no there's not cumputer up grade, the onboard "computer" figures out what you need as far as power versese speed goes and optimises it to give you the maximum power and speed output

 

I'm not saying there's no power loss, theres NO NOTICEABLE POWER LOSS.

Ride 2 identical bikes, and with the exception of a little highend speed/acceleration, your not going to notice crap all difference, and the gains in ground clearance and traction far outweigh the speed. If your only worried about acceleration and top speed you bought the wrong quead to start with anyway.

 

The bigger the tires are causes your gear ratio to change. That equates to less torque. I don't know what kind of riding you guys do but last I checked you need that torque to climb over stuff in the woods. Going up in tire size is fine, just make sure that you don't over do it for the type of riding you plan on doing.