50 large chainring
 

Do to arthritis I am replacing my 53 large ring with a 50 chainring, both 130 mm Shimano D/A.
and leaving the 39 on.
My cassette is 12/25 and may replace that with a 11/25 have not decided yet.
53/39---to 50/39

Not to concerned with the gearing but I am curious on how many links I would take out of the new chain as well as the amount of drop to the front derr.
any information and suggestions would be greatly appreciated.

Shouldn't have to take any links out if you are not changing the small chain ring and leaving the same cassette on. You should be able to use your old chain for a reference. Why go to an 11-25? Sounds like a counter purpose move.

Your front der should be 1 to 2 mm above the large ring in the same orientation it is now relative to the chainrings. If your bike was shifting well then look closely at how it is now on the large chain ring and try and match it for the 50.

Not much, and not much. Chain length should be noise (there will be 1.5 link less engaged on the chainring), and the FD drop is probably in the 1-2mm range. I would try it as is to start with.

I don't quite follow why you want to swap 12-25 for 11-25, assuming you have 10sp you will be exchanging a very useful cog (16T) for a less useful one (11T). 53->50 is 5.7% gear ratio change, while 12->11 is 8.4%.

Your 53/12 top gear is 119 gear-inches. A 50/12 would be 113. If you go to a 50/11, you'll have a 123 gear-inch top gear. :eek:
Are you making this change because you need a higher top gear?

50/12 is plenty high for me.

Yep, I will keep the 12/25.
thanks for your input.

No I will be keeping the 12/25.
I appreciate your advice.

No I was actually thinking of down hill, but all of the advice above as well as yours pointed out where this would be useless.

I will stay with the 12/25., thank you.