Tiagra cassette range question

[ootini]

Hello all.

I'm currently riding a Pinnacle Arkose D2 2030 gravel bike, which I love to bits. I've always assumed I'm just rubbish at climbing, but, people wiser than I, pointed out on the WRT, that I'm running some pretty chappy gearing for climbing.
In short, its stock Tiagra from the shop, so:
2x10, based an FSA 48/32 double, tiagra 4700 gs rear mech and hg500 11-32 cassette.
So my question is, given that I really struggle to spin on proper gradients, can I go for a wider cassette (11-42?) Without masses of faff, or is there another option ?

Id rather not swap out the whole groupset, and I certainly don't want to change bike, so suggestions are welcome.

[whitestone]

There's a couple of figures you need.

Firstly the capacity of the rear mech which according to https://bike.shimano.com/en-EU/product/ ... 00-GS.html is 41T. You currently have (32 + 48) - (11 + 32) or 80 - 43 = 37 so you can go 4T larger at the back so 41T. You are at the maximum of 16T difference on the front so unless you got a super compact you can't really change that.

Secondly you need the maximum sprocket size which is 34T. Ah But Shimano are pretty conservative in their specs so you could probably go to 36T as the largest sprocket.

That would drop the smallest ratio from 1:1 to 1: 0.89.

Getting a super compact like the Shimano GRX without changing the cassette would drop the chainring sizes to 44/30 meaning the smallest ratio goes from 1:1 to 1:0.93. If you could find a 44/28 then the smallest ratio goes from 1:1 to 1:0.87. However you'd need to check if the front mech would be compatible with the smaller size.

The GRX plus a cassette with a maximum sprocket of 34T would give you a ratio of 1:0.88, a 44/28 would give you 1: 0.82

[Bearlegged]

If you're careful about avoiding big/big and small/small gear combos, if you screw the B-tension screw right in (or even add a longer one), you might need to add a gear hanger extender... you might be able to get a 4700 mech to cope with a 40+ sprocket. It can also depend a bit on the hanger geometry of your bike. Plenty of anecdata out there for people using Shimano mechs beyond their stated limits.

[thenorthwind]

More than likely. I have a similar setup on my Arkose, though it's a 105 groupset. I use a hanger extender with my gravel wheels which have, from memory, an 11-42 cassette. I think it would be worth your while getting a cheap extender and giving it a go, though you'd have to buy the cassette as well I suppose... unless you can borrow one to try.

[due]

I run an 11-40 10sp MTB cassette using a 4700 Tiagra mech and a GRX 46/30 chainset, so near enough your exact set up. If I remember correctly it worked fine without, but I still got a cheapo extender to be safe. All on my touring bike so been used fairly extensively without a hitch, I concluded it was the most painfree way to get wide gearing with proper road shifters.

This is the exact extender: https://www.merlincycles.com/sunrace-re ... 34836.html

Can't vouch for 11-42 but I'm sure it will also be fine. Or it might burst into flames

[ootini]

Thanks for all the advice folks. I'm thinking that I'll just try a cassette and mech extender and see what happens.
I'm assuming I just need any 10sp, wide range cassette that's hyperglyde compatible?

Like this https://www.chainreactioncycles.com/p/s ... eth=11-42t

[Bearlegged]

Yup.