February 2010 Tech Tip: Guard Rub - The Pitfalls Of Wider Tyres And Lowered Suspension

GUARD RUB – THE PITFALLS OF WIDER TYRES AND LOWERED SUSPENSION

A common complaint when fitting a lowered suspension kit to a vehicle is that the owner now finds, that after spending a considerable amount of money and effort on Mag wheels and tyres let alone the cost of the suspension kit, he or she experiences the annoying issue of the tyres rubbing on the guards.

Damage to tyres, paintwork and body panels can occur and front wheels can catch on the wheel arches when turning.

In extreme cases the vehicle can be dangerous to drive.

The perceived cause of the problem is often deemed to be the lowered suspension, this however is actually not the case as the following will explain:

In the design phase of a new vehicle the manufacturer puts considerable efforts into ensuring that the suspension system works correctly.

This includes ensuring that the maximum amount of allowable travel is derived from the suspension system without the wheels fouling on the vehicles bodywork. In technical terms this is referred to as full bump (maximum compression), and full droop (maximum extension – when the wheels are fully off the ground).

In effect this means that if the suspension springs where removed from the vehicle and it was allowed to sit down onto its bump stops, no fouling of the tyre onto the bodywork would occur with the original factory fitted, or equivalent, wheels.

THE FITTING OF SOME STIFFER SPRINGS WILL NOT FIX THIS PROBLEM

It may reduce the amount of rubbing, or the harshness of it, but it will not fix it due to the fact that no matter how hard the springs or shocks are the suspension movement is still determined by the amount of force applied to it. If the bump or the load is of considerable force rubbing will still occur before the suspension comes up against the limit of its travel.

On certain vehicles with rear panhard rods fitted (such as earlier model live axle rear Commodores) ride height alterations can cause the axle to shift sideways and cause guard rub. In these cases the fitting of a modified panhard rod can realign the axle to a centralised position, again though aftermarket wheel and tyre combinations may affect this.

Ultimately a simple way to test this is to change the wheels back to original equipment and see if the rubbing problem has gone.

Within acceptable limits it is possible to fit aftermarket wheel and tyre combinations to most makes of vehicles without issues, if you know what those limits are and work within them you will not have issues with rubbing.

In conclusion, trying to solve the problem by installing a harder suspension will result in disappointment.