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Discussion Starter · #2 ·
OK. I knew it couldn't be that simple. I took the front sprocket size from the sale blurb where it says 14 teeth. Other documents which I now have say its a 15 tooth sprocket and that makes a big difference.
Here is the graph for 15/45.

Now I'll just have to go and count the teeth!
 

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Ok, the graphs are clear in terms of performances but now It wuold be nice to now why the stock one is a 14?
Do you think the 15 could harm the engine?
What about the speedometer? It will be coerent whit the actual speed?
Thanks!!!!
 

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Discussion Starter · #8 ·
Ok, the graphs are clear in terms of performances but now It wuold be nice to now why the stock one is a 14?
Do you think the 15 could harm the engine?
What about the speedometer? It will be coerent whit the actual speed?
Thanks!!!!
14 is the stock sprocket for the 125 and 200. 15 is stock for the 390. Its just that the sales leaflet is wrong because they forgot to change that detail. I haven't done enough miles on mine to know whether the engine will reach peak revs in 6th gear but even if its an overdrive the bike should manage 90 in 5th thanks to the close ratios.
 

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14 is the stock sprocket for the 125 and 200. 15 is stock for the 390. Its just that the sales leaflet is wrong because they forgot to change that detail. I haven't done enough miles on mine to know whether the engine will reach peak revs in 6th gear but even if its an overdrive the bike should manage 90 in 5th thanks to the close ratios.
check with Mos he was doing some sprocket work with his..http://www.ktmduke390forum.com/foru...sories/5505-custom-sprockets-2.html#post35529
 

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Brilliant!
Could you post graphs for 14/46, 14/47, 15/46 and 15/47?
 

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Discussion Starter · #11 ·
Brilliant!
Could you post graphs for 14/46, 14/47, 15/46 and 15/47?
I will try to attach the spreadsheet which you can open in Libre Office or Excel then you can plug in your own figures.

Change cell B3 to your own ratios and everything else should recalculate.
 

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