15T sprocket question - Honda CBR 300 Forum
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post #1 of 4 Old 09-30-2019, 05:54 PM Thread Starter
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15T sprocket question

Being somewhat vintage myself, all my bikes (except an R3) had a speedo driven by a cable to the front wheel hub. If you changed gearing, the difference was reflected in the speedometer reading.
With the 14T sprocket my CB300F speedo read about 80 kph at 5000 rpm.
With the 15T sprocket it still reads 80 kph at 5000 rpm, but I believe the bike is going faster.
Am I correct, is that how a sensor based system works?

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post #2 of 4 Old 09-30-2019, 07:29 PM
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Quote:
Originally Posted by r100 View Post
Being somewhat vintage myself, all my bikes (except an R3) had a speedo driven by a cable to the front wheel hub. If you changed gearing, the difference was reflected in the speedometer reading.
With the 14T sprocket my CB300F speedo read about 80 kph at 5000 rpm.
With the 15T sprocket it still reads 80 kph at 5000 rpm, but I believe the bike is going faster.
Am I correct, is that how a sensor based system works?
Yes your correct BUT it depends where the sensor is positioned on the bike. For example my Ninja has a rear wheel speed sensor positioned AFTER the final drive (which is the bit you are changing) so now that I have changed my gearing it still shows the correct actual speed of the bike, only the tachometer reads less at the same speed. But on the CB/CBR the sensor runs off the out put shaft in the transmission which is BEFORE the final drive so that is why it still shows the same speed at the same RPMs in top gear say but the bikes actual speed is faster.
Clear as mud??
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2018 Ninja 400
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post #3 of 4 Old 10-01-2019, 12:22 AM
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And what kiwi rider surprisingly fails to mention is that the approx. 7% change in final drive ratio actually corrects a horribly optimistic speedometer. I find that with the 15T, my actual speed is now just a hair below indicated speed, instead of the 10+% error of the stock gearing. Not that I pay much attention to my speedo.
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post #4 of 4 Old 10-01-2019, 09:17 AM Thread Starter
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Thanks for confirmation KIWI.

DAN - that sounds good. Now instead of my speedo telling a Trump size lie, I can zip down the road just shy of a speeding ticket.

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