Top Speed Failed!


So I wanted to build the mazda mx5 mk1 to a drift build so I started by swamping a v8 and switching everything to race specs but
once I switch to tuning section on top speed and braking benchmark instead of showing the speed they had a FAILED !

At the beginning it was funny because i thought that I build the next DK but when i tried to check the gears it was hard for me to know the top speed and breaking

So is this an in-game bug or it’s my mistake ? or maybe i did build the next dk ?

I really don’t know because it’s my first time happening in FH4. Also i don’t know if that could happen on other cars but especially happens for the mk1