A road triple (3x7) is used where there is climbing and a granny gear is needed without sacrificing high end speed. Typical chainrings are 52/42/30.

If the terrain is fairly flat, then a double (2x7) should cover any gearing requirement with 52/42 chainrings.

Going from a 3x7 to a 1x10 is somewhat dependent on what 7 speed gearing you have and how much of it is used.

If you are running a 7 speed freewheel with a pretty generic 13-28, your high gear is 52/13, or a 4:1 ratio. A 30/28 is 1.07:1. Running a 42/28 the ratio is 1.5:1. It is best to calculate gear inches but for a simple illustration this is easier since the actual gearing is not known.

If you run a 48t and an 11-40 (1x10), you get the same 4:1 high gear ratio and a 1.2:1 lowest gear ratio. That is 12% higher than running a triple with a 30/28. The 1x10 “might” provide a lower gear than a 2x7.

Your 3x7 will have some duplicate ratios and with eliminating cross-chaining gears, you are not getting 21 unique ratios.

Of course, the wider the range of the 7 speed freewheel/cassette (13-34) the more low end you lose going to a 1x10.

John