In most cases with drivers who have been sim racing less than 2 years, this comes from too much brake. when a tire has too much brake it tends to slide or hop way before lockup. The classic brake skid is is really obvious and I'm sure you're not doing that. It is a subtle thing where you have just a bit more brake than traction. Using a little less brake pedal can often stop faster than pushing hard. On cars with huge brakes it is sometimes easier to drop the brake pressure from the 95% default to maybe 93 or even 90 if you don't have load cell pedals. On real life Formula open wheel cars brake traction is linked to air pressure on the wings. Some of the open wheel sim models now calculate this correctly, even though they didn't 10 years ago. So you can brake hard at 250 KPH but you have very little grip at 60 KPH and you need to trail off somewhere in between. There is also some ability to trail brake on some, but not all cars if your brake bias is correct and you brake very lightly. The best way to understand this is to take a car that responds a lot to weight transfer and try it. I suggest the 911 GT3R using brake bias from 57 to 51 two steps at a time. Do 2 laps then change the bias 2 clicks. This can be mapped to a button on this car so you don't have to warm tires in between. Of course a car that under-steers too much has a lower mid-corner speed and those setups will make you brake earlier.