Bicycle Mechanics - maximum rear cog

Trying to whittle down my options for converting my Raleigh International to some sensible touring gears while keeping the vintage road bike character of this old classic. Want a triple chainring (steep hills around here!) with a 20 inch low gear. Can do with a 46-36-24 crank and a 32 cog low but can a long cage Dura-Ace derailleur shift a 32 tooth cog and wrap 44 inches? Shimano says no. What do you guys think?

I doubt it. I don't know about Dura-Ace, but the other Shimano long cage road derailleurs sre only rated for a 27 biggest cog and 37 teeth of chain wrap. Most guys will say that you can cheat a little on both specs, but I doubt you'll be able to cheat that much.

An XTR SGS, on the other hand, is rated for a 34 big cog and 45 teeth of wrap up. Good luck on finding a non-rapid rise derailleur.

I doubt it. I don't know about Dura-Ace, but the other Shimano long cage road derailleurs sre only rated for a 27 biggest cog and 37 teeth of chain wrap. Most guys will say that you can cheat a little on both specs, but I doubt you'll be able to cheat that much.

An XTR SGS, on the other hand, is rated for a 34 big cog and 45 teeth of wrap up. Good luck on finding a non-rapid rise derailleur.

You're on the edge of the envelope with the DuraAce at 32T. The specs are so conservative that you can cheat the 27T by at least 3T, a narrow majority of bikes by 5T (depends on the hanger mount) and once in a blue moon a 34T would work. Also, 46/32 is a combo you should never hit, so with good managment you could also avoid it, but there is always that time 1-2 years down the road you forget that could wami your rder.

I've seen people exceed wrap limits on recumbents by 16T or more, but there is a little more slack available there with the long chain and extra tensioners. 7T would be a pretty mild bit of cheating on the wrap that if you are just right on the chain length, you should get that aspect to work.

Also, 46/32 is a combo you should never hit, so with good managment you could also avoid it, but there is always that time 1-2 years down the road you forget that could wami your rder.

I've seen people exceed wrap limits on recumbents by 16T or more, but there is a little more slack available there with the long chain and extra tensioners. 7T would be a pretty mild bit of cheating on the wrap that if you are just right on the chain length, you should get that aspect to work.What does shifting the 46/32 have to do with with RD wami if the chain is long enough??....As for the rest of it, I would not waste my time with a DA RD on a touring ring.Just get a proper mtb RD.

What does shifting the 46/32 have to do with with RD wami if the chain is long enough??....As for the rest of it, I would not waste my time with a DA RD on a touring ring.Just get a proper mtb RD.

I see your point. I was thinking that if there was insufficient wrap, one might keep the chain short enough to avoid the slip when on smaller rings/sprocket, but if you think about the consequences of too short vs. too long, I guess chain skipping is the lesser of two evils.

anchojoe,
Is there some reason you want to use a DA der? Do you already have one? Just get an XT rear der. To most of us mortals there is little noticable difference in shifting. The DA might shift a bit more quickly and crisply, but so what. I have DA, 105, XT, and LX. All shift just fine with STI shifters.

A touring bike should have a long derailleur anyway for this very reason. A der is not expensive.

Sorry about the confusion, my mistake, I don't have a DA. I do have an Ultegra GS medium cage RD for for a triple. Don't know if that changes the equation at all. Just like the the looks of a road derailleur on a road bike but I'm not married to the idea. You guys are great, thanks for taking the time to reply.

I guess it depends on whether you are more concerned about style or function. Road ders are nicer looking, but I use what I need to accomplish an objective. Each to his own, but on a bike like a tourer where I want gears low enough to handle anything I might run into I use a mtb rear der and a triple. Since you are probably only going to use the bike for touring occasionally put the road der and smaller cogset on for most of your riding then slap on an XT der and big cogs for touring. Since you are hopefully going to give a touring bike a good overhaul anyway before heading out on a long trip changing ders and cassettes, even crank and bb, is no big deal. My commuter wears a single chainring and a 13-23 cassette. When I take it on tour I will switch to a triple crank with a 24 small ring, appropriate bb, and a 14-34 custom cassette.