I currently have a Specialized Sequioa triple (50, 39, 30). I am looking to upgrade later this spring (Roubaix). I either ride 1 hour after work or 5 hour ride on weekends. All during good weather. Thus what gear ratio or combination will represent a compact double's 34/27? I would like to make sure I still can make it up the hills in my area before pulling the trigger on a compact double otherwise I need to stay with a triple.

You might ask both of your knees how they feel about it.
What cassette range do you have?

I alternate between a Surly CrossCheck with 50/39/30 with 12-27 cassette, and a Cannondale Synapse 50/34 also with a 12-27, and I climb better on the Cannondale. Combination of weight (mostly I'd guess), efficiency, and frame design seems to tip the scale. If you've got a 12-27 cassette on your Sequoia and only rarely use the 27, you'll be fine. If your relying on the 27 continually, you may be better with the triple.

Only you know the kind of rider and capabilities you have. What is good for one guy is not for the next, and so on. Use Sheldon Brown's gear calculator to obtain values for your current setup and compare the compact double to it. If you can climb a hill in a specific gear with your triple and the double has the same value then a compact double is an option. https://www.sheldonbrown.com/gears/

34/27 is 34 gear inches, same as 30/24.

Nice to have a triple . . . more gear choices than a compact.
You ever head west from Jersey, you'll be glad to have a triple!

Presume a "normal set up" for the 8 spd triple and 10 spd double-
will provide the following ratios:
Double 25-
2130 622
26.7 34 50
12 76 111
13 70 103
14 65 95
15 61 89
16 57 83
17 53 79
19 48 70
21 43 64
24 38 56
27 34 49

Triple 25-
2130 622
26.7 30 39 50
12 67 87 111
13 62 80 103
15 53 69 89
17 47 61 79
19 42 55 70
21 38 50 64
23 35 45 58
25 32 42 53

The lowest gear on the triple compared to a compact double using a 12/27 10sp cassette is 8.8% easier. I would test ride a compact double up one of your tougher climbs and see how you like it.

Started riding on MTB's and the gearing settled out on those was 22/34 as the lowest gear. Used to do a few hilly road rides on that bike and it was surprising how often I was using that lowest gear. Then I went road and got a triple-52/42/30 and 12/26. Road bikes may be more suitable on the road than MTB's but I still used that lowest gear of 30/26 and when I went to the Alpes- I modified this to give me 28/28. For mountains- that may not necessarily be steep but are mostly long- that 1 to 1 ratio works for me.
Then came the 2nd (-And 3rd and 4th) road bikes and this was fitted with a compact double with 50/34 and a 12/27 cassette. Took a bit of mind training but those hills I struggled up with 30/26 (And 22/34 on the MTB) were no harder with the 34/27.

I know it does depend on your body and the hills you want to climb but for me short sharp hills of 1 mile at 15% average of 10% are doable on a compact. It's just when they get longer that you might be wishing for the triple or that 1 to 1 ratio to be fitted.

It looks as though both the compact double and the triple can provide decent ratiometric progressions, with no inordinate gaps. With the double, however, you may find yourself doing more double shifts (going across several cogs in back while changing the front). If you are accustomed to a 30/27 low gear now and feel as though a 30/24 would be an acceptable alternative, then the compact double's 34/27 should suffice.

Some folks prefer the double's Q-factor, which places ones feet closer together and may be easier on the knees for that reason.

I wouldn't expect to notice a big difference between a 31 and 34 gear-inch combination.

All,
Thanks for your responses. I will answer all in one response. My Sequoia has a 11-25 cassette. Thus if I can ride my hills in 30/24 then I should be okay with 34/27. Using Sheldon Brown's calculator and gear inches it matches BluesDawg answer. I do go west to ride. I ride in PA with colleagues from work on Saturday and Sunday mornings and we have plenty of hills. The team actually seeks out hills as part of the training. However I do have one knee that needs to be fixed at some point and thus spinning needs to win out over crunching. It appears to me from my research and how I ride, if I get a compact double I may be spending time shifting between the 50 and 34 as 39 on my triple is where I spend most of my time. Thus a compact double looks to be in order and triple will serve as a back up.

That's what I was going to post. If you ask some people the time they'll tell you how to make a watch.

and what kind of watch they like best.

But I just realized I don't have 24 on the triple. LOL. Not perfect but will have to settle for 23.

I'll also add front d/r shifting is much crisper with a compact and you get better use of the rear cassette by eliminating/reducing cross chaining.

Luckily for me, I have a couple of road bikes, one with a triple, on with a double. There's no hill in Los Angeles I can't climb, at least once, with either bike.

But when I'm climbing 5,000 feet in the Santa Monica Mountains north of my home in 30 miles, or riding 100+ miles with thousands of feet of climbing, I'll choose the triple-equipped bike. Cycling shouldn't be easy, but it should be doable.

Even at my age (62) I don't want to be compelled to rest, or walk my bike, because of my choice of gearing (at least not for a few more years). I've seen lots of fit riders stop turning the pedals because they can no longer push the gearing on their doubles (standard and compact).

On the other hand, while I've only been to New Jersey a few times and haven't seen that much of the state, I'd think a 34/25 would be overkill.

It was the mind training- 30/26 and by the end of some of our hills- I was just getting to the end of energy levels. So changing to 34/27 was going to be harder. It is a higher gear- But I forgot the other side. When you run out of gears- you cannot go lower so you just have to do the best you can. With me that means that I do not walk up any hill. For longer steep slopes though- there is no way that the mind can overcome the body for a long time. There comes a point where low gearing is necessary and the difference between 34/27 and 30/36 would become noticable.

I have a compact on one bike and a triple on the other, and the triple just seems to give me a little extra oomph up the hills.

Just my $0.02 worth.

I've got one of each and I don't think so.

I guess that it's possible to imagine somebody using the big/big with a triple but I certainly never do. I can't even imagine anybody ever using the granny ring with any but the largest 2 or 3 rear cogs. I do use my middle chainring across the entire rear cassette.

Shifting wise, 34 to 50 is a pretty big change. Mine shifts fine but certainly no better than 30 to 42 with my triple.

FWIW, I think that the biggest drawback of a compact double has to do with the flat road gears. If your favorite flat road gear turns out to be near either end of the cassette you're going to hate a compact double. If you basically only use the small chainring for climbing hills, a compact double is great because you won't find yourself in a lot of situations where you need to shift both derailleurs at the same time.

With the compact, it is typically 34/30-1 = 13% harder on the low end (you lose about a full gear for climbing) and 1-50/53 = 6% slower on the top end for the same rear cassette. There is little difference in ease of shifting between double and triple for comparable quality components. With the compact double there will be more instances of "double shifting" (shifting front and rear at the same time ot maintain cadence) but this is no big deal.

IRD makes after-market 10-spd cassettes with bigger ranges than the standard Shimano or Campy ones: For example 11/24 or 12/30. They don't shift quite as smoothly as the OEM's but are okay. They typically also require a mtb rear derailleur.

I have followed your exacty path with the bikes- began with a Sequoia Elite Triple, which I love/loved, and now have a Roubaix, which I love even more!!! I have not at all missed the third chain ring gear and essentially agree with all the previous replies. Good luck!

The nice thing about a triple is that you have a 52-39 for the big rings while still having the little ring in reserve. I much prefer 52-39 over 50-34 for most riding.

I have 52-39-30 and a 12-27 cassette. It's a wonderfully versatile setup.

Having said that, if I could afford a second bike, I might get a compact to use on some flat routes where I am never out of the big ring.

I remember a time several decades ago using 42 in front to 25 in back for same hills that I use my triple now. (sigh!)

Look at the other part of the data posted by hermes. There is a big difference in the percent change in shifting gears in a double vs a triple. Unfortunately bikes are getting more and more marketed to just the young and what's easy at 30 or 40 may be next to impossible after 60.

I don't care what drive system is used, I still can't find a sweet system:
Criteria:
1-- low GI at least 24, ideal 22
2-- high GI at least 130
3-- steps between gear shifts never greater than 9%
4-- minimum double shifting

Best i have found is: 28-42-53 with 11-27.

That's pretty tough criteria.^^^