Ossa Mar 1972 Sprocket Sizes

[spinningplates]

Just about to replace sprockets. what would be the best sprocket sizes front and back for genral trials sections.

Many thanks.

[woody]

Rear sprockets come in two sizes, 46 which was fitted to MK1 and 42 which was fitted to MK2 onwards.

MK1 MAR is listed as having 46 / 12 but I'm pretty sure that would be quite high. I've never used a 12 tooth front sprocket.

I always used to run 42 / 10 on my MK2 as I prefer low gearing using the smaller rear sprocket but you can have problems with the chain riding over the boss on a 10 tooth sprocket, so 11 is better. 42 / 11 gives higher but perfectly useable gearing in sections and you can use bottom for virtually everything with that. 46 / 11 is not far off the 42 / 10 combination for a lower option.

If you don't mind the bigger of the rear sprockets, you could go for 46 / 11 as a lower option.

Ultimately it's personal choice, but either of 42 / 11 or 46 / 11 will work ok.

[spinningplates]

Thank you Woody very comprensive answer.

Its a mk1 so have gone for 46 / 11.

fingers crossed should be the last thing I put on the the bike which was meant to be a cheap rebuilt renovation project. What was I thinking ?

[woody]

fingers crossed should be the last thing I put on the the bike which was meant to be a cheap rebuilt renovation project. What was I thinking ?

HaHa - I know what you mean - if ever you find the secret to one of those, let me know...