Thanks to Sheldon Brown's Bicycle Glossary, I don't have to provide definitions for my terms. Thanks Sheldon!
The following notes and instructions(*) assume you're converting a "road" style bike with drop or moustache or similar non-straight bars. If you have straight bars, every shift lever ever made to fit on them will work with triple cranks, so you can skip the part on shift levers.
There are two paths to take: Converting your double-chainring cranks or purchasing cranks specifically designed for three chainrings.
You will need what's often called a "Tripleizer" chainring. This is a specially designed chainring with a built-in spider, usually for 74mm bcd chainrings. Rivendell Bicycle Works sells a very fine Willow brand tripleizer chainring. To use one of these, you will need to change your Bottom Bracket spindle by perhaps as little as 5mm, but more likely 9mm. How much exactly? Alas, I do not know. The safest thing to do is to call Rivendell, order the tripleizer chainring from them, and tell them the cranks to which you'll be attaching it, the small chainring you expect to use (they sell very fine small chainrings too, I'm using a 29T Willow 'ring which I got from them), and what kind of bike you'll be putting it on (thickly tubed bikes will require more clearance, and thus a longer spindle, than normal-sized tubes). If you have a cup-and-cone bottom bracket, you'll just need to exchange the spindle, if you have a cartridge bottom bracket, you might be able to get a new spindle installed (for some of the really expensive "boutique" brands), but you'll probably have to replace the whole thing.
The most important thing to consider when purchasing a new crank, is that you do not have to purchase a special "road triple" crank, but you can use a more standard 110/74mm bcd triple crank (which, unfortuantely, are not as popular as they once were, so maybe I should't be calling them "standard"). Unfortunately, most off-the-rack 110/74mm triple cranks are equipped with the old MTB-standard 24-36-46 setup, which is not likely to be suitable for people converting from a road double. Fortunately, many chainrings are still made to fit these cranks. 74mm bcd chainrings can be as small as 24t, and are easily found in 24, 26 and 28t. 25 and 29t are made by Willow and available from Rivendell (and I think they may be making 30 and 32 by now). 30, 32, and larger are available from other manufacturers, but may need to be special ordered. 110mm bcd chainrings can be as small as 34t and are easily found in even numbers up to 56t, as well as (less commonly) some odd numbers (37, 39, 47, 51 and 53 Willow chainrings are available, others may make odd sizes too), and some very large sizes. Shimano's RSX triple crank is a 74/110 crank with 26-36-46 rings, so it might be a useful cranks for conversion, provided you either like the small chainrings or replace them.
Shimano "road triple" cranks are available in their 105SC and Ultegra groups, and use a 130/74mm bcd. This allows you to use the most common "road double" chainrings from Shimano, Suntour, Mavic, Sugino, Stronglight, Willow and many other manufacturers for the middle and outer chainrings should you not like the default setup. The default setup for Shimano happens to be 30-42-52, and there don't seem to be any other setups available. 130mm bcd chainrings can be as small as 38t, and are available in 1t increments up to about 57t, as well as larger sizes. Many sizes would have to be special ordered.
Campagnolo "road triple" cranks are made in a couple of their lines, Veloce and "Racing triple" (formely the Athena triple set) for 9-speed (still works with 8, no doubt), Their other groups, Daytona on down, also offer triple cranks. They use a 135/74mm standard and are listed as available with 30-40-50, 30-42-52, or 32-42-52 chainrings, but it may require a special order to get anything other than 30-42-52. 135mm bcd rings are not particularly common, but are available from Campagnolo, Stronglight and a few other manufacturers in 1t increments from 39t up to 57t, as well as some larger sizes, but expect to pay more than for 130mm chainrings.
The big advantage of going to a triple chainring setup is that it's really easy to figure out what bottom bracket to use, as there is generally one made specifically for the crank (in the case of the Shimano and Campagnolo cranks) or a specific spindle length is specified for that crank. Ask your local bike shop for the correct spindle length if you're not sure.
If you have down-tube or bar-end shifters, rejoice! You need do nothing to get them to work with a triple chainring, except for adjusting them and/or the front derailleur, of course.
If you use Shimano STI, you probably need to purchase a new pair of triple-specific dual-control levers (RSX for 7-speed, 105SC for 8-speed and Ultegra for 9-speed), unless you can find someone to sell you just the left unit. Alternately you can use a device such as the Erickson Gizmo that essentially adds a second mini-shift lever in between your STI lever and front derailleur so that you can shift a triple with double-chainring-specific STI levers.
If you use Campagnolo Ergo (and perhaps Sachs, but I'm not sure), you should be set, as they are supposedly all triple-compatible and always have been. You could probably test this by backing both set screws out almost all the way on your existing front derailleur, and then seeing how much distance the front derailleur now covers to see if it would cover the 5-6mm more space needed for a triple.
You probably should change the front derailleur, but you might not have to. Some front derailleurs designed for double chainrings have the capacity to shift up to 16t difference between the smallest and largest chainrings, so if you want to use a 32-42-50 setup (which has an 18t difference) you might be able to get it to work, since listed capaciteis are often conservative in order to keep people from doing silly things like this and having shifting problems. If not, get another one. Modern "MTB" front derailleurs are generally designed to handle a large chainring of no larger than 46t, so could be problematic for this purpose. Older triple-compatible front derailleurs are likely to do a better job with chainrings up to 50 or 52t, and the modern "racing triple" specific FD's from Shimano and Campagnolo are designed for a 52t max, so could probably go a few teeth higher with little or no problem.Return to my bike page.
You do not have to get a long cage rear derailleur, but you probably should. I have a whole page, "Triple Chainrings with Short Rear Derailleurs," that describes how to do this and the special considerations of using a short rear derailleur. Should you opt for a long-cage rear derailleur, you can, of course, use either an "MTB" or "Road" style. The "MTB" style ones are generally designed to handle a 32t or 34t largest rear sprocket, while the road ones are designed for a 26t or 28t largest rear sprocket (and therefore tend to shift over clusters with small jumps between sprockets a wee bit better.)
Return to my home page.
Disclaimer: The author assumes no liability for property or personal damage that could result from following these directions. If you do something stupid, it's your fault, and it's time you got a spine and owned up to that. Life's tough, and there shouldn't be monetary reward for stupidity. Nobody owes you anything, not me, not any big or small corporation, not the government, and not even your parents. Deal with it.