Derailleur selection?
 

I am restoring a Bianchi for fitness hill climbing. The crankset is triple, 50, 39, 30, front derailleur is triple 10 speed, chain is 10 speed and the Shimano 10 speed cassette goes up to 42 t. All Shimano. What would be a good choice for the rear derailleur?
Thanks for the add, by the way.
Barry in PA

You cant get there from here. I stand to be corrected but not aware of a derailleur that has over 50 teeth capacity.

Agreed. Drop the cassette to a 34 large cog and use a Deore 9 speed RD. If 30 by 34 won’t get you up the hill, you either need better fitness or a different inner ring on your triple.

And/or go with a smaller crankset and coast downhill.

Yea, I've found triple's granny 1/2 the big ring is good; 50, 24. / 52,26 / etc..

Grandpas
 

I can live without the largest drive sprocket so a 10 speed that goes to 42t seems it might work. I'd rather hit a deer at 15 than 35.

Sprocket!
 

I meant to say drive sprocket. Sorry. Egg on face.

Get a Deore GS 10speed rear derailleur. Should cover that 42 in the rear.

Depends on what shifters they have. Shimano 10 speed mountain is NOT compatible with road shifters. 9 speed is.

Shifters
 

I am starting with a vintage pair of down tube shifters just to see how that works.

Friction doesn't care about speeds, road, mountain, but the cable drum on the shifter needs to be able to wrap enough cable to move the derailleur across the whole cassette.

Indexed shifters do care, so if you plan to someday move to indexed shifters the RD has to be compatible or shifters purchased to match the needs of the RD.

Is this an old heavy steel Bianchi? 30x30 will get you up pretty steep hills. I doubt you'd have reason to go beyond 32 or 34 on a road bike and even then gears like this only apply to heavy bikes/tires/wheels and heavy out-of-shape riders, and hideously steep mountainous rides encountered on a daily basis without adequate recovery times for your legs. If you're thin and young 30x30 is great for mountains. Hill climbing speed is primarily about your body weight and the weight of tires and wheels.

Shifter
 

Guess I need a 10 speed mountain bike shifter to cove Rd the 42t sprocket.

You have a few options...

First off, there are no downtube, bar end shifters or dropbar mountain brifters.

You can get an M6000 GS, medium cage, and run your 39-30 chainrings in friction with an 11-42 in friction and and hit then numbers; Max Cog 42t, max capacity 41. Depending on your downtube shifters, you may or may not cover all 10 speeds within the 180 degree lever swing. But if it works, that is the cheapest way to go. If it doesn't work well enough for you for friction shifting, it does open up a can of worms.

You can get a 9 speed Deore 592 SGS and run a Wolf Roadlink with an 11-40 10 speed cassette, ('might" be able to go to 11-42) with your 39-30. The 592 SGS has a max cog of 36t without the Roadlink and a max capacity of 45. For that matter run it with 39-28 chainrings straight to an 11-36 cassette. You can then run in friction, or you can run in 10 speed "road" index with 7900 downtube or bar end shifters or go to a Microshift 10 speed downtube or bar end, or brifters, or Gevenalle shifters. Road 10 speed shifters will work with mountain 9 speed rear derailleurs and a 10 speed cassette. This option does open up the shifter selection.

Note: The can of worms would be a potential cable hack I saw done on an XT 10 speed Shadow Plus, to work with 9 speed mountain, which would make it work with 10 speed road. I would never recommend this to anyone else, but if I had a 10 speed road setup I would try just because I love any hack that works and goes against Shimano's blind eye to supporting older systems. The RD-M6000 attach is a little different, but it would be a fun test; but only if the rear derailleur is expendable if it doesn't work.

John

Tuning
 

Finally learning to tune the 10 speed derailleur. The bike climbs great.