Switching a bicycle crankset for a triple crankset

May 3, 2007 10:44 PM

How difficult is it to swap out the (double) crankset on a bike I'm hoping to buy for a triple? Will it require a new shifter? Chain? Etc?

So I've found a small (50 cm) road bike that fits me, used, for a reasonable price- it's a mid-90's Trek 5200 for $600. It's got 8 speed Ultegra components, which I'm fine with. Thing is, it has a double crank, and I live in hilly Seattle, where I'd really like a triple.

If I buy this bike, and then ask a bike shop to swap out the crank for a triple, what else will I need to change? Will I need a new shifter, and if I do, since it's a STI model, will I need new brake levers to boot? Etc. Plus, since it's an older bike, am I going to have trouble finding a compatible crank in the (slightly rare) 167.5 size I need; are current 9 and 10 speed cranks compatible with the rest of the bike?

All advice welcome- yes, I know I should have posted on a bike forum, but I trust you guys...

posted by carterk to sports, hobbies, & recreation (15 comments total)

Answering first, but just use this answer until something better comes along as the last time I did this it was on a bike a little less modern than yours and therefore the job was simpler.

BTW, definitely do this -- having a small (in my case 30T) ring in the front kicks ass.

First, is the STI front shifter indexed? There's no problem as long as your front shifter isn't indexed. I don't know enough about indexed fronts to offer a good opinion if that isn't the case.

I swapped a Shimano RX-100 double for a Campy Racing Triple on my road bike a couple of years ago. No chain compatibility problem between the 9-speed front crank and the 7-speed Shimano rear. I'm moving between fronts by hand anyway -- if indexed you might need a shifter pulling more/less cable per click -- again, I don't know.

Had to get a new front der'r capable of handling the extra ring and bigger drop -- you will most likely need to get a der'r designed for triples. Existing downtube front shifter handled the shifting just fine. Since the original der'r was clamp-on there wasn't a problem mounting the new one but I don't know what the deal is if your der'r is braze-on -- will you have to move the b/on? I don't know.

The new crankset needed a new bottom bracket because the crank interface was different, but even if your new triple uses the same interface you'll probably need a new b/b with different width -- check with the crank manufacturer for the appropriate b/b.

Dunno enough about odd crank lengths to comment on availability of 167.5 mm.

The whole job was pretty straightforward using the manufacturers instructions so if you're dealing with a clamp-on and you have the tools and a decent comfort level working on the bike go for it yourself. It's the compatibility issues I wish I could give you better info on.
posted by Opposite George at 11:36 PM on May 3, 2007

Oh, and I bought a new chain for the hell of it but the existing chain should be fine as long as the new crankset doesn't have a bigger large ring than the existing one. If it does, you will probably need more links and therefore a new chain.
posted by Opposite George at 11:57 PM on May 3, 2007

Finding a 167.5mm triple crankset's going to be a little difficult, but the age of the bike shouldn't have anything to do with it. You'll replace the bottom bracket and cranks at the same time. As already mentioned, you'll almost certainly need to replace the front derailleur, which probably means replacing the front shifter. Or you could give up integrated shifting and add a clamp-on or bar-end friction shift lever for the front. That's probably how I'd do it. But, realistically, unless you're going to be doing the work yourself, you're probably going to spend nearly as much modifying this bike as you're paying for it in the first place. At that point, wouldn't you rather just have a bike built up from your specifications to start with?

(Alternately, keep the double chainring in front and get a lower-geared rear cogset. That's what I did on my road bike, and since I'm not racing it, I don't mind losing the high end.)
posted by hades at 12:07 AM on May 4, 2007

hades has it, I think. Excellent point on the cost.

Even with me doing all I could to minimize cost, the parts and tools for my job came to about 150-175 bucks. Add a downtube shifter and we're looking at about two bills before labor.

I don't know if I'd up the cassette but that's just personal taste -- I'm a weak climber who also likes to pedal downhill. Only you can decide what you want there. Instead of swapping the cassette you could also try swap one or both rings down to something smaller -- that should be pretty inexpensive and might be good enough. Check peterwhitecycles.com and harriscyclery.com to figure out what'd fit on your setup. You could keep the front derailer that way as long as you keep the drop within its spec.

But the real deal is, as hades suggests, you can get a really, really nice used bike with the triple already installed, maybe for no more than what they're asking for this bike but certainly for less than it'll cost to swap everything out, and not have to monkey with kludges. Consider that.

If you go that route, you'll have much better luck finding a bike with a more standard crank length -- do you really, really need 167.5mm cranks?
posted by Opposite George at 1:31 AM on May 4, 2007

If you're willing to step up to 170mm cranks, you open up a whole world of options, and you get a little extra leverage for climbing, too. Longer cranks are mostly a liability when spinning at high RPM (part of why fixie riders like short cranks); otherwise, even if you have short legs you're unlikely to notice the difference in most conditions.
posted by ardgedee at 2:47 AM on May 4, 2007

It's not worth it. New bottom bracket, new cranks, new front derailleur, new front shifter, probably also a new rear derailleur if it is not a long arm one already, all those parts add up and the swapping out process is not trivial. You can easily trash the frame if you screw up the bottom bracket installation.
posted by caddis at 5:01 AM on May 4, 2007

I know this isn't exactly your question, but if you're looking to make things easier on yourself, and you have the room in the back, add a big ring at the top end of the cassette -- same effect and usually cheaper.
posted by nnk at 6:57 AM on May 4, 2007

As others have mentioned, this is getting expensive relative to the cost of a different bike. It's perfectly doable, just maybe not economically sensible. Depends how much you want to keep the rest of the bike. To swap for a triple, the minimum you're likely to have to buy is a new bottom bracket, the crankset and rings, a new brifter and the labor to have them all swapped by a competent mechanic.

You might not need a new front mech. Shimano says you do, certainly, but I've got a Shimano 600 front mech shifting a Sugino triple that works just fine in friction mode. If you're dead set on brifters and indexing the front, you'll probably need a new mech. You don't change the front as often, so maybe consider a front downtube shifter, instead? You may or may not need a new rear mech. Depends on the size of your largest rear cassette sprocket and the size of rings you end up with at the front. Again, despite what Shimano says, a shorter double rear mech can be made to work OK with a triple setup if the cassette is fairly narrow and the big ring at the front isn't bigger than about 48.

I don't think Shimano even makes 167.5 cranks any more(?). Intermediate lengths like that tend to come from the less mainstream and up-market brands. I think TA are the brand to look at if you want funky lengths, these days. Are you sure that's an essential requirement? 2.5mm difference is quite small. Sure you can't survive with 165 or 170?

There are ways to get lower gears without getting a triple. You might consider a compact double with bigger rear sprockets, although in the end it might not work out that much cheaper. Alternatively, leave the front alone and get some really big rear sprockets, like on the Shimano Megarange cassette. You'll still have to pay for the sprockets, a new rear mech, and a chain, but it'll be cheaper in parts and labor. Or buy a touring/randonneur style bike instead and be done.
posted by normy at 6:59 AM on May 4, 2007

Another thought... It's unconventional, but if it's low gears you want and don't mind losing the highest gears (which many folks hardly ever use if they're not racing), consider getting a triple and removing the outer ring entirely and adjusting the front mech accordingly. That'll probably only cost you the crankset, rings and bottom bracket only. I've made a 28/42 double work ok without replacing with the shifters. Needs a little care adjusting the front changer to make it work, but it can be done.
posted by normy at 7:07 AM on May 4, 2007

Nthing a cassette change instead of converting to a triple. Either that or hold out for another used bike in your price range that already has a triple. There's no shortage of used bikes out there and unless there's something about this Trek you cannot live without, I'd keep looking.
posted by hollisimo at 8:08 AM on May 4, 2007

I believe the other answerers make extremely good points about the expense.

However, they may be neglecting a very important point: you live in Seattle, home of Recycled Cycles and Wright's Bicycle Co-op. It's been a few years since I've gone to either, but I would be shocked if you couldn't get all you need at RC for ~$120 even in a worst case scenario. They will also do the work of installation if you so desire.

Wright's Bicycle Co-op has less of a selection of used parts, but the owner, Charles, specializes in this kind of thing and is extremely patient and kind.

I haven't tried to look it up, and I'm assuming that Trek has a steel frame. I doubt you will easily find a new factory-made steel frame of that quality in such a very small size.
posted by jamjam at 8:28 AM on May 4, 2007

A more feasible option may be to go with a compact crankset (you'll also have to get the compact front derailleur). I believe Shimano's 8-speed product line was sold at the same time that their bottom brackets had adopted the proprietary Octalink interface -- Ritchey makes a compact crank that is compatible.

Although in theory you should replace the chain and cassette too, in practice it's not a big deal unless the chain and cassette are very worn (in which case you'd have to replace them anyway). You won't have to replace the shifters.
posted by randomstriker at 9:34 AM on May 4, 2007

Thank you all- it does sound like I should wait for a bike that *really* fulfills my needs. Too bad- this one looked sweet.
posted by carterk at 9:18 PM on May 4, 2007

Seems like changing the rear is more straightforward. The cassette and chain are consumables, so they will need replacing eventually anyway. That leaves a possible rear derailleur swap, and the shifter. Good cranks seem to be very pricey..
Technically, many derailleurs shouldn't need to be changed when changing the number of gears. It is the shifter that takes care of the amount of movement, and the overall range of motion is fixed. It is the width of the gears and chain that changes when going from 8 to 9 to 10 speed cassettes. However, if you want to change to a large range cassette, it is my understanding that you would probably have to change to a long cage derailleur, because of the large change in excess chain length from the biggest to smallest gear. Don't quote me on all that though :P

How fast do you spin? I find that I rarely ever want my top gear of 44/11 on 26" wheels - about 48km/h at 100 rpm cadence, if my math is right. Road bikes seem to have stuff like 56/48 on the front, with 13-23 ish cassettes, and bigger wheels. Seems ridiculous for everyday use. I do occasionally notice that my 11-30 8 speed cassette sacrifices fine adjustment for wider range, but I'm pretty sure it is a sensible trade off.

Anyway, Sheldon Brown has lots of helpful info on the technical side, try starting with 6-speed, 7-speed, 8-speed, 9-speed, 10-speed?.
posted by Chuckles at 5:40 PM on May 5, 2007

Don't quote me on all that though :P

I'm pretty sure you nailed it. Spacing varies by # of gears. Larger sprockets need a long derailer so they don't hit the der'r pulleys, and also because long derailers can take up more slack and therefore support a larger drop. The manufacturer spec sheets tell you the max sprocket size and drop a der'r should handle (though you can usually push it a tooth or two.)

Don't quote me on that though, either. :)
posted by Opposite George at 11:17 PM on May 5, 2007