Fixing the 2008 M3 differential

I wouldn’t call myself a newb but I will admit I don’t understand how some people magically fix cars that handle poorly. With that said, this car is supposed to be an amazing handling driver’s car in real life. I’ve found it tends to go sideways at anything above half throttle. First thing I bought was the race diff, i turned down accel to 40% and left decel at 55%, still having a ton of issues keeping the car stable around the track. What do you guys recommend to fix this car?

9/27

Even at those settings, it still is a bit squirly. I found the CTS-V had less slide out yet more power. Perhaps I need to go fully adjustable suspension and do lots of shock tuning? I am terrible at doing this however, and dont even know where to begin a baseline for adjusting. Downloading someone elses tune doesn’t really give me any satisfaction either.

We need a little more information in order to help.

First what class are you working with?

Second how much HP do you have?

Third when is the car breaking loose? Ex: off the line, coming out of the corner?

Fourth how are you getting on the throttle? Ex: Are you jumping on power or being smooth?

Diff can totally mess up your entry and exit. The car can be a pain in the ass or become a sweet, controlled french toast with bacon.

If the car is getting squirrely at the exit, you need higher diff. The car is getting squirrely because the power is unevenly distributed between left/right tires, especially coming out of the corners.

I was having exit oversteer issue with F458 but once the accel diff was raised to +70%, the car started behaving nicely. I have it at 80% but I think I need to tone it down a bit.

Do the same for the decel diff. If the rear is kicking out during braking and turning in, don’t be afraid to INCREASE the decel diff. I have 60% on F458 and can feel a lot of wheel scrubbing (through controller vibrations) so I’ll have to fine tune that further. You don’t want too much gap between the accel & decel because as you feather your throttle the diff will kick in/out erratically. You want the diff to to stay engaged or disengaged so the response is predictable. That’s my goal at least.

So, try increasing your accel in 10% increments. When the car behaves the way you want it to then dial back 5% (you gotta be driving on the edge, right?) Then leave it there for several days/races then fine adjust +/- to get it perfect. Do the same for decel. I am guessing you need about 75%/60% on that big car.

What class are you working on ?