What size is first gear on a mountain bike Is it a big gear or a little gear?

First gear on a bicycle with external/derailer gears is with the chain on the smallest chainwheel(by the pedals) and the biggest sprocket(by the rear wheel).

Answer These terms are often confused, probably because bicycles pre-date automobile transmissions. For anyone who has driven a car, "first gear" is normally associated with the gear that has the most acceleration. For most multi-geared bicycles, the combination of the smallest cog on the front chainring and largest cog on the rear cassette gives the greatest acceleration or power. Using an automotive analogy, this is your first gear.

"Big gear" and "little gear" is a holdover from the Penny Farthing "boneshaker" bicycle in which more speed was gained from each turn of the pedals by making the front wheel larger (ow!). It now refers to the measure of how much chain passes through the gears for each turn of the pedals. A big gear is one that is normally associated with a combination of gears using the large chain ring on the front and a small gear on the rear cassette. A little gear uses a small chain ring on the front and a large sprocket on the rear cassette.