I have an older Whyte Suffolk, which has been plodding along for 5 years now on 10 Speed 105 with TRP Hy/Rd brakes.

I’ve just splashed out on some new Hope 20five’s and critical to why I’m writing this RX4’s as i’m retiring the Hy/Rds for now.

I’ve got some Tiagra 4700 Hyro/Mechanical STI’s on the way, so brakes are sorted.  But 4700 changes the pull ratio compared to 10sp 105, so I’ll grab a RD-4700 GS, and theoretically we’re all working on the 10 speed cassette again all good, right?

Whilst i’m doing this, i’m thinking i’ll 1×10 the whole lot and put a wide range cassette on the back (hence the long cage).   What do I need to watch out for here?  Is it the same as I did with my mtb?

Now days you can readily buy 11-42 10sp shimano cassette.  So is it a case of me just doing that, putting a front narrow wide on, and pushing the b limit right out on the rear mech?  Will the RD-4700GS have just enough to play nice with an 11-42 in single ring config?  Total capacity is 41t so should be ok in theory?

Can I/Do I go bigger with an aftermarket set from OneUp etc..?  Will bigger fit?