Converting to a compact from a 52/36 - compatibility

[jamiebae]

I have a Cannondale bike with a 52/36 chainset which I want to swap/convert to a 50/34 but I'm not sure the best way to do it. It has a BB30 bottom bracket, which is a little annoying as I'd just grab a 105 or Ultegra unit and fit it otherwise.

Current chainset is an FSA Gossamer, and I'm not Chris Hoy so don't see a need to upgrade it, which I guess means the easiest thing is to swap the rings over. The alternative appears to be the new version of what I already have: http://www.wiggle.co.uk/fsa-gossamer-crankset-bb38...

However, the chainring option is confusing me, can someone point me in the right direction for the rings I'd need, am I right in thinking it's this for the inner: http://www.wiggle.co.uk/fsa-super-road-inner-34t-c... but I'm struggling to find a 50T outer there.

Thanks!

[Jacobyte]

I've bought chainrings from Ebay in the past with some success.

Here's someone selling a 50 / 34 pair:
http://www.ebay.co.uk/itm/Pair-50-34-110-PCD-SRAM-...

[TwistingMyMelon]

Id just put a bigger cassette on, one of my bikes has a 36/30 as lowest gear (not my choice came speced like this) and it will get up anything, much easier gear than the 34/25 lowest on another bike (again not my choice)

[Daveyraveygravey]

What cassette do you have? I have a 52-36 and have swapped the 11-28 for an 11-32, in time for the Fred last year. You need a long (or is it medium?) cage mech too, but if you shop around you can get the cassette cage and chain for about £100. It's a slightly more "climby" gear than a 50-34 with an 11-28 too, I believe.

[jamiebae]

Already got an 11-32 cassette, but I could do with an extra gear for the really tough climbs. I think I'll be quicker up them if I can spin a bit more rather than grinding a cadence of 70 because it's 11% and I've run out of gears/power/balls.

[TwistingMyMelon]

jamiebae said:

Already got an 11-32 cassette, but I could do with an extra gear for the really tough climbs. I think I'll be quicker up them if I can spin a bit more rather than grinding a cadence of 70 because it's 11% and I've run out of gears/power/balls.

fair dos, looks like compact is your only option

[jamiebae]

TwistingMyMelon said:

fair dos, looks like compact is your only option

I have a 34/25 on my bike in England and can just about get over Ditchling Beacon on that, but in the Alps, in summer, I'm happy to forget all about Rule 5 and fit the easiest gears I can get on the bike

I know one guy here who ran a 34/36 on his bike - compact chainset and 36T MTB 10 speed cassette pared with a SRAM long cage mech and somehow that worked. It did look a bit silly though...

[TwistingMyMelon]

jamiebae said:

TwistingMyMelon said:

fair dos, looks like compact is your only option

I have a 34/25 on my bike in England and can just about get over Ditchling Beacon on that, but in the Alps, in summer, I'm happy to forget all about Rule 5 and fit the easiest gears I can get on the bike

I know one guy here who ran a 34/36 on his bike - compact chainset and 36T MTB 10 speed cassette pared with a SRAM long cage mech and somehow that worked. It did look a bit silly though...

I agree, just use whatever ratio you are comfortable in , ironically the fitter I am the more I spin

[jamiebae]

So basically, as long as the PCD and bolt pattern matches I can use SRAM rings on an FSA chain set with Shimano chain and cassette is what I'm reading from this.

£10 off when you spend £50 at Amazon today so time to go shopping!

[waynecyclist]

If it is 110bcd easy enough to just change rings or look on ebay for a 50/34 fsa unit and just swap the complete chainset over.

[Jacobyte]

Yes. Some years ago I put a 38 Stronglight inner chainring on my 53/39 Dura Ace chainset for a visit to the Alps. (plus a 12-27 cassette, as you can't fit lower than 38 on a standard double chainring).

[jamiebae]

So bits have arrived and I can't seem to get it set up properly. I used an FSA outer ring (different design to the one which came off) and a SRAM inner as the FSA one was out of stock, fitted to a BB30 FSA Gossamer chainset. I've also swapped the front mech for an Ultegra one at the same time for completemess (the rest of the groupset was changed last year). The chainset itself hasn't been moved and the rings were swapped with it in situ.

Basically, I can set it up so it runs perfectly in the little ring but then it rubs on the big ring 2/3 of the way down the block, or vice versa. Limit screws are fine, the alignment looks OK and it seems to be impossible to get working as it should.

I'm thinking maybe the SRAM inner ring is half a mm offset compared to the FSA one - it does say '10 speed only' on it too but I didn't think that would be an issue. Unless anyone can shed some light on it I'm guessing all I can do is put the FSA 36T inner ring back on and see if that solves it, or order the right FSA 34T ring and see if that works.

Any thoughts appreciated

[Jacobyte]

Your smaller chainring teeth are now sightly lower down, so slide the front derailleur downwards a bit until the chain no longer touches it. You'll need to re-tension the cable afterwards as it will slacken off in that process, but that should do the job.

[jamiebae]

Jacobyte said:

Your smaller chainring teeth are now sightly lower down, so slide the front derailleur downwards a bit until the chain no longer touches it. You'll need to re-tension the cable afterwards as it will slacken off in that process, but that should do the job.

Already done that, and it still doesn't work unfortunately - I changed the front mech and set it up according to the instructions, and a GCN tutorial online.

Not much to see really, but this is the chainset now (before the mech was fitted)

[Jacobyte]

Nothing looks unusual there, other then your pint-sized bike mechanic - are you sure he didn't interfere?

It might warrant a trip to your LBS for them to check if something else is out of kilter.

[jamiebae]

Jacobyte said:

Nothing looks unusual there, other then your pint-sized bike mechanic - are you sure he didn't interfere?

It might warrant a trip to your LBS for them to check if something else is out of kilter.

Yes, said pint-sized spanner-monkey kept running off with my allen keys which did cause come issues.

LBS changed the BB in late summer and it's barely been ridden since, I'm a reasonably competent mechanic so I think I'd spot obvious stuff. From what I can see the shifter isn't allowing the range to cover the full set of gears which is steering me towards the (just fitted) mis-matched chainrings as the culprit but I don't want to pull it all apart again, waste another chain pin, and have another hour of my small helper running away with my tools while giggling uncontrollably unless I have to!

[Jacobyte]

If you can't eliminate the rub, you could just try setting it up so that it has an equal balance of rubbing only when you're fully crossing the chain, i.e. big-to-big and small-to-small.
It'll also discourage you from being lazy with your shifting.

[jamiebae]

Jacobyte said:

If you can't eliminate the rub, you could just try setting it up so that it has an equal balance of rubbing only when you're fully crossing the chain, i.e. big-to-big and small-to-small.
It'll also discourage you from being lazy with your shifting.

At the moment I can't even get the 34/32 and 50/11 combos without rubbing so clearly something is wrong. I guess I'll swap the inner rings over tomorrow to see if going back to the old 36 works better.

[jamiebae]

Now sorted, after a massive amount of messing around with front mech angles - no issue with the rings themselves.

[ALawson]

I have a 56/36 paired with a 11/32, also thinking about whether to man up for the Marmotte or get a compact. I bet swapping the 36 to a 34 on the front will cause all sorts of problems.