Double Chainrings Odd / Even Teeth

[Oceanic]

I've noticed that on 'standard' double chainsets, if the inner chainring has an even number of teeth, the outer does too (50/34, 52/36, 46/36, 48/34). Similarly if the inner has an odd number of teeth, the outer does too (53/39).

Is this just because of convention? Or do double chainrings shift better if they both have an odd, or both have an even number of teeth?

[Mick F]

My Campag Chorus triple came brand new with 30/42/53 rings.
Therefore I don't think there's a problem with odd/even teeth.

[Spinners]

I've had too many 52/39 chainsets for this to be a convention - unless it's a new one brought in with compact chainsets.

[Oceanic]

@Spinners - I don't think you can buy 52/39 doubles any more (Edit apart from old stock), maybe their demise is to do with a desire for higher gears rather than a desire for smoother shifting?

Off topic but related...

Specialities TA say that you should never have a smaller gap than 12 teeth between chainring sizes with 10/11 speed systems ( http://specialites-ta.com/media/support ... nglais.pdf ), but I've just discovered that Campag produce 11 speed triples with 30/39/52 rings.

Maybe Campag do something special with ramps, pins and tooth design that enable them to break TA's '12 dents' rule?

[Brucey]

I have a theory or two about this.

First, all 11s systems (with the possible exception of the campag triple) have a deep inner cage plate on the front mech; if you fit a large inside chainring, the front mech will hit it, and if you raise the front mech, the chain may overshoft off the big ring (which happens easily enough anyway with some systems...).

Also;

Chainring spacing hasn't changed that much all the way from 6s to 11s, yet chains are undoubtedly a lot narrower now.

I think that big chainrings now have 'slopey shoulders' on the spider arms so that the chain is pushed leftwards, and thus engages with the inner ring teeth, instead of sitting on top of them, (as can happen if you use very narrow chains with chainrings that are not meant for them). If you fit a bigger inside chainring, the chain can't be pushed so far sideways, so you may get the 'sitting on top' problem all over again.

cheers

[Tonyf33]

On my old commuter bike I ran a 49/39/30 and it shifted just as well as the original 52/39/30. I've also had a 53/40, 55/38
I NEVER dropped a chain or had skating.

[whoof]

It's just what the manufactures choose. There's a maximum gap between the number of teeth but within that unless the chain-rings have an intelligence an even small ring isn't going to know if the large ring is odd or even.

Here's a Shimano triple Tiagra 30/39/50

http://www.chainreactioncycles.com/shim ... prod137766