Putting a 520 chain on and wondering what you racing/track day guys have gone with for sprocket sizes. I was thinking of going with a 15/41 instead of 15/39. Any suggestions?

what you using it for road or track? each circuit will require a different combination, as a start point 14 & 15 front and 40, 42 and 44 rear sound something like, sure thats what i used to have for my tri-arm

Track only bike which will visit several tracks in the US/Canada. Both long tracks like Road America and Mosport which are pure horsepower tracks with long straights to more flowing tracks like Calabogie and NJMP. Also can you get away with a 41 and 43 without having to change the chain length?

I dont ride a NC29 on the road, but if you do, changing the gearing will (i think) give you false mph/kpm readings, not a problem but just be aware of this. I would say, for road, leave as standard and for tracks, as a general rule go up 2 on the rear leaving the front alone. But to be specific my race NC29 runs at Brands 15/43 and I revs out to 15500, dont know what a standard NC29 runs up to?
Col

the chain length will depend on extremes, a 14/40 will need a shorter chain than a 15/44 most probably, it all depends on your combination, need to try and check

best thing is to do a simple excel spreadsheet and work out the overall gearing for various combinatons, at least then it the chain is to long or short you can work out the next best compromise.