I believe we can pretty much agree here that the size of the bush, the toughness of tires, and the weight of vehicles is actually totally irrelevant. The bottom fact is that you cannot drive vehicles through fields because of bushes, and you cannot drive them through streets because of debris. This is no longer fun, and the game has lost appeal. All realism aside, it's detracting from gameplay experience and making a very large part of the game totally unworkable.
I hadn't driven in game for a pretty long time. I finally tried to again. I had great luck getting an elongated motorcycle through fields, even with a driving skill that had barely worked its way up to 1. Granted, I kept my speed to 30 MPHish.
Then, while turning, I broadsided a bush - the side of my loooong turning bike collided with the bush. There was a collision, but my vehicle was not stopped by it. I nervously stopped and checked it over - no damage, at least not enough to appear damaged or allow me to repair it.
A bit later I rammed a full sized blob at about 30-40 mph. Massive damage to blob, but it was not killed, just thrown some distance. I wasn't thrown off the bike, but the bike took massive damage - the front wheel went from perfect to destroyed, with some lesser damage to the first and second front end structures.
I tell you, finding and then painfully, slowly, very-interruptedly changing that bike's wheel in the middle of an area just 5 map squares from a fungal spire required much patience
So I'm tentatively wondering if broadsiding things with a very thin part of your vehicle is safer than ramming or broadsiding it with a thicker one, and a bit later I'll try to test that when I have time