Crank regearing
 

I recently got a TCR Advanced with Ultegra 10 speed. Even though it was 6-7 years old it only had a little over 100 miles on it.
Where I live my rides fall into one of two types. Nearly flat bike paths or steep climbs to a plateau that's between 1-2K feet above the start, followed by rolling hills and a steep decent.
The 28 big gear in back is fine with the 34 in front for almost every climb, but there are a few places I wish for a bit lower. The other day I noticed that if I'm in the 50 in front I almost never get to the small cogs in back.
That gearing would be too fast for the bike paths and on the roads the descents are steep enough that I don't pedal. It seems that something like 46-30 would make more sense but I looked and couldn't find any smaller gears for my 6700 crank.
Do I have to go mtb crank? Would that work?

Just get a bigger cassette.

Well, ignoring that it goes above max on the rear derailleur ( I know it's done) I'm still left with a bunch of small cogs not being used.
Of course something like 32-16 in the rear would be just fine.

It'll be cheaper to change out the cassette, if your rear derailleur can handle it - I think that both the SS and GS officially top out at 28t, but many had success with a 30t .One revision officially handles a 30t, but might cover a 32t. Do some searches along those lines unless someone with direct knowledge chimes in.

Otherwise, 110mm is the BCD (bolt circle diameter) for compact cranksets and the minimum teeth possible for that diameter is 33t (34t is most common), so yeah, you can't effectively go any lower, than what you already have, with a double. There were 5700- and 6700-series triples with a 30t small ring, but then you'd need to source a new left lever (unless your existing lever supports a triple, which was common with early 5700).

Ok, so the only way to get lower is a new cassette. The other issue is a smaller big ring. Anything there?

You can go lower you just have to purchase a new crankset(and bottom bracket). You could change the big ring to a 46T common on cyclocross cranksets that match the 110bcd, but I wouldn't bother

Get a medium cage RD and install a cassette with a 32 tooth large cog... that's your best bet. It'll be hard to find a smaller chainring than 34 and if you don't spin out your 50 well, no big deal.

NB: I don't know anything about 6700 medium cage RDs, I assume they're out there somewhere.

You won't be able to use your existing cranks, but there are 46-30 road cranks. FSA offers that combo across some of their lineup, for instance.

While I applaud the 46/30 idea (I want one for myself :-),

https://www.bike24.com/p2273545.html?q=46/30

I will just mention that 50 -> 46 in the front is very close to 11 -> 12 in the back. In the Shimano 10 speed line up there is a 12-28 cassette and, I believe, a 12-30 as well.

https://www.bike-discount.de/en/buy/...0-12-28-450887

Wickwerks may have some options for you.

https://wickwerks.com/products/cyclocross-4434/

I'd keep it simple and swap out for a 12-30t cog first. I think you would be suprised at how much easier a 30t is to pedal than a 28t. Its about 6-7% easier to spin. You should be able to get your current deraileur to work with a 30t.

If you need more than that you can look at spending more on a deraileur and bigger cassette. I think if you are on the road you wont gain much by switching out to a 48 or 46 on your big chain.

Go the cheap easy route first before spending all that time and money and then deciding the gears are so easy you never use them.

-Sean

https://www.ebay.com/itm/46T-30T-BCD.../263934089592?

you might want to look into these if you want to go subcompact without going to a MTB crankset.

Before you sink money into this venture consider your front derrailleur. If you have a brazed on font there is a possibility the derrailleur will not go low enough to work the 46-30T drop. (The cage might hang the chain when it is in the 30T ring it will be the same concern if you go with a MTB cranks also)

Going with a larger cassette would be the easier route. If you are running 6700RD SS you would be able to shift at 32T cassette. I was able to do it on a 7900RD.

I'll let others with more knowledge chime in on whether this is actually possible, but perhaps buying a 10-speed 11-32 cassette, eg HERE as well as a 14-25 cassette, eg. HERE
Then combine the two cassettes' cogs in some manner for resulting 14-32 ? This is not much larger than an 11-28 methinks.

THIS! I was investigating this last night. Ran across this table:
https://www.sheldonbrown.com/k10.shtml

There is a CS-6600 that with a change to the bigger gears could be a 16-30 maybe?

I was worried about this too. Carbon frame so braze-on style FD.

You may want to take this question to the bicycle mechanics forum. I wouldn't recommend a 16 as a high gear in the rear, unless you're really really certain that you don't pedal at speeds over 20mph. The 14-32 range I would suggest would make a more practical solution. It would also ensure your 16-tooth cog is actually usable (without cross-chaining) when you're in the 34T chainring.

Yea, 16 is probably overdoing it. Maybe start with the 14-25 and change out the top three.

I forgot about the Wolf Tooth - good suggestion if the 30t doesn't cut it.

You're doing moderate climbing on a lightweight road bike with a compact crank and it's fine for most climbs? I would ride more, train harder, lose some weight etc before making drastic changes to your bike. A 30 or 32 tooth in the back is reasonable and if you are in decent cycling shape you should be able to climb any hill with 34/32. Not sure why you need something smaller then 50 big ring up front or how that's relevant to this. You need easier gearing for climbs and that's what the 34 ring is for. I ride with guys in their 60s who do 10k feet of climbing with a compact crank and 28t. When I started riding road a few years ago I struggled up 1000 ft climbs with 34/32 and 6 years later I easily get up same climbs with 36/28. Maybe you need to work on climbing technique?

The OP isn't looking to specifically reduce his 50 in the front, he's just aware that to reduce the 34 ring in the front to make climbing easier, he'd need to also reduce the big ring (ie. a 50/30 chainring isn't likely to work).

I made a 14-36 cassette by ordering a 14T lockring and a few spare sprockets and spacers... I used a 14T from the 14-25 junior cassette and a 16T from an XT cassette and it shifted fine. The 14T sprocket I used is numbered Y-1ZD1400D. I ordered online but you might try an LBS and see if they are listed in the shimano catalogue.I think I ended up with a 14-15-16-17 so it is nice to have tight gaps and still get some serious bailout gears.

Cassette
 

I have Ultegra 10s 6600. I have a 30x12 cassette with the short case I got to replace my 25x11 for steep rides. Like 15 percent grades. It works but I put the b screw all the way in and be more careful not to cross shift too far. The 53 30 is tight. I could use a medium cage but in Ultegra is hard to find and expensive. You could go that route but maybe a compact up front would work better in the long run. Changing to a triple up front would cost the most but give the widest range. My first good bike was a touring bike with a triple. It was fun riding up hills with a group pushing their racing gearing. Then anouce “Oh I have this granny gear. I can sit and spin.” Then suck others into a conversation. Good times.

For those of you running a 32 cassette, what model? Ultegra doesn't come in a 32. I'm 10 speed.

I ran Nashbar 11-32T 10 speed cassette which is a rebrand of Microshift.
Sram and SunRace also have a 10 speed cassette with 32T.