Derailleur Max Cog size
03-28-16 | 07:38 PM
#1
Thread Starter
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Joined: Jan 2014
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From: Utah
Bikes: '88 Trek 1200, '91 Trek 1400
Derailleur Max Cog size
Hey,
I bought an old Shimano MT62 Deore derailleur for it's chain wrap capabilities and the idea that I'd be using a 32t cog on my bike. However, as I look at the cog break down, the HG50 13-34 is exactly what I'm looking for. 90% of the cassette is like what I have now, but it's got that last really low gear for bailing out.
So, the MT62 is rated for 32t max. Reading on here I see that most of the derailleur's out there are pretty conservative with their ratings. So I'm going to assume that this is the same case. Maybe a longer b screw will be needed?
My 1055 derailleur will clear the 28t cog it's rated for but I have the b screw maxed out which is why I'm asking.
Thanks!
I bought an old Shimano MT62 Deore derailleur for it's chain wrap capabilities and the idea that I'd be using a 32t cog on my bike. However, as I look at the cog break down, the HG50 13-34 is exactly what I'm looking for. 90% of the cassette is like what I have now, but it's got that last really low gear for bailing out.
So, the MT62 is rated for 32t max. Reading on here I see that most of the derailleur's out there are pretty conservative with their ratings. So I'm going to assume that this is the same case. Maybe a longer b screw will be needed?
My 1055 derailleur will clear the 28t cog it's rated for but I have the b screw maxed out which is why I'm asking.
Thanks!
03-28-16 | 08:25 PM
#2
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It's not necessarily that the derailleurs are rated conservatively but that there is quite a bit a variation in dropout hanger geometry (specifically length) and that there are ways to cheat. The longer the hanger, the bigger the cog size that your derailleur can accommodate. Pushing the wheel farther back in the dropout will also allow larger cogs but at the expense of a larger chain gap and shifting crispness, particularly with indexed systems. A lot of modern manufacturer use vertical dropouts specifically to avoid shifting issues caused by non-optimum position of the axle. Maxing out the B-screw also helps, but depending on the angle of the hangers stop tab, it may not be enough and require a longer screw. The bottom line is that there are enough variables that it is impossible to predict. You'll just have to try. There are some combinations where a 34T would work and others where it wouldn't. You could probably even find a combination where it wouldn't work with the spec 32T.
03-29-16 | 12:20 AM
#3
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From: Port Angeles, WA
Bikes: A green one, "Ragleigh," or something.
It'll probably work.
For all those reasons T-Mar mentioned above and those which have been discussed at length on other threads, you don't really know until you try. Fortunately, B-screw adjustments, placement in the dropouts and chain length adjustments give you a lot of wiggle room. And all Deores are pretty copious derailleurs. I've got an MT-62 on my Tempo right now, 52/40 (BioPace) up front 12-34 out back. Works fine.
For all those reasons T-Mar mentioned above and those which have been discussed at length on other threads, you don't really know until you try. Fortunately, B-screw adjustments, placement in the dropouts and chain length adjustments give you a lot of wiggle room. And all Deores are pretty copious derailleurs. I've got an MT-62 on my Tempo right now, 52/40 (BioPace) up front 12-34 out back. Works fine.
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● 1971 Grandis SL ● 1972 Lambert Grand Prix frankenbike ● 1972 Raleigh Super Course fixie ● 1973 Nishiki Semi-Pro ● 1979 Motobecane Grand Jubile ●1980 Apollo "Legnano" ● 1984 Peugeot Vagabond ● 1985 Shogun Prairie Breaker ● 1986 Merckx Super Corsa ● 1987 Schwinn Tempo ● 1988 Schwinn Voyageur ● 1989 Bottechia Team ADR replica ● 1990 Cannondale ST600 ● 1993 Technium RT600 ● 1996 Kona Lava Dome ●
Last edited by Lascauxcaveman; 03-29-16 at 12:23 AM.
03-29-16 | 12:49 AM
#4
Disco Infiltrator
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From: Folsom CA
Bikes: Stormchaser, Paramount, Tilt, Samba tandem
Aren't standards great, that you can hook up a 28yo derailleur to a brand new cassette?
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."
03-29-16 | 05:51 AM
#5
Extraordinary Magnitude
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Bikes: 1978 Trek TX700; 1978/79 Trek 736; 1984 Specialized Stumpjumper Sport; 1984 Schwinn Voyageur SP; 1985 Trek 620; 1985 Trek 720; 1986 Trek 400 Elance; 1987 Schwinn High Sierra; 1990 Miyata 1000LT
I've had a 34 working on both a MT-60 and M735 RD.
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Commence to jigglin’ huh?!?!
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Commence to jigglin’ huh?!?!
"But hey, always love to hear from opinionated amateurs." -says some guy to Mr. Marshall.
03-29-16 | 09:56 AM
#7
feros ferio
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From: www.ci.encinitas.ca.us
Bikes: 1959 Capo Modell Campagnolo; 1960 Capo Sieger (2); 1962 Carlton Franco Suisse; 1970 Peugeot UO-8; 1982 Bianchi Campione d'Italia; 1988 Schwinn Project KOM-10;
Where are you, Chas.? This guy can cram incredible numbers of low gear cog teeth over all sorts of rear derailleurs.
As others have mentioned, it's a game of hanger tab or claw geometry, rear axle position, chain length, and front chainring drop.
As others have mentioned, it's a game of hanger tab or claw geometry, rear axle position, chain length, and front chainring drop.
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Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069
"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069
03-29-16 | 10:14 AM
#8
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From: CID
Bikes: 1991 Bianchi Eros, 1964 Armstrong, 1988 Diamondback Ascent, 1988 Bianchi Premio, 1987 Bianchi Sport SX, 1980s Raleigh mixte (hers), All-City Space Horse (hers)
It's not necessarily that the derailleurs are rated conservatively but that there is quite a bit a variation in dropout hanger geometry (specifically length) and that there are ways to cheat. The longer the hanger, the bigger the cog size that your derailleur can accommodate. Pushing the wheel farther back in the dropout will also allow larger cogs but at the expense of a larger chain gap and shifting crispness, particularly with indexed systems. A lot of modern manufacturer use vertical dropouts specifically to avoid shifting issues caused by non-optimum position of the axle. Maxing out the B-screw also helps, but depending on the angle of the hangers stop tab, it may not be enough and require a longer screw. The bottom line is that there are enough variables that it is impossible to predict. You'll just have to try. There are some combinations where a 34T would work and others where it wouldn't. You could probably even find a combination where it wouldn't work with the spec 32T.
03-29-16 | 11:25 AM
#9
verktyg
Joined: Jul 2006
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From: SF Bay Area
Bikes: Current favorites: 1988 Peugeot Birraritz, 1984 Gitane Super Corsa, 1980s DeRosa, 1981 Bianchi Campione Del Mondo, 1992 Paramount OS, 1988 Colnago Technos, 1985 RalieghUSA SBDU Team Pro
As the experts above have mentioned.....
The RD-MT62 was part of the Deore II group from ~1989 to ~1991. It was the replacement for the Deore XT group?
It's rated at a 38T wrap with 32T max cog. Specs set by lawyers!
Heck I can get 32T with a 1st gen 105 RD (not that much chain wrap though).
This is either a 30T or 32T cog.
The pulley cage on the RD-MT62 can probably wrap up 6" of chain. You may have to add a link or two but it should easily cover a 34T FW cog with a very small chainring. Trial and error.
On triples I usually only run the largest 3 or 4 cogs with the smallest chainring. Eliminates possible chain rub on the middle ring.
I prefer steel pulley cages on my long arm RDs. Crisper shifting, plus they're stronger and less likely to get damaged. The few grams more than alloy arms is worth the security.
Deore LX, it's only running on a 28T cog but the small chainring is a 28T.
Later model Deore LX running the same 28T x 28T combo.
First generation steel cage Huret DuoPar Acier RD from 1975-76 (not an Eco), 13-32T FW, 30-46-50T CRs.
Except for 2 or 3 of my bikes I can at least shift into and out of all the gear combos without any problem. I'm not currently running any 34T FWs, they're a lot of "iron" to drag around. A 30T or 32T with a 28T to 30T CR is usually enough.
If I need anything lower, I shift to my "W" gear... I get off and walk - need to preserve my olde knees!
verktyg
Chas.
The RD-MT62 was part of the Deore II group from ~1989 to ~1991. It was the replacement for the Deore XT group?
It's rated at a 38T wrap with 32T max cog. Specs set by lawyers!
Heck I can get 32T with a 1st gen 105 RD (not that much chain wrap though).
This is either a 30T or 32T cog.
The pulley cage on the RD-MT62 can probably wrap up 6" of chain. You may have to add a link or two but it should easily cover a 34T FW cog with a very small chainring. Trial and error.
On triples I usually only run the largest 3 or 4 cogs with the smallest chainring. Eliminates possible chain rub on the middle ring.
I prefer steel pulley cages on my long arm RDs. Crisper shifting, plus they're stronger and less likely to get damaged. The few grams more than alloy arms is worth the security.
Deore LX, it's only running on a 28T cog but the small chainring is a 28T.
Later model Deore LX running the same 28T x 28T combo.
First generation steel cage Huret DuoPar Acier RD from 1975-76 (not an Eco), 13-32T FW, 30-46-50T CRs.
Except for 2 or 3 of my bikes I can at least shift into and out of all the gear combos without any problem. I'm not currently running any 34T FWs, they're a lot of "iron" to drag around. A 30T or 32T with a 28T to 30T CR is usually enough.
If I need anything lower, I shift to my "W" gear... I get off and walk - need to preserve my olde knees!
verktyg
Chas.
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Don't believe everything you think! History is written by those who weren't there....
Chas. ;-)
Don't believe everything you think! History is written by those who weren't there....
Chas. ;-)
Last edited by verktyg; 03-29-16 at 11:32 AM.
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