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Discussion Starter #103

Anti-Seize is your friend when working on motorcycles, so lube the Output shaft, retaining plate and bolts.


Slip the sprocket into the chain.


Put the sprocket onto the shaft.
Install the retaining plate then turn it to where the bolts line up,
You may need to rotate it 180 degrees because the 2 bolt holes have a different PCD.
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Hard to know where the anomoly is. My bike's a 2012 model. That should not make a difference. But think I will look at a different option. When you google the issue some other bikes had same issue. They drilled out the holes a bit, which I thought about doing. Just risky drilling out plate hole.
So the threaded bolt hole locations on the sprocket are off by just a very small amount?

It sounds like JT must have had a batch of these sprockets with incorrectly machined bolt holes, which somehow slipped past QC. Might be worth contacting JT's customer service dept... I would think that they would just send you another sprocket.
 

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Flip the retainer over and try all of the different positions of rotation. One way will fit. Three ways won't. and make sure it is the way that has the teeth of the retainer engaged.
We covered those possibilities on the previous page of this thread.
 

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I determined that at 66 mph my speedometer is reading approximately 10% higher. Took exactly 1 minute to ride a mile at 66 mph. Question: Is the odometer off too or is it reading off the wheel?
 

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i changed to a 13t for 1 day and changed it back the next...too much wasted torque....acceleration dropped in everything, except immediately off the line...engine ran smoother and speed shifting was much smoother though...i think a 39t rear would be the better bet...
 

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i changed to a 13t for 1 day and changed it back the next...too much wasted torque....acceleration dropped in everything, except immediately off the line...engine ran smoother and speed shifting was much smoother though...i think a 39t rear would be the better bet...
Actually, changing to a 13T front sprocket on this bike, while not very noticeable in 1st and 2nd gear, does significantly improve acceleration in 3rd through 6th gear. Changing the rear sprocket to a 39T would be such a small improvement in acceleration, I don't think it would be worth doing given the higher cost and limited availability of aftermarket rear sprockets. Comparing the ratios, a 14/38 = 2.714 vs 14/39 = 2.785... the 13/38 combination gives you a ratio of 2.923.

As long as you don't mind losing about 5 - 6 mph on top end speed, the 13T sprocket is the way to go on a CBR250R.
 

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I agree. For under $20 this is a significant improvement. Following the threads on this forum have enabled me to make some great mods, this sprocket change being the most cost effective. New forks, tires, and a 13t sprocket. I just found a nail in my new Pirelli. Plugging it when the kit comes in.


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Actually, changing to a 13T front sprocket on this bike, while not very noticeable in 1st and 2nd gear, does significantly improve acceleration in 3rd through 6th gear. Changing the rear sprocket to a 39T would be such a small improvement in acceleration, I don't think it would be worth doing given the higher cost and limited availability of aftermarket rear sprockets. Comparing the ratios, a 14/38 = 2.714 vs 14/39 = 2.785... the 13/38 combination gives you a ratio of 2.923.

As long as you don't mind losing about 5 - 6 mph on top end speed, the 13T sprocket is the way to go on a CBR250R.
the difference between 2.714 and 2.785 would be very noticeable imo. Ive felt a difference in less than that with other bikes ive messed around with.

but different strokes for different folks. If you like the 13t party on, but for me i know its wasting torque. The engine rides much smoother with the 13t though, ill give you that.

try this, torque the axle nut only by hand, but not that one last bump. Check rear wheel spin by hand, until its most free. Then try the 14t again. A difference in just a quarter turn of the axle nut makes a difference like night and day.
 

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the difference between 2.714 and 2.785 would be very noticeable imo. Ive felt a difference in less than that with other bikes ive messed around with.
Seems like you would need some very accurate, sophisticated timing equipment to be able to measure such a small (0.07) ratio difference. Also, as far as I know there is no such thing as less than a 1 tooth change to a rear sprocket... A +/- 1 tooth change to the rear sprocket is in fact the smallest increment of change available for final drive ratios on any motorcycle.

but different strokes for different folks. If you like the 13t party on, but for me i know its wasting torque. The engine rides much smoother with the 13t though, ill give you that.
That's because the lower ratio of the 13T sprocket increases the engine RPM for a given road speed, in other words, it moves the operating RPM up in the power band. For example, at 60 MPH in 6th gear the engine is turning 6000 RPM with the 14T sprocket... with the 13T, the engine is turning 7000 RPM at 60 MPH in 6th gear.

try this, torque the axle nut only by hand, but not that one last bump. Check rear wheel spin by hand, until its most free. Then try the 14t again. A difference in just a quarter turn of the axle nut makes a difference like night and day.
What? :confused: I'm not understanding this... are you suggesting operating the bike with the rear axle tightened to less than the specified torque?
 

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Sometimes a major change is worthwhile. My "dirt" bike was geared mainly for pavement, and on steep stuff I had to feather the clutch in 1st gear. When the drive (small) sprocket was replaced due to wear, I changed the rear sprocket from 39 to 48 teeth. Now the bike hits the rev limiter at 55 mph, but it sure handles the mountainous stuff better, and I can live with cruising at 50 mph to the trail head.

In fact, it has warmed up enough that it's time to go do that now.

 

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Sometimes a major change is worthwhile. My "dirt" bike was geared mainly for pavement, and on steep stuff I had to feather the clutch in 1st gear. When the drive (small) sprocket was replaced due to wear, I changed the rear sprocket from 39 to 48 teeth. Now the bike hits the rev limiter at 55 mph, but it sure handles the mountainous stuff better, and I can live with cruising at 50 mph to the trail head.

In fact, it has warmed up enough that it's time to go do that now.
Both my XR650L and XR400R got big gearing changes... went from the stock 15/45 (3.00 ratio) sprockets, to 14/47 (3.357 ratio). The most noticeable result was that 2nd and even 3rd gear are so much more usable in some of the slower technical trail sections. 1st gear now feels like you could pull stumps. Tight corners that previously required shifting down to 1st gear can now be taken in 2nd with no clutch chatter. Overall it means a lot less shifting over the course of a day's ride.

Yeah, really nice temps right now for riding... todays high temp in Santa Fe will be 65 F. Had the CBR out for a good ride yesterday afternoon, today I'm heading up to the Santa Fe National Forest with the XR400R for some fun on the old logging roads and single tracks... life is good!
 

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Seems like you would need some very accurate, sophisticated timing equipment to be able to measure such a small (0.07) ratio difference. Also, as far as I know there is no such thing as less than a 1 tooth change to a rear sprocket... A +/- 1 tooth change to the rear sprocket is in fact the smallest increment of change available for final drive ratios on any motorcycle.

no you dont, you just need experience. Who mentioned a less than 1 tooth change, wasnt me - dont make things up., if you cant feel the difference thats just an indication that you havent experimented to see the effects.

That's because the lower ratio of the 13T sprocket increases the engine RPM for a given road speed, in other words, it moves the operating RPM up in the power band. For example, at 60 MPH in 6th gear the engine is turning 6000 RPM with the 14T sprocket... with the 13T, the engine is turning 7000 RPM at 60 MPH in 6th gear.

Youre still wasting torque. The CBR 250 is a high torque low rpm engine. You arent gaining diddly squat with a 13t, its just louder and in your head.

What? :confused: I'm not understanding this... are you suggesting operating the bike with the rear axle tightened to less than the specified torque?
yes i am. The stock torque setting is too high. Fuel mileage will also increase by 10-15 km. You should be able to spin the rear wheel freely atleast 75% of the way around for best performance. If your only getting 25%-50% of a turn your too tight. Of course youd have to adjust chain slack accordingly also.
 

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Factory Torque Specs.

yes i am. The stock torque setting is too high. Fuel mileage will also increase by 10-15 km. You should be able to spin the rear wheel freely atleast 75% of the way around for best performance. If your only getting 25%-50% of a turn your too tight. Of course youd have to adjust chain slack accordingly also.
The torque specs of the front and rear axle fasteners are set to lock the inner wheel bearing(s) race(s) to the axle shaft. If the inner wheel bearing(s) race(s) are not lock, they will spin on the axle shaft. This will cause a spinning metal to metal contact, without lubrication. This will cause the inner wheel bearing(s) race(s) and axle(s) to overheat. Resulting in the wheel bearing(s) inner race(s) to gall and be welded to the axle(s) shaft(s).

The wheels on my motorcycles, will rotate over 5 revolutions when spun with no weight on the tires.
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