Thinking about changing compact crank to triple?

[Matt B]

Hello, I'm going to be riding LEJOG this year and I wanted to change my crankset from a shimano 105 compact FC-5650 50.34 to a 105 triple FC-5603 50.39.30, will I have any problems from doing this? Also, would it even be worth it?

 

[MacB]

You need to work out what you need first, so need to know detailed specs of what you have, I find a popping into my LBS can supply this info:-

front shifter - is existing double and triple compatible
front mech - as above
bottom bracket - will it work with triple re chainlines etc
frame - will you have clearance at chainstay for what you need

alternatively could you fit a new longer cage rear mech and a wider ratio cassette? You'll probably have a max range at the back of 11-27 with a road mech. So 34x27 gives you a low of 33 gear inches. A 30x27 would change that to 29 inches, whereas a 34x34 would give a low of 26 inches. With the triple you'll get closer ratios in each front ring, most people seem to ride in the middle ring and treat inner and outer as overdrives. With the compact and wide range cassette you'll have bigger gaps between gears and may need more front changes.

So it depends on how you ride, if you like to maintain a cadence and adjust gears to accomodate then triple and close is better. If you don't mind varying your cadence then you may prefer compact and wide. Some people don't like long cage rear deraillers and don't like big cogs at the back, for aesthetic reasons. Personally that doesn't bother me, I could quite happily tool around on 50/34 with an 11/12-34 at the rear. Staying in the 50t ring most of the time, 40-120 gear inches and treating the inner ring as a bail out for hills. But it does mean closer to 10 inch gaps between gears rather than the 5-6 inch gaps you'd have with a triple.

I'm sure I've missed some bits and other, more knowledgeable folks can fill in the gaps.

 

[PpPete]

Couldnt have put it better myself!

But reading a few people's LEJOG journals - a common factor seems to be they wished they had lower gears than they had - whatever they started with.

Because I'm vain I'm going to keep my cassette with a 30T biggest sprocket (about the biggest my Ultegra rear mech can handle - and I don't want an MTB mech) but for my JoGLE this summer I'm going to drop down from 52:42:30 at the front to a 50:38:26 which I'm hoping the front mech will handle (or a 50:39:28 if not)

My OH, who has far more sense and less vanity, is running a Deore rear mech, 11-32 cassette and 48:38:26 Impact triple - and will stick with that for the JoGLE.

 

[Matt B]

Ok, front shifter is compatible, it's 105. On the cassette, I'm running a 105 11-25. Front mech is 105 too, bottom bracket is Shimano FC-5600. The frame should be ok, because the bike I've got was available in a triple option too.
I like my compact, but because I'll be carrying panniers and tent etc, some easier gears for the hills would perhaps make more sense.
Would it be worth changing the chainset but leaving the existing cassette, or would it be in my interest to go for something like a 12-27? All in all I'm considering 50.39.30 with 12-27 cassette - up from a 11-25.

 

[Kirstie]

Want some 105 chainrings? I've got a standard triple for sale 52 - 42 - 32.

 

[Matt B]

Hmmm... how much, and what condition are they in?

 

[Matt B]

Just the chain rings? Cause I'm probably after the whole crankset.

 

[monnet]

I'm pretty sure you'll need a long cage rear mech in order for the chain lines to work. Come to think of it, to my knowledge only Dura Ace triples have standard cages because they have an extra tooth on the jockey wheels.

 

[jimboalee]

Check the entire route for the hills.

Note them all down and at what distance each day they are.

Get to know how fast you ride up various STEEP gradients and what your favourite cadence is, UP STEEP HILLS !!!

Work out what gearing you need.

 

[Kirstie]

Just the chainrings, they've only done 500 miles, 5 arm, 130/74 BCD.
Was thinking 20 quid for all 3.

 

[andrew_s]

alternatively could you fit a new longer cage rear mech and a wider ratio cassette? You'll probably have a max range at the back of 11-27 with a road mech. So 34x27 gives you a low of 33 gear inches. A 30x27 would change that to 29 inches, whereas a 34x34 would give a low of 26 inches.

105 56xx is a 10-speed groupset so the largest available cassette is 11-28, unless you fancy paying £100 for one of the 10-speed 34T cassettes that exist.

SRAM are meant to be bringing out a new groupset that includes cassettes up to 32T later in the year. It's at a 105-equivalent level, so the cassettes may not be too expensive.

 

[PpPete]

Ok, front shifter is compatible, it's 105. On the cassette, I'm running a 105 11-25. Front mech is 105 too, bottom bracket is Shimano FC-5600. The frame should be ok, because the bike I've got was available in a triple option too.
I like my compact, but because I'll be carrying panniers and tent etc, some easier gears for the hills would perhaps make more sense.
Would it be worth changing the chainset but leaving the existing cassette, or would it be in my interest to go for something like a 12-27? All in all I'm considering 50.39.30 with 12-27 cassette - up from a 11-25.

On your existing compact and 12-25 your lowest gear is 36"
changing just the cassette takes you to 33"
changing to triple but leaving cassette at 12-25 takes you to 32"
changing to triple and to 12-27 cassette takes you to 28"

Only YOU can figure out which of those is what you need for hauling yourself, bike, camping gear, over whatever hills lie on your chosen route.

FWIW I'm running a 26" bottom gear, and my changes for JOGLE outlined above will take me down to 24" or 23".
My OH will have a 21" gear.
But one of the fitter members of the group will be quite happy with an old 52:42 front and 14:28 6 speed rear, giving him a lowest gear of 40"