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!

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.

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.

Aren't standards great, that you can hook up a 28yo derailleur to a brand new cassette?

I've had a 34 working on both a MT-60 and M735 RD.

Awesome guys, thanks! I'll try the 34 and see what happens. If it doesn't work, cassette's are cheap enough and I can save it for another bike.

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.

So great to have you back, Tom. That's a really nice summation of the issue. :thumb:

As the experts above have mentioned..... :thumb:

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! :lol:

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.

http://bikeforums.net/attachment.php...hmentid=512312


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.

http://bikeforums.net/attachment.php...hmentid=512315

Later model Deore LX running the same 28T x 28T combo.

http://bikeforums.net/attachment.php...hmentid=512319

First generation steel cage Huret DuoPar Acier RD from 1975-76 (not an Eco), 13-32T FW, 30-46-50T CRs.

http://bikeforums.net/attachment.php...hmentid=512322


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! :roflmao2:


verktyg :50:

Chas.