I have 49×15 on my track bike and have a spare 14 sprocket too – there is quite a big gap between those two so looking at getting another chainring option.

Am i better going with a bigger chainring and sticking to a 15 or a smaller chainring and going to a 14 at the back? Changing the sprocket will be quicker to do but is there an advantage to having a bigger chainring and sprocket?

And now for what i suspect is a stupid question – assuming im using the same chain with a bigger chainring (say 50×15) that will mean my wheel will be closer to the seat tube – roughly how much closer will this be? I’ve got less than a cm to spare so will this mean a new chain too?

Depending on tyre sizes the approximate GI for each setup using the sprockets you have is 49/15 = 85GI and 49/14 = 91GI. All within the realms of normality for the track. 50/15 = 87GI which isn’t so different from what you already have.

I think (and I’m remembering from a long time ago so I may be wrong) one extra/less tooth moves the wheel position 4mm.

Personally I’d keep the 15 and the 14 on a flip flop hub for different race types.

If you’re riding on the road and encounter hills then that gearing massive and you are a riding god.

It is just for track use so no hills other than the banking so im definitely no riding god! A flip flop hub would have been ideal but they are banned i think.

hmmmm, velodrome shop appears to agree with you. damn, possibly time to rethink my wheels and gearing for spring.