Ok i Just got a few of those tricky acheivements on Grid and was going to post how i got them

First: Full rep 10g

this is the achievement where you have to have:
all assists off
extreme dificulty
locked camera
Pro mode

i choose a drift gp ( the one with the grand oktamato circuit)

use the pontiac gto as it has just enough torque to keep drifts going

all i recommend is a steady hand and not using the handbrake just a gentle tapping on the brakes and the accelerator

Second: Keep Rolling 20g

i found and easy spot to get this achievement its on the spa franchomps track and after the hairpin and the weird chincane the road shoull sommoth out with a few mild turns then when you see the tyre wall approaching take the grass the car 9/10 will flip then just replay repeat

ill take requests and these wer the two i got today