Bicycle Mechanics - 7 speed 8 speed tandem conversion
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05-10-08, 05:11 AM
hi i just got a tandem which came with grip shifters and a 7 speed set up (inc. a shimano back hub). i want to swop them with an old set of shimano xt 8 speed shifters.
can i just put a new, 8spd. cassette and chain on and change the shifters or is it more complicated than that? sheldown brown (rest his soul) says i can run a 9 spd casette, but just take one cog off. has anyone tried this or does anyone know how it work in practice? i cant see how you could fix it to the hub.
any advice appreciated, i am very new to the world of tandem mechanics.
05-10-08, 08:03 AM
How picky are you?
7-speed and 8-speed rear cog spacing are pretty close. Many folks claim to mix and match 8-speed shifters with a 7-speed cassette or freewheel with good results. Personally, I've never been satisfied with that but YMMV. If you want to try doing that, adjust your cable tension so that it's spot-on when the chain's on the middle rear cog.
A 8-speed cassette won't fit on a 7-speed freehub body. Incidentally, does your bike have a freehub or 7-speed spin-on cassette?
Sheldon's "8 of 9" scheme involves using a 9-speed shifter and chain and throwing away the largest cog from a 9-speed cassette. Eliminating the largest cog will allow the cassette to fit onto the narrower 7-speed freehub body.
05-10-08, 09:22 AM
cheers for that.
i'm not too picky, and i have all the bits, so it would be a just matter of a wasted afteroon if it didn't work! certainly the sheldon brown method won't work: i'd rather buy a new hub than new shifters (and bite the bullet and learn how to build wheels).
From what i understand, you think i could just change the shifters and leave the 7 speed cassette, chain and all. did i get the right end of the stick?
"Personally, I've never been satisfied with that but YMMV." i'd be really interested to know what went wrong when you tried, if it's a matter of slow shifting for example, i'd be happier than with the grip shifters (i hate those things, they give me blisters)
05-10-08, 09:49 AM
8 speed shifters and 8 speed cassette is fine as long as you have the needed clearance in the drop outs.
05-10-08, 11:11 AM
"Personally, I've never been satisfied with that but YMMV." i'd be really interested to know what went wrong when you tried,
I've had non-matching shifters and rear cogs do a couple of different things:
In a couple of cases it would work fine as long as you're going in the same direction. Shifting to a faster gear, for example, one shift would move the chain one cog just like it's supposed to. When I'd go to shift back to an easier gear, however, it would take two shifts to move the chain the first cog. After that it would be one for one until I started shifting into faster gears again.
In other cases I'd have times when, to get into the next gear, I'd have to shift up two and down one.
I've never found it to be unrideable, I'm just picky about everything on my bikes working the way that I think it should. If you already own the shifters I'd definitely recommend giving it a try. If you're buying shifters, I'd look for some 7-speed shifters to buy.
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