Swapping chainrings

1964johnr

I have a 10 year old Giant SCR 2 Tiagra equipped winter bike which has a triple chain ting. I would like to convert it to a compact double. Someone on a previous post suggested just switching chain rings to achieve the desired gear ratios. I am happy with the small chain ring and would like to remove the middle ring and the outer ring and replace them with a 50T chainring. It all sounds very simple - remove the chainrings, purchase a 50T chainring and connect it to the spider. But I know it can't be as simple as that. For instance, at the moment my middle and outer chain rings are connected at the same points on the spider, so if I am removing them both and only replacing one ring will this be an issue? and what about shifting. Will my current Tiagra triple front mech cope with the reduction to 2 chainrings? Any thoughts/tips would be appreciated.

bondurant

I have admittedly never tried this but cannot see how it would work. You would get chain drop on every front shift due to the gap between rings.

Bumo_b

You could only go as low as the lowest chainring the middle of the cranksett will take, ie 39 teeth (if I remember rightly).Alternative buy a compact double crank off ebay. The front mech is not a problem as long as the jump is just one chainring. Hope that makes sense.

pilot_pete

You will need a suitable STI (front shift lever) for a double front setup as you will currently have an STI for a triple. The pull ratio may be different and of course the triple STI will have extra clicks to get you onto a third ring!

PP

imposter2.0

It's possible to set up a triple shifter to run as a double, simply by twiddling the limit screws on the FD - that much is simple enough. But you will have to fit the chain rings in sequence, without a gap where the middle ring should be - otherwise (as pointed out) the chain will drop.

In other words, you can't run an inner and an outer with no middle, you would have to run inner & mid or mid & outer for it to work.

burnthesheep

Dumb question, wouldn't changing a chain ring to different tooth count mean the diameter is off of the part of the crankset that has the "ramps" on it for the shift?

keef66

So you're planning a 50/30 chainset? That's a heck of a jump

Simpler I think to find a used compact double chainset and Tiagra double shifters & front mech on Ebay. Or maybe find a used 105 groupset for a bit of an upgrade?

You should then be able to shift the triple kit since it's still useful to the touring / audax crowd and is less commonly available.

chippyk

All seems a bit of a fanny on. Either stay as you are or buy a double chain set and a new front shifter. For all the practical difference it will make I’d stick as you are.