How can I get current lateral and longitudial friction forces from standart WheelColliders?

U can calculate it yourself, you would unfortunately have to write a small physics script to calculate it though. Not to discourage but I wrote a $$anonymous$$i physics engine for wheel colliders so that i can use values such as ones you seek, it's about 1500 line but mostly just calculations based on speed, weight and values provided by the defaults. It's like 2 days worth of work, consider it because you have access to other constants as well.