UKC

I have a Gravel bike with a 1x 11x46 casette and a 40t chainring. Am thinking of changing the chainring to a 36t or 38t any ideas whichwould be best.

You could climb Flying Buttress Direct with either. 

There's plenty of on-line calculators which translate the various combinations of front and back sprockets (and wheel size) into a single number which can then be used for comparisons.

As you would  expect from an idea to make life simpler, there is a wrinkle and that is there are two methods to do this - one the old imperial system still popular in the US and UK and then there's other one.

The imperial system converts all the various combinations into an equivalent front wheel diameter on a penny farthing bicycle that would give the same speed for the same number of pedal revolutions. A very large diameter front wheel would go really fast but be a bugger up hill and conversely a small diameter would be easy to go up hill, but your legs would spin out on the flat.

The common range quoted is that gears for loaded touring (and traditionally the lowest on a mountain bike is around 18 inches.  Average people in hilly areas on a road bike use something around 28 inches for a lowest gear, pro cyclists use something like 45 inch gear in the Alps, most people pootle along on the flat with a 60 inch gear, and 100 inch is tops for a touring cyclist and Chris Hoy likes a 126 inch gear for popping to the shops.

You at the moment have got a 23.5 inch lowest gear and even by going to the 36 only reduces it to 21 (or a 10% reduction).  So not really anything in it.

Only you can answer that really. Both will give you lower gearing, one slightly lower than the other. Both would be pretty low for a gravel bike. 

Are you struggling to get up hills with the current gearing?

I run a 1x on 38t with a 9-46t on my gravel bike.

The 38 to 46t works really well on the steeper/techy Peak MTB trails I often go on with the gravel bike.

But I think you'll be spinning out too much on the 38 to 11t on more normal gravel / road / DH sections (aren't you already spinning out on the 40t front?)

36 if you live in Calderdale or need to cycle over buildings rather than going around them. 😉

Wow, my road bike is semi compact so 36 x 28 is what I’ve been used to when I go up hills, I live in North Wales and I’ve yet to get off and push, I can’t really imagine what would require such a low gear 36x46

I am interested as I’m keen to get a gravel bike some time soon as there are a number of things I want to do in Wales and Scotland that would suit a gravel bike, and if I do 1x seems the way to go my MTB’s are 1x so I can see the attraction maybe no so much for road bike though I like the idea of having 52x11 available even if I can’t push it super hard 😏

I had a 36 chainring (11-42) on my mountain bike in the netherlands (before I moved to 34 for an oval ring)... I imagine 36 on a gravel downhill would be comedy.

I'm struggling to visualise what a 46 tooth sprocket would look like never mind using it with a 36, I run 32x32 on my Cx bike, can get up most stuff with a bit of grunt.

I've just fitted an 11-51 cassette to my MTB. If I break my wheel I'll probably be able ride home on the big sprocket!

If you want an even bigger 11 sp gear range, go E-13's 9-46t next time

And if you run 12 speed, you could go to E-13's 9-50t ! 

They need a different freehub though don't they? 

Don't know about 'different', but they need an hub.

Many hubs, eg. Hope ... which you should be running anyway ... , allow swapping of the freehub body. 

Note: for Hope rear hubs, you'll need the extra shim provided by E13 as Hope (as usual!) do things their own way and their free hub is not quite fully to the specification.

The newer E13 'Helix' cassettes claim to be fully compatible with both SRAM and Shimano drivetrains (though you still need the hub).

Not tried the Helix versions yet, but been using the E-13 TRS cassettes for a good few years now and they're on all my bikes.  Currently using an E13 cassette with a Shimano derailleur & shifter on the gravel bike, with no issues, so the Helix compatibility claims seems a bit superfluous.