Gearing

[MR INDY]

just wondering if I have 42/24 Gearing and I wanted to put a 43 bottom and assuming it would fit can I do this because some Gearing combination are not on the polaris chart so if a 43 tooth in and wanted a higher gear ratio can I do this or do I have to follow the recommended chart

 

[OutCast]

Centre to centre is 7.5.
The 24/42 and the 24/43 will both use a 74p chain.
24/42 being a 1.75 ratio and 24/43 is 1.79. I wouldn't go more than a 1.75 unless you are running bigger than a 1.5" track.