I do find some of the stat changes odd. Like in some AWD swaps if you add the race transmission the top speed stat goes up without a PI kick and seemingly ignoring the fact the final drive was already adjustable.
The key is always get out on the road to test and preferably do it on the tracks you are likely to use the car on.
In Forza it’s generally accepted that a drive train swap results in a transmission swap as well because the entire category gets changed. The PI differences are calculated in as part of the drive train conversion.
What someone asked, I’ve only noticed the Race Transmission not dropping to 6 gears every time in FH2.
As Eduardo stated earlier as well, the changes to the top speed don’t mean much unless you are going for a top speed build or racing down the highway and back. Rarely will you find yourself exceeding 180 in the actual race events anyways… What is more important is how well you can control the car and take the corners because you won’t be racing around at 270 anyway.
Damn how many gears do you want, some cars have 7
Just checked the 360 version, and it retains the behavior from FM4. Putting a race box in a 7 or 8-speed car locks out all gears above 6th.