Trek 7.7FX Size
 

I just bought a new 7.7FX in the UK and will be using it for commuting.

I had to buy the bike blind as the cycle shop did not have any in

The seller measured me up and recommended the 20" 5 cm size.

I ve had it delivered and I need to put the seat up about three inches

Is it better having a big bike with a low seat then a smaller bike with a higher seat?

There are a few different ways to measure up. The majority of multi-size bikes are meant to have the top tube be about 1" from your crotch when standing over it. If you are directly on it, it's probably to big, if it's way low, probably too small.

The 20" 7.7FX is meant to comfortably fit people around 5'10" - 6'3" (typically). A good judge for that bike is to sit on the saddle, and have a little more than tip-toe touching the ground.

The ol' standby works as well: Sit on the saddle, place the heel of your foot over the pedal axle and pedal backwards to the lowest position it can reach. Your leg should be at or near fully straight. Slide your foot back so the ball of the foot is over the pedal axle, and you should have a comfortable bend in your knee.