Here's pictures of one of my retracts with wheel.

Now I have to decide on either an air system or mechanical. I will be getting a circuit board that will allow me to change the speed of the servos to be more scale-like so I am leaning towards mechanical. I know you can do the same in air systems with restrictors but have heard of a few problems with the air systems as a whole, so I'm searching for opinions on each. Also,  would I be saving any weight with mechanical vs. air?

Thanks for your input.