Broken Speedometer in Alpha GTV-6

I am, again, doing the Super Street volume races but this time with the Alpha GTV-6 and after about 30mph the speedometer in the car falls behind the actual speed according to the Forza given speed. For example at 90mph the speedometer in car is indicating 60. I have my own tune on the GTV-6 obviously. This might be realistic though and not an actual bug if you have a GTV-6 with a broken speedometer. I am not trying to find bugs and this is definitely a funny one worth keeping to me. Just reporting it.