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I bought a 82 Motobecane Grand Touring bike new (in 82). It's been a great bike for me but I would like to get a lower (granny) gear for touring. The cassette(5) has a 32 teeth gear so I think I will need to change the crank and/or ring gears. My present crank says "motobecane" and may be a Takagi Tourney SP. I read older French bikes use Swill threads.
I can live with the present triple crank but would like to be able to ride up the very steep hills when loaded(the bike).
Anyone done this or know info/sites?
Thanks
Craig
 

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Chainrings

Craig Knox said:
I bought a 82 Motobecane Grand Touring bike new (in 82). It's been a great bike for me but I would like to get a lower (granny) gear for touring. The cassette(5) has a 32 teeth gear so I think I will need to change the crank and/or ring gears. My present crank says "motobecane" and may be a Takagi Tourney SP. I read older French bikes use Swill threads.
I can live with the present triple crank but would like to be able to ride up the very steep hills when loaded(the bike).
Anyone done this or know info/sites?
You need to figure out the bolt circle diameter of your current crank, and then you can choose a smaller inner ring. You don't say what size you have now, but a typical bike from the early 80s would likely have a 30t or smaller, so you're not going to be able to get a much lower gear. That vintage bike could be French threaded BB, but it could be English as well (not likely Swiss, but possible). With a 32 in the rear, your gearing is already pretty low, and you may need to to go to an MTB crank to get a truly small front inner chain ring, though there are touring cranks available too. If swapping cranks, the first thing to figure out is your BB threading. It might be marked on the cups (English is 1.370 x 24, French is 35 x 1). A bike shop might be very helpful in getting these things figured out for you.
 

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Older Motobecanes did use swiss threads, and if it uses them, you will find your choices extremely limited. However, by 1982, there is a good chance it used English threads (AFAIK, Motobecane never used italian or french threading).

If you have a 5 speed rear, you don't have a cassette, you have a freewheel.

Why not try buying a new (or old stock) 6-speed freewheel, and get one with a 34 tooth low? That would be easier and cheaper than trying to find rings for old junk.
 
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