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Mine isn't.
That's interesting Mike. All US riders have reported that their speedo's are more or less accurate, that is until you said this (you are in the US, aren't you?). Mine's about 10% optimistic, according to my sat nav, which I trust more than my speedo. I'd rather mine was accurate. In my view, it has safety implications. Over here, if you do 27 mph in a 30 mph zone, you'll be holding the traffic up, and constantly have people tailgating you, and trying to overtake you, even when it's not safe to do so. I compensate for this by doing 33 mph on the speedo, but those that don't know, and are trying not to speed, are putting themselves in unnecessary danger.
 

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15 t

Nice photos. The same procedure applies to fitting a 15T front sprocket with the additional step of trimming the nubs from the plastic sprocket cover so that the metal guard piece can be positioned all the way forward against the bolt holes to make sure it doesn't rub.
I have installed 15T for CBR 250, the metal guard needs to be removed. Now the bike is different.
 

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I have installed 15T for CBR 250, the metal guard needs to be removed.
Without the metal guard (known as a "Case Saver") in place, if your chain breaks under power, you run the real possibility of major damage to the engine crankcase.
 

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My 13T Renthal sprocket arrived today and I installed it. Wow, what a difference. In the past, my son, on his 1985 Honda V45 Magna (750cc, 80HP, 550lb bike, ~300Lb rider) was able to pull away from me very easily, now I can actually keep up with him. We left a gas station tonight, and he went full out and I was able to just barely keep up with him. It's much more responsive around town etc. as well.
 

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I just clicked "Buy Now" on a 13T Renthal... Let the games begin!!

Now I don't plan on purchasing a speed labs dr thing because I'm used to an off-speedo, but can anyone confirm that the mileage/odo will still be accurate? I'm guessing that the speedo and odo are measured differently but haven't read anything confirming this yet.
 

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I just clicked "Buy Now" on a 13T Renthal... Let the games begin!!

Now I don't plan on purchasing a speed labs dr thing because I'm used to an off-speedo, but can anyone confirm that the mileage/odo will still be accurate? I'm guessing that the speedo and odo are measured differently but haven't read anything confirming this yet.
Actually the speedometer and odometer both operate from the same signal coming from the speed sensor in the gearbox. Any sprocket size changes will affect both meters.
 

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So i know there's lots of talk about the ratio.

so the ratio for 13/37 = 2.85
and the ratio for 14/40 = 2.84

my question is does the size of the actual sprockets matter or do you really care about the ratio. Is there any real difference between the 2 set up? The only thing i can think of is it's 'less' weight. Hopefully this makes sense

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So i know there's lots of talk about the ratio.

so the ratio for 13/37 = 2.85
and the ratio for 14/40 = 2.84

my question is does the size of the actual sprockets matter or do you really care about the ratio. Is there any real difference between the 2 set up? The only thing i can think of is it's 'less' weight. Hopefully this makes sense
If your goal is a ratio close to 2.850 it would make more sense to go with 14/40 (which is actually 2.857) rather than a 13/37 (2.846), as you are only having to change the rear sprocket. From what I've seen, the only aftermarket rear sprockets that are currently available for the CBR250R are made of aluminum so they are lighter, but at the expense of shorter service life. I haven't seen any steel aftermarket rear sprockets available for this bike.

Most who change to the 13T front sprocket are using the stock 38T rear sprocket, for a ratio of 2.923... front sprockets are always made of steel, so they are much less expensive than what aluminum rear sprockets sell for.

One more thing to consider is that the average rider will not notice a huge difference between a 14/40 (2.857) and a 13/38 (2.923) set up as far as typical riding goes... the 13/38 ratio will have a slightly lower top end speed.
 

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Yeah I'm aware of that I guess my question wasnt clear my apologies

I'm just trying to figure out which ratio has less top speed for 13/37 & 14/40 given the ratio has a difference of about .01. I'm probably thinking too hard haha. These 2 have the 'same' ratio practically but since the 13/37 are both smaller than 14/40 will that affect anything. Im attempting to get into racing so life service isn't an issue.


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One more thing to consider is that the average rider will not notice a huge difference between a 14/40 (2.857) and a 13/38 (2.923) set up as far as typical riding goes... the 13/38 ratio will have a slightly lower top end speed.
I guess from that statement the 13/37 should have the slightest higher top speed from my understanding

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I guess from that statement the 13/37 should have the slightest higher top speed from my understanding.
Yeah, it would be a slightly higher top speed, though it's really splitting hairs as far as the difference between those ratios.
 

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Thinking about changing to the 13T sprocket. With 9,500 miles on the bike am I going to have to get new chain and rear sprockets? When changing sprockets on a bicycle you have to change both.
 

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Thinking about changing to the 13T sprocket. With 9,500 miles on the bike am I going to have to get new chain and rear sprockets? When changing sprockets on a bicycle you have to change both.
Kind of a tough question, considering that your chain & sprocket set are about mid way through their lifespan at 9500 miles.

What kind of condition are your chain and sprockets in now? If they look to be in good condition, you could just get an inexpensive 13T sprocket (JT Sprockets has one for about $12, through partzilla.com) and install it with your current chain and rear sprocket, although doing that will accelerate the rate of wear on the drive chain as well as the new 13T drive sprocket.

If your current chain & sprockets are worn out, then obviously just replacing the whole works all at once is the way to go. I'm at 10,500 miles on my CBR, and the chain & sprockets are in pretty good shape, although I changed to the 13T sprocket back when the bike only had about 2500 miles on it... expecting to get another 6000 to 8000 miles from this set.
 

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Correction

Updating the post below. I eventually got the ordered J.T sprocket on after trying different locations on the spline in addition to flipping the plate over. I tried this initially but learned you may have to try putting the sprocket on several different locations. I actually tried to match the same tooth location from which the old sprocket was removed and the plate aligned quite easily,

So learn from this post below but don't make the same mistake:
Unfortunately my experience with the J.T. sprocket from Motorcycle superstore yielded nothing but frustration. The retainer holes on the sprocket did not align with the stock retainer plate. The sprocket fit the spline like a glove but the retainer plate holes were too wide. Seems like they would pair the retainer plate with this sprocket. I noticed a touch of later play in my 14t sprocket. Bike ran fine after putting it back together. But it took a few tries to the get the stock sprocket back and the plate aligned.
 

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Unfortunately my experience with the J.T. sprocket from Motorcycle superstore yielded nothing but frustration. The retainer holes on the sprocket did not align with the stock retainer plate. The sprocket fit the spline like a glove but the retainer plate holes were too wide. Seems like they would pair the retainer plate with this sprocket. I noticed a touch of later play in my 14t sprocket. Bike ran fine after putting it back together. But it took a few tries to the get the stock sprocket back and the plate aligned.
Did you try flipping the retainer plate over?... the bolt holes on the plate will only line up with the sprocket holes from one side of the plate.

Also, it's a good idea to use some anti-seize compound on the output shaft splines. If you don't have anti-seize, some bearing grease would be better than leaving it dry.
 

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Yes, tried flipping it over. I aligned the sprockets atop one another. With the spline center teeth aligned, the plate holes on JT sprocket do not align with the stock sprocket. Too far apart.
What JT part number is on the sprocket?

For the CBR250R it should be a JTF1321-13

Specs for JT CBR250R Sprockets : JT Sprockets: Catalogue
 
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