Gravel build - Gearing

Gearing choice for the bike is a sub-compact 48/32 double oval-chainring on a Shimano 6800 crankset.
Why not single ring ? Well.... single is simpler and better for the rough stuff, but in the case of a do-it-all bike, if you want to do some "fast" road riding as well, double is still a nice thing to have, as you have more gear range with smaller gaps.
(Not going into why oval right now, as that is topic for a whole new post eventually)

So, in this case, paired with a 11-34 SLX cassette, the resulting gear range comes to:

CLIMBING - 32 / 34 - with 700c-40mm tires

How fast will I be going at 50-90 rpm in these gears?

Cadence Gear	50	60	70	80	90	Cadence   Gear
32x34	6.22	7.46	8.71	9.95	11.19	32x34

This basically means that for climbing cadences on extreme gradients, I have a gear that allows me to climb at 7 km/h and keep turning the pedals.
Should be enough for all things, as lower than 6 km/h you are better off walking anyway.

Max Speed - 48 / 11 -with 700c-40mm tires

How fast will I be going at 80-110 rpm in these gears?

Cadence Gear	80	90	100	110	Cadence   Gear
48x11	46.15	51.92	57.69	63.46	48x11

So, for descending, flats, tailwind, etc, you are more than covered with this. If you want to pedal at 60 km/h, you can still do it, 110rpm is still manageable.
I don't have the power to ride at more than that, unless it is a steep descent, and in that case you are probably better off coasting and aero-tucking anyway.

Full-range of the gears is like below.
(Note this is a cheap MTB cassette, so not much optimization done for road/gravel purposes).

How fast will I be going at 80-110 rpm in these gears?

Cadence Gear	80	90	100	110	Cadence   Gear
32x11	30.80	34.66	38.51	42.36	32x11
32x13	26.04	29.30	32.55	35.81	32x13
32x15	22.55	25.37	28.18	31.00	32x15
32x17	19.90	22.39	24.88	27.36	32x17
32x19	17.78	20.01	22.23	24.45	32x19
32x21	16.09	18.10	20.11	22.12	32x21
32x23	14.71	16.55	18.39	20.23	32x23
32x26	13.02	14.65	16.28	17.90	32x26
32x30	11.33	12.74	14.16	15.57	32x30
32x34	9.95	11.19	12.44	13.68	32x34
48x11	46.15	51.92	57.69	63.46	48x11
48x13	39.06	43.94	48.83	53.71	48x13
48x15	33.87	38.11	42.34	46.58	48x15
48x17	29.85	33.58	37.32	41.05	48x17
48x19	26.78	30.13	33.48	36.83	48x19
48x21	24.24	27.27	30.30	33.33	48x21
48x23	22.12	24.89	27.66	30.42	48x23
48x26	19.58	22.03	24.48	26.93	48x26
48x30	16.94	19.05	21.17	23.29	48x30
48x34	14.93	16.79	18.66	20.52	48x34

Translating the table, this is the speed you will be going in a given gear @ a given cadence.

In the above examples, you can use the tools at BikeCalc.com to check if you will have a low enough/high enough gear for your riding.

In this example, I created a table with every combination to check the gear steps.

To ilustrate this, check the 33 km/h speed highlighted in red. This is a common speed for road group riding etc, so a good example on this. Looking at the table you can see that with this gears, I am able to ride at 33km/h at all of my cadence range, from 80 (or even less, just not plotted) to 110, there is a gear that you can use.

You can also see, that each gear change will affect cadence by around 10 rpm.

(same 10rpm can be seen at 30km/h, 27km/h, etc, just check diagonal lines in the table)

If I change from the 17 to the 19 in the back, my legs will need to spin from 90 to 100 rpm to match the speed.

10 rpms is well within my cadence range, so I not caught in an awkward cadence if I up or downshift.