Advice: Changing truck tyres safely

Back in the bad ol’ days of 10.00x20 ‘rag’ tyres it was quite common to get a flat tyre. Even we journos, who are widely considered to have an easy life of truck testing, had a boiler suit stowed in our road test kit, just in case we had to get ‘down and dirty’. When it did happen, it seemed to be always an inside tyre in a set of duals that went flat!

One day you’re probably going to have to jack up your truck. In an ideal situation – on a level, concrete depot driveway – it’s pretty straightforward, but on the roadside, it’s far from an easy operation.

Globally every year, thousands of people die, or are seriously injured, when jacking up vehicles. Clearly, it’s a potentially dangerous procedure.

Firstly, it’s important to distinguish between jacking up to change a flat tyre and jacking up to extricate a bogged vehicle or do maintenance underneath it. The latter operations are extremely dangerous and require hands-on training. They’re best done with air jacks or floor jacks and are not covered in this article.

A key part of jack-up preparation is a trial of your equipment in the depot. During this operation, pay particular attention to the way the jack fits to the vehicle maker’s nominated jacking point: normally under an axle flat point.

If you position the jack under the rounded section of a drive or trailer axle, relying on a shallow depression in the head of the jack shaft to locate it, the contact area is small and offers no positive location. We know from experience that’s asking for trouble. Find a flat-faced jacking point, or get a U-shaped adaptor for the head of your jack.

Some air/leaf rear suspensions have cast spring brackets at the point where the spring attaches to the axle. There’s often a hollow section in the underside of the bracket that allows access to the centre bolt that clamps the spring leaves together. If you position the jack head inside that hollow you’ll damage the centre bolt, so that’s a big no-no.

We use tyre pressure monitoring, to ensure that our tyres always operate at the right pressures for load and speed conditions.

If we do get a puncture the TPMS warns us instantly that there’s pressure drop. If it’s a slow leak we can use our on board compressor to re-inflate it and get to a tyre workshop pronto.

However, we always suggest you carry the following equipment: two jacks that are rated to suit your vehicle; two 25mm-thick compressed-plywood jacking plates; a tyre air compressor and a suitable wheel nut spanner. So, you’re well set up for jacking if you have to.

For light trucks our spanner choice is a Ufixit ratchet type that is designed to ‘crack’ an over-tight wheel nut. For heavy vehicles there are ‘nutcracker’ ratchet sockets available, or a very strong socket and a metre-long breaker bar.

Even with TPMS, a persistent fast leak may mean you have to remove a road tyre and wheel and replace it with a spare. To do that job, it’s essential to select a firm level surface, away from traffic hazards.

If you’re unlucky enough to have to do the job on the side of a road or track, safety is the primary concern. Jacking on a slope is a big no-no and can never, ever be a safe procedure.

If the tyre still has some pressure in it, the vehicle can be driven a short distance at low speed, to a safe, level spot.

If the tyre is dead flat and won’t hold enough air to lift the sidewalls off the ground, it’s probably never going to be safely used again, so manoeuvring the vehicle on it and crushing the sidewalls won’t matter.

Once in a safe, level spot it’s time to start jacking up. Firstly, though, put the vehicle in low gear and apply the parking brake.

Turn on the emergency flashers, put on your high-vis vest and set out your safety triangles in front of and behind the vehicle.

Get all the equipment you’ll need out of the vehicle and don’t let anyone go near the vehicle until the entire wheel changing process is finished. People boarding vehicles, or slamming doors or bins is a primary cause of vehicles falling off jacks!

Lower the spare wheel and roll it near the wheel you’ll be jacking up. Make sure the hub-mating face of the spare wheel is clean and free from rust or flaking paint. Any contamination will comprise wheel nut clamping effectiveness.

If the jack won’t fit in the vertical space between the jacking point and the ground plate you may have to increase ground clearance by putting some air into the flat tyre, or driving the flat tyre onto a piece of timber.

Use chocks in front of and behind tyres that won’t be raised on the jack.

Put the jack ground plate in place, under the nominated jacking point and position the jack carefully and slowly in position under the axle jacking point.

If you have two jacks, use both, close together. Having a second jack spreads the load and covers the situation where a jack jams in place. You can use the second jack to free the first.

Before using the jack, ‘break’ the wheel nut tension on all the nuts. Doing that before you jack up the vehicle means you’re not putting too much twisting action into the jacked-up wheel end. Truck nuts have up to 600Nm tension, so that’s why you need a long bar or a geared socket.

While operating the jack, observe what’s happening and be ready to stop and restart the process if the jack or the jacking plate get out of shape.

Raise the wheel until there’s just sufficient clearance to position the spare in place. Then undo the wheel nuts carefully, without causing the vehicle to move on the jack.

Inspect each stud thread as you undo the nuts and, if there’s any burring on the end of the stud, it’ll need to be filed off, or there’s a risk that the nut will be damaged when it’s forcibly unscrewed over the burred thread.

Don’t let the nuts drop into the dirt: put them in a container of some sort.

Single nut dual-wheel assemblies use only a single nut to attach both wheels, but the Japanese two-nut system uses a pair of engaged nuts: one is a normal-looking hex nut and the other is a sleeve nut with threads on the inside and outside.

The dual rear wheels on these vehicles have two-piece wheel nuts, where the outer hex nut releases the outer wheel and the inside, square nut release the inner wheel.

These trucks also have left-hand threads on their left-side studs and right-hand threads on their drivers’ sides. Fortunately, they’re stamped with ‘L’ and ‘R’, so you’ll know which is which.

To remove the inner wheel it’s necessary to take off the outer wheel, then lower vehicle once more, so that there’s tyre contact with the ground, so that you can safely ‘crack’ the square-head nuts that secure the inner wheel.

Putting the wheels back on is also a two-stage operation.

With the wheel nuts removed, take the wheel off, using the jack handle or breaker bar as a lever, to lift the wheel, rather than drag it across the wheel stud threads. An alternative removal method is to stand with knees bent, with your back towards the wheel, then reach behind you and lift the underside of the rim.

Sometimes, the wheels won’t move, even with the nuts removed, so you may need to tap around the tyres with a rubber hammer, to dislodge the grip between hub and wheel nave.

Use the jack handle or breaker bar as a lever under the spare wheel and tyre, to lift it gently onto the wheel studs. Make sure the valve stem locations for inner and outer dual wheels are correctly positioned. Then spin-on the nuts. Tighten them gently with your spanner, but only to seat the wheel on the hub. Don’t apply enough force to move the vehicle off the jack.

Now, slowly lower the jack. When the tyre is contacting the ground enough so that it won’t rotate, partially tighten the wheel studs in a staggered pattern: starting at the 12:00 position then down to 6:00, up to 10:00, down to 4:00 , across to 8:00, across to 2:00, down to 7:00, up to 1:00, down to 5:00 and up to 11:00. Then completely lower the jack and put full tension on the wheel nuts.

Pull the jack and jacking plate out from under the vehicle and check the pressure in the newly-fitted tyre. Fit the TPMS sensor cap.

After driving for a few kilometres, stop and check the wheel nut tension. When back at the depot, have the wheel nut tension confirmed with a torque wrench.

The jack that comes with your truck has one purpose: to raise the vehicle temporarily, while a wheel is changed. It’s safe, if used in accordance with instructions.

All jacks sold in Australia, including those that come with new vehicles, are required by law to comply with Australian Standard AS/NZS 2693.

Trolley jacks or floor jacks are required to comply with another standard, AS/NZS 2615.

Both specify the requirements for the design, construction, performance and labelling of jacks and are your guarantee that the product meets the required safety standards.

Jacks of any sort are not intended to support vehicles while they are being worked on: that's what safety stands are for. Safety stands are covered by AS/NZS 2538.

The following are a few basic jack safety precautions: use a jack only on a hard level surface; do not exceed the jack’s specified lifting capacity; jack only under the designated lifting areas to ensure the vehicle is not damaged and that the jack will not slip; wedge chocks under the vehicle’s tyres that remain on the ground, so that the vehicle cannot roll while being lifted.

Some people advocate using a trolley or floor jack, rather than a bottle or scissor jack. The relative strength and stability of a four-point floor jack is attractive. However, a trolley jack’s wheels need to roll as the vehicle is raised, because the lifting ram works in an arc, not directly vertically.

If the small-diameter wheels can’t roll, because the ground is uneven, soft or rocky, the vehicle may slip off the jack.

Never crawl under a vehicle that is supported only by a jack. Before going underneath, place jack stands under appropriate parts of the vehicle and lower the vehicle onto the stands. Make sure that the vehicle is securely settled before going underneath.

Use safety stands to support a vehicle. Do not use bricks, concrete blocks or wood.