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Discussion Starter · #1 ·
I have a cbr250R 2012 with a yoshimura slip on, K&N air filter and a DYNOJET fuel commander. I want to get my bike tuned at the dyno but I would like to change the sprockets first. I want to get my bike as fast as possible. What is the best sprocket ratio for this bike?
 

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Discussion Starter · #2 ·
suggestions on kit

I have been looking at this kit and just dropping the front sprocket down from a 14t to a 12t and keeping the rear at stock size. suggestions?

AFAM Sprocket Kit
 

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A 12t on the front would kill any upper end speed. People have had good luck with 13t's on the front. Many combos for the back have yielded good results, but I know you can run a 13t front without changing the chain. Other than that, I think a 13/38 rings a bell in my mind for a good setup for quicker starts, but I can't remember because once I knew I'd have to change my chain, I lost interest. :)
 

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A lot of 250R riders (including myself) are running a 13T front sprocket with the stock 38T rear sprocket for improved acceleration (particularly in the upper gears) without losing too much top end speed. As cbrlocal said, with this set up there is no need to change to a longer drive chain.

A 12T front sprocket is pretty small in diameter and is not the best solution if you want to go with a ratio lower than what the 13T/38T gives you... it would then be better to go up on the rear sprocket by a couple teeth, along with the 13T front sprocket, to achieve an even lower final drive ratio. However, this would require a longer drive chain. And you would lose a significant amount of top end speed.
 

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I find the 13T perfect. Should be how it is stock. 4th and 5th gear are now peppy enough to get the job done. I never bothered with the speedohealer. The smartphone app I use in conjunction with the bluetooth headset has a built in bitching betty that tells me when I hit 60km/h, 80km/h and 100km/h. Seems the speedo is off by a total of 9% with the -1 up front and the factory error.
 

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Fast cbr

I want to get my bike as fast as possible. What is the best sprocket ratio for this bike?
Top Speed covers many different areas of riding. To name a few.

Stop Light to Stop Light.
60 ft or 100 ft.
1/4 mile Drag Strip.
Bonneville Salt Flats.
Pike's Peak Mountain Run.
Maxton Mile.
Canyon Carving.
Etc, etc, etc...
 

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A 12t on the front would kill any upper end speed. People have had good luck with 13t's on the front. Many combos for the back have yielded good results, but I know you can run a 13t front without changing the chain. Other than that, I think a 13/38 rings a bell in my mind for a good setup for quicker starts, but I can't remember because once I knew I'd have to change my chain, I lost interest. :)
most people ride a 13 / 38-40.

i DO have a 12/40. i love it, but don't do a lot of highway driving. i've gotten her up to probably 100 kph or higher (about 62-65 mph, exact speed not known since my gauge is off now) at around 6-7k rpm in 6th gear, and she could do a bit faster than that. but i'm guessing not much beyond 70mph. so a drop in about 20kph off my top end. a 12/38 wouldn't be quite that extreme.

that's the con. the plus is a first gear that's super low and REALLY pulls (for steep grades in the mountains, in my case) and VERY noticeable pull increase in ALL gears. i remember it pulling well in 3rd-5th, and especially 4th, in stock... it loved highway speeds. now i get that pull, acceleration, and power all the way from 2nd-6th.

use Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator to get an idea. gearing commander suggests about a 15kph drop off the top end for 12/38. the speeds reported match my experience, so i think it's a good tool...
 

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Discussion Starter · #8 ·
thanks

I dropped my front sprocket -1 and kept the rear sprocket stock. My bike now does wheelies as well as improved performance. Thanks for your help guys.
 

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I realize many people can't help fiddling with their bikes, but I think the stock sprocket set up on the CBR is perfect the way it is. I had a Ninja250R with a sprocket mod and although it had slightly better top end acceleration it generally rode like a complete DOG the rest of the time.
My CBR has more than enough usable power & torque across the entire range to even think about doing any kind of sprocket mod on it. I just don't think the end justifies the means for this particular bike. Honda got it perfect right out of the box, IMO.
 

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Honda chose the 14/38 final drive ratio to meet emissions requirements, as well as the fuel economy target for this bike... however, it's not the ideal ratio for real world, all around performance for the typical rider. Sure, by going to a 13 tooth front sprocket you'll lose 5 MPH on the top end, but how often does anyone need to ride this bike at 95 MPH? But by changing to a 13T front sprocket, what you get is a much more responsive bike for everyday all around riding conditions. The improved acceleration in the upper gears is significant... 3rd, 4th, 5th, and 6th gears pull a lot stronger with the 13t sprocket. Even just cruising along in 4th gear on a 45 MPH road, the 13T sprocket moves the RPM's up just enough to be running where the engine is making a bit more power.

I don't think of changing to a 13T front sprocket as a "mod", rather it is a real performance upgrade done by changing a hard part... in today's internet jargon, the term "mod" has seemed to evolve to mean things that are cosmetic, superficial, and mostly non-functional. Fender eliminators are a good example of that. I find it laugh out loud humorous when people talk about putting Monster Energy stickers on their bikes, as a "mod". Just like the kid who puts a neon green mohawk on his helmet, and calls it a "mod". :rolleyes:
 

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I realize many people can't help fiddling with their bikes, but I think the stock sprocket set up on the CBR is perfect the way it is. I had a Ninja250R with a sprocket mod and although it had slightly better top end acceleration it generally rode like a complete DOG the rest of the time.
My CBR has more than enough usable power & torque across the entire range to even think about doing any kind of sprocket mod on it. I just don't think the end justifies the means for this particular bike. Honda got it perfect right out of the box, IMO.
this isn't the Ninja 250r site. don't be so quick to judge. try the 13t front. it's what, $10-15? if you don't like it, don't keep it. but there is a noticeable improvement, IMO (and i've actually tried both stock and mods, so i actually have a basis for an opinion here).

anyway, glad the OP found something that worked for his riding needs!
 

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12T is too tight a turn for the chain and you get losses.
Bigger front sprocket is usually preferable and change the rear,
but on the cbr it just so happens that the 13T front can be fitted without changing the length of the chain and its about perfect gearing.

Any higher and 23hp just wont pull it (ie its so slow stock), and any lower and the slow revving single runs out of revs and hits the limiter too early.
 

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Honda chose the 14/38 final drive ratio to meet emissions requirements, as well as the fuel economy target for this bike... however, it's not the ideal ratio for real world, all around performance for the typical rider. Sure, by going to a 13 tooth front sprocket you'll lose 5 MPH on the top end, but how often does anyone need to ride this bike at 95 MPH? But by changing to a 13T front sprocket, what you get is a much more responsive bike for everyday all around riding conditions. The improved acceleration in the upper gears is significant... 3rd, 4th, 5th, and 6th gears pull a lot stronger with the 13t sprocket. Even just cruising along in 4th gear on a 45 MPH road, the 13T sprocket moves the RPM's up just enough to be running where the engine is making a bit more power.

I don't think of changing to a 13T front sprocket as a "mod", rather it is a real performance upgrade done by changing a hard part... in today's internet jargon, the term "mod" has seemed to evolve to mean things that are cosmetic, superficial, and mostly non-functional. Fender eliminators are a good example of that. I find it laugh out loud humorous when people talk about putting Monster Energy stickers on their bikes, as a "mod". Just like the kid who puts a neon green mohawk on his helmet, and calls it a "mod". :rolleyes:
Not that I disagree with what you're saying in general, but I think changing a part in the power train has to be called a "mod" considering the dictionary meaning of the word "modification":

"the act or process of changing parts of something : the act or process of modifying something"

Much of the other stuff you mention rightly belongs under the heading of "farkles"

So you're telling me that adding a 13T sprocket to my CBR is going to make it pull better in the upper gears, but how does it effect 1st and 2nd? On my Ninja it made those gears noticeably taller and more useable, but lower gearing of the Ninja was crappy to begin with. I find it hard to believe it would have as dramatic a difference on the CBR, which already has the most perfectly useable 1st and 2nd gearing and torque I've ever experienced on a bike.
I just happen to have a 13T cog that's been rusting in my garage and I could use a project for the pretty boring weekend I'm having so far...
 

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12T is too tight a turn for the chain and you get losses.
Bigger front sprocket is usually preferable and change the rear,
but on the cbr it just so happens that the 13T front can be fitted without changing the length of the chain and its about perfect gearing.
13t is ideal for MOST people.

but it's just untrue that a 12t is "too tight". i run a 12t, and it's a VAST improvement over stock. i also bought a 13t when i bought my 12t. i've seen the difference. and it's noticeable. 12t IS tighter. it's a tooth less.

however, i've seen just as tight of turns on other bikes front sprockets (just google it, plenty of bikes with stock 13 that people mod to 12). a chain can double over on itself. so of course it can make that turn. now, is a looser turn preferable? of course. a bigger rear would be better. then you'd need a longer chain.
 

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The 13t sprocket was definitely a cost effective mod. It made first a little grabby which you adjust to it by feathering the clutch turning out of the driveway. But all the gears above 2nd are noticeably improved. You are going to run higher rpms on the interstate, You can accelerate in 6th with lots of pull to pass. No more dropping into 5th unless you are at lower speeds. My bike would not hold its speed in 6th on an uphill interstate grade with the 14th but no problem with the 13th. Mileage only dropped slightly to around 67 mph and i ran the bike hard. I just bought a CBR500R and traded in my little CBR250 which was a gem to ride around town because it is so nimble. The 500 is bigger and a little heavier but smooth as silk. So much more bike but I can tell it will probably not be as nimble in the corners. Still needed to make a move to a bigger bike for longer trips with bags.


Sent from Motorcycle.com Free App
 

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13t is ideal for MOST people.

but it's just untrue that a 12t is "too tight". i run a 12t, and it's a VAST improvement over stock. i also bought a 13t when i bought my 12t. i've seen the difference. and it's noticeable. 12t IS tighter. it's a tooth less.

however, i've seen just as tight of turns on other bikes front sprockets (just google it, plenty of bikes with stock 13 that people mod to 12). a chain can double over on itself. so of course it can make that turn. now, is a looser turn preferable? of course. a bigger rear would be better. then you'd need a longer chain.
Ive noticed going anything less than 14t on dirtbikes really chews them out quickly. (and yes I run 13 on most dirtbikes as they are always geared too high as a cheap way to pass stringent noise /emission standards for ADR's.)

As for my Ninja I run crazy low +4 on the rear and it still does a genuine 163kph, just into 13,500 rpm ,stock would do a theoretical 188kph but I could only get it to 175.
 

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I've never had a problem with the stock setup. 6th is a little gutless, but I cruise at 35mph in 6th and I'm just fine with smooth, roll-on acceleration. On the interstate in the powerband, 65 MPH puts me at 7k RPM which is peak torque range. So I've never had an issue with the stock gearing. But the mid-range dead spots in fueling I can see being helped by slightly lower gearing with quicker revs. I've debated going to a 13t, but I've also debated going to a 15t for mileage as I do a lot of highway commuting.

Either way, I think the stock gearing is just fine. Kicking it down into 5th makes up for the lack of acceleration in 6th with the stock setup, which you'll get in top gear with the 13t front. I always prefer to have an "overdrive" for cruising anyway.

But glad the 13t helped you out OP. It seems to be the best compromise for all around driving if you're not concerned with trying to squeeze every MPG you can out of your baby blade. :)
 

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I ran a 13T for a while then i found that the chain was wearing away at the plastic chain slider (situated on top of the suspension swing arm). Went back to the stock 14T and preferred the longer gearing. I found it exhausting having to shift out of 1st so early with the 13T - prefer the 14T personally.
 

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I just wanna ask if the rear sprocket of honda cr250r is fit to honda cbr250r
I just want to install a 43T rear sprocket for my current build up. Thanks in advance and godbless us all
 

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I just wanna ask if the rear sprocket of honda cr250r is fit to honda cbr250r
I just want to install a 43T rear sprocket for my current build up. Thanks in advance and godbless us all
In my opinion it is NOT the same dimensions. It is best to measure the sprocket that on your motorcycle, because maybe more changes/Modification have already been made to your motorcycle. Also you should have to check that it fits according to the model year, because in models from different years sometimes the dimensions are also different.
Note
1. Changing the gear ratio will cause the speedometer to fake, because the speedometer reads the speed according to the engine RPM.
2. Another problem, as a result of changing the diameters of the sprockets the chain also changes its place, and it can damage other parts of the motorcycle and cause them damage.
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