Big ride across Europe in the summer and wanting to use my Defy.
Anyone know the biggest cassette you can fit in the back?
32,34?

What rear mech are you running? a long cage Shimano road one will take a 32 easily, poss more if pushed.

Think it’s a standard short mech, but no issue changing it over to a long one.
Interested if there would be any constraint factor.

In my defy advanced I’ve got an XT 11-40 using a lindarets road link, long cage ultegra di2 and a compact up front- works fine in every gear

I think this covers it all

Low Gear Range: Road Shifters & Gears For Easier Hill Climbing

I used a 32t in a defy with a short cage mech. Didn’t work too well, but I didn’t spend too much time finessing the setup. Only used it temporarily for a weeks trip so didn’t want to invest too much. Plenty of people report getting this setup to work fine though even though it is officially outside the range of the mech. For 34t I’d go to medium cage though.

Ironically though I didn’t use the 32 cog much though nice to know you’ve got a bail out gear if needed on a long ride. I was in the southern alps so maybe not as tough as the northern alps where the well known TDF climbs are. The climbs are long but not that steep 5-6% average with short sections up to 10 and over.

I think 32T would suffice. Guessing you won’t be loaded with luggage on a Defy. I put a 32 and a medium mech on for a trip to Pyrenees in autumn and got up everything comfortably. Not felt the need to change back to the 28, gear ratios feel fine. So for the £30 or so for a new mech I’d say it’s worth the investment instead of risking damage using the short one.