BoraxKid

Well, that's because I'm right, and you know that I'm right. I have no reason to back off from my position, because everything I said was in the context of OP's request for help selecting a cassette to climb an exceptionally steep grade. That you and others ITT have chosen to be willfully obtuse and once again attribute statements to me that I never made speaks only to your love of attacking someone you perceive as an outsider to your online bike club. I am here to stay, Koyote, and I give sound advice when people ask for it. Get used to it.

Bill Kapaun

Ignore list made.

DiabloScott

Yeah, that's what I figure too... and I REMEMBER having a car behind me when I did that PR effort.
For the uninitiated:

Koyote

There are various tests for that. Mine was when, in the middle of an all-out interval, two German Shepherds started chasing me. 186 bpm ain’t bad at 57 yrs old.

tgot 

I've got that! It's like a nice, close-ish (BITD) 6-speed rear like my C&V ride came with...plus bailout.

When I get that big jump, it's a reminder "you've got no lower!" It feels about like skipping one of the regular gears.

Still not low enough, I didn't realize there was a 14% stretch on a recent ride, and the 39 x 34 was painful.

Kapusta

I have always understood “spin” to imply seated pedaling at a relatively higher cadence.

”spinning vs mashing”

phughes

Yes, a compact double like that would work well with a 34 on the back, if you aren't carrying a load. I went with the 24 since I do fully loaded touring. I like to spin. When I got the 24, I was commuting in the Ozarks, which also has a lot of good hills. It made the commute a bit more pleasant, especially since I always had bags on the bike.

Larry Lem 1

I use a 50-34 crank and 11-40 XT 11-spd cassette, Ultegra R8000 rear derailleur. Whenever the grade rises above 10%, I'm in first gear. At 15 to 20%, I'm mashing, not spinning. Those stretches need to be less than half a mile as I'm well into the red and can't sustain it. First gear is my best friend.

schind1324

I think you would find that since you would only be riding this for extreme climbing having the larger jump between 30 and 34 you may not notice that much it is not as large of a jump between the middle of the cassette when you are riding on more level ground.

johnd01

Learning to ride slow helps. Lean rover your arrow bars and ride slow up the hill. I have 24 36 for my low gear. I bought a 17 chain ring but have not installed it.

Here is how to get a low gear tripper or quad set of chain rings.
abundantadventures.com/mt_triple.html
abundantadventures.com/mtfaq/FAQ.html
abundantadventures.com/mtfaq/frontderail/fr.derail.mods.html

marcpotash

I have an 11 spd 50-34 with a 11-34 cassette. The jump from 30t to 34t isn't an issue. Don't forget, the 11-34 comes with a spacer to go between the 34 and the freewheel... it is different than the 11-30 cassette. The 25% grade.... you are insane!

Brian Chapman

I faced the same issue last year, heightened by plans to ride a good deal in the Italian & French Alps, including the Maratona dles Dolomites & several of the classic French climbs, including Mont Ventoux & Alpe D'Huez. I recall that Shimano recommends a maximum 34T cog for my Ultegra Di2 rear derailleur, but encouraged by several YouTube videos, I went much further, and have a standard 11-40T on the rear, with a sub-compact 46-30 crankset, also with oval rings, on my Canyon Endurace. It didn't make climbing trivial, of course, but I'm really glad I made the change. Several thousand km later, I've yet to have the slightest problem with shifting on my Shimano Di2 set-up this way.

rosefarts

I use 12-30 on a compact and have certainly run out of gears on the super steep stuff. If your derailleur can swing 11-36 or 40, you still might not be spinning but it'd be a lot better.

run50

If you're going to be climbing hills as steep as 25% you're going to be pushing the bike up those climbs. An
11-34, unless you have the legs of superman, is going to be extremely taxing and difficult on that gearing.
You might consider going with a mountain bike rear derailler so you could go up to an 11-42 or higher.

marcoguzm

Sun Race cassettes are a good option.

KC8QVO

A couple thoughts:

1. There is a point of diminishing returns in low end gearing for hill climbing. If you are on a short, steep hill you can get by with much lower gearing and crank fast for the short duration, yes. I've done it and I will do it. On a long hill - you're better off walking. Seriously. I have a couple stories - see later down.

2. You might want to look at a Mountain Tamer Triple adapter. It will turn a dual chain ring crank in to a triple chain ring crank. Or, in my case, I already had a triple and it turned it in to a quad chain ring rank. Pretty cool. See the thread in the link below for a couple pictures I posted from earlier this season. I put it on around 2015 I think - it used to run with a 17 tooth chain ring but I swapped it out for a 20 tooth.
https://www.bikeforums.net/touring/1...e-picture.html
Mountain Tamer Triple adapter - LOWER GEARS for bikes of all kinds

Stories:
1. I was on a trip last Fall and neglected to look at the topography of where I was riding to, for the most part. I looked at routing based on how to get from the long distance trail I rode to my destination. There weren't many options, unfortunately. The route I picked had a steep climb, with switch backs, out of a river valley. As I approached the hill I geared down to the small chain ring and set my cassette in the rear to a higher gear so I could shift the cassette back as needed. I had plenty of gearing - I had the gearing to ride the bike straight up a wall if I could stick to it. What I didn't have was the energy to spin at a high cadence to crank up the hill (a long climb). I had to stop.

Now comes one of the big points to this story. When you stop on a hill that is necessitating ridiculously low gearing you can not restart very easy, if at all. The most logical way to restart is to start on one shoulder of the road and ride perpendicular to the hill across to the other shoulder as the ground would be more level. Then you would need to steer up in to the climb again. Depending on traffic that may or may not be possible. On a blind curve in a switch back - forget it. If you are going slow in a ridiculously low gear - when you make that turn to head up the hill again you are probably going to loose your balance. So again - trying to restart after a break on the long hill climb is going to be a pain in the a$$.

2. With the 20 tooth chain ring in place earlier this season I did a 60 some mile day trip. I only had rear panniers and a handlebar bag. The route I took had me along some popular MUP's going in and out of a big city. Parts of the trails paralleled a river and went across it in a few places. So the trail would go up to the roads where the bridges were, then drop back down on the other side. I went out one way then when I was on the return I looked at the trail routing in one area and thought it made more sense to cross on the opposite side of the road this time - it avoided crossing a busy road. The down side to it, as I found out, was the climb from the river to the intersection at the road was an extremely steep climb. It was so steep I almost back-tracked to go the other way. I decided to go for it. I made it 1/2 way up the hill, did a backflip, and wrecked. "Gearing" wasn't the problem. If I could have stuck to a vertical wall I could pedal up it. I didn't have any front panniers to keep the center of gravity further forward and that was that. Up and over the front end of the bike went.

With all that having been said - the Mountain Tamer is a good option to have. I'm glad I have it. One big note on using it is the bottom bracket needs to be wider to make it work right. Sometimes you can get by with spacing a stock bottom bracket out (and the kit comes with spacers) but I didn't have decent enough luck with it. I got a bottom bracket from Phil Wood that is quite a bit wider than the stock one, I want to say it is 10-20mm wider. How I figured the size was the offset I needed to get the chain rings where I wanted them on the one side, then doubled it and added that to the stock width of the bottom bracket. That way the pedal centers are centered on the frame, if that makes sense, as opposed to shifted to one side or the other (actually, anatomically speaking that offset won't hurt - I just wanted it centered).