As we all know, wheels can make or break the look of a Porsche, but they can also deliver significant improvements to the way your car handles, accelerates and stops. Indeed, wheel design has much more of an impact on performance than many people give it credit for. Unsprung weight, the cooling efficiency of your brakes and the geometry of your suspension are all affected by the rims you fit — the design of a wheel is essential in the search for peak performance. In this opening article to a series of 911 & Porsche World features focusing on wheels, we highlight the most popular forms of production. First, let’s look at the basic principles of wheel design.
UNSPRUNG WEIGHT
The term ‘unsprung weight’ refers to any mass on the road side of your Porsche’s suspension springs. Typically, this includes hubs, driveshafts, brakes and wheels. You can reduce unsprung weight by fitting alloys in place of steel wheels. Doing so will result in quicker turn-in, sharper steering response and better braking. In rallying and other motorsport disciplines (where suspension components are worked hard), having a lighter unsprung weight puts less stress on dampers, meaning they’ll perform better and last longer.
WIDTH
The main reason for fitting wider wheels is to use wider tyres offering greater grip through a bigger contact patch with the road. Contrary to popular belief, rim width is measured from inside lip to inside lip (as opposed to the overall outside dimensions of the wheel) in order to take the thickness of kerb lip out of the equation. It’s not uncommon to see modern fourby alloys with a kerb lip of over 20mm thick, making the outside measurement of an eightinch rim appear to be more like nine inches.
It’s not always true to say wider wheels are the best choice for a car. For example, ten-inchwide wheels may work well at the back end of a 911 due to the amount of weight over the rear axle and the amount of downforce generated by the car’s aerodynamics,
