front derailleur for a 46/36 or 48/36 double?

One of my bikes is set up with 48/38 (Salsa rings on Ultegra
crank, 105 front double derailleur). Works perfectly.

Mike Yankee

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Quoted message said:

When you set up a double with small chainrings, is it
better to use a typical road double front derailleur, or
an MTB triple? I'm looking at combos like 48/36, 48/38, or
46/36. These all are 'in spec' for an XT 751 front
derailleur (48 teeth max). But maybe a bit small for a
road double, like the older 105 I have on now with a 48/39
and working fine?

This is with bar end shifters, so indexing is not an
issue.

Thanks.

I have a 50/36 with the chain derailed by an old 105 front
mech operated by even older 105 friction downtube shifter,
moved by an even older rider ! This setup was in place
before STi came along and IMHO the operational parameters
are most significant when STi shifting is used. With
friction shifters one has plenty of fine trimming available
and one can usually overshift to force the jump - less so
with STi so matching of components is more important.

I think most road doubles are designed with a curvature for a big ring at least 50T. That said, if you can get the derailer low enough without it hitting the chainstay, it will work with smaller rings. I use a road double to shift a 44x29 combo on my touring bike.