Vintage XT rear derailleur capacity

[oliver1850]

Building a touring bike and had the idea to swap the cage from an M730 parts derailleur to a 1055 or 6400 to get more capacity. When I dug the XT out, I found that it only has 28T total capacity, same as 5500 and 6400. My question is: What was the intended use for the short cage XT? The 1991 Shimano catalog doesn't show a MTB crank with anything less than 20T differential (all triples), which leaves only an 8 tooth spread for the cassette. It doesn't seem there was any logical reason for making the SS XT, unless to use them with something in the range of a 26/40 to 28/39 double (depending on cassette). I don't remember MTB double cranks in that era; think of the standard MTB crank as 26/36/46 or 28/38/48. Were there MTB doubles, and how commonly used?

[jasonlee]

There were not any doubles back then from what I know.

Maybe there was an application for a downhill bike that was using a single chainring?

[pinkshogun]

the largest cog on my mid 1990's Giant mtb has a 28t large cog in back. i dont remember mtb's having 32 or 34 tooth cogs back then

[buldogge]

Mark...I think I grabbed one of those (M735?) at BWorks to stick on Nigel's '93 Kona...I have the same concern, but his gearing is 12-28, so I'm hoping it can handle it.

What crank are you running up front?

-Mark in St. Louis

[gdw]

The short cage 730 series XT derailleurs were popular with some racers in the early 90's. They were believed to shift faster and used shorter chains which saved a few grams. The short cage was also less likely to be damaged in rough terrain. Most people ran them with 12-28 or smaller 7 speed cassettes and tried to avoid shifting onto the larger rear cogs when riding the big ring. Shimano produced cassettes with 14-32 and 13-34 spreads during that era but they weren't meant to be used with the short cage derailleur.

[Saint Vitus]

This RD-M730?

http://velobase.com/ViewComponent.aspx?ID=4A92B92D-00F7-40E0-9694-551AC9E9E554&Enum=108&AbsPos=253

My understanding was that the cog rating erred on the conservative side.

[carpediemracing]

When I raced mtb in the mid 90s I ran I think an 11-24 with a 22-32-44 (on the last mtb I had) or something like that. Before that I ran the normal 46 big ring. I may have taken the small ring off with the last couple bikes - if I needed that gear I was done anyway so I'd run up the hill.

The short cage XT was definitely a race thing.

[oliver1850]

Thanks for the replies.

Mark: Still looking around for a crank, but thinking 1990ish triple in the 26-48 range (wish I had a Ritchey). The only component that's pretty much set is 1056 calipers, as the frame needs med. reach and nutted and 1056 is what I found. That's what led me down the XT path, as there weren't any long cage road derailleurs at the time. I may try to see if an RSX cage will fit.

I did look around for XT stuff for Nigel. I have a rear shifter missing the name plate. The XT shifter is the same as LX, only the mount is aluminum vs. LX's steel. I have a pair of XT brake levers coming if you want them. Also, Centaur FD is here (and lots of Mirage and Veloce hubs).

Re comments on cogs: No mention of what was available in the 1991 catalog, but I think 12-28 was the norm until the compact cranks came out. After that wider range cassettes were more common.

Saint Vitus: That's the RD, but I'm referring to the short cage version. Now tell me you have a Vitus with Shimano Saint group.

gdw: Max cog on the SGS cage M730 is listed at 32, so that's probably the biggest cog Shimano sold at the time. The ground clearance argument makes sense, as does the shorter chain.

carpdiem: That's a little later, when Hyperdrive-C cranks were the norm, but interesting that you raced with a 24 large cog! That setup still exceeds the rated capacity of the M730 by 7 teeth. But I (not for me but for a strong person) could see running a 12-28 cassette with a 34/46 double, and I'm wondering if that's not what the good racers did: ditched the small ring and put the smallest ring that would fit in the middle position.

The thing that doesn't make sense to me is that Shimano made this RD, evidently for the hard core race crowd and not for production bikes, yet they are so easy to come by now.

[gdw]

This site is a pretty good source of info on older mtb components.
http://www.bikepro.com/
Most bikes in the early 90's came with a 12 or 13-28 or 13-30 cassette but other variations were available. I ran a single 36t chainring with a 7 speed 13-34 cassette for a few months back then and don't believe it was a custom model.
http://www.bikepro.com/products/freewheels/shimcass.shtml

[oliver1850]

I love the bikepro catalog, have it in printed form. Too bad they didn't last long enough to expand on the concept.

[Davist]

I had the short cage xt derailleur running with a 24-34-48 front and an 8 speed campy 12-32 in the back 7 speed xt thumb shifters with the 8th click (remember that?) with no problems at all. We thought it would shift quicker as someone said above, it looked cool anyways, I called it Italian xtr at the time.