Quote:
Originally Posted by
JMo
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As a thought - Presumably the speedo reads off the gearbox output shaft? - hence the smaller front sprocket spinning faster shows a higher top speed right?
Now correct me if I'm wrong (I'm no mathematician) but you kept the 15T front and you put a larger rear sprocket on instead (say 47 teeth), the rear wheel is now effectively turning slower for the same engine revolutions? - would than not correct the speedo over-reading?
If so, perhaps this is the problem - that the bike actually ought to be running slightly lower gearing (that is using a larger rear sprocket), but they put on a 45 tooth in an effort to keep the revs down at speed and improving MPG?.......
xxx
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Placing a 47 on instead of a 45 would do the same thing as going from 15 to 14 on the front (well about 65% of it anyway). The pickup is indeed in thre gearbox and the only way to make the speedo read correctly would be to put something like a 42 on the rear or a 16 on the front. Both these would likely make the bike struggle in top gear against a strong wind or slight incline and make off road a nighmare.
The calculation is a simple division sum. e.g.
Standard ............45T/15T = 3.00
Mine ..................45T/14T = 3.21
Your proposal ... 47T/15T = 3.13
I have now calibrated the speedo and I have programmed in an 18.5% (Yes 18.5%) correction to get the speedo to agree with TomTom. This is all very dandy and I now know exactly how fast I am going but the downside is that the odometer is now out by about 7%. After 100 real miles my odo thinks I've only done 93.
It appears that in the stock setup the gearing is correct for the odo but way out for the speedo - possibly in a vain attempt to slow us down.