Balancing BG along with Exercise

Diagnosed Type 2 in 1993. Diet & Exercise maintained control for 15 years. Now take insulin (fast) at meals and (long) at night. Have lost 45 lbs in past 1.5 years. (1) Have taken up cycling. Before cycling: if w/i 1 hour of meal, I reduce insulin by 50%. If more than 2 hours to cycling - take full dose (5 units). Always test before getting on the bike. BG must be > 5.5 otherwise most take quick carbs. (2) If using a pump, your BG is determined and then the pump provides sufficient insulin. If not rise in BG, no insulin. So - with fast acting insulin at meals, can I eat, then monitor (test) every 30 mins for 2 hours & if BG rises, inject. If not, skip injection. This may happen at supper time when I have a drink. It is my understanding that the liver works on the alcohol and not the carbs in your system. Suggestions anyone???