I’ve always really loved Forza but I haven’t really done much in the way of tuning my cars. In Forza 6, my 2005 BMW M3 fully upgraded has an incredibly hard time turning. It also takes a bit too long to brake before a corner. How could I fix this? Any help would be greatly appreciated!
It’s the fully upgraded part that’s the issue. It’ll have too much power for its own good, much more than the chassis can handle.
The only effective fix is to tone it down 
Not sure I agree with the above, as I’ve seen mates do rather well in S-Class M235i’s etc.
It doesn’t help that you have chosen to take it beyond it’s obvious territory, but with a good setup and a good driver you should be able to get some use out of it. All depends on what you want to do with it in the end, it’s more than likely never going to set the world on fire around the tighter twisty tracks where handling is needed, but could have a lot of potential at Le Sarthe. For instance I have a BMW 1M with the enzo engine fitted in S-Class running only 5.7 handling, it’s a bit of a handful in the turns but is bloody quick at Monza/Le Sarthe with a top speed of 246mph (still pulling). You wouldn’t see me take it round Lime Rock Park though lol.
If you tell us more about what you are trying to achieve with it, maybe we can help you more?
HW