Currently I’ve got a 1×10 with 30t at the front, and 40t at the back. It’s a 29er.

A friend has persuaded me to go riding around the Alps this summer. There might be a bit of uplift, but it’s mostly going to be getting up hills the old fashioned way. I think that ratio will stop being funny after a few days.

How much lower can I realistically make my lowest gear ratio?

My other options are to go back to 2×10, or lose some weight. I haven’t yet quite decided which of these would be easier. Both are pretty hard.

30 is the Lowest at the front of you don’t have direct mount cranks, can’t go much lower than 40 at the back…

Put a stealth granny on? Long climbs so I doubt the lack of shifter will be particularly annoying.

Do you not have an old triple you can fit? That way you have 22-40 and should be able to track stand while pedalling all day… But seriously, if you really want a proper low gear, it’s the obvious way to go.

Get a sunrace 11-42 10 speed cassette (steel ones -ms- on offer from the Germans or look for uberbike doing a sale on the ally ones -mx) + a goatlink/radcage and it’s a very slick setup

You’ll be able winch up anything, slowly….

Anything’s better than 2×10

You’ll be able winch up anything, slowly….

You may be able to. That’s a higher bottom gear than i regularly use.

The obivious answer is only you will know what is the lowest for you.
Not very helpful I know so to give you a rough point to start from use the lowest point from your 2x set up.
A couple of years ago I went to the Lakes with a 11-40 cassette while I was waiting on a 45t one up expander. As I didn’t have the expander in time for the trip I decided to try the 11-40 2x with a 22 granny. 22 40 was just way too low I was caught in a no mans land between wheelying, no traction and loss of balance due to the low speed but shifting to the 35t the equivalent of 22-36 on 2×10 worked well.
So from then on I have always gone with the 22-36 ratio as my benchmark lowest gear ratio when deciding how low my set up can be if I’m going to some extreme hills.
This was all on 26″ wheels and the low ratio I decided on was 16.2 gear inches.
I use this site to calculate what chainrings and cassette options will work best for where I’m going.

Kimbers is right – Sunrace.

Sunrace 11-42 and one of these in 28T
https://absoluteblack.cc/xx1-style-shimano.html
You’ll also get a better chainline when in the 42.

What you describe is what stealth grannies were made for. No messing around with different cassettes to gain an ever so slightly easier gear, just grab an old granny ring out of the spares box and you’re done.

+1 for Sundance 11-42 & goatlink

I run 32 (oval) into a 50 tooth ring on the back. Plenty low enough for even the Alps on my 27.5 incher, but you could keep your 30 at the front and the result would be pretty much the same on your 29er

Irun 30 front and 42 rear on a couple of bikes using a Shimano 11/36 cassette with an expander ring and a 16 tooth replacement gear. No issues over several thousand kms for past few years. Running SRAM X0 medium cage rear mechs which handle the big gear with no problem at all.

I was 30 oval and 11-42 XT on my 29er, now 32 oval and 11-46

11 speed though, but if your changing…

Or stealth granny.