thinking of changing to a compact chainset ?

robadub

hi, just purchased my first ever road bike !

the cranks are threaded and i need new pedals so basically i am thinking of having a go at replacing my existing with a compact (2 rings on the front)

apologies if the terminology i am using is not correct but i am brand new to road bikes and even more brand new to bicycle repair !

i was wondering if i can just replace the the crankset at the front (from triple to double)
or will i have to replace the rear mech and shifters aswell ?

also could someone give me some advice on the technical terms on what sort of 105 second had chainset i need to source ?

i am a total noob so any advice greatfuly recieved

i have attached a couple of pics, if you want to know anything else please ask, thanks in advance



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Mister W

Hi
You have a square taper bottom bracket so you will need a new bottom bracket with your chainset. This is because square taper BBs for triples are longer than those for doubles. You can either hunt down a chainset that fits a square taper BB (and buy a shorter BB) or go for a different BB (Isis, Octalink or external bearing BB). If you want 105 then this is the sort of thing you're after http://www.chainreactioncycles.com/Models.aspx?ModelID=46041 and this bottom bracket http://www.chainreactioncycles.com/Models.aspx?ModelID=35354

Next you'll probably need a new front mech as Tiagra mechs are designed for double or triple. Fortunately you won't need a new shifter.

If you're doing it yourself you'll need a crank puller to get the old cranks off. You'll then need a BB tool to get the old BB out and possibly a different tool to fit the new BB. Fitting the new mech can be done with a set of allen keys and a cable cutter. Look on the Park Tools website for more information on how to do it.

brin

What type of riding do you usually do? going by the pics the bottom ring (small tooth) looks well used, maybe try a few more months just using the 2 bigger rings to make sure you can cope on any hilly terrain. You will find when/if you do change to a compact your cadence increases when using the 34t ring.
Agree with most of previous post, but not sure you won't need new shifters?

robadub

thanks guys, im sure i will be asking plenty more questions soon !

brin the bike is second hand so has not been used by me, if i was to stick with triple are there any technical details for what i need to pick up ?

what sort of price do you think this bike would be worth second hand just out of interest ?

jomoj

Hi - I may be wrong but I'm going to respectfully disagree with Mister W on a few points

If I understood correctly and the pedal threads on the crank are knackered, hence the need to buy a new one then you have a couple of options:

First, as you have a 9 speed shimano 105 hollowtech I crank I think you have a splined Octalink bottom bracket, not square taper. This doesn't help you a great deal if you still want to fit a compact chainset as I don't think Shimano made them for that BB type - just triples or 'regular' doubles which both use a 'bolt circle diameter' (spacing of the chainring bolts) of 130mm. That defines the size of chainrings you can fit and the smallest that will fit on the 130BCD is 38, more commonly 39. A compact chainset has a BCD of 110 which will take down to a 34. On a 130BCD triple, the inner ring is mounted on a separate smaller BCD (90?) that will take down to something like 26T if you really want to climb walls.

still with me?

So if you want a compact then you'll need a new chainset and bottom bracket. For this you need to know the width of the bottom bracket shell - which is probably 68mm in the case of your bike but check anyway. One thing to note is that many newer compact cranks are designed for 10 speed drivetrains but *should* still be fine on a 9 speed. A mate of mine has a 10 speed 105 compact on a 9 speed transmission, no problems whatsoever.

The good news is that you shouldn't need a new front mech, a triple front mech will work perfectly well on a double or compact but not the other way round.

You also don't need a new rear mech, that one will work fine.

You can probably also use your triple front shifter by just setting up the front mech to use the lower and middle positions on the lever but it might be possible to damage the shift mechanism if you tried to accidentally force it past the middle position.

The safest option if you don't mind going second hand is to pick up a replacement chainset for your existing bottom bracket and triple setup. If you shop carefully you'll be able to pick up a 105 or Ultegra of the correct vintage on ebay for under £30 - the main thing to be wary of is the state of the chainrings. The models you are looking for are the FC-5503 and FC-6503 to fit hollowtech 1 bottom bracket.

To be perfectly honest, unless you're really offended by the look of a triple or are desperate to lose a few grams i would just stick with it. They're a bit out of fashion right now as the press and bike cos are pushing compacts as the new big thing but there's nothing wrong with 3 up front.


Hope that makes sense! Nice bike by the way..

robadub

WOW ! haha thanks Jomoj, didnt realise it could be that complicated !

following some reading on the web i think that due to my lack of fitness and experience riding road i am best of sticking to the triple chainset, so from what you have said am i right in saying that i need a 150 FC-5503 and FC-6503 triple chainset which i can just fit onto my existing hollowtech 1 bottom bracket ?

if i decide to upgrade to ultegra do the FC-5503 and FC-6503 models still apply or are they just 105 ?

thanks again

jomoj

No problem mate, it's a bit of a minefield. 5503 is the 105 triple, 6503 is the ultegra both will fit your current bb.

The shimano serial numbers are fairly easy to decode, first number is the groupset, second number is the generation of that groupset (I think current gen is 7) next 2 numbers usually tell you if its a double 00 or triple 03 component if that's relevant.

A lot of parts are interchangeable between generations except when they do something major like go from 9 to 10 speed or redesign the entire bottom bracket and crank interface. As they like to do regularly...

Ok, I'm a bike nerd.

With the triple, most of the time you'll be on the middle ring but the granny ring gives you a bailout option on long or steep climbs

satanas

Also, make sure you don't buy any MTB Octalink crankset except XTR as these have different splines. No matter how cheap they might be you *will* need a new BB with XT, LX, etc.

These are one or two Octalink compact cranksets around, like the Ritchet WCS with carbon arms, but they are rare and I suspect they will not fit in your price range.

PCD of inner ring on 5503, 6503 and 6603 is 74mm BTW, not 90mm. IIRC the new XTR M985 double MTB cranks are 90mm (4 arm) and the Dura-Ace 7703, 7803 and Ultegra 6703 are 92mm.

robadub

jomoj wrote:

No problem mate, it's a bit of a minefield. 5503 is the 105 triple, 6503 is the ultegra both will fit your current bb.

The shimano serial numbers are fairly easy to decode, first number is the groupset, second number is the generation of that groupset (I think current gen is 7) next 2 numbers usually tell you if its a double 00 or triple 03 component if that's relevant.

A lot of parts are interchangeable between generations except when they do something major like go from 9 to 10 speed or redesign the entire bottom bracket and crank interface. As they like to do regularly...

Ok, I'm a bike nerd.

With the triple, most of the time you'll be on the middle ring but the granny ring gives you a bailout option on long or steep climbs

ok thanks alot very helpful !

other than the classifieds on here and ebay is there anywhere else i can keep an eye out for these 2nd hand chainsets ? also am i likely to be waiting long for one to come along or are they fairly common 2nd hand ?

Mister W

I apologise, jomoj is quite correct. You have an Octalink bottom bracket not a square taper. But you still can't fit a double chainset onto it, even if you can find one that fits an Octalink BB, because the BB spindle will be too long. But he's wrong on the mech. You might be able to get it to work but it's never going to give a smooth change and it is likely to drop the chain off the inner ring. This is because the shape of the mech is different as is the geometry.

Octalink chainsets for road bikes are few and far between. There's nothing on eBay at the moment. TBH I would just change BB then you'd have a huge range of chainsets to choose from. If you're working on a budget an FSA chainset (with a Mega Exo BB) would work out cheaper than Shimano without compromising on quality.

robadub

OK i am getting confused again !!

I am sticking with a triple chainset due to me blowing out of my arse everytime i go up a hill.

If your saying i would be better changing the BB to open up more options on the chainset front then what BB tech spec do i need ?

I am doing everything 2nd hand due to lack of funds aswell.

Would this BB definitely fit my frame ?

http://www.jejamescycles.co.uk/fsa-slk- ... 34699.html

John.T

That BB will fit your frame but it also needs to match the chainset. Better to get a chainset and then look for the correct BB. Also better to get a new BB as you can not see if a second hand one is ok or not. You can tell with the chainset.

robadub

any idea if this would fit and function ok on my bike ? its 10 speed where as my cassette is 9 speed, but a few people have told me this makes no odds ? is that correct ?

It is 6603 10spd Triple 172.5 crank arms and 52, 39, 30 teeth. I also have the matching 6600 bottom bracket which is also included. This is for a 68mm English thread.



http://cgi.ebay.co.uk/ws/eBayISAPI.dll?VISuperSize&item=120693360987

keef66

Can you confirm a couple of details?

The only reason for wanting to replace the chainset is because you need to fit new pedals and the threads are knackered?

Apart from that, is it working OK? (I'd agree with an earlier poster that the chainrings look to have worn a bit, but they can be replaced separately)

If so, you could get the threads repaired using Helcoil inserts, fit your new pedals and off you go!

Mister W

Yes, the one you've linked to on eBay should fit your bike but I think keef66 has made a good point, that the rest of us missed. If the only problem with your current chainset is that the threads for the pedals are stripped then you can get them repaired with a helicoil. That should work out a lot cheaper and easier.

keef66

But sadly nowhere near as shiny!

robadub

ok thanks the helicoil sounds interesting

is this something i could do myself ?

could someone explain in idiots terms how they work ?

jomoj

http://en.wikipedia.org/wiki/Threaded_insert

probably need an machinist to do it, I doubt the average bike shop has the required gear.

robadub

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 97.c0.m619

if i win this is there anything else component wise i will need ?

thanks again jomoj

Tom Butcher

Are you certain the threads for the pedals are knackered on the cranks. Sometimes they can be a little difficult to start off or need a bit of a clean up - if you haven't already then definitely get an experienced cyclist or mechanic to see if they can make the new pedals work with the cranks as they are.

If you really need new cranks then I'd just replace like with like or at least something compatible with the existing bottom bracket. This has the advantage of being cheaper and meaning you can forget about compatibility problems. While you have the cranks off you might want to whip the bottom bracket out and grease the threads - though if you are new to it you will need some tools or the assistance of someone who has them to do that.

Just something to be careful of - when using a crank puller make sure it is screwed well into the cranks (this requires you to screw together so it's short before fitting it) otherwise it's very easy to strip the thread that the crank puller screws in to. If you are chucking the chainset anyway maybe not so important but worth knowing.

edit - crossed post - yes if you can get the bottom bracket and chainset together that looks fine - not sure if you existing bb will work with that chainset so you could keep the new one spare or not - worth asking shimano users. I found the Tacx bottom bracket tools useful - they screw into the bracket so you can really get some purchase if it is slightly seized in the frame.

Bikehawk

Hi, in relation to using the helicoils yourself, you can buy a kit which includes the helicoils, instalation tool and tap. It's possible but from my own experience on machines if the holes are off even a little then the new threads and the helicoils will be off.This means that everything that follows will be off and the pedal will not rotate concentrically (?) and feel like it is wobbling when you pedal which will wreck your head in all likehood. If you can't be sure of getting the holes perfect then defo tkae them to a machine shop, shouldn't cost that much or take that long

griffter18

Can I ask why you think the pedal thread is knackered.
I dont mean to sound condisending but you mention this is all new to you........ You are screwing the pedals in the right way arent you?
They screw in opposite directions.

Would hate to think your heli-coiling or changing a crank over a simple easily overlooked fittement issue.

robadub

i was told by the mechanic in my lbs that the pedals had been put on back to front by the previous owner (ie left pedal on right crank and vice versa) he seemed to think that when i removed the pedals the cranks would be threaded

ride_whenever

sounds like bs, as the pedals wouldn't be the right way up if on the wrong sides.

Tom Butcher

They'd be the right way up but pointing the wrong way wouldn't they ?

When I first started out with bikes I managed to fit a pair of pedals on the wrong sides - I assumed the threads would be knackered but I still managed to get them off and fit them the correct way. In other words I wouldn't go shopping for anything until you know for sure you need stuff.

robadub

yeh thats right tom, right way up but pointing the wrong way

Gary D

Hello,
I have posted this in response to another thread, but thought you might be interested:

I have a brand new Shimano 105 Triple Chainset (52/42/30) and matching new BB. It is a 9 speed version and is Part No. FC-5503 and the BB is the Octalink splined style (Hollowtech 1?).

Edit: Just checked, and it is 170mm crank arm length.

Please PM me if you are interested and make me a sensible offer!

Gary.