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How's the fuel efficiency?..
 

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I put 14/50 on my bike a few months ago. I have just ridden from wollongong to cobargo and back again in the last week, and I made it from cobargo to berry, which is about 240k's, and I hit reserve just outside of berry. At about 10,000 in 6th rpm I was doing 100 kph, and I found that it was pretty close to being that the revs matched the speed in 6th; so 6,000 rpm would be 60 kph 14,000 rpm would be 140 kph etc. Power is also much more evident when overtaking, for instance it is quite easy to overtake someone from 90kph in 6th without changing down a gear, unless you want to do it really quickly that is.

I hit the speed limiter at 18,000 rpm in 6th, and found myself cruising at about 11 - 14,000 rpm so it's not exactly a mod to do if you do a lot of touring. However, it is great if you commute in the city or just ride for fun.
 

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banana.logic said:
I hit the speed limiter at 18,000 rpm in 6th
That's unpossible, your speedo must be miles out. I'm quite sure my 250 rocked stock gearing, and it revved more than that to get to ~194 (limiter).

Justin.
 

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the speedo doesn't read the correct speed, it reads higher so even though I was only doing around 180kph the speedo read 194 and thus hit the limiter.
 

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17 / 52 = 0.3269
14 / 53 = 0.2642

0.2642 / 0.3269 = 0.8082 (your speedo correction multiplier)

194 * 0.8082 = 156kph <- your speed when you hit the speed limiter

Probably high 140's after you've factored standard clock over-read in.

Edit: I missed where you said you put 14/50 on. Your speed would actually be 166kph, high 150's after minusing the clock over-read.

Justin.
 

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could do it.. wouldnt have any effect on the speedo on a mc19 tho, coz it runs off the front wheel
 

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I've got a Jade which runs the MC-14 engine.

I've just done my sprockets and have run with a 14/42 set up. 100km/h = 9000RPM in 6th.

On the track I've done 170km/h no problem with more to go.

Acceleration is good and no need to chop down too many gears.
 

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Hey guys.
I just bought a;
- 520pitch rk xring chain $99
- 14 teeth jt $39
- 48 teeth jt $42 (picking this 1 up tmr)
Can't wait to stick these on.
Expecting good results.
 

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Mate I think the smaller rear sprocket will just cancel out the benefits from the smaller front sprocket. Usually it's a larger rear, or smaller front for added acceleration.
 

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the VTR250 stock is;
Front 14
Rear 41

I bought;
Frong 14
Rear 48

= Big difference.
My original sprockets were;
Front 17
Rear 54

HUGE HUGE difference. took me around 4 hours or so today, and went out for a lil test ride.
I'M BLOODY happy with the results.
haven't tried wheelies yet :p
 

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But i thought if u had a bigger front sprocket or a smaller rear u can get more high speed??? I know u can get wheelies with a bigger rear but on a stretch can u get the maximum ??
 

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Done 190.
Was interesting but if busted i would have
BEen in deep shit.
Also i dont see the need for higher top
Speed coz first of all u will never need it.
Second; at 190 i felt this old 1989 bike was
Going to fall to bits.
What u need in this traffic filled with shit &
Crazy drivers is acceleration so hopefully
U can get out of sticky situations.
Front 17
Rear 54; guarantee 180 or 190 speed
My new setup i havent tested yet.
I havent even gone up to 100kmhr yet
 

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Ok so today i got this sprocket mod installed, couldn't be stuffed doing it myself so i had a shop do it.
at first they freaked out a bit and kept on asking me if i knew what i was talking about.
but eventually they just shut up and put it on for me.
i have to admit i was pretty worried about it while it was getting done thinking, shit, what have i done, i cant afford to put it back to stock if this turns to shit.

so when i first jumped on to ride it home wound it out a bit through 1st, meh, nothing life changing yet. So once i got a clear run in front of the traffic i opened her up abit more looked down at the speedo and it says 150... i shit you not, i was doing maybe 70-80 tops. and the tacho was sitting somewhere around 12 million or so in 6th.

but the more i ride it the more im getting used to it, still always going for another gear though.

thats my quick spill about my latest mod.
cant wait for the hour long ride down the M4 to work though. that'll be fun...
 

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Ninexz said:
it does take a while to get used to.
First rideout to palm beach and the empty 3 lane roads going home around 1am at night had me never look back to going stock again.
How'd you get used to the speedo? This is next on my list of mods after tires
 

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Pfft, who looks at the spedo...

You judge by the other vehicles around you, I generally let the needle sit around ten k's above the legal limit (when I'm not intentionally speeding) and haven't had any problems yet.
 
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