Front derailleur for 24/34/40 ?

[zoxed]

I bought a CX70 and just fitted it last weekend. First thing I noticed is that actually the large ring on my bike is 46T, not 40T as per my gear chart !!
But the CX70 does shift perfectly over 28/34/46 even though the range is 2T more than the CX70 spec. (I did not try it with the 24T: 28T is plenty low enough for a day bike and I had the 28T already !) and it is a triple (CX70 spec. is for 2 chainrings).
(I had first also tried 28/46 (46 on the middle ring position) and it also changed perfectly, but I decided that as I already have the 34 I prefer the smaller steps, and with the 34T I can spend 95% on my ride on 1 ring !)
Thanks for all the tips/pointers above.

[freeflow]

Thanks for posting. That's really useful information.

[zoxed]

Minor update: I changed the smallest ring from 28 to 24 and the CX70 still shifts perfectly over now 24/34/46 even though the range is now 6T more than the CX70 spec.

[Brucey]

there is always a little leeway in the design; after all it has to work OK even at the maximum allowable included angle (which is usually a fair bit more than you get on a bike with 700C wheels). This in turn has to allow for those frames that have the rear axle slightly below the line of the chainstay, too; this makes the measured chainstay angle slightly optimistic.

Even so, 6T is going some; that equates to about 1/2" difference in the height of the tail of the rear mech, or a similar effect to a change of ~7 degrees in the chainstay angle.

cheers