...to lose the belly you need to eat less calories.....you are goin the right way with the riding though....Sit ups wont shed any beer gut as you are finding out..LOL...i do 150 situps daily have done for years but youd never know it ...you need to shed all fat to really show the abs....and although i eat sensibly i am a sucker for alcohol

Get a plan...i personally train every other day..was doin it daily but i couldnt hack it at 36 years old ...

I do these:-

Bench press
Butterfly
Concentration curl
Triceps press down
Preacher curl
Lat pull down
Underhand lat pull down
Leg extension
Leg curl
Sit ups

All on a fitness centre and as said everyother day..i do 3 sets of 5 on each excersize except the situps..i do 100 to warm up and then 50 warm down.