My mini schnauzer does the same thing.
For Momo, the following works:
If the chair cushion is slanted backwards, make it flat by laying newspaper. It provide a larger surface for her to balance herself when you turn around the corners / stop at lights.
If she is still tiny and can't see anything outside, pile more newspaper so that she get to see whats going on. I tried to blind my eyes while my mum drive around, it is not fun at all.
Make sure the doggie seatbelt on !
You probably have read this somewhere before but it does work !
Start with getting in and out of the car and give lots of praises when she get in - Until she do not look nervous
2 - 3 mins of really slow driving around the block then lots of play when she is out of the car
Slowly lengthen the time and again, lots of play after the "trip"
I have also tried "Travel Calm Ginger" by Blackmore but it did not work for Momo unfortunately. :/