Bump Steer
Bump Steer and Roll Centre Correction
When you lower a car you alter the handling characteristics due to the change in geometry. The main two problems are the introduction of bump steer and excessive body roll. Bump steer occurs when the track rods sit at an angle as they run from the steering rack to the track rod end. The angle leads to the arms shortening as the wheel travels upwards through its travel leading to the arms pulling the back of the wheel in towards the vehicle and so causing the car to change direction. This is often why lowered cars feel nervous and twitchy on bumpy roads as the wheels travel upwards independently of each other. If both wheels travel upwards at the same time then the bump steer cancels itself out but if just one wheel hits a bump then that wheel momentary toes out as it travels upwards leading the car to turn in that direction.
The Hardrace rod ends help eradicate bump steer by moving the track rod back to a horizontal position so eliminating the toe out tendencies as the wheel travels upwards over bumps. We offer two types of rod ends to deal with bump steer. Forged fixed rod ends and adjustable rose jointed. The forged ends are the most durable but being fixed you have less flexibility in perfectly the cars geometry.
Roll Centre Correction
By lowering a vehicle you lower its roll centre which effectively raises the centre of gravity. Contrary to popular opinion lowering a car actually increases body roll, not decreases. To counter this many suspension manufacturers that offer a lowering kit, either in spring or complete replacement suspension format, stiffen up the product to prevent excessive roll. This leads to an overly stiff and harsh ride. The correct way to improve a cars handling when you lower the vehicle is to reduce the relative difference of the location of the roll centre and centre of gravity. Hardrace offer ball joints specifically designed to minimise the difference between the roll centre height and centre of gravity height to reduce weight transfer and body roll. The knock on effect is that you don’t need to run suspension with a high damping rate or spring rate so improve the ride quality of the vehicle whilst improving its handling characteristics. It’s a win win situation. The Hardrace ball joints feature a longer shaft that the original. It is this longer shaft that is the crucial aspect of the roll centre correction. Other companies simply offer tall ball joints with the same length shaft with the pivot point just moved upwards. This will do nothing for roll centre correction.
Roll Centre Explained
