Ok I recently got a Trek Hybrid. It has 3 speeds in front small, medium, big crank and it has 8 gears in the back. I thought I read somewhere that you do not want both your front gears and back gears to be in high gears at same time this will ruin the chain? I am riding it now on 3rd biggest crank in front and riding between a 6-5 speed on the back gears. The only reason not riding back speed at a 7 or 8 is I am concerned this would ruin the chain since both front and back gears would be in high gears which is considered bad right?

I guess what I am asking what would be the ideal gear range to be in? On the 3rd gear in front and 5th gear in back or would a better gear combo be better? That is a little too easy I would like to be in 7-8 gear range in back, but worried that might ruin the chain if both front and back gears are in high gears. I am peddling wheels very fast right now at the current gear setup I got and could switch into higher gears if wanted to.