Taking on the Zoncolan - crazy SRAM MTB gearing on a road bike

I'm not that great a climber but I did Zoncolan on 34/29 and while it was horrendous it was doable... Just. I'd say a 32 would make it manageable if you're taking your time. Agree with earlier comments about Fedaia, that shouldn't have been that hard, and yet it was one of the worst rides I did in the Dolomites.

"My initial thoughts were to go for a Praxis chainset with 48/32 rings but I wasn't sure that my front mech would go down far enough (the mount is riveted to the frame)".

Take a look at this adapter.

https://wickwerks.com/products/fit-link-adapter/

I got up the Col du Tourmalet on my old road bike by slapping an 11-32 MTB rear cassette on it.

Standard chainset and no change to the rear mech apart from fiddling with the B-screw.

Nothing useful to add other than to say when I grovelled up the Zoncolan on a 34/32 I saw quite a few others spinning away on MTBs or triple chainsets and felt very jealous!

Nothing else on the Maratona route is anything like as bad.  The only Dolomites climb that comes close is the later sections of the Fedaia.

have you seen the Wolf Tooth Roadlink, it might be a cheap and simple answer to your situation as it allows your existing road mech to work with large cassettes 

Bondirob has the cheapest effective way to get low gearing. 

If you need more, you could go mtb/cyclocross crank and 11-40 cass. 

My bike is setup with a 44/28 crank, and a 11-40 cass for mountains.  I can spin up the likes of Ventoux and I dare say the Zoncolan no problem.

The other end of the spectrum I did the Tour of Cambridge last weekend and averaged over 21mph with the same bike, different wheels, 11-25 cassestte

yeah, the first issue is because the mech doesn't quite have enough capacity, but it's unlikely to be much of an issue. i'd experiment with the front mech position, it may be that it only needs a slight tweak that won't affect shifting. gluing a bit of old inner tube to that section of the cage will cut down the noise considerably if it's bare metal right now

Here's what I did.
Compact chainset up front with 11 speed 11/40 cassette.
Used standard Shimano medium cage derailleur and a Lindarets road link from 18bikes (£22) which basically extends the derailleur. Put a longer chain on (obviously).
Worked fine, took it for a spin up Pea Royd lane which they use for national hill climb championships and knocked a over a minute off my fastest time.
This is the easiest and cheapest way to get appropriate gearing
Alternatively my winter bike has an 11/36 mtb cassette with compact up front. I did this by simply fitting a longer 'b' screw to a medium cage.

Could you have not bought a 33T chainring for your 110mm BCD chainset? It wouldn't buy you much (about 3% lower ratio) but it might have meant a 34T at the rear could have worked out and thus save you from buying a different rear mech.

I've just fitted a 11-32T Shimano 'dustbin lid' to my gravel bike, with an Ultegra 6800 short cage it works just fine on the big big, not that I would do that tbh and neither should you, you're not in a race.

Some frames/setups just don't allow you to work much beyond their specified capacities, Shimano seems to go beyond by quite a bit o almost all frames. The older 6700 short cage had a 30T big limit and though I never tried it I reckon it would have coped with a 34T.

Have fun.