Roll vs. Lean
Vehicle body lean is a trait of soft suspension setup which is true of almost all passenger vehicles. Vehicle body roll is a distinct trait of a stiff suspension setup however, the sensation to the driver of either trait is similar. Both of these distinct sensations can be, and are often, easily interchanged in diagnosing handling related issues. It is not uncommon for anti-roll bars to be the default recommendation for either. The tables below offer examples of common handling traits and the causes of these, which we hope you find useful in diagnosing handling related issues.
There is a difference in the cause and therefore the resolution of these traits, both explained below.
- - a vehicle body roll will visually look flatter during the cornering phase and indicates a stiff suspension setup.
- - a vehicle body lean will visually show excessive body movement on one side and indicates a soft suspension setup.
Side View of Vehicle Body Roll
Side View of Vehicle Body Lean
5 KEY THINGS ABOUT LOAD TRANSFER
- 'Load' transfer is the correct definition in relation to vehicle suspension and NOT 'weight' transfer as commonly noted.
- Softer springs on a vehicle does NOT increase the load transfer to be managed.
- Wider track on an axle reduces load transfer FROM that axle.
- Lower centre of gravity (CoG) reduces overall load transfer between axles or on same axle.
- Increasing the spring rate reduces body lean however that does NOT prevent load transfer between axles or per side on same axle.
5 KEY THINGS ABOUT RIDE HEIGHT
- Raising ride height on one corner of a vehicle marginally drops ride height diagonally on the opposing axle.
- Equally, dropping ride height raises ride height diagonally on the opposing axle.
- Lowering the ride height can reduce body roll and pitch.
- When the ride height on the front axle is higher than the rear axle, that is referred to as reverse rake.
- When the ride height on the rear axle is higher than the front axle, that is referred to as positive rake.
5 KEY THINGS ABOUT UNDERSTEER & OVERSTEER
- When the front of the vehicle or steered axle will not turn in to a corner that is referred to as understeer.
- When the rear of the vehicle is sliding sideways left or right, that is referred to as oversteer.
- Oversteer can be induced with aggressive throttle application when steering is turned full lock either way.
- Excessively stiffening of the front axle with high rate springs or anti-roll bars can cause understeer.
- Understeer is considered safer for a passenger road vehicle compared to oversteer especially on wet roads.
5 KEY TYRE MAINTENANCE TASKS
- Inflate or deflate tyre pressures to recommendation when cold or typically first thing in the morning.
- Visually check for tyre wear or embedded nail every 1,000 miles on the inside and outside facing.
- Rotate tyres between axles or on same axles (if sizes are staggered) every 3,000 to 5,000 miles.
- Check tyre pressures and inflate/deflate to the correct manufacturer recommendation weekly.
- Vehicles being left standing for 30 days+ should be supported on 4 sturdy jacks to avoid tyre flat spot.
5 KEY CHECKS BEFORE A TRACK EVENT
- Check there are no loose items in, outside or underneath the vehicle.
- Check cold tyre pressures all round for slow puncture on the morning of the event before setting out.
- Check/tighten all wheel bolts on the morning before setting out, on each visit to the pit lane and at the end of the track event.
- Check rear brake lights and indictors all function a day before the event, resolve any issue before the event.
- Check oils and fluids are all topped up a day before the event and again on the morning before the event.
5 KEY THINGS ABOUT ROAD GOING VEHICLE SUSPENSION
- Main duty of springs on a vehicle is to support weight of the vehicle.
- Vehicle shock absorbers stops the springs from oscillating too much.
- Ride comfort can be improved by simply swapping out springs and NOT Shock Absorbers.
- The vehicle suspension spring is governed by 3 factors - rate; load; height - however any 2 affects the 3rd.
- A suspension bump stop serves to protect the shock absorber from damage from excessive travel and also acts as a load bearing tool designed to be engaged either full time, part time or not at all.
Common Vehicle Handling Causes and Effects
We have put together information that can help drivers and mechanics accurately link the behaviour or 'feel' of a vehicle to specific components of the suspension systems. The information can be used to determine the effects of changes being considered and the desired outcome or likely unwanted side-effects.
|- Harsh and choppy ride|
|- Car cannot put power down on corner exit due to excessive wheel-spin|
|Front and rear axle springs are too stiff with little or no suspension travel|
|- Vehicle initially points in well however the front easily loses traction over bumps|
|- Front tyres lock up while braking over bumps|
|Springs are too stiff with little or no suspension travel on front axle|
|- Excessive wheel-spin immediately on application of power|
|- Rear of the car has a tendency to want to slide around especially on wet roads|
|Springs are too stiff with little or no suspension travel on the rear axle|
|- Floating ride leading to pitch and roll|
|- Sloppy and inconsistent response to steering input|
|Front and rear axle springs are too soft|
|- Car feels bouncy over bumps and slow to a settle|
|- Excessive squat on acceleration accompanied|
|Relatively soft spring rate on rear axle|
CATEGORY: ANTI-ROLL BARS
|- Lack of feedback and a tendency to exaggerate steering input|
|- Lack of grip in low speed cornering phase with excessive wheel spin|
|Front and rear axle anti-roll bars are set too stiff|
|- Tendency to push forward in cornering phase, commonly referred to as understeer|
|Front axle anti-roll bar set too stiff|
|- Can cause corner entry oversteer in the extreme of cases on wet roads|
|- Inability to put down power causing oversteer due to inside wheel-spin|
|Rear axle anti-roll bar set too stiff|
|- Lack of immediate response to steering input|
|- Slower left to right directional change|
|Front and rear axle anti-roll bar set too soft|
|- Where the springs are appropriately specified there are no adverse effect|
|- Traction is improved particularly on wet or low grip surface|
|Rear axle anti-roll bar set too soft|
|- Car darts over bumps, under heavy braking and and is generally unstable|
|- Car wanders under heavy braking and may be unstable in a straight line|
|Too much Front TOE-IN especially on front wheel drive cars|
|- Rear feels light and unstable during corner entry|
|- Car slides through corners rather than rolling freely|
|Too much Rear TOE-IN|