Out of curiosity, if you can get your hands on a properly engineered splitter, what kind of handling difference would I see?

Any recommendations for a splitter that's not just for show? Any effects on fuel economy?


tl;dr: You will almost certainly notice no effect at all other than the loss of fuel economy due to the increased weight.

It is very unlikely that a splitter or diffuser will have any measurable benefit unless you are driving a car that is:

  1. Very low to the ground over a ...
  2. Very smooth surface at a ...
  3. Very high speed.

Needless to say, the street is not a good place when considered under any of those criteria.

As a practical example, let us consider the efforts of the good folks at Grassroots Motorsports. In working on their Le Grand Mk 18, they felt that it was worth their time to install a diffuser (the caboose to a splitter's engine on the aerodynamic train). This is because their car is super low:

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and because the car is "A purpose-made race car built in the 1970s for SCCA's D Sports Racing category."

All that said, a perfect splitter will increase overall downforce if combined with the rest of a properly engineered aerodynamics package. It will also reduce your top speed and decrease your fuel economy because of the primal law of the universe: there ain't no such thing as a free lunch.


A splitter is designed to force air around the car instead of allowing it to go under the car. This will affect high speed driving, but won't do much (if anything) for you at highway speeds. The splitters you see on cars on the road are there primarily for looks, not for function. If you are racing your car on the track, you might see some difference, where you'd actually see down for (or reduction of under vehicle pressure) added stability while going fast. This won't improve handling per se, but will improve control of the vehicle at these higher speeds.


A splitter is really part of a ground effects system, here air is forced under the floor of the car and accelerated out of the back via a rear diffuser. The increased airflow velocity under the car creates a low pressure area which creates down-force.

However for this to be effective it needs to work as an integrated system. The floor needs to be flat and ride height, roll stiffness and rake angle will have a significant effect on how it works. It can also be disrupted by other aerodynamic effects for example if turbulent flow from the tyres gets under the floor it won't work properly.

The airflow out of the back of the diffuser can also potentially interact with the rear wing, if present, and with airflow over the top and sides of the car.

Unless you have a very good idea of what is going on just bolting on an aerodynamic part in isolation won't tend to produce predictable results.

So unless the whole vehicle has been properly analysed in a wind tunnel or good CFD system there is no way to know whether it will work or not. Indeed the compromised in suspension setup needed to make ground effects work may end up making handling significantly worse under normal driving conditions.

Ultimately the only real way to be sure that aerodynamic parts are working is to test them on a track with an experienced driver who can give consistent feedback and allow systematic adjustments to the overall car setup to be made.

Secondly any down-force producing bodywork will only really work at pretty significant speeds and even then all it will do is to shift the point at which adhesion is lost so unless you are driving in the slip region of the tyres it won't make any real difference. Equally unless aerodynamic forces are properly balanced they won't necessarily improve handling.


In addition to the other answers, the "splitter" fitted on most road cars is mainly down to the designer and the "look" but they can also be designed to increase the flow of cooling air to the brakes, which can be very handy to prevent overheating and brake fade or even total loss.

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