Suspension lifts and modifications

Suspension is one of the most popular upgrades for touring four-wheel drives. As vehicles are loaded with bull bars, winches, drawers, water, fuel and camping gear, factory suspension can sag, bottom out and lose control on rough roads. Aftermarket suspension designed for the load can restore ride height, improve control and comfort on corrugations and add some ground clearance.

But lifts, larger tyres and weight upgrades are regulated, have trade-offs in stability and handling, and can affect insurance and warranty. This guide explains the options and the rules.

Why upgrade suspension

The main reasons to upgrade suspension are carrying load, improving ride and control on rough roads, and gaining clearance. Quality shock absorbers manage heat better on long corrugated roads, where cheaper shocks can fade. Springs rated for the weight you actually carry keep the vehicle level and stop it bottoming out. A modest lift can help clear obstacles and fit larger tyres.

Start with an honest assessment of your vehicle's loaded weight and how you use it. Weigh the vehicle fully loaded at a public weighbridge. Suspension should be matched to that weight.

Types of lift

Suspension lifts use longer or stiffer springs, spacers and matching shock absorbers to raise the body and chassis. They increase clearance under the chassis, though not under the differentials, which are set by tyre size.

Body lifts raise the body relative to the chassis using spacer blocks, without changing suspension. They're less common today and may not be permitted in all states.

Tyre size increases raise the whole vehicle, including the differentials, but change gearing, speedometer accuracy, braking and stability.

The rules

After registration, modifications are regulated by state and territory transport agencies, based on the National Code of Practice for Light Vehicle Construction and Modification (VSB 14). Rules commonly cover:

• the maximum suspension lift allowed without certification;
• the maximum tyre diameter increase;
• combined limits on lift and tyre size;
• requirements for engineering certification for larger changes;
• GVM changes and their approval.

Limits and processes differ between states, and they change. Before buying a lift kit or bigger tyres, check your state transport agency's current rules, and get advice from a qualified suspension specialist. Some lifts sold as kits exceed what is allowed without certification.

GVM upgrades

Many touring vehicles end up at or over their gross vehicle mass (GVM), the maximum weight they are approved to carry. A GVM upgrade raises this limit using approved suspension and components, and it is recorded so the vehicle can legally carry more. Some upgrades are designed to be fitted before first registration, while others can be done after registration with certification; requirements differ by state. A GVM upgrade may affect the gross combination mass (GCM) and towing capacity, as well as licence requirements if the GVM rises above certain thresholds. Get advice before committing.

Trade-offs

• Stability. Raising the centre of gravity increases body roll and rollover risk, particularly with heavy roof loads.
• Handling and braking. Larger, heavier tyres increase stopping distances and change handling.
• Driveline wear. Lifts can change driveline angles, increasing wear on CV joints and uni joints.
• Fuel use. Height, weight and larger tyres increase drag and fuel use.
• Electronics. Driver assistance systems, headlight aim and stability control can be affected.
• Access. Higher vehicles are harder to get into and may not fit in car parks.

Choosing a supplier

Choose a reputable suspension specialist who asks about your vehicle's weight and use, explains what is legal in your state and provides documentation. Ask about warranty, wheel alignment and recalibration of driver-assistance systems after fitting. Keep all paperwork for registration, insurance and resale.

Insurance and warranty

Tell your insurer about suspension and tyre changes and GVM upgrades. Undisclosed modifications can lead to claims being refused. Consumer guarantees under the Australian Consumer Law continue to apply, but faults caused by aftermarket parts or poor installation may not be covered by the vehicle manufacturer.

Other common modifications

• Bull bars: must suit your vehicle, be compatible with airbags and comply with rules on design and protrusions.
• Long-range fuel tanks: add range but significant weight.
• Drawer systems and canopies: add weight; secure them properly.
• Engine tuning: may affect emissions compliance, warranty and insurance.
• Seating changes: generally need certification.

Weigh first, modify second

Many touring vehicles are overweight without their owners realising. Weigh the vehicle at a public weighbridge fully loaded, with passengers, fuel and water, and compare the results with the vehicle's GVM and axle limits. Mobile weighing services can also weigh each axle and wheel. Knowing your real weights helps you choose the right suspension and decide whether you need a GVM upgrade or simply a lighter load.

Common mistakes

• Buying the biggest lift kit without checking state rules.
• Fitting suspension that doesn't suit the real load.
• Ignoring GVM and running overweight.
• Forgetting to tell the insurer.
• Not recalibrating sensors and headlights.

Wheels and offsets

Changing wheels as well as tyres affects how far the tyre sits from the vehicle and the load on wheel bearings and steering parts. Wheels must have the correct load rating, stud pattern and centre bore for your vehicle, and wheel offset changes are often limited by state rules. Wider tracks can push tyres outside the guards, which may not be permitted. Check rules before buying.

Test and adjust after fitting

After a suspension upgrade, have a wheel alignment done and check headlight aim, as the vehicle's angle may have changed. Retighten fittings after the first few hundred kilometres as recommended by the installer. Drive gently at first to get used to the vehicle's new handling, especially with a full load.

Load-carrying alternatives

If extra weight is the main problem, a lighter load may be better than heavier suspension. Review what you carry, choose lighter drawers and racks, carry water and fuel only as needed for the trip, or consider a trailer, which moves weight off the vehicle within towing limits.

Key points

Upgrade suspension to suit your loaded weight and use, check your state's rules based on VSB 14 before lifting or fitting bigger tyres, get certification where required, consider a GVM upgrade if you're overweight, understand the stability trade-offs and tell your insurer about every change.