In Forza Horizon 5, a lot of players will want to tune their cars, but tunes that they downloaded from other players can't be modified or adjusted to suit personal tastes, so it's not the best option.
After upgrading a car, you'll find that your new set of wheels is either at a ridiculously low speed or not making use of all the gears in the transmission, which is not the car's most perfect condition, so IGGM will tell you how to do.
The Gearing Tab
All you need to do is to adjust a single variable on the tuning screen. Once you've finished customizing your vehicle, you'll need to navigate to the "Upgrades and Tuning" section of your nearest festival site or any home you've purchased. Then visit the "Custom Tuning" section, from here, you can switch to the "Gearing" tab.
The 130MPH Dodge
If you like the six-speed racing transmission, you can find on the "Gearing" tab that your car has a top speed that is "way less than you expected.”
Adjust the final drive settings
Every car has a maximum top speed, which is based on factors such as power, weight, and aerodynamics. Quickly find the "aero max" of your car and move the “final drive” slider to the left.
Then, you just need to fine-tune the Final Drive. Let it keep moving to the right, increasing the number each time.
As for the other advice, you need to consider the gearing when you tune the car. But it should be noted that if you have the best FH 5 Cars then adjusting the parameters will be icing on the cake and make your car better, but if your car is very average, doing this will not give you better progress.