I have replaced the freewheel on my bicycle with a singlespeed. However, the chain line appears to move inwards from the rear to the front. picture
I have measured the rear frame spacing as approx. 127mm. picture I then measured the distance from the center of the freewheel (teeth) to the inside of the rear fork, which was 25.4mm. picture As per Sheldon Brown's website, the rear chainline measurement calculates to 38.1mm. I have measured the distance from the teeth of the chainring to the middle of the seat tube which is approx. 42mmm. Does the difference between the front and rear need to be within 1mm?
I think the only way I can achieve a straighter chainline is by removing the bottom bracket cartridge ring and placing a 2.5mm BB spacer from eBay between the ring and the BB shell. But I'm not sure this would work.
Alternatively, could I add a slightly longer spacer to the rear axle on the freewheel side, a shorter spacer on the non-drive side to move the rear chainline inwards and then redish the wheel?