I'm installing a mid-cage rear derailleur on my road bike. Going with a 10 speed 12-32 cassette paired with a 50/34 front. I know there are a few methods out there. Which do you find tends to work best when sizing a new chain to a new size cassette?

Size in small-small

Chain How-To - Part 1 - Slowtwitch.com

I prefer to size to the small-small combination, so that the chain doesn't drag on the top pulley/cage plates. I know sometimes that ends up longer than the more accepted method of running the chain on the large-large without weaving through the rear derailleur plus two links, but my rational for having a slightly longer chain is if I ended up getting a bent or broken link, I can shorten the chain without issue. I've never broken a chain out on a ride, but I do have a portable chain tool in the bag just in case.

Also don't forget to check the chain in big-big to make sure it's long enough. If it's still too short after using the small-small sizing method, then your gearing choice exceeds the chain wrap capacity of the rear derailer.

The other advantage of small-small is that because you are getting the longest-possible chain size, you can change to larger cassettes up to the rated capacity of your derailleur without needing a new chain.

For such a scenario to occur...I can only imagine it if you are not properly doing small-small (allowing FAR too much space between the chain and the RD arm in small-small)...or if you are using a cassette beyond the rated chain wrap of your RD.

I do it on the Bike in front of me rather than in theory over the web.

Around the Big_Big and thru the RD, stretched as far as reasonable so it shifts there on the road. , then still using a bent spoke to hold the loop,

May try the small Small .

Nowadays want a new/ different cassette get a new chain . pack the old combo together since they wore into each other .

Wrap the chain around the largest cog and largest chain ring. Do not wrap it thru the RD.
See where the chain connects and add 2 links. Cut there and attach the chain.

Its worked for me up to now and I havent read reasons why its a bad process, though now that Ive typed it there is a 60% chance I will be told why its a bad process.

Anyways, its quick and simple.

Large-large, because a good fit on that cross-chain is important to me

I use as much as the RD will allow. Links thrown away are money wasted.

For road bikes I do small small with just enough tension to keep the chain from flopping and then check against large large. Easy to remove more links if you find it necessary.
For MTB I do large large for the maximum chain/derailleur tension.

I use the big-big method for two reasons:

1) That's the way I was told to do it when I was first learning to size a chain.
2) I've seen the results of using a chain that's too short for the big-big combination on the road.

The first reason I listed is probably the actual reason I do it that way because I've never even tried other ways, but for those who don't know and are curious about the second reason, the result is that when you accidentally shift into the big-big combination the chain goes into the spokes of your rear wheel, likely cutting a few spokes and possibly breaking either your derailleur hanger or even the derailleur itself. I don't want to do that again so I use the method that I know will avoid it.

Funny, but I've NEVER had a chain the proper length to use the big/big combo using that method.

I run the chain on the big chainring the big cog and through the rear derailler and cut the chain where needed.

Cheers

I had a bike shop install a new chain for me once. Never again. They had the chain too short for the big/big combo and I accidently shifted into prior to crossing a highway. The chain and rear wheel jammed solid and I tumbed. Good thing there were no cars coming down or up the highway I was crossing.

I make sure all the chains on all my bikes can go into the big/big combo even though I try to avoid that gear and also the small/small combo. Just in case.

Cheers

Big-big, through the rear derailleur as it will actually be used.
No guessing or hoping involved.

4 or 5 methods to choose from !

I use small small and run it in the rear derailleur. I put a little bit of tension in the derailleur and it`s done.

WWSD?
The late great Sheldon says big-big plus two.

Thanks everyone. I tried big-big plus 2 as many have suggested, and it seems to be spot on!

Exactly; works every time...

Big-big, not through the derailleurs + 2 PAIRS of links. Guaranteed to work every time.

It guarantees that you can uses big big, it doesn't guarantee you can use small small, depending on your drivetrain combo

Which is actually fairly common when swapping cassettes for a big hill ride if your bike is fitted with a short cage RD. Its still fine though if the chain is long enough because small-small isn't that useful

But if your drivetrain combo is such that you can't make BOTH big-big and small-small work, big-big is the one to choose because the consequences of getting that wrong are pretty expensive.

Agreed, Never said otherwise. Just pointing out that it doesn't always result in a fully functioning drive train that works in evry gear, and people should be aware of that. saying "big-big always works" isn't true

Fine, it works 95% of the time. The other 5% are when people replaced their long cage derailleur with a short cage and thought it would work...

As Marcus_Ti pointed out, small-small is helpful if you use a variety of cassette sizes, all within the stated wrap capacity of your RD. I am currently running a triple crank with a 12-27 cassette and a short cage rear derailleur, so small small might work if I used the middle ring, but not the granny. I do big-big, as I am not going to put on a larger cassette, and want the shortest chain that won't go into the spokes if I accidentally go into big big.