What Does a Rear Diffuser Do? Rear Diffusers Explained

A rear diffuser is the finned panel under the rear bumper. On race cars it is a serious downforce device. On street and drift cars it is part aero, part protection, and a big part of the look.

How a Rear Diffuser Works

Air flowing under a car speeds up and its pressure drops. A diffuser gives that fast air a gradually expanding exit, slowing it back down smoothly at the rear. That reduces drag-causing turbulence behind the car and, on a car with a flat floor, creates downforce by keeping pressure under the car low.

Does a Diffuser Help on a Street or Drift Car?

Without a flat underbody, a bolt-on diffuser adds little downforce. Its real benefits are a cleaner rear end, a shield for the bumper when you put the tail near a wall, and a tidier exit for the exhaust area. That makes it one of the most popular drift aero parts.

Choosing a Diffuser

Carbon fiber or carbon-look: light and sharp looking; replacement cost is higher.
ABS: tough, flexible and affordable, a good choice for cars that see contact.
FRP: easy to repair and paint, but brittle on impact.

Chassis-specific diffusers bolt to factory mounting points, like the 2003-2008 Nissan 350Z rear diffuser and the 2009-2020 Nissan 370Z rear diffuser. Universal lip diffusers fit a wider range of bumpers.

Install Tips

Test-fit before drilling and check exhaust tip clearance.
Use stainless hardware; the rear bumper sees water and road salt.
Recheck clearance over speed bumps if the car is lowered.

See all rear diffusers, or compare this selection of rear bumper diffusers.

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FAQ

Does a diffuser add downforce?

Meaningful downforce needs a flat floor. On most street cars, a diffuser is mainly aero tidy-up and styling.

Will a diffuser fit with an aftermarket exhaust?

Often, but check tip position. Some diffusers are designed around quad or center-exit tips.