Question,what size sprockets do people use in general.At the moment i swap between 15/40 for short track and 15/38 for tracks with longer straights.With the 15/38 thensr is reving to about 12,300/12,500 on the back straight.So what do youb think?.

No-one can say really, it's down to the tracks. I was using a 42 rear on some tracks.

As long as you top out somewhere near the end of the longest straight in 6th, you're spot on.

If this leaves you with crap drive from a couple of corners, shorten the gearing, as the time lost cornering will be greater than that lost on the straight...

Unless you wanna drop the gearbox and swap ratios at the track!
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

hello dave, dont suppose you would have a starting point for me for the anglesy grand next weekend(ie gearing) Not trying to nick your set up secrets or anything, just trying to save my clutch a little after discovering that my road gearing barely pulls 5th at oulton and made 6th redundant even at aintree, where, trust me they could land jumbos on the straight no bother!!!!!!!! Any help greatly appreciated, by me and my long suffering clutch. Si

Road is waaay too long for almost all tracks. You wanna go up two on the rear to start with and see how that works. You may top out, but I doubt it. It's better to go up on the rear rather than down on the front as smaller sprockets give the chain a hard time. Two up should be ok with a standard chain - another reason for not going down on the front.
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

cheers dave nice of you to help, Its hard enough in the f400 on a mc18 without crippling myself with only three available ratios!
The bike will be pretty competetive in the forgotten era though i reckon, at club level anyway.
Anything you want to pass on regards racing/setting up an nsr would be greatly welcome by my mate and myself who will be around the club scene next year trying to get rid of our orange jackets(at 37 we should know better eh?)
we've done the obvious tuning/maintainence stuff regards bike and engine prep but ???????
we are just doing a couple of events this back end to see where we are with the bikes before the long nights(development season ) kick in.

Thanks again si