Auto body repair & detailing: Aerodynamic Improvments, front air dams, rear axles

Question
Dave,

I have an 03 VW Gti (MKIV) and wanted to improve the aerodynamics of the vehicle. I see a lot of products on the market that appear to be just cosmetic, but I would like to actually improve the down force at speed and increase gas mileage during normal driving.

I understand the air in the wake of this body style is a mess and understand that a smooth under-body and diffuser at the rear as well as a drop of an inch or so will help, but I do not know of a combination that works together to achieve the goal.

Do you have any suggestions?

Thank You,

Robert

Answer
Hi Robert!    Not really my area of expertise, but this is what I can offer. Most of which you probably already know........Although you mentioned the accessories you have looked at look more cosmetic than functional, they actually are functional to some degree.......Side skirts and front air dams will cut down the airflow passing under and around the vehicle...You can install what we call here a "Drag Plate" also....You might have to make this if you can't purchase one. It is usually made out of fibreboard, fibreglass, or even wood....It is installed covering the undercarriage from front to rear axles....As for the rear wing, it will obviously provide a down force as well. How much will depend on the rake......If you are looking to lower the vehicle, you can take the oldschool approach by cutting the coil springs.... General rule of thumb is no more than one/half a turn at a time...This is obviously a trial and error effort....Once satisfied, you will need a 4 wheel thrust alignment.....As for gas mileage, there are computer chips available for this vehicle...My suggestion is to contact VW itself, and see if you can talk to their racing division...They should be able to help you out further..Hope this helps..............Dave