The ability to read a license plate. Just let me tell you now that reading license plate is a MYTH! Yes, I'm sure you have seen a lot of comparison video and how they show freeze frame from varies cameras (even on the same vehicle) and how some camera seems to read plates better than other. The truth is that being able to read a plate depends on so many other factors that it often seems more luck than the ability of the camera. Here's a few factors that will affect your camera performance.
a) Your windshield angle and curvature, how much glass you have to see through and the angle can make a noticeable difference. For clear front and back view. A straighter window like those on a bus or pickup offers the least distortion while a sharper angle on something like a sport sedan might have more distortion and pickup more reflection from the dash . The curvature of the window also matters. It all depends on the curvature of the camera lens vs the curvature of the windshield. The closer match between the 2, the less distortion. But in general, don't count on reading plate at more than 20ft and often less especially for vehicles to the side in other lane.
b) The color, shape and material of your dash surface matter. The flatter the dash and the lighter the color, the better chance that you will get a fairly amount of reflection onto the windshield during the day and under bright sunlight. While you eyes tends to automatically dismiss the reflection. They will show up as bright area on the recorded image and may interfere with you ability to read a plate that's right in front of you.
c) The speed differential between the 2 vehicle. Speed differential makes a lot of difference. I would say that your chance of being able to read a plate on another vehicle traveling more than +/- 10 mph compare to you is almost nil.
d) Low light opens another can of worm. It's depends a lot the type of sensor, the angle between the two cars, the brightness of your and the other car's headlight/taillight, the color of the car, the color and contrast of you country/state's license plate, the amount of ambient light from street lights, buildings, signs and other vehicles on the road with you and how much reflection you're getting in combination,
All that said, some unit does work a bit better than others in some circumstances. 4K unit tends to let you read a plate a bit further away and a 60 frame/sec unit tends to have a larger speed differential margin. But compounded with all the factors above, the actual difference (being to read the same license at 25ft vs 20ft or while a car is travelling +/- 15 mph vs +/- 10 mph) is just not something you can depend upon despite all the caught on camera clips you see on Youtube.
