How far up the years do I need to go to shift a 42T cog on the rear? I was given a 11-42T cassette and would like to see if I can make it work on my daughter's beater mountain bike. Currently it has a Shimano Deore XT M772. It is rated for 34T capacity, I can abuse it into chewing up to 37T, but 42t is certainly a bridge too far.

I guess another option is the derailleur hanger extender? How well do those work?

I really don't know the mtn bike gear, but on Ultegra I needed a R8000 long cage RD to get up to 42t.

You may be able to get there by using a derailleur hanger extender like the Wolftooth Goatlink/Roadlink or similar. Just be aware of your rear derailleur's capacity. 11-42t is more often used as a cassette for 1x drivetrains. Friends using the extenders have had good luck with them and swear by them.

This works. But better is to get a Long Cage Derailleur. You also need to consider rear wheel Dish changes...

There is no reason this would affect the dish of the wheel.

The craziest old stump puller RD that I'm aware of is Suntour's AG Tech (alpine gearing). It's only rated to 38. Maybe you could make it work without a stupid wide range in the front mounted on a long claw hanger?

I run one on an old Ross MTB with a with a uniglide rear that goes up to (I think) 32 or 34, and it's clunky but okay. I seldom ride that bike because it's in my family's garage and I now live in the same city. It was my get-around while visiting for years and I liked it.

My favorite derailleur for mountain and touring is the long cage Shimano Deore XT (M772 I think). That one is rated for 34t but you can torture it into chewing on 37t. I'm guessing that the extender should let it handle the extra teeth.

The extenders are cheap. I'll give it a try.

Is this actually a C&V topic? It seems to me that you might get better answers if you posted in a different forum.

I run Wolftooth RoadLinks on my old mtb’s. I’m running 13-40 8 speed with a 90’s XT SGS 9 speed RD; 24/34 chainrings.

I have read that the shifting performance is not as good on small cogs. No issues with a 13t, but not sure with an 11t.

One of the keys is making sure you cover the RD capacity (chain wrap). With a 1x and a SGS it should not be an issue, but with a double you might need to avoid the small-small. A triple would probably not work well.

John

That is mostly the short and long of it. While my experience has been 1x, I have learned the following: If you are gonna go really big on chainring and cassette, use the steel wolftooth. I experimented, years ago, with an 11-50 and a forgotten, but large-ish chain ring. Worked for a while, but on a simple, up hill, non-stressed shift from third to second, something went wrong and the aluminum goat link sheared off and the derailleur arm wound up in the spokes. What really happened, I don't know: exceeding the Altus derailleur by way too much; cheap link, other act of f.o.d.? Currently I still run an aluminum link, BUT I only exceed my derailleur a little. An old Deore with a 42/11-42 setup.

My other possible contribution is backing up the chain wrap caution. 7 speed, 50/11-34, Acera derailleur. Very happy setup, but could be better on hills. Having an MTB double, a spare 28 tooth chainring, hilly roads, and getting a trailer, I set a manual shift arrangement in the 64bcd position. When on the "towing" ring, the chain (after link adjustment) maxes out the wrap ability of the derailleur. On the other end, the 50/34 arrangement (same chain) works safely and fine but can't stand any more links out. So, in the future (and if I want lower gears for towing) I will have to reduce the 50 chainring as I reduce the 28.

Has anyone mentioned the possibility of using a longer B screw?

Otoh, experiment, do what you would like, and let us know what you find out.

Trust me, what I'm after is well rooted on the C&V side of the house. I don't mind modernizing a tad but I want to keep my bike grounded on its vintage heritage. Were I to ask in a mountain bike forum most would not even comprehend the concept of trying to stay with 80's tech.

So far the best route seems to be a Suntour AG (which by itself can chew on a 38t cog) with a hanger extender, paired with a Specialites TA crank sporting a single speed 44t ring. That would give me a gear-inches range from 103 to 27. I would go smaller on the crank but finding sub 44t rings for the outside 5-bolt position on the TA crank is not trivial.