Why SUVs Need Rear Wipers, But Most Cars & Trucks Don’t: The Physics Explained

While driving in the rain or snow, you’ve probably mumbled to yourself, “It sure would be nice to clear the rear windshield.” But if you’re in a car, you are often out of luck due to a lack of rear windshield wipers. Meanwhile, SUVs appear to have that luxury, and that all comes down to the vehicles’ shapes. 

Aerodynamics play a big role in this contrast. Sedans have a sloped rear windshield with a smooth surface, which allows air to flow over it. For this reason, water is naturally carried away from the windshield’s surface. The wipers may even disrupt that airflow since the surface would no longer be smooth. Meanwhile, SUVs and hatchbacks have a more upright shape — especially as boxier styles return. This can lower the air pressure behind it, pulling in surrounding air and water into a vacuum. Since the air is not flowing against a smooth surface, it can end up swirling around the windshield, meaning water and dirt won’t disperse on its own.

While water flows off of sedans’ windshields, that doesn’t mean dirt and snow are going anywhere. It can get difficult to see out of the back of a sedan in some cases — so why aren’t there windshield wipers? Aside from aerodynamics, there are a few other reasons why sedans and windshields don’t mix. 

Fuel efficiency is a big one. Remember how we mentioned windshield wipers take away from the sedan’s aerodynamic design? This means adding wipers would also add to more fuel consumption (like when you drive faster), since it would break up the streamlined profile and create drag. Sedans also lack the space to add the electric motor required to power the wiper. It may also get in the way of opening the trunk. If you’re getting fed up with dirty rear windshields, try applying a protective coating (RainX is popular, but we also recommend a few alternative brands) and keeping some windshield cleaning products in your car in case you need to take them out mid-journey.