Yellow underground belt unchanged.
Red replaces 2x yellow.
Blue replaces 3x yellow.
Belt speed sets distance and will scale X number of yellows (bobs next two belt speeds shown in screenshot).

Clone of Schmendrick (https://mods.factorio.com/mods/Schmendrick/longer-belts)

Change Log:
2.0.0 Update for Space Age release.
18.3 Pass at supporting Ultimate Belts + Double Belt Speed
18.2 Support for loading when conducting belts is installed.
18.1 Bobs basic underground no longer affected.
17.2 Dyworld compatibility fix
17.1 Fix Pyanodons conflict
16.1 nil check potential error line
16.0 Update for game version
15.0 Update for game version
14.3 Fix conflict with compound splitters mod.
14.2 Added config to turn off recipe change (default recipes are changed, which adds belts equal tier to underground recipe)