Help me in my chainring saga!

curium

I have a 2009 Specialized Tricross Sport.

It came with an FSA Triple Crank - 50/39/30

I want to replace the 50t chainring. I've measured it and it's 130 BCD.

Surely it is as simple as buying a 130BCD 50t chainring to replace it, right?

One of the websites I've ordered from is telling me that the 50t chainring they have is a double - FSA Pro Road Chain Ring 130 BCD

How can a chainring be a double? Surely whether it's a double or triple is down to how many chainrings are on the crank?

In any case they are now saying that they have no stock till mid-October despite the website saying in stock

Are 50t chainrings that rare? Are chainrings really double or triple specific? In both cases the 50t is the outer ring.

Can anyone clarify so I can decide whether to cancel and end this whole, sorry saga!

markos1963

http://www.spacycles.co.uk/products.php ... b0s149p435

Any good?

markos1963

http://www.spacycles.co.uk/products.php ... b0s149p398

Or these if price is an issue

I have a ceramic 55t on my TT bike and it's as smooth as silk

curium

I would like the replacement to be FSA as the other 2 rings on the crank are FSA and I know someone who had issues with shifting when he replaced one chainring of 3 with a chainring from a different manufacturer from the other two.

What about my question, Do you know if chainrings are double or triple specific?

Cheers!

verloren

They are specific, kinda - the chainring will be ramped and pinned (http://www.sheldonbrown.com/gloss_ra-e.html) to make shifts easier. Those ramps and pins should in theory be placed differently depending on the size of the chainring the chain is coming from. So a triple 50 might typically be mated with a 39 tooth middle chainring, whereas a double 50 would usually go with a 34 (or possibly 36). So the outer ring doesn't know how many other rings there are, but it does make assumptions about how big the next ring is. It will still work with a different sized chainring, but not quite as well.