I'm not a cardiologist, but the formulae for estimating maximum HR are all bunk, there is no real science behind them. Maximum HR varies dramtically from person to person, and isn't a very important number.

Your maximum is your maximum, you can't exceed it and your heart won't explode if you reach it.

As for whether you should be riding differently, that depends on how you are riding now and what it is that you want to achieve. Certainly just going hard all the time with an average HR of around 170, if that's what you're doing, probably isn't the most effective way to train.