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-   -   Short Cage RD NOT for triples? Really? (https://www.bikeforums.net/classic-vintage/1245025-short-cage-rd-not-triples-really.html)

thook 01-12-22 12:01 AM

Short Cage RD NOT for triples? Really?
 
I know this has been discussed ad nauseam, but I was bike pRon roving and found this beautiful example of a salsa drop bar mtb built by the guy that was building for salsa bikes. There were two models of the XT line up; the long cage and short cage. The man used a short cage!!


https://cimg7.ibsrv.net/gimg/bikefor...c8cbeac378.jpg

1984 Salsa Custom #37 - Vintage Mountain Bike Workshop

thook 01-12-22 12:08 AM

Here's another one....
https://cimg3.ibsrv.net/gimg/bikefor...b5a3ccf0c7.jpg

I mean, if it was/is such a bad idea, then why were the pro's doing it? Were they just insane mavericks? There had/has to be some genuine benefit/reason it was practiced.

Darth Lefty 01-12-22 12:34 AM

Ross might just be that good

AeroGut 01-12-22 06:33 AM

In the early days of Bridgestone MTBs, their higher end models were specced with short or medium cage derailleurs and triple cranks. But it was considered unusual enough that they included this note in the 1991 catalog:

"This bicycle has a short-cage rear derailleur, which shifts faster, weighs less, and has more ground (or obstacle) clearance than the usual long-cage rear derailleur.
However, the small price you pay for the above advantages is that, with the chain on the inner chainwheel and the three smallest rear cogs [note: this was out of 7 total cogs], the shorter cage won't take up sufficient slack; the chain rubs on the derailleur cage, and flops around excessively over bumps.
On any mountain bike (regardless of rear derailleur), the small chainring is should be used only with the three or four largest rear cogs. For the reasons noted above, this especially important with this style rear derailleur"

(side note: the misplaced "is" in the last sentence is their error not mine.)

RobertUI 01-12-22 11:20 AM

I worked as a mechanic at a Bridgestone dealer in 1991 and I seem to recall a LOT of confusion when discussing this with customers. I then recall that many other folks wanted to switch over to the "cool new compact shimano" setup. I definitely remember the sales point being all about the weight savings with smaller cogs, chainrings, and the shorter derailleur cage. Nothing really to add, other than it was interesting.

John E 01-12-22 11:44 AM

I have used short cage SunTour Cyclone / Cyclone II derailleurs in two different triple setups:

1/3 step 3x5: 49-46-43 / 13-16-19-23-26

half-step + granny 3x6: 48-45-34 / 13-15-17-19-21-24

Both worked fine.

Road Fan 01-12-22 12:00 PM


Originally Posted by thook (Post 22370700)
Here's another one....

http://www.vintagemtbworkshop.com/up...76861_orig.jpg

I mean, if it was/is such a bad idea, then why were the pro's doing it? Were they just insane mavericks? There had/has to be some genuine benefit/reason it was practiced.

Its all a matter of whether the largest rear sprocket can be handled by the rear derailleur, and the total change in the number of links that must be wrapped by the derailleur cage are within its design capability. The rear derailleur only cares about those two parameters, not how many rings are on the chainset. The sizes of the rings, yes, but the number of the rings no. Master how all of that works and you, too, will be a master gear finagler! I'm pretty sure Sheldon Brown covers all of that, it's not so obscure or hard to find.

AeroGut 01-12-22 12:04 PM


Originally Posted by RobertUI (Post 22371182)
I worked as a mechanic at a Bridgestone dealer in 1991 and I seem to recall a LOT of confusion when discussing this with customers. I then recall that many other folks wanted to switch over to the "cool new compact shimano" setup. I definitely remember the sales point being all about the weight savings with smaller cogs, chainrings, and the shorter derailleur cage. Nothing really to add, other than it was interesting.

Interesting! It's also worth remembering that even with the triple crank, the total range of these drive trains was still pretty narrow. The one with the short cage derailleur had 24-36-46 chainrings and 12-26 7 spd freewheel, so the derailleur capacity that you'd ideally want is only 36. The short cage XT DR was specced conservatively by Shimano as a max capacity of 28.

thook 01-12-22 12:07 PM


Originally Posted by Road Fan (Post 22371264)
Its all a matter of whether the largest rear sprocket can be handled by the rear derailleur, and the total change in the number of links that must be wrapped by the derailleur cage are within its design capability. The rear derailleur only cares about those two parameters, not how many rings are on the chainset. The sizes of the rings, yes, but the number of the rings no. Master how all of that works and you, too, will be a master gear finagler! I'm pretty sure Sheldon Brown covers all of that, it's not so obscure or hard to find.

Oh, I know about all that. The max cog for those short cage XT's is 28 and the total capacity is 30. Either of the bikes' capacity is at least 39t, though

thook 01-12-22 12:24 PM


Originally Posted by AeroGut (Post 22371270)
Interesting! It's also worth remembering that even with the triple crank, the total range of these drive trains was still pretty narrow. The one with the short cage derailleur had 24-36-46 chainrings and 12-26 7 spd freewheel, so the derailleur capacity that you'd ideally want is only 36. The short cage XT DR was specced conservatively by Shimano as a max capacity of 28.

I'd read 30 somewhere. I think it was the shimano PDF
Where'd you come up with the cassette gears used? I counted 12-28 from the photo

AeroGut 01-12-22 12:39 PM


Originally Posted by thook (Post 22371296)
I'd read 30 somewhere. I think it was the shimano PDF
Where'd you come up with the cassette gears used? I counted 12-28 from the photo

I found the 28 on a forum post somewhere, so easily could be wrong. The cassette values came from the specs page in the 1991 Bridgestone catalog for the MB-2, which had the short cage XT rear DR.

coolkat 01-12-22 01:26 PM

Someone posted a NOS Rocky Mountain Blizzard a few years ago that had this warning on the short cage XT derailleur. These had a triple up front, of course
https://cimg9.ibsrv.net/gimg/bikefor...6a5823995e.jpg

Drillium Dude 01-12-22 02:24 PM

Link in first post doesn't work for me - and I see no link in post #2.

Is it just me?

DD

qcpmsame 01-12-22 03:22 PM


Originally Posted by Drillium Dude (Post 22371492)
Link in first post doesn't work for me - and I see no link in post #2.

Is it just me?

DD

No go here, gives me a notice I am not private(?).

No link in #2 either.

Bill

squirtdad 01-12-22 03:43 PM

FWIW when pushing capacity I have found that using small/small chain sizing gives the max possible chain length / flexibility





Andy_K 01-12-22 04:24 PM

I've put together a couple of bike with semi-narrow range triples (49-42-32) and Campy NR/SR rear derailleurs (one with each). The chain wrap on a NR rear derailleur being what it is, I had to choose between rather narrow gearing in the rear and having some chain slack with the small-small combination. I went with the latter. The results of accidentally shifting into the big-big combination with a chain that's too short can be catastrophic so I won't do that, but accidentally shifting into the small-small with too much chain slack is usually benign.

https://live.staticflickr.com/65535/...7850306e_b.jpg

https://live.staticflickr.com/65535/...d3062035_b.jpg

https://live.staticflickr.com/65535/...706ce09e_b.jpg

Andy_K 01-12-22 04:27 PM


Originally Posted by AeroGut (Post 22370805)
"This bicycle has a short-cage rear derailleur, which shifts faster, weighs less, and has more ground (or obstacle) clearance than the usual long-cage rear derailleur.
However, the small price you pay for the above advantages is that, with the chain on the inner chainwheel and the three smallest rear cogs [note: this was out of 7 total cogs], the shorter cage won't take up sufficient slack; the chain rubs on the derailleur cage, and flops around excessively over bumps."

Why choose between a short cage and ample chain wrap?

https://live.staticflickr.com/65535/...1f661288_b.jpg

thook 01-12-22 04:35 PM


Originally Posted by Drillium Dude (Post 22371492)
Link in first post doesn't work for me - and I see no link in post #2.

Is it just me?

DD

the link in post 1 doesn't work? there isn't a link for my second post. but, i'll see if i can "redo" things. for some reason the two photos i posted don't want to show up, either. in post 1 and post 2. strangely, when i hit "edit" to readd the photos, they show up again. then it shows i've edited the posted when i haven't. perhaps the site doesn't like the link or photos being shared

edit: Okay. Had to save the images to my computer and upload them as attachments to get them to show up on the post/s. Still gotta treat the link as noted below in post #19

BFisher 01-12-22 04:40 PM

In the address bar, it is everything before the "www" that is causing issues. If you delete the "https://" the link should work.

dddd 01-12-22 06:32 PM

The short cage on a mtb derailer is longer than on a similar road derailer. I've swapped them and the difference was there.
They are intended for use with triples, just not combined with the x-32t cassette in most cases.

Road Fan is dead-on, the derailer's capacity and largest cog size defines what it can handle. Shimano derailers having two sprung pivots (unlike SRAM's) will handle considerably-larger than recommended largest cogs, but at some cost to shift quality going up to the largest cogs due to the fast-closing chain gap. So those shifts may have more of a jank to them.

Drillium Dude 01-12-22 06:52 PM


Originally Posted by thook (Post 22371693)
the link in post 1 doesn't work? there isn't a link for my second post. but, i'll see if i can "redo" things. for some reason the two photos i posted don't want to show up, either. in post 1 and post 2. strangely, when i hit "edit" to readd the photos, they show up again. then it shows i've edited the posted when i haven't. perhaps the site doesn't like the link or photos being shared

edit: Okay. Had to save the images to my computer and upload them as attachments to get them to show up on the post/s. Still gotta treat the link as noted below in post #19

I see photos now. I was confused by the wording because I thought you were referencing the link since originally the photos were not showing up.

Apparently I can't connect to the link because of this: Error code: SEC_ERROR_REVOKED_CERTIFICATE

Wonky computer stuff - I get it :)

DD

Drillium Dude 01-12-22 07:00 PM

If the biggest cog out back on that Salsa is a 28, a short-cage RD would prolly work just fine. If an old-school NR RD can handle a 28, why not a modern slant?

I think many people might think a long cage is needed to get all the gears, but really, who would use the smallest cogs out back with the smallest ring in front? Or big/big? Cross-chaining extremes would likely not work with this setup, but gear-smart riders know the limitations inherent in their drivetrains.

Every time I see a photo of a bike on the Forum in the big/big combination I wince a little and think "those components are going to have a shorter life than normal..."

Of course, YMMV.

DD

tyrion 01-12-22 07:03 PM


Originally Posted by thook (Post 22370697)

I bet the chain is floppy when it cross-chains into small/small. But so what? It hardly ever happens, and when it does it's not catastrophic.

Drillium Dude 01-12-22 07:41 PM


Originally Posted by thook (Post 22370697)

After taking a detailed look at the rest of the bike, it seems the rider came up with a novel way of turning a rigid seatpost into a shock-absorbing one by removing the binder bolt and installing that V-shaped spring unit. If that makes sense; there doesn't seem to be any other reason for it.

Also like the brake reinforcing plate on the rear brake vice the front.

DD

sincos 01-12-22 08:13 PM


Originally Posted by tyrion (Post 22371841)
I bet the chain is floppy when it cross-chains into small/small. But so what? It hardly ever happens, and when it does it's not catastrophic.

Is making a big deal of this a new thing? Who actually rides fully cross-chained like that?


Originally Posted by Drillium Dude (Post 22371876)
After taking a detailed look at the rest of the bike, it seems the rider came up with a novel way of turning a rigid seatpost into a shock-absorbing one by removing the binder bolt and installing that V-shaped spring unit. If that makes sense; there doesn't seem to be any other reason for it.

BITD those came with a cam operated binder bolt. Heading downhill you would loosen the bolt, lower the saddle, and go. On the flats and uphill, you would loosen the bolt, the seat would come up to the correct height without any faffing about. Now they're battery operated from the shifter.


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