Why does your car shake when you are passed on the hwy?

I'm curious about this, and thought that the engineering/technical community here at the automotive forum might have some answers--why does your car shake (or feel like it's shaking) when you're passed on the highway? Does it have to do with the difference between your speed and the speed of the other car? Or how close the other car is to your car? If your car shakes, does it mean the other car is going at least a certain speed?

Any answers or information on this topic would be much appreciated!

Thanks.

I think it is just the turbulence comming off of the other vehicle. Large trucks are the worst.

Yep. Its just the air being forced out of the way of their car. How rough the shaking is depends on the size and speed of both vechicles, and the suspension of yours.

don't forget wind. Can have a huge effect on it. if you have a strong wind coming across the vehicle that is pass, towards your vehicle, it will be a lot more violent, than if the wind was going the opposite direction

Semi's punch such a large hole in the air, right around the cab doors usually there is a low pressure zone thats big enough to move you towards the truck, then at the bumper, you hit the high pressure zone and it pushes you out. When wind conditions are right, the low pressure zone can be really powerful and will scare teh crap out of you if you're on a bike

It shakes alright. Even if you're sitting still, the air has to get split by the passing vehicle, then it slams back together behind the vehicle. The way it affects you is that all the air beside you takes one massive step to the right, then the left as it gets pushed out of the way by the passing vehicle.

Cars that have low profile tires don't shake nearly as much. I think the shaking comes from the tires just as much if not more than the suspension.

I only have larger wheels for my car, not aftermarket suspension... and I rarely notice shaking passing trucks at 90mph.