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I'm bike shopping for my first road bike, and I've asked for a lot of advice from my father who was a serious cyclist once upon a time. After showing him one prospective bike, he dismissed it with a simple "you don't want a triple" with zero explanation on why.
What are the pros and cons in having a Triple, vs having a Double crankset? Does it differ from road bikes, to mountain bikes?
The idea used to be that a triple was just a double with an extra small, 'granny' ring (i.e. only grandmothers would need to use that one) so there was definitely some snobbery in a triple; that it was designed for those who needed a little more help. So on the club training run, you might be teased for it. (Google for 'triple granny ring' for various forum discussions and banter; don't worry, most of the responses are SFW.)
Practically, what it tends to mean is not necessarily a bigger gear at the top (i.e. big front ring & small back ring) but a much lower gear at the bottom, for the hills. So with the same rear cassette you might compare a 50/34 double for a 50/39/30 triple (although a 50/34 is probably more what is called these days a 'compact'). That range of triple combined with a typical rear cassette of 12-28 would work for most hills.
You also get a lot more options; so you'll get the similar effective ratios in several ways, because the ranges on the big ring overlap more with the middle, and the middle with the little one. Also, the gears are closer together - so you're more likely to find something that works well at the right time.
It is also easier to change on the front ring of a triple, on a compact you'll often need to change down a gear or two on the back when you move on to the bigger front ring, which means the chain is being yanked both ways and strained that bit more. But on the triple, you're not as far away, so you'll often not need to change the back at the same time as shifting the front.
As the others have stated, there's nothing wrong with any various drive train types (triple, double, 1x, single, etc). Compact drivetrains and triples are becoming more common because they provide an easier set of options for casual riding. A traditional double for a road bike may be more than most people want for casual riding. For example, if you take a brand of bike and look at their entry road bike it will typically have a triple or compact. The high end bike will often have a traditional double or compact.
In my experience (read, my opinion) a triple does offer a couple of "cons":
Obviously, the simpler the better, and a triple is a little, er, "crankier" to maintain and use than a double. But on most bikes it will mean that you have both a slightly larger large gear and a significantly smaller small gear, in addition to having closer "jumps" between gears. Exactly how this all will work out depends on the manufacturer's choice of sprockets, of course (or on your choice of after-market replacements).
Though bicycle snobs may turn up their noses at triples, there's very little wrong with them and a lot that's "right". The only two negatives are a slight increase in difficulty shifting the front derailer (minimized with properly adjusted indexed shifters) and the negligible additional weight.
Whether or not to get a triple really depends on:
If you aren't (currently) in cycling shape then a triple is a really good idea. If you are buying a bike for recreation and to hoping to improve your fitness, the last thing you'll care about is saving a few grams on a lighter crank with less gearing options. What you will care about is having a bike that will allow you to ride wherever you want to go without having to make the decision of "oh no, here comes that hill that I can't go up because I don't have the right gearing". That said even with a triple there are still bound to be hills that an unfit cyclist won't be able to ride up (I live in Boulder, CO and there are a few climbs that even "fit" cyclists have a hard time going up).
Geography plays a huge part in gearing. Like I said I live in Boulder, CO and primarily use a compact double for training (a compact double has easier gearing than a regular double). I use a regular double for most racing, but have been known to race with a compact. It's pretty common to see cyclists around here using triples as there are some pretty stiff (and long) climbs in the area.
What's your reason for buying a bike? Training for a century? Getting back in shape? Commuting? Getting into cycling and hoping to do some racing?
Honestly, there is no right\wrong answer.
My advice would be to get the bike shop to let you demo a bike with a double for the weekend and do some riding. If you feel like you need more gears, get a triple crank.
The positive of a triple crank is a greater range of gears. A triple crank will give you a lower low gear which may be useful for climbing steep hills.
The negative of a triple crank is weight. You have an extra large gear which will likely weigh around 8 or 10 ounces. Since those ounces are on a part of the bike that rotates, they matter.
So if you plan to ride up really steep hills, a triple crank can help. Otherwise you probably don't want it.
As an aside, I recently purchased a bike with a triple crank and wish now that I'd gone with the double crank. I almost never use the lowest gear, so it's just extra weight. Of course I don't climb any steep hills.
90rpm = 1.5 Hz, a 300g chainring of radius 6.5cm, assuming all the mass is at the radius to get the worst case, has rotational kinetic energy 0.5 * m*r^2 * w^2 = 0.0087J. Compare this to translational kinetic energy for the same chainring at even just 10mph, 3.00 J. I don't think the rotation matters.
Nobody has mentioned the best thing about a triple. Ease of shifting. I have a double now and the problem with shifting is you always seem to be in the wrong gear. With a triple if you're at 20 mph or more your in the big ring. If your 10 mph or less your in the little ring. All the rest of the time (Which is 70%+) you're in the middle. With a double at a average speed !5 mph to 18 Mph you're reaching up in the little or down in the big. You end up changing the chainring through out the whole ride. Triple is just easier.
Consider climbing a 15% grade when you are on a 60 mile quick spin, versus when you have completed 150 miles of a double century with 20,000 ft of climbing. Or supposing you are on a 1200 brevet? Any rider is going to face some distance hilly ride where it would be advantageous to have lower gears.
An advantage of triples over compacts is that the changing between the gears is easier: you have to move between more gears in the rear on a compact.
By the way I'm just estimating. I'm about to put on a triple for a very hilly double century.
The main reason to avoid a triple is ego. If you have any, you don't want one. If you are less egocentric, and ride in a place where low gears matter, then by all means consider it. The weight doesn't mean much (without the ego related stuff), and there are darned few people strong enough to ride up serious hills who don't also have egos to match that ability.
I'm 180lbs and ride up 3000' grades with around 200w (powertap) on a normal day. I have a triple on the bikes I take up those hills and I'm not afraid to use it with my 34t cluster. I'd have to be able to do 240w for an hour to give the low gears up, and at my age, that improvement isn't going to happen.
Traditionally, pure road bikes don't have a triple crank. It's a cultural thing, like admitting you're not strong enough. There's something macho about it, I think.
That, and weight. When you pay an extra thousand $ so that the bike be a bit lighter, you're not going to want to add unnecessary weight.
But then again, it all depends on the geography where you ride and your physical condition.
Figure out what type of riding you're going to do and get the bike that fits the needs. And if you want a triple crank, don't not get one just because your father told you not to get one. It's you that's going to ride the bike, not him.
I rode a high end 9-speed triple for many years. Although I rarely used the granny gear, when I needed it, I was very glad to have it. My new bike, though, has a compact crankset (double). With a 28 rear cluster, it goes almost as low as the triple, which had a 25. With a ten-speed cluster, you don't lose a lot of gear spacing. So with a 10, I'd go for compact cranks. With a 9, a triple is still a contender.
First, if you're a Clydesdale then you should probably have a triple.
But overall, the advantages of a triple are:
A triple can spin up an elevator shaft.
Gear changes are more natural and accurate.
Your legs will spin out before the top gear does.
In practice, a triple has a better chainline.
A triple is kinder to your knees.
The advantages of a double are:
A few less ounces and a few less dollars.
A narrower pedal stance, 7mm.
On paper, a double has a better chainline.
A double is a leetle more aero.
The weight cost of a triple comes down to:
Inner chain ring + chain ring bolts, (Chorus, 767 - 670 = 97g)
Long cage rear derailleur vs short cage, (Record, 205-187 = 18g)
Triple front derailleur vs double, (Centaur, 107-92 = 15g)
Wider bottom bracket, 115 vs 108, (Phil Wood, 221-208 = 13g)
Actually, it's less than the 97+18+15+13 = 143 grams total. The 97g compares a 175 vs 172.5 because that's the data WeightWeanies had available.
This is a very good history of chainring sizes.
http://www.bikehugger.com/post/view/the-rise-of-the-compact-crank
I'd add that Campagnolo reintroduced the triple into their 10S and 11S lines.
Pro riders use race and compact doubles, especially after Tyler Hamilon's heroic performance in the 2003 TDF. If you're sponsored and you want a 6800 gram bike, maybe you don't want a triple. But you only have to spin past someone standing up once to get the point of a triple.
BTW, the 11S exists mostly to hide some of the shortcomings of the double. For me 3x10S, 53/42/30 x 13-29 covers everything everywhere ever. I don't see the point of 3x11S.
Well, it should be pointed out that Campy etc now have RDs that can handle up to 32T. A compact's 34-32 is comparable to a triple's 30-29. Sheldon Brown points out that you can go lower than a 30 on a triple by swapping out the inner, down to about a 26. But this is pointless for most people and for myself, I'm happy with my triple.
I'm 67 years and live in Norway. As an active athlete I feel that the discussion on gearing is too concentrated on max. performance. I'm going to a triple because the majority . in time, of training is at low intensity. The problem is not how to go fast enough but how to maintain a low enough intensity AT ALL TIMES so as not to over train on the hills. Over training is very common on long tours. 118-120 on the flat , 140 - ? uphill.
I ride a triple that gives me a low gear of about 22 gear inches, I don't use it often but when I need it, I can spin past others on a compact. We are a senior cycling group and the triple becomes more important with ages above 70 years.
For me the big advantages of the triple (eg 52/39/30) are:
The two cogs 52 & 39 on the front for almost all riding - a classic double with ratios not too far apart, 39 ideal for rolling country. I never spin out on downhills unlike compact riders with their 50/34
30 on the front for very steep hills or when I am weary/totally knackered towards the end of a big sportive eg the last climb on the Etape du Tour. I combine this with a 12-30 10 speed cassette for a lowest of 30 - 30. I have seen many compact double riders unable to maintain a sensible cadence and cramped from the strain on steep hills or very long climbs (though I suppose they could have used SRAM 'climbers' kit with a cassette biggest sprocket of 32)
However, my MTB did have a triple, and I rarely felt the need to use the smaller gear, even on very steep inclines.
Either you are very fit, or your MTB rides aren't that steep...
Anyway, let's consider a typical weight weenie race bike :
chainring 34T / cassette 24T * wheel circumference 2.1m = about 3m per crank revolution
On a MTB you'd get a 32-34T middle chainring and, so the same gearing corresponds roughly to :
chainring 34T / cassette 23T * wheel circumference 2.0m
So, check which number corresponds to the 22-23 teeth cog on your MTB, this should be number 4-5, and go climb the steepest hill you'd ride with your race bike, not using any easier gears than this one. That will give you a good preview on how easy/hard you can expect it to be.
I have a 38/48T crank setup and 11-30T cassette on my custom-built Surly Long Haul Trucker.
Originally the 38/48T crank set was a triple (28/38/48T), but I removed the smallest chainring, not foreseeing any use for it, and adjusted the front derailleur to not drop the chain from the 38T chainring to the removed chainring.
Most of the time, I use the 48T chainring. For steep climbs, I occasionally (but not always) shift to the 38T chainring.
I do this even though I'm relatively heavy (>100 kg), the bike is relatively heavy (>15 kg) and I had a 5-year break from cycling, having cycled only bit over 100km since the break.
Despite the 5-year break, my high weight and the bike's high weight, I still don't miss the 28T chainring that was removed.
Considering that today it's easy to find road bikes with a "compact" crankset (34/50T), and that the cassette may very well have 28-32T largest sprocket in today's road bikes, there is absolutely no reason to select a triple.
With a crankset that was originally designed for a double, the chainline is better than it is for a triple crankset with smallest ring removed.
In fact, it could be argued that today's large range cassettes (11-32T) may allow you to use only a single large chainring. However, single chainring has no redundancy: if it breaks, you have to walk home, whereas with a double you use the other ring. Besides, there will be an occasional steep hill which would make you wish for that smaller ring.
road-biketag here? Riding on road is quite different than mountain biking in that there is at least some visibility behind corners and surprise uphills (combined with poor traction) are not that much of a problem.