I've got a huge Hope 10-48 cassette on a full suspension bike.
On the 10 tooth and the suspension unloaded, the chain is slightly slack but okay at sag. On the 48 tooth, the bike won't fully compress without ripping the rear mech off. However, next cog down is okay.
In my shoes, where would you compromise? After all, who bottoms out a bike while in the lowest gear and at the other end, how hard can I pedal with the bike unweighted?
I'd get a longer cage mech that could cope properly with the gear range.
No-one bottoms out their bike in its lowest gear (well not one that low!) Even if you're doing techy climbing with triallsy moves you won't be in the very lowest gears because hey don't give you enough impulsion.
That's my thinking. Maybe compromise the two lowest gears so that the tallest gear is fully functional even unloaded.
If your chain goes slack at full negative travel in the smallest sprocket then you will lose your chain on descents (or when in the air!)
I'd compromise at the bottom but just remember not to do any uphill hucking.
Thanks folks, that was my thinking. Make sure the 10 works and compromise the travel in lower gears. Ill be sure to carry a spare mech hanger as well.
Use the longer chain and add a bit more 'b' screw.
Can I ask what mech you are using out of curiosity?
Already got a lot of b-tension on there. It needs it to clear the 48 tooth. It's an XTR rear mech that I was using previously using with a 10-42 cassette.