When driving on wet roads after a rain I don’t like to follow a semi. They kick up just too much mist from the wet road. I do like to be able to see when I drive. Some others don’t seem to care that much. We get accidents when they drive full speed into fog.
So I am driving down the highway after a rain storm and watching cars going the other direction. I can see just how much mist each one kicks up. Some leave a big plume and some hardly anything at all. I thought it may have to do with number of tires, like an 18 wheeler, but that is not all of it. An ambulance left behind it as much or more as the big boys and it has 6 tires.
So what is the difference. The only other factors I can think of is weight per tire, tire width, and tread design. Assuming I care about the guy behind me what tread design do I want for less plume. Or, is leaving a larger plume safer (for me the driver that is) or is leaving a small one safer. I was thinking kicking up more water might give me more traction but I don’t know.
Tread design and design of the physical parts that surround the tires probably have the biggest impact in creating the “wash” you see trucks raising off of wet roads. I believe it’s more dangerous than most people realize. There are brush-like “side curtains” that can be installed on trucks to significantly reduce this cloud effect. UPS has them on their trucks (well, I haven’t looked lately but they used to have them). The feds were going to mandate them for certain classes of truck some years back, but for some reason the initiative never came to fruition. I wish they would. They make a huge difference.
Tires, mudflaps, pavement, speed and the number of wheels all seem to affect the spray. And I too find it difficult to deal with excess spray from vehicles most noticeably semis. I sometimes drive significantly faster than I prefer in the rain to avoid being passed by semis. The spray can restrict vision to a few yards and unless I’m on level, straight roadway I prefer to stay ahead so I keep the speed up.
Forgot about the mudflaps. In my experience they don’t seem to make a big improvement. I have seen trucks with them that still leave a big spray. Fender design is something I didn’t think of. That may play a big role.
I would say fender design is the major factor. This is really noticeable in the motorcycle world.
You may have seen these custom bikes on TV with bobbed off rear fenders and/or shortened front fenders.
That may look “cool” on a custom bike but in practice on wet roads they can be a pain in the neck. The tires will kick up rooster tails which places the water/mud into the eyes (front fender) or will saturate the back of the rider (rear fender).
I’ve ridden bikes like that on wet, muddy, and icy/slushy roads and hated every minute of it.
Semi trailers don’t have fenders and while that worsens the problem trailer axles are moved depending on the load and highway and when the rear axles are pushed fully to the rear more spray will exit the rear.
I have noticed that UPS tractor/trailers use mud flaps made like brooms that are long enough to nearly touch the pavement and they improve the situation somewhat regardless of the axle’s location. Of course those mud flaps are installed on the tractor and trailer on UPS trucks and that is a great improvement also.
One of the few good things about my Volvo was that it came from the factory with very good-quality, large mud flaps.
At highway speed, a glance in the rearview mirror confirmed that my car threw almost no mist/spray behind it–unlike almost all of the other vehicles on the road.
