This mod reduces the chance of flipping most cars by 1/3, but when you flip over it's also harder to get it back on it's wheels! Chance also reduced by about 1/3.
It also means it's harder to do jumps, however I have not touched the bikes, so use bikes for that.
I have tweaked the handling file a little by adding about 2000 mass to each car.
I find this better because I hate losing my favorite car because I didn't see a small stone. Sometimes cars flip over the smallest things. Now that won't happen anymore.
Make a backup of 'handling.cfg', then extract the file from the download and paste it to the 'Data' folder.