converting a triple to a compact

[samsbike]

can I convert a triple chainset to a compact - ie. are the bcds the same. The one in question is a shimano 105 from 2008.

thanks

[WOOLIFERKINS]

That depends whether your triple is 110BCD or not. Your chainline will be a bit outboard if you remove the inner ring or you'll need a set of single ring bolts if you remove the outer. There should be enough adjustment in your mech stops to prevent the overshift. It won't be perfect but it should work.

[samsbike]

thanks for that. Its probably not worth the bother I may as well just get a decent compact chainset.

[Brucey]

might I ask why you might wish to do such a thing?

cheers

[samsbike]

might I ask why you might wish to do such a thing?

cheers

In my foolhardiness I thought it maybe cheaper to get a triple and run it as a compact. Misguided youth and all that.

[meic]

I think that your original question left too many gaps for the readers to fill with their own interpretations, well me at least.

If you have bought a 2008 105 triple then it has BCD 130 for middle and outer and 74 for inner.

Cranksets marketed as compacts nowadays are 110BCD doubles. These can go down to 34 tooth rings.

Your 130BCD would only enable you to go down to 38? (I am not wholly sure).

You do have another option, which doesnt look pretty, of using the inner and middle of your triple which would allow an even more compact compact.

Generally it is more economic to buy whole cranksets anyway as individual rings are relatively costly, if cranksets came with my ring choice on I would probably do that all the time and have even more cranks cluttering up the workshop.

[samsbike]

Thanks, but I had no idea about the bcd and assumed that they would be the same.

As you call I have little idea as to what I am doing, but I think buying a compact maybe the way to go.

[Mark1978]

But what's wrong with your current triple setup?

[meic]

It is more hassle, having to think and adapt things but with square taper bottom brackets, I would not buy a compact double, just as I would not buy an ordinary double.

I would buy a 110BCD triple and run it with just the two outer rings fitted. That is because I feel a triple is more useful and at a later date the crankset may be used as a triple. A double can not easily become a triple but a triple can easily be a double.

This is a compact double in effect

This is almost the same thing but can take an inner ring.

However as you probably have an external BB using a triple as a double would probably result in a chainline that is too far over.
I am not quite sure how it plays out with them.

[meic]

But what's wrong with your current triple setup?

I think that you have made the same mistake that I (may have) made. I think the bike is presently a double and he wants it downgearing to a compact double.

[samsbike]

Apologies for the confusion, bike hasn't been built as I am still sourcing parts. Triple cranksets seem to be cheaper than compacts, hence my query. I think the 'new' bike has an external BB.

[Mark1978]

Hmm really?

http://www.ribblecycles.co.uk/gsg/road- ... O&tmp=_CAR
Triples are usually the more expensive option.

[cycleruk]

What kind of riding / terrain do you envisage or already ride on?
I have various bikes with various gears arrangements. One has a compact 50/34 and although it's fine it's not ideal.
Most of the time I have to use the 50 ring as the 34 is too small for the flat or shallow climbs. (Currently running a 12/29 cassette.)
This gives a lot of bad chain angle to the extent that when on big ring to big sprocket the chain will sometimes derail itself onto the 34T ring.
With a triple you can spend all day on the middle ring (say a 40T) with option of the big or granny gear when needed.

The factor with a triple is you obviously need to have a triple shifter, triple front derailleur and long arm rear derailleur.

Edit: The chain dropping onto the small ring only happens with my 10 speed compact Campag. None of my 8 speed or 10 speed Shimano triple has this problem.

[samsbike]

I intend to use the bike mainly for commuting. My current bike currently has a compact and generally I am on the inner ring only using the outer going downhill. I have a rear 11-25 cassette and tend to use the lower gears more than the lower ones I.e. 11, 12 etc.

Currently committed to a compact as my sti's are doubles.

[Brucey]

If you stick with you present shifters, you are commited to a double perhaps, but not a compact double.

Unless maximising your downhill speed is top of the agenda for some reason, (on a commuter...? In traffic...?) I'd suggest you consider something more like an alpine double.

This might be a 44, 46 or 48 T outer ring with a 12-28 block. Inside ring of your choice. You will mostly use the outer ring.

You can buy a ST triple and BB (e.g. from Spa) for less than an external BB chainset alone, and it will probably be more reliable. Remove the middle ring or the inner ring, maybe even fit the outer ring in the middle position and fit a chainguard ring.

You can trade the double STIs for triple ones in the future maybe if you want.

For commuting, sensible gear ratios and reliable, durable, (and preferably inexpensive, they wear out you know) components are the best thing; you are not riding the TdeF. In the long term IGH's have an awful lot going for them for daily commuting; maintaining a derailleur transmission through our cruddy winter weather gets both tiresome and expensive.

cheers