Custom Crt.5 Project

[MetalMan]

First off, it's nice to see you have the motivation to take on a project like this.

Second, 50mph might be doable on 3s, but I'd bump up to 4s minimum for that speed. My CRT.5 geared for ~47mph on 3s is pushing the limit of the MM (with a CCBEC).
To determine what gearing to use, you can plug in the values into BrianG's "Parameter Solver":
http://scriptasylum.com/rc_speed/_solver.html
Just remember your tire diameter, and that the spur has 46 teeth.

Third, bracing is a very good idea because you can make the chassis lighter overall. The way you're thinking of it now that chassis would weigh as much as a brick, although would be very rigid.