WHEELS 'N CUSTOMS TECHNICAL GUIDE: STAGGERED FITMENT & 4WD/XDRIVE FITMENT

A staggered fitment (internationally known as staggered fitment) means that the wheels and tyres on the rear axle are wider than those on the front axle. Think, for example, of 8.5J up front with 225/40 R19 tyres and 9.5J at the rear with 255/35 R19. Where this has long been the standard on rear-wheel-drive sports cars for maximum traction and a muscular look, it raises major questions with four-wheel drive: "Can a staggered fitment be used safely on a 4x4, BMW xDrive, Audi Quattro or VAG 4Motion?"

The answer is yes, provided you strictly adhere to the maximum rolling circumference tolerance. In this technical guide the specialists at Wheels 'N Customs explain how rolling circumference is calculated, what the consequences are for the transfer case and how a staggered fitment affects the balance between understeer and oversteer.

On cars with four-wheel drive (AWD/4WD) the front and rear axles are linked via a centre differential, a transfer case with a multi-plate clutch (as with BMW xDrive) or a Haldex coupling (as with VAG 4Motion). These systems assume that all four wheels rotate at exactly the same speed.

The tolerance rule of thumb: The calculated difference in rolling circumference between the front and rear axle must never exceed 1.0% (for BMW xDrive Wheels 'N Customs preferably uses a margin of even 0.5% to 0.8%). Also take tyre wear into account: always fit four tyres of the same brand and model and do not swap worn rear tyres with brand new front tyres.

Tyre sizes (e.g. 255/35 R19) consist of the width in millimetres (255), the aspect ratio as a percentage (35%) and the rim diameter in inches (19). With the formulas below you calculate the total wheel diameter and circumference:

Besides mechanical compatibility, a wide setup also changes the car's handling and balance:

• Traction & Power (RWD): On rear-wheel drive cars a wider tyre provides a larger contact patch. This makes it possible to transfer considerably more power and torque to the road without wheelspin.
• Effect on Understeer: By fitting wider tyres at the rear, the rear axle gains relatively much more mechanical grip than the front axle. In high-speed cornering near the limit the front will lose grip before the rear. This results in an increase of understeer (the car wants to push straight on).
• Less Oversteer: For road cars this is actually a safe factory characteristic; the chance of the rear stepping out suddenly (oversteer) is drastically reduced.
• Road Imprint & Fuel Consumption: Bear in mind that wider tyres are slightly more prone to road imprinting on the motorway and generate a fraction more rolling resistance.

For many car enthusiasts the visual aspect is the deciding factor. Because the rear rim is often 1.0 to 2.0 inches wider (for example 8.5J front and 10J rear), wheel manufacturers such as Concaver Wheels, Japan Racing (JR-Wheels) or Wheelforce can make the spokes of the rear wheels curve much deeper inwards (Deep Concave or Extreme Concave). This gives the rear of the car an aggressive, muscular stance that cannot be achieved with a square setup.