Originally Posted by Maj_Overdrive

Are we talking outright top speed runs or drag racing to a finish line because this is the drag racing section? For drag racing the answer is it depends on the vehicle. Purpose built drag racers are 2wd but they're feather weight and built to maximize the 2wd. If you're adapting an existing vehicle then 4wd is probably better.

For top speed runs it's basically the opposite. In theory a vehicle with less drivetrain loss should end up going faster. But in reality there are other factors that come into play. The biggest of which is limited distance (both space and sight distance) to get up to top speed. Limit traction and you limit the amount of acceleration in your limited space to get to top speed. Not to mention your overpowered vehicle is harder to control with less traction.

The only time 2wd is going to be an advantage is when you artificially try to limit the vehicle instead of going all out. An example would be trying to have the fastest 2s vehicle. 2s doesn't need as much space to reach top speed so drivetrain losses and aerodynamics play a bigger part of the equation than the space needed to get there. For 2s a 1/10 buggy or touring car make the most sense and will get to top speed easily. But put those vehicles on 4s and you're going to need a bunch more room since the vehicle will be overpowered and you won't be able to just mash it. Have a look at the fastest rc cars, the ones going 100+, they're all 4wd.