maddmaxx 

The compact road double is a straight 110mm

The MTB compact crank (not so often used any more) is a 110/74 triple. This bolt circle is sometimes used for a compact touring triple.

The more common MTB crank is a 104/64 triple. This also comes in a touring triple form with 26/36/48 rings. (still sold in the Shimano MTB ranges)

I believe that you can find a couple of inexpensive compact road cranks made with 110/blanked out 74 bosses, but most are machined to a more sophisticated standard than that.


Here's a reasonably complete list (not up to date with some of the newer more exotic MTB bolt circles.

Track 144 BCD (Gebhardt)
Road double 130 BCD (Shimano, Gebhardt and others), or 135 (Campagnolo)
Road triple 130/74 BCD (Shimano and others), or 135/74 BCD (Campagnolo)
Compact/touring double 110 BCD or (Campagnolo carbon 4×110/1×113 BCD, Gebhardt)
Compact/touring triple 110/74 BCD
Mountain bike (4 arm)104/64 BCD(Gebhardt)
Mountain bike (5 arm standard) 110/74 BCD
Mountain bike (5 arm compact) 94/58 BCD

stapfam

The "Compact" standard MTB cranks have a smaller BCD than the Road Compact crank but the older "ATB"- as they were termed over here- have the same BCD as the Road Compact. I say older but have noticed that Deore and XT are offered with the larger BCD and there may be others.

The Compact MTB generaly uses rings of 44/32/22. The ATB will have something like 48/36/26 fitted although down to 24 is possible for granny and a 34 is available for the middle ring. My ATB as fitted on the Tandem has 48/36/24 crankrings and is used with a 9 spd 11/32 cassette. And that thing will not climb a wall offroad but we cannot fit a granny lower than a 24- or a middle ring lower than 34. And we bend 12/34 cassettes.

But then there is the new double crankset in 10 speed that is coming available for MTB's and I have no idea what BCD they are.

canopus 

I just switched to a compact double 10s from a std triple (30,42,52) 7s and I got to say I like the change. It works well enough for me in my area on the woods on the hills we have or I travel to and I get a nice tight cruising range on the 10s cassette. I can go a little lower with a cassette swap if needed or higher depending on where I might ride. I liked the triple but I didn't like the 30-42 jump on the 10 speed and couldn't get a 39 to work using the triple front der. I certainly didn't like the gearing I got from the triple with the 10s rear either. It didn't give me enough options in the inch gears I ride in. The compact did. The compact swap also cleaned up the chain line so that it was usable and not overly wearing my rings like the triple did. That said I don't think it is for everyone and if i lived somewhere hilly I would definitely swap it it out for lower triple. It all depends on where you ride, how you ride and your conditioning.

Philipaparker

I had both the triple and a compact double and I prefer the double. Triple just doesn't shift that well. My compact is Ultegra 50/34 with an 11-28 cassette, I have a rain bike that has a compact 50/34 with a standard 12-27 cassette. Both work great. Just so you know I live in San Francisco and ride around the hills of Marin, not uncommon to do 3000 to 4500 ft of climbing on a 50 mile ride.
My friend Bill has a triple an swears by it so I think it's a matter of personal preference.

chuckb

[QUOTE One thing to note, you can treat a triple as a double, you can't treat a double as a triple.[/QUOTE]

Bingo. I started out, at age 52, with a Trek 5200 with 39/52 and 12/23 gearing. I soon realized that this was not gonna do it for me on the climbing rides I wanted to do. I first tried a compact 34/50 and ultimately went to a triple 30/39/52 with 12/27, the widest gear range you can get with ultegra components. This solved the climbing issues.

After 4 years of pretty serious riding, I'm better, and 90% of the time, I just treat the triple as a double. On rare occasions, and climbs over about 8%, I'll use the extra ring on the triple. Two reasons: (1) lower gears if I need them, and sadly, my knees are telling me that I do, (2) less cross chaining. 30/21 is in the center of the rear cog and almost identical in gear ratio to 39/27, but nicer to pedal. Up to about 6%, that's my standard climbing gear.

The "triples weigh more" always makes me laugh. ANYONE can diet off the 1/4 lb weight difference.

Wogster

You may be onto something here, the crank and the cassette need to match. Maybe a compact double with a wider cassette could work as well as a triple with a narrower cassette, for example if you have a cassette that is say 12-27 and have a 30/39/50 crank. You switch to a 34/50 crank and switch the cassette for a 12-31
would it work as well, hmm lets see. A 27 tooth cassette and a 30 tooth chainring is 29.3 gear inches with a 700c wheel and a 25mm tire. A 31 tooth cassette gear and a 34 tooth chainring is 28.9 gear inches, so actually slightly lower. These numbers come from Sheldon Browns Gear Calculator. You could accomplish this by using more 2 and 3 tooth jumps.

For touring, I would still want a triple.

JimT

I was just thinking about that today while I was mounting my new pump and top tube bag so I can carry my cell phone and small digital camera. Then there's the new bottle cage I need to add so I can carry my new small thermos with coffee.

Jim

Terex

Instead of a triple, just buy a small sports car like I did. A used Mazda Miata cost about the same (probably less...) than my road bikes, and my wife can ride with me. No, I don't sit up nearly as high as I do on my bikes, but it's a trade off that I'm willing to accept. The short throw shifter is far smoother than either my DA or SRAM shifters, and the bento box-like trunk comes in handy if I want to take along a snack. I don't know the gear ratios, but I'm sure several of you guys will post a chart. And if you drive one too, please, please, don't flip your freakin' lights at me or expect me to wave. And yes, I DO notice an additional 1/4 lb weight difference when I drive it. Unless I shut off the AC.

Wogster

Actually you don't need to diet to lose 1/4lb, just make use of a bathroom. The lowest number I could find for the urge to purge is about 150ml, which should weight a little over 150g (the actual weight varies a little, pure water weighs 1g per ml) or just under 1/3lbs. Of course doing a #2 should be good for a pound at least. This is why the best time to weigh yourself is in the morning, after you go, but before you eat or drink. The best day, is Friday, because your likely to have your lowest weight then, after being "good" all week, before you get into the PIE on the weekend.

stapfam

I ride my local hills and on an average ride I will take in 3 or 4 hills with about 2,500ft of climbing. Each hill is between 10 and 12% and I can do this comfortably on the compact double with a 12/27 cassette. BUT- If I go out for a longer ride- with extra Climbing then I will use the triple 50/39/30 and still with the 12/27 cassette.

Then there is the basket of .7 of a mile at 16%. With training I can do it on the compact- but not at this time of year.

Up to a point- lower gears are not necessary for me for the degree of slope. What does get me though is extra hills or the same hills with longer milage. I no longer have the stamina that I used to have.

BluesDawg

Adding to the options available, Shimano has just announced new XT and SLX 10-speed MTB groups. https://www.singlecrown.com/index.php...sys-xt-and-slx

Presumably, a Shimano 10-speed equipped road bike can now add one of these new rear derailleurs and cassettes and get a wider gear range. The cassettes come in 11-34 and 11-36 versions.

gtragitt

I don't understand why there is a debate. I have both a compact double and a triple. I like the compact double for my current situation in Houston where I never use the small chain-ring. Somebody suggested I would be happier with a regular double. Maybe - but a standard double wasn't available on the bike I wanted. Although I am fairly strong I most likely could not spin a 90 cadence on the flats with the tallest gearing on a standard double. The 50 tooth chain-ring is big enough for me on the flats. I could use taller gearing if I had some nice downhills.

If people are happy with their triples - that is great, but I should not be begrudged for my selection of a compact double. I do find it shifts better than the triple with the longer cage. I rode the same road bike with a triple before I bought the compact double. I don't know that the difference in shifting would sway me away from buying a triple if I lived in Tulsa where they have steep grades on long hills. I am fairly strong but would probably find that the compact double was not low enough for some of the hills I used to ride when I lived in Tulsa. I loved my triple when I lived there.

I also lived in Porto Alegre in Brazil. they have some nice hills there also. I could get my hybrid (that I still own) up to 45 mph on some of the downhills with the triple and used the small chain-ring on some of the climbs.

I never owned a double in the last twenty years and was somewhat skeptical about buying a bike with a double. My skepticism has now vanished. I would also never question anybody's wisdom for buying a triple or a standard double.

BluesDawg

+1
Many options exist. Choose the one that works for you. In fact, thanks to N+1, you don't even have to choose just one. Different bikes for different purposes or different moods can have different setups. 3, 2 or 1 chainring; 10, 9, 8, 7, 6, 5, 2 or 1 rear cog (maybe with 3, 7 or 8 internal ratios). It's all good.

tcs

The "3 versus 2" debate was pretty much over by 1907-1908, although a few "2s" have appeared from time to time since.

tcs

Dchiefransom

I love people like that. I look them straight in the eye and tell them that all people need is the right pair of running shoes and more training to run a 3 hour marathon. Most can't make the connection between the two.

Dchiefransom

Change the biggest rear cog to a 34 on the 52/42/30 chainrings, and see what the gear inches look like. At 60 rpm, you'd be spinning up a hill at 4.2 mph, and at 80 rpm, you're going 5.5 mph.

Lobby

As a n00b who's sorta new to this site, I find myself merely using the middle gear in the front and pretty much all the gears in the back. I've thought that I'd be just fine with only 2 in the front, instead of three.

I mean, looking at this issue from the 50,000 foot level, does one really need 30 speeds on a bike, or is 20 speeds enough? I dunno....

Road Fan

It sounds like what you are calling two-step is the same as the oft-discussed half-step. What you called an Alpine is close to what we get today with a 50/34 compact, just now with 9's and 10's we can get smaller steps for a given chainring, or more range overall.

Kotts

My commuter runs a classic double, my "fun bike" an FSA triple. I have pretty much the same ranges available to me with the top two rings on the "fun bike" (with 2 more shifts at the "low end" and less overlap than the commuter.)

I rarely use the low chainring on the triple, but those few trimes I need it, I'm glad I have it. What's the point of a "fun bike" if it's a b&*^% to climb with?

BluesDawg

What you will find is that half of the gears you now use on the middle ring will be on the big ring of a compact double and half will be on the small ring.

revelstone

when i pedal the bike moves forward. do i need to know more? i have a schwinn, the front is 48,38,28 the back is 11,14,17,21,24,28. i used the 28 on the front once to see what it was like. mostly snapped my knee off cuz it pedaled so easy. so i just do the middle and the big one on the front use most of the back for hills and downhills. even with 48/11 on the downhills i can only hit 26 mph on a downhill, although i did 28.5 on the same downhill with a tailwind the other day. and i almost never even notice the entire extra 1/4 pound of the chainring i almost never use. and yet with all this, when i pedal the bike moves forward. who knew?

Lobby

So if I went with a compact double, I'd be shifting more than I am now? Therefore a triple would be better for me?

stapfam

I find I change less on the compact than on the triple. On the flat and I will stay in the big ring. When gravity goes the wrong way and severely- then I use the small ring. For a flat ride with undulations it will still be the big ring and even short sharp rises on a flat ride and I will stay in the big ring and "Crosschain" but put more effort in rather than change down.

But all you have to think about is the rear cassette. Compact and I need the 27 on the cassette. With the triple I can get away with a 25 and possibly even a 23 as the lowest gear.

Hermes

Settled... I just received a new SRAM S900 crankset https://www.sram.com/node/103/brand/sram-road/src/cat with Quarq cinqo power meter and D/A chainrings 54/44. This is going on my TT bike. I took that D/A rings off my old crankset and shipped them to Quarq. They mounted them on the new S900 crankset and calibrated and tested the power meter. In addition, I have the new 53/39 rings that come standard with the S900. Quarq set up the power meter so I could use either set of chainrings.

jimmuller 

So much fuss over a spare chainring. Compact double?? What's that supposed to be? I realized 30 years ago that I had high gears I never or rarely used. So I just bought a chainring or two and presto! a 48-36. It was recently changed to a 48-34. (I ain't sayin' what's on the rear.)