Modify tyres and suspension legally Part 2

Muddy PB Challenger

Modify tyres and suspension legally

In a previous post, I discussed my experience when trying to modify tyres and suspension legally to raise the height of my car by less than 50mm… As you’ll read, I didn’t have much joy.

It’s important to make sure you do keep within the legal boundaries of modifications. If you don’t then you may end up with a yellow sticker, but also your insurance company may have a way out of making payments should anything terrible happen. Although you may find some insurance companies say that they’ll insure your 4×4 modifications, call them up and ask them if they’ll insure something that’s effectively illegal. I’m sure you already know what the answer will be.

My vehicle is fitted with Electronic Stability Control. Most cars have it now days but it may be called something slightly different (perhaps Active Stability Control or ASC). So this post and the previous one focus on modifying the height of a vehicle that is fitted with this technology.

So lets get to it…

VSB14 and the NCOP

VSB stands for Vehicle Standards Bulletin. It’s basically a design guide to make sure all vehicles in Australia comply to a bunch of safety regulations. These regulations are outlined in NCOPs.

NCOP is the National Code of Practice. Each NCOP relates to a particular item.

We’re interested in VSB14 and NCOP11 – Section LS Suspension and Steering V2.1 last edited on 15 November 2015.

Since my last post there have been some changes that relate to vehicles fitted with ASC. The previous version of this document basically said that if your vehicle has ASC, then to raise the height of your vehicle in any way, you’d need to ensure that there is no impact on the ASC by one of the below methods:

  • Get vehicle manufacturer signoff – Never going to happen… Trust me. I tried…
  • Modify the ASC code to allow for the change – Yeah right…
  • Prove it through testing – You can read my previous post to see how much luck I had there.

Now, however, the NCOP clearly states what you need to comply with, and what you need to do if you don’t. And there are 3 different stages. Well 4, if you count lowering your car… Note that raising your vehicle height includes all methods of raising the height. So it’s a total height increase taking into account suspension, body lifts, tyre diameter, spacers… everything.

Raising your car by more than 150mm

The short of it is “Don’t do it”. It’s not legal in any way.

Raising your car by more than 50mm but no more than 150mm

You can do this, but you need to pass a lane change test.

Raising your car by 50mm or less

You can do this without any kind of certification. It’s legal. Go ahead and do it. Have fun. Enjoy the ride.

Lowering your car by any amount

Go for it, but you have to comply with other things. But who really wants to lower their 4×4 anyway?

Now this is my interpretation of the rules so please read the NCOP and make your own judgement. Don’t just trust the stuff you read on some random page on the Internet…

Mass Air Flow – Cleaning the MAF Sensor

MAF Sensor - PB Challenger

I’d been having problems with oil leaking from the turbo in my PB Challenger and had also noticed a significant decrease in fuel economy. This was coupled with an increase in black smoke blowing from my exhaust under moderate to light loads. In a previous post, you can read all about my turbo replacement, but I’d also been told that cleaning the MAF sensor might also make some difference in regards to fuel economy and black smoke.

What’s a MAF Sensor?

MAF stands for Mass Air Flow. So the sensor sits between your air filter and your turbo and detects the temperature, density and quantity of air flowing into the engine. The computer then calculates the correct balance of fuel and air to achieve maximum efficiency. However because the MAF sensor sits in the air-flow, and your air filter isn’t perfect, after a time it gets dirty. Once it’s dirty it can give inaccurate readings to the computer.

MAF Sensor - PB Challenger

What you’ll notice if you have a dirty MAF sensor is a decrease in fuel efficiency and more black smoke in your exhaust.

Luckily cleaning it is very simple. But you do need to take care.

Locating and cleaning the MAF Sensor

The sensor itself is very easy to locate. Open the bonnet and locate the turbo and the air filter. Between the two is a fat pipe that has a plug with electric cables running to it. It looks like this:

MAF Sensor Location - PB Challenger

 

Removing it is quite simple. There are a couple of screws that you remove. Then pull it out. You can unplug the electric cables as well.

Take great care once this is removed. You don’t want to drop anything down the hole that is left behind. There is nothing between the MAF Sensor and the turbo. Anything you drop in there will go straight into the turbo and the engine. They’re not designed for handling screws and nuts and screw drivers so keep those kinds of things out.

Mine looked like this. Take a look at the tiny bulb thing. That’s the temperature sensor. It’s completely covered in dust, as is the whole device.

MAF Sensor - PB Challenger

 

Cleaning the MAF Sensor is very easy. But you need to use the correct stuff. I went to Supercheap Autos and purchased some CRC Mass Air Flow Sensor Cleaner.

Following the instructions on this, I was able to clean the MAF Sensor quickly and easily. Give it a good squirt all over, inside and out… Afterwards it looked like this:

MAF Sensor - PB Challenger

Take a look at that little bulb thing. That’s more what it’s supposed to look like! Semi-see-through.

What’s the difference?

So the big question is, “What difference did it make?” Well before I did this, I had people behind me commenting on how much smoke i was blowing under only very minor load. Like going up a hill, or taking off from lights. My fuel efficiency was down to about 450mks on a full tank of fuel (as reported on the dash). And towing our camper trailer seemed much harder than I thought it should be.

After the turbo replacement AND the MAF Sensor clean, towning the camper is much better, I have almost no black smoke even under reasonable load and last time I filled my tank it said I had 620kms in it. Most of our driving is around the city…

So did it make a difference? Yeah it really did! What made the most difference? Unfortunately I don’t know because I cleaned the MAF Sensor pretty much the same day they replaced the turbo.

But my neighbour borrowed my MAF Sensor cleaner to clean the one on his Navara and he said that it made the world of difference. We’ll be cleaning our MAF sensors regularly from now on.

Would I recommend that you do it yourself? Only if you’re a handy person. It’s not a difficult job but with any mechanical activity on your car, you do it at your own risk.

4wd Tips and Tricks – Steep Terrain

Billy Goat Ridge. Bendleby Ranges, Southern Flinders

4wd Tips and Tricks – Steep Terrain

Driving your 4wd on steep hills is one of the most exciting and potentially dangerous things you can do in your 4×4. Exciting because it’s adventurous. Dangerous because there is a real risk of rolling your vehicle. And on a steep hill, you could keep on rolling… All the way down…

Driving your 4wd up steep hills

When driving up steep hills, your first goal should be to retain traction. As soon as you loose traction, you lose forward momentum and risk not making it.   There are a number of things to remember

Billy Goat Ridge. Bendleby Ranges, Southern Flinders
Billy Goat Ridge. Bendleby Ranges, Southern Flinders
  • Tyre pressure – You’ll need as much traction as possible. To help achieve this, reduce tyre pressure. Read more here: 4wd Tips and Tricks – Tyre Pressure.
  • Gear Ratio – Select 4wd Low Range and a low gear to ensure adequate power to drive you to the top.
  • Momentum – That depends on the terrain. Sand you’ll probably need more momentum than harder ground. Try not to overdo it because you may damage the track and your 4wd. Remember, maintain traction.
  • Gear Selection – This will depend on how much momentum you feel you need to get up the hill.
  • Walk it – If you’re not familiar with the track, or if it may have changed since you were last there, then walk the track. If you can’t walk it, it’s a fair bet that you won’t be able to drive it.
  • Plan your line – Decide which line you’re going to drive, but the best traction will probably be in the existing ruts created by other drivers.
  • Stall Recovery Technique – Before you start, make sure you know what to do if you don’t make it.
  • Drive it – Take it easy and steady. Drive carefully and maintain traction.

How to recover if you don’t make it

If you don’t make it up, then it’s very important to know how to get back down. It doesn’t sound hard, but there are some pitfalls to avoid.

The pitfalls

The biggest pitfall is the uncontrolled descent. The automatic reaction when you are about to stall on a steep hill is to prevent stalling by putting your foot on the clutch. What this means is that you no longer have any forward drive, but worst of all, you have nothing preventing you from rolling backward. And on a steep hill, you’ll roll backwards very quickly.

Billy Goat Ridge. Bendleby Ranges, Southern Flinders
Billy Goat Ridge. Bendleby Ranges, Southern Flinders

Once you’re rolling backwards, your next automatic reaction will be to hit the brakes. On a steep hill, this won’t stop you. The momentum of your vehicle will keep it moving backwards, but with no wheel rotation, you will loose the ability to steer your vehicle.

To avoid these very dangerous pitfalls, you need to know the Stall Recovery Technique as described below.

Stall Recovery Technique

The Stall Recovery Technique is the strategy used to reverse down from steep hill climbs.

Manual Vehicles

Stall recovery steps in a manual transmission vehicle.

  1. Allow the vehicle to stall. Do not touch the clutch. This is harder than you think. It’s difficult not to automatically put your foot on the clutch.
  2. As you stall, put your foot on the foot brake.
  3. Engage the handbrake. You now have 3 things preventing you from going backwards.
    1. You’re still in gear,
    2. Your foot brake,
    3. Your hand brake.
  4. If you can, get someone else to double check the track and guide you down. Don’t get out of your car because that’ll mean releasing the foot brake. Your handbrake may fail and the engine can turn over under compression. But it’s handy to have some help in getting back down.
  5. Put your foot on the clutch.
  6. Put the vehicle into reverse gear and engage low range if you haven’t already.
  7. Take your foot off the clutch.
  8. With your foot brake on, release the handbrake.
  9. Carefully and slowly remove your foot brake. With reverse gear engaged, but the engine turned off, you’ll remain still.
  10. Turn the key to start the engine with your foot off the clutch.

Now you’re on your way. Try not to touch the accelerator or the brake. If the hill is steep enough, you may need to lightly touch the brakes. This is risky though. You don’t want to lock your wheels and start to slide.

Billy Goat Ridge, Bendleby Ranges, South Australia. Photo by Mauchit

Automatic Vehicles

Stall Recovery is a little different in automatic transmission vehicles because, as a general rule, they don’t stall. However, on occasion they do. So if you decide you’re not going to make it up the hill, you still need to know how to retain control and back out safely.

  1. Put your foot on the brake.
  2. Engage your handbrake.
  3. If your engine has stalled, put it into Park. At this point, you have 3 things preventing you from rolling.
    1. You’re still in drive or park (you lose this when you go to Reverse),
    2. Your foot brake,
    3. Your hand brake.
  4. If you can, get someone else to double check the track and guide you down. Don’t get out of your car because that’ll mean releasing the foot brake. Your handbrake may fail and the engine can turn over under compression. But it’s handy to have some help in getting back down.
  5. If your engine has stalled then you need to start it up if you can.
  6. Occasional when you shift from a forward gear to a reverse gear, your vehicle rocks slightly backwards. This can be enough to start your vehicle sliding.
    1. Put your vehicle into Neutral first.
    2. Engage Low Range if you haven’t already.
    3. Then move your vehicle into Reverse.
  7. With your foot brake on, release the handbrake.
  8. Carefully and slowly remove your foot brake. You’ll start your descent.

Now you’re on your way. Do not to touch the accelerator. If the hill is steep enough, you may need to lightly touch the brakes. This is risky though. You don’t want to lock up your wheels and lose control.

Have another go

Once you’re down, change your strategy. If you didn’t make it once, you probably won’t make it a second time unless you try something different. Try reducing tyre pressure, pick a new line, lock your diffs if you can, and have another go. Or take the chicken track.

Driving your 4wd down steep hills

Driving down steep hills in your four wheel drive is much simpler because you’ve got gravity on your side. This isn’t always a good thing if the track is too steep. As with driving up, it’s important to retain traction.

The steps to take to safely descend a steep hill in your 4×4 are:

  • Walk the track – If you can’t walk it then you won’t be able to drive it
  • Pick your line – Decide on the best path. Usually the line that’ll give you the best traction will be right down the middle of the existing ruts created by other drivers.
  • Increase traction – Reducing tyre pressure increases the surface area of your tyre in contact with the track, increasing your traction.
  • Gear Ratio – Use low range. If you don’t, your car will run away from you and it’ll get scary.
  • Gear Selection – Use first gear. A combination of first gear and low range will keep you in control.
  • Backout plan – If it gets too steep and scary then you’ll need to have a backout plan before you head down. Remember that getting out will probably mean reversing back up a steep hill.

How to recover if you don’t make it

If you decide you’re not going to make it, then you’ll probably need to reverse up a steep hill. But first you need to stop going down.

Assuming you’ve followed the steps outlined above, you probably won’t be travelling very quickly. To stop yourself, apply the brakes gently until you come to a stop. Don’t hit the brakes hard or you’ll lock up your wheels and risk losing control. Remember that just because your wheels have stopped, it doesn’t mean your vehicle will.

Once you’ve come to a complete halt, put your handbrake on, then engage reverse.

From here it’ll be a simple matter of reversing up the way you’ve come.

Driving across steep hills

Simple… Don’t to it. Driving sideways across steep hills vastly increases the chances of losing control of your vehicle; as soon as you lose traction, your vehicle will slide sideways. You’ll also run a very real risk of rolling your vehicle all the way to the bottom. And I don’t mean on the tyres… So DO NOT drive sideways across steep hills.

Other Information

This information is provided for interest only. Although every attempt to ensure accuracy has been taken, please don’t rely on it when you’re out there. Everybody’s car and skill leves are different so what works for one may not work for another. Please make sure that you know what you’re doing. I would always recommend joining a 4wd club and/or undertaking some training before heading out into the wilderness. I would also always recommend traveling with at least one other vehicle.

4wd Tips and Tricks – Sand Driving

4wd Tips and Tricks - Sand Driving

4wd Tips and Tricks – Sand Driving

The tips and tricks outlined below are applicable to driving in any sand, be it on the beach, in sand dunes, in the desert or in the forrest. Anywhere you come across soft sand, these techniques will be applicable.   If you are driving on sand dunes, then please read the 4wd Tips and Tricks – Driving on Steep Terrain article as well. In particular, it is worth mentioning again, that you should NEVER drive across a steep hill, especially sand dunes. Doing so can have disastrous consequences. There is a serious and very real risk of rolling your vehicle all the way down to the bottom of the hill.

Elements of Sand Driving

There are two elements to driving your four wheel drive on soft sand. These are:

  1. Tyre Pressure
  2. Momentum

Applying these elements do your driving technique will result in your vehicle ‘floating’ on the sand, decreasing your chances of becoming bogged. Naturally there is no guarantee that you won’t bury yourself to the axles, but your chance of success is increased if you pay attention to these elements.

Tyre Pressure

Reducing your tyre pressure will spread the weight of your vehicle across a greater surface area, and increases the surface area of the tyre in contact with the ground and achieves two objectives: 1. Increases traction 2. Prevents the tyres from sinking into the sand quite as much.

4wd Tips and Tricks - Sand Driving
Jeff-WA heading up a sand dune

There are many schools of thought on how much you should reduce your tyre pressure when driving on soft sand, but a guide would be to reduce your tyre pressure to half that of your normal road driving. If you find your engine struggling then reduce tyre pressure some more. You can try reducing in 4psi increments until you’re satisfied. Finding the right pressure for your vehicle and the current conditions can be a lot of trial and error. For more information, please read the 4wd Tips and Trips – Tyre Pressure article.

Momentum

Driving on soft sand can be compared to a speed boat on water. When the boat is travelling slowly, it sinks into the water a little and the engine is required to work harder to maintain forward momentum. As soon as the boat speeds up it starts to plane along on top of the water. The engine requires much less effort to push the boat along and the boat is able to quickly skim along the surface of the water.   Similarly, driving slowly on soft sand will allow the tyres to sink into the sand much more than driving more quickly. When the tyres sink in a little, the engine must work much harder to maintain forward movement.   As you increase your speed, your tyres will float on top of the soft sand much more, and the effort required to maintain your forward momentum will be greatly reduced.

Use low range initially. If you start to get bogged, low range will provide you with the power you need to drive out, but will also allow you adequate speed to keep you on top of the sand. If you decide that the beach is hard enough then you can change to high range.   CAUTION: Do not overdo your speed. Driving on sand is nothing like driving on the road and driving quickly greatly increases the chance of serious accident.

Bogged

If you regularly drive on the sand, then eventually you’ll get bogged. Accept this fact and prepare for it and your day will be much more enjoyable.

When you do get bogged in soft sand there are a number of techniques to getting back out.

  • Firstly, it’s important to realise early that you are bogged. There is no point in spinning your wheels. This just digs you in further and makes any recovery effort more difficult.
  • Don’t panic! The vast majority of the time, if your car stays bogged for a while then the only consequence is that you’re late to your campsite. So stay calm and take your time to think it though.
  • Reduce your tyre pressure even more than you already have. Remember that the more you reduce your tyre pressure the more your vehicle will ‘float’ on the sand.
  • Try to reverse out. Often the tracks you used to drive in are solid enough for you to drive out on. Then you can have another go or take a different route.
  • Slowly drive backwards and forwards over the same track. This compacts the sand and hopefully allows you to drive out.
  • If these tips don’t get you out then get your shovel out and start digging. Choose which direction you want to drive out and then dig out the sand in that direction. Don’t forget that you’ll need to clear the sand from underneath your axles and differentials as well. And if you’re bogged enough then you’ll also need to clear the sand away from your undercarriage as well.
  • Make a track for your wheels. You could try lining the track with dry seaweed (wet seaweed can be slippery), sticks, leaves etc. Anything to gain some traction.
  • Also, try something like Max Tracks. Static methods of recovery and those that don’t use other vehicles are much safer.
  • If these fail then get out your snatch strap if you have a travelling companion. Keep in mind that you don’t need to tear the car in half in order to pull someone out of the sand. Often a gentle ‘tow’ is enough.
  • Still bogged? Do you have a winch? If not then don’t give up, just do it all over again, but try harder.

More sand driving tips

4wd Tips and Tricks - Sand Driving
It wasn’t really that steep… was it?

Now that we’ve covered the fundamentals of driving on sand, below are some more tips and techniques for driving your four wheel drive in the sand.

Be aware of steep drop-offs on beaches. These are caused by wave action eroding the beach sand and forming small cliffs. Driving too close to the edge will cause these cut-aways to collapse, resulting in your vehicle rolling and probably becoming very wet.

Bright sunshine will make features on the beach harder to see. With the glare off the white sand in your eyes, it’s very easy to not see holes, cut-aways, erosion etc. Driving your vehicle into a sand hole can bring your day to a very sudden and complete stop.

Don’t get caught too close to the water. If you do a quick google search you’ll find any number of photos of 4wd vehicles being destroyed by pounding surf. Or buried to the roof after a high tide.

Don’t turn sharply. With reduced tyre pressure, turning sharply will increase the chances of your tyre separating from the bead of your rim. Tyres that separate from the bead deflate very rapidly.

Not getting bogged is much easier than digging yourself out of a bog. Err on the side of caution in all aspects of sand driving.

What to take with you

  • Long handled shovel
  • Snatch Straps
  • 4wd acceptable recovery points (factory tow points are often not strong enough).
  • Shackles to connect your snatch straps to your recovery points.
  • A tree protector or bridle. This can be used to disburse the load across multiple recovery points.
  • MaxTrax or equivalent.
  • A sand flag so that people can more easily spot you from over the top of a sand dune.
  • Tyre deflator to let your tyres down before you hit the sand
  • Compressor to re-inflate your tyres
  • UHF Radio so you can ask someone else for help

4wd Tips and Tricks – Water Crossings

4wd Tips and Tricks - Water Crossings

4wd Tips and Tricks – Water Crossings

These 4wd tips and tricks are provided for guidance only. I strongly recommends that you undergo 4wd training with a qualified and recognised training school. I also suggest that you join one of your local 4wd clubs to further your experience.

When you’re driving your 4×4 off the beaten track it’s inevitable that eventually you’ll need to cross a waterway where no bridge exists. Water crossings in your 4×4 can be an exciting and spectacular part of any 4wd experience. However it can be dangerous and result in damage to your vehicle, yourself and others. Not to mention damaging your pride if you get it wrong. Remember to keep it slow and steady.

Water crossing Techniques

It’s important to get water crossings right if you don’t want to risk serious damage to yourself and/or your vehicle.

4wd Tip and Tricks - Water Crossings
Lykey playing in the pool

Things to consider

There are a number of things to keep in mind when considering a water crossing.

  • It’s important to remember that if the water is moving and the level is higher than your undercarriage then it’ll start to push against your bodywork. As the surface area that the water has to push against increases significantly, there is a much greater risk of being washed away.
  • Know the safe depth for your vehicle:
    • Know how deep your vehicle will allow you to go before it start to float. Some cars float more easily than others.
    • Know where your air intake is located. You don’t want your engine to suck water into it, particularly if it’s a diesel engine. Install a snorkel.
  • Consider attaching a tarpaulin to the front of your vehicle. This assists in keeping water out of your engine bay.
  • If the crossing is deep then wind down your windows before you enter the water. Particularly in a vehicle with electric windows. In an emergency, this will be the easiest and quickest exit.
  • Spray your under-bonnet electrics with a water repellent (such as WD-40).
  • Consider loosening the fan belt if your vehicle does not have a viscous coupling type fan. This prevents your fan from becoming a propeller and potentially damaging your radiator. If your fan does have a viscous coupling, then simply tie a piece of string to a solid piece of the vehicle and loop the other end around the fan blade to prevent it from turning. When you exit the water, simply slip the loop off the fan blade and the fan will begin spinning again.
    • To determine if you have a viscous coupling fan, turn your engine off and try to turn the fan with your hand. If it turns then it has a viscous coupling.

Before you cross

  • Make sure it’s safe to do so (no crocodiles, water is not flowing too fast to walk in), then walk the crossing first. Sure, you’ll get wet, but it’s better than getting stuck or floating away in your 4wd. Even the bottom of a very shallow crossing can be sticky mud.
  • Don’t cross with a hot engine, transmission and diffs. It’s important to allow it to cool. The sudden cooling and contraction of metals can cause serious damage. Your vehicle can cool down while you are checking the crossing.
  • Mark any holes or obstacles with a stick. Plan where to a going to drive and mark your path with sticks.
  • Select the right gear for the crossing. This allows you to maintain a steady speed. Many experienced 4w drivers use 2nd gear low range, but this will depend on the exact situation you find yourself in.
  • Watch someone else do it first if you can.
  • Attach recovery straps to your recovery points before you enter the water otherwise you may need your scuba gear. If you’re recovery gear is just a hook then try to work out some way of ensuring that they stay attached. For example, cable tie them to the recovery point. Also ensure that your recovery straps are not going to be dragged under your wheels as you try to cross. Tie them tightly so that there is tension between your recover points and your roof racks for example. Pre-attaching recovery gear allows for quick recoveries.
  • Select the correct tyre pressure before you enter the water. Remember that the opposite bank could be sandy, muddy, rocky, steep… If in doubt about the safety of the crossing, DON’T DO IT. Better safe than sorry.

While crossing

4wd Tips and Tricks - Water Crossings
Jeff-WA Getting wet in Margaret River, WA

During the water crossing:

  • Enter the water slowly. Less than walking pace. Once the front bottom of the vehicle has contacted the water then accelerate gently. Maintain a steady speed that allows a bow wave to form in front of your vehicle. This assists with keeping water out of your engine bay. Following the bow wave also means your vehicle does not have to work as hard to maintain momentum and traction.
  • Follow your line. You planned your crossing so try to stick to the plan.
  • Remember that the other bank may be steep and muddy. Ensure you’ve selected the correct tyre pressure before you enter the water.
  • Do not change gears in the water. This assists with maintaining a steady speed and also, more importantly, keeps water from entering between your clutch plates causing them to slip.

After you’ve crossed

When you are out, it’s important to:

  • If you can, stop at the opposite bank to let the water drain from your vehicle. Don’t do this if you need momentum to get up the opposite bank, or if the crossing is shallow. This achieves a number of things:    Carrying excess water makes your vehicle heavier which means it can be harder to climb the bank. Dumping water on the exit track can make is wet, muddy and slippery for the people following you.
  • Dry your brakes out by ‘squeezing’ them. A couple of solid presses on your brake pedal is a start.

So you didn’t make it

If you don’t cross successfully then you’ll need to be recovered. If the water is deep enough then expect wet seats and carpets. If your engine is in danger of becoming waterlogged then turn your engine off. Otherwise leave your engine running. The exhaust exiting your exhaust pipe will prevent water from entering your engine from that direction.

When recovering your vehicle it’s 4×4 etiquette for the owner of the stranded vehicle to get the wettest. Don’t sit in your car and expect others to get wet for you.

Before exiting the vehicle, ensure that it is safe to do so. If the water is flowing too fast for you to stand in, then stay with your vehicle (if your vehicle is not being swept away). If there are crocodiles around then stay in your vehicle or make yourself comfortable on the roof racks and wait for rescue.

Video

S1mon with his nissan submarine

4wd Tips and Tricks – Tyre Pressure

TyrePressure - Sand Mountains - Harry Lewellyn - (Extract from book - SHIFTING into 4WD)

4wd tips and tricks – Tyre Pressures

When four wheel driving, changing the tyre pressure is one of the best 4wd tips and tricks you’ll learn. It is the most effective ways of changing the performance of your 4wd in almost all off-road situations. The only point of contact between your 4wd and the earth is its tyres. So it makes sense that modifying the tyres in some way has a huge impact on the performance of your 4wd when you’re off road. The cheapest and simplest modification you can perform on your tyre is to change the tyre pressure. And in almost all off-road situations, this means reducing your tyre pressure.

It’s important to mention, however, that not re-inflating your tyres when you get back onto the black-top is dangerous. You could risk your tyres, your 4wd, and even your and others lives. Driving with reduced tyre pressure at highway speeds for long periods of time will cause tyre failure. With reduced tyre pressure, the flexing in the rubber will cause heat build-up. This weakens the rubber causing tyre blow-outs. Also, high speed turns with reduced tyre pressure can cause your tyre to separate from the wheel rim, increasing the chance of vehicle rollover

Reducing tyre pressure is also better for the environment. With reduced tyre pressure, your four wheel drive will sit on top of the surface rather than digging in. When vehicles dig in, they cause damage to the tracks. Other vehicles then try to drive around this damage and the track becomes ever increasingly wider, encroaching into the surrounding environment.

Tyre pressure in soft sand

TyrePressure - Sand Mountains - Harry Lewellyn - (Extract from book - SHIFTING into 4WD)
Tyre Pressure – Tiny sand mountains

When driving on soft sand, the forward motion of your four wheel drive will create small sand mounds in front of each tyre. Although the ground may appear to be flat, as shown in the image on the left, your vehicle is constantly trying to climb a very steep slope. The only part of the terrain that is important to your vehicle is the part that is in contact with your tyres.

As you move forward, your vehicle is constantly forced to try to lift its entire weight up and over these tiny hills, however with harder tyres, rather than climbing these mountains, the sand is pushed in front of your tyres, and your 4wd effectively slides back down again. This constant effort and wheel spinning can cause your tyres to dig in further until you become bogged.

Reducing your tyre pressure increases your vehicles ‘foot print’. This increased surface area spreads the weight of your car over a larger area and helps to prevent your four wheel drive from sinking into the soft sand, thereby helping to prevent the build-up of these mountains and enabling your vehicle to maintain forward momentum with significantly less effort. And also greatly reduces the chances of you becoming bogged.

It’s important to note that this strategy can, and should be applied to any tyre in contact with soft sand, including non-powered wheels, or wheels on a camper trailer. Leaving the tyres on your camper trailer fully inflated will mean that the tiny sand mountains will be created, forcing your 4×4 to tow the trailer up a never ending sand mountain.

Reduced tyre pressure in other terrain

TyrePressure - Profile - Harry Lewellyn - (Extract from book - SHIFTING into 4WD)
Tyre Pressure – Profile

There are a number of advantages gained by reducing your tyre pressure in terrain other than soft sand. The three main advantages are:

  • Larger footprint – this allows less sink-ability in soft terrain, and increases the surface area in contact with the ground, increasing traction. At very low pressures, the size of the contact patches can increase as much as 250%.
  • More comfortable ride – Over rough and corrugated tracks, decreasing your tyre pressure softens the tyre. This then absorbs a significant amount vibration that would normally be transferred through to the suspension.
  • Shape-ability – Increases the tyre’s ability to shape itself around obstacles, rather than have to climb over them. A softer tyre shapes itself around objects, where a harder tyre will need to drive over the top. This ability to conform to the terrain reduces the chance of puncturing the tyre, but also greatly improves traction. The more of the tyre in contact with the ground, the better grip the tyre will achieve.

However reducing the tyre pressure does decrease clearance under all parts of the vehicle, including the axles and diffs.

How low should you go for off-road driving?

Let me answer this question with another… How long, exactly, is a piece of string? The school of thought on how much you should reduce your tyre pressure is very varied. Asking 10 different 4wd specialists how low to reduce your tyre pressure will produce 10 different answers. But there are many factors contributing to how low you should go. These include:

  • Sidewall stiffness
  • Tire aspect ratio (vs.wheel diameter)
  • Driving speed
  • Trail surface/softness
  • Vehicle Weight

Sidewall Stiffness

If you’re tyres have stiff sidewalls, then the sidewalls will provide support and will prevent the tyre from flattening out. Reduce your tyre pressure more to allow the tyre footprint to increase.

Tyres with more flexible sidewalls will allow the tyre to balloon sooner, allowing a larger footprint to be created at higher pressures.

Tyre aspect ratio

The lower the profile of your tyre, the less you’ll be able to reduce the pressure without risking damage to the rim.

Driving speed

Driving quickly with reduced tyre pressure will cause damage to your tyres. The constant flexing of the tyre causes heat build-up and eventually will cause catastrophic failure of your tyre. There is also an increased possibility of the tyre separating from the rim in high speed turns.

Either of these events can cause you to lose control of your vehicle.

So if you intend to drive quickly then increase your tyre pressure without exceeding the recommended maximum.

Trail surface/softness

On smooth surfaces, tyre pressure may not need to be reduced at all. And in fact perhaps should not be reduced. With smoother surfaces, the tendency may be to travel faster. Travelling at higher speeds with lower pressure tyres can be dangerous.

On more rugged surfaces or on steeper terrain a lower tyre pressure may be required. Remember, lowering your tyre pressure will increase the footprint of your tyre and therefore increase traction. On harder surfaces, however, the lower the tyre pressure, the greater chance of rim damage occurring. Harder tyres offer more protection to the wheel rims, but provide less traction.

On corrugated roads, reducing your tyre pressure will assist in the absorption of the corrugations, making your ride significantly more comfortable.

When it comes to driving on sand and mud, the softer it gets the lower you will probably need to go. It’s all about increasing your footprint to keep your vehicle sitting on top of the surface rather than digging in. Just keep in mind that lower tyre pressures increase the risk of popping your tyre off the rim.

Vehicle Weight

Lighter vehicles, or less loaded vehicles, will need a lower tyre pressure to achieve the same ‘balooning’ effect.

Trailers

Remember to reduce the tyre pressure of whatever you’re towing as well. If you’ve got a camper trailer hitched behind you when you’re driving on soft sand, and you don’t reduce it’s tyre pressure, then your car will be trying to drag the trailer up those constantly moving hills.

As a general rule, reduce the pressure in your trailer tyres to the same as what you’ve reduced your vehicle tyre pressure to.
Alternatively, before you leave on your trip, reduce your vehicle tyre pressure to what you expect to be using on the soft tracks. Once you have done that, measure the footprint length that you have achieved. Then reduce your trailer tyre pressure until you achieve that same footprint with your trailer tyres.

So how low then!

As a general rule, the looser the surface (snow, mud, sand) the lower the tyre pressure required.

For harder surfaces (rocks, hard clay, hard rutted dirt), a starting point would be to reduce your tyre pressure by one third of the standard road pressure.

On softer surfaces (Sand, snow, mud), you could start by reducing tyre pressure by one half of your usual road pressure. This will vary depending on the surface you’re driving on, and the types of tyre you’re using. If you notice your vehicle struggling then reduce the tyre pressure in small increments (2 to 4 psi at a time).

But remember, the lower you go, the slower you go.

References

TyrePressure – Profile – Harry Lewellyn – (Extract from book – SHIFTING into 4WD)
Sidewinder News – Week 4 2010
Warn Industries – Airing down your tyres for offroad use