How to fix?

[vapid bane]

Just use Animator component and animate one model instead of turning individual models on or off

[quartz thistle]

What Derpy said. Just like to thank you for providing all the needed screenshots.

[vapid bane]

then make speed detectors for each speed state and change animation speed or even add separate animation clips accordingly

you need it, you make it, lol

because the vehicle most likely calculates its speed with an invisible wheel