I have a Giant Escape, with a 750 BBS02. Like most bikes it is "legally" limited to 20-28 mph, and power is cut off when that speed is reached.
The progamming allows specifying the wheel size. I am thinking that the measured speed of the bike (mph) is determined by the distance per wheel revolution (wheel diameter x pi ) x the number of revolutions per hour (which is counted by the speed sensor ring). If I set the wheel size as 20" vs actual approx 28", will the bike "think" it is traveling less distance per wheel revolution than it actually is, and therefor allow for an actual higher top speed.
Yes you can trick your controller to get higher top speed but it makes no sense , your speed will always be wrong on your readout, like I said get an eggbeater or a controller that has no top speed limitation.
None of the above answers the question. Once you set a max speed, the only way the controler can determine when the bike gets to that speed, is by counting the number of wheel revolutions and multiplying that by the distance traveled per revolution, right? But a 27 inch wheel travels further than a 20 inch wheel. Longer travel in the same time = higher speed. So if you "tell" the controller that the top speed is 20 mph and you have 20 inch wheels, but you really have 27 inch, then the bike should actually be traveling faster than the speed displayed. Right?
I would get an eggrider controller you can set it on your phone and set max speed, and wheel size, it is in kph, but but reads in mph, it has 2 modes i set my road mode to 20 MPH legal on trailways in my state and 30 mph max for off road, but you can go higher, like you said 30 mph is plenty to cutt off. 32 and 48 kph respectively
without knowing for sure how the sensor calculates speed you may be guessing. Id recommend using the exact wheel size for accuracy in metrics. I think you can program the controller for max speed, and or have the throttle untied to PAS levels so it can override them. This way you are uncapped, if you need to prove legality (not sure who would request that) you can set the speed cap in the Display using the buttons, then change that later if needed. Though capping around 28-30 mph is not a bad idea for safety, still plenty fast. my 2 cents.