Answer

Ben,

Thanks for your email and your concern over the use of the centre diff-lock is worth raising to ensure the safety of your fellow drivers and the longevity of the vehicles.

Firstly we have to be careful in making the recommendation I'm about to make because there has been a system employed by Toyota that has largely remained the same since the inception of the Prado here in Australia (the 90 series in 1996), being a Full-Time 4WD driveline. But with the recent release of the current 150 series, there's been some subtle changes and in light of me recently driving the 200 series Land Cruiser, the Prado's bigger brother, there's a chance its electronics may (or will) have already snuck over to the 150 Prado.

So for Prados built between 1996 and 2009 (90 and 120 series) the recommendation is that use on any dirt road surface should be accompanied with centre diff-lock (CDL) engaged. This locks up the transfer case to provide the same sort of mobility (50/50% split of torque across front an rear axles) as you'd expect with your 70 series Land Cruiser trayback utes which are Part-Time 4WDs. In their normal "open" Full-Time mode there's a 30/70% bias to the rear which can lead to oversteer on dirt.

The 120 series Prados from 2002-2009 had a Torsen (Torque-Sensing) centre-differential which is a bit like a limited slip differential (seen in rear axles) or LSD, able to recognise an imbalance in the torque delivery (say in the case of excessive wheelspin) and clamp up to direct the torque across the driveline to where it could be better used. That's useful but from our experience the reaction delay will be long enough to get the vehicle out of shape in an emergency. Better to lock the CDL in advance.

Something else seen on the 120 series in the upper class models was the introduction of electronic traction control (ETC) and vehicle stability control (VSC) mated to the anti-lock braking system (ABS), so all VX and Grande models got this as standard, dumbed-down GX and GXL didn't. Both ETC and VSC add significant other safety enhancements in vehicle handling and should form the basis of any new vehicle purchases for your fleet in concert with ABS. By the way don't buy any secondhand 120 Grandes, they come with air suspension in the rear and are difficult to live with in a 4WD environment, they're really only a "townie" 4WD.

ETC is useful in off-road situations because it brakes spinning wheels on loose surfaces and directs the torque to the wheels that have grip, great for banging over rocks or in mud to maintain momentum. ETC will also work on-road, say in a situation where gravel or ice might be on a bitumen road and likely to induce unwanted wheelspin. Again as the wheelspin occurs, the brakes are applied in rapid pulses to that spinning wheel to correct the imbalance. VSC works at higher speeds countering over or understeer by decelerating the engine and applying the brakes to one or more wheels and thus preventing the potential for a serious accident. This will all be going on irrespective of what you are doing as a driver, because the technology is smarter and faster than a human in reaction times.

From my experience with the new 150 series, use of the CDL still permits the ETC/VSC programs to operate in the background in HIGH range and this is desirable. Having the transmission locked up 50/50 affords the most neutral handling/control and offers greater safety than the 30/70 around town mode with the CDL open. We're trying to prevent a situation from occurring before it happens in using it this way.

My worry as I stated in the earlier paragraph is that the 200 series Land Cruiser disappointingly disables the ETC/VSC programs when the CDL is engaged in HIGH range leaving the driver to rely on the advantage of 50/50 torque delivery coupled up to their personal vehicle handling skills in a slide or loss of control. Some of us are good at that but most aren't.

If you are running 150 series Prados I want you to let me know what happens when you engage the CDL in HIGH range? Does an amber warning light come up on the dash saying VSC is off? If so then we have to run contrary advice and recommend CDL is left alone on the dirt roads you are driving on, that way the ETC/VSC package will still operate.

I'm sorry there's been a bit to digest here but without knowing which model we were talking about I had to canvass all possibilities. Full-Time 4WDs are really good on wet bitumen roads, much better than a 2WD. On dirt historically they were better with CDL engaged, but with the advances in ABS technologies and how its applied we need to look closely at what each manufacturer is doing before making any sweeping statements.

Please note this:

• In a Part-Time 4WD use HIGH range 4WD on all dirt surfaces
• In a Part-Time 4WD NEVER use HIGH or LOW range 4WD on bitumen/concrete/paving, you'll damage the transmission
• In a Full-Time 4WD use of the CDL is recommended (with caveats above considered) on dirt surfaces
• In a Full-Time 4WD NEVER use the CDL in HIGH or LOW range 4WD on bitumen/concrete/paving, you'll damage the transmission
• Always wear a seatbelt
• Always run with headlights on
• Never drive faster than 80kph on dirt

Regards,

David

Answer

Tracey,

By chance we have in here today on a course a Prado with hopefully the appropriate tyre placard.

It will help to illustrate what the manufacturer recommends for inflation and should be used as a starting point. The danger for people out in the field without the benefit of a lot of experience is serious tyre damage that can leave them stranded or worse create the potential for running off the road and maybe even rolling the vehicle. Whilst manufacturers insist on putting unsuitable tyres on their vehicles this danger will persist. If you had your own dedicated vehicle I'd recommend selecting an "LT" or Light Truck type of tyre as they are significantly stronger, but I'll leave the explanation on that to another time.

Depending on which Prado Andrew has hired (there's 2 likely models either the GX or GXL based on the shape that's been out for around 9 months now) the tyre placard will state the following:

2010 GX Prado - 245/70R17 - Front 200kPa + Rear 200kPa (unladen) or Front 200kPa + Rear 220kPa (laden)
2010 GXL Prado - 265/65R17 - Front 200kPa + Rear 200kPa (for both unladen & laden situations)

Here's a pressure conversion to PSI

200kPa = 29PSI
220kPa = 32PSI

Now our formula for tyre protection whilst operating on less than perfect surfaces follows:

When you go onto well-made dirt tracks try a 20% reduction in pressure and accompanied by 20% reduction in speed, now no faster than 80kph (and don't forget to use HIGH range 4WD). You may find that when you get to significantly corrugated dirt roads that have sharper rocks a further reduction is warranted, say another 20% and no faster than 60kph.

Of course on your genuine 4WD tracks whether they be sandy or muddy, getting down to between 15-20PSI is highly recommended, but again reduce your speed to between 25-50kph and at the lower end of the pressure scale make sure your turns are wide and gentle. Excessive speed may cause the tyre to pop off its rim.

Additionally there's too much hoo-ha written about pressure creep due to the ambient temperature and speed/friction. To keep it simple set your primary pressures at the start of the day when the tyre is cold. Make all your adjustments at the time you need to make them and at what the gauge is showing you at that time. When you've done with the off-road elements and it's time to return to higher speeds on bitumen, pump them up again to the above on-road recommendations. Next morning check/adjust/reset again once cold.

Hope that helps, don't hesitate to call me if there's additional advice you require.

Regards,

David

Answer

John,

This isn't the first time I've been asked this so I went back to some correspondence I wrote back in 2008 as it's still relevant and amended it where I thought appropriate.

The general tone of the internet advice you provided is intended to be helpful and for the most part is useful in reminding drivers of their responsibilities when driving in less than perfect conditions, however the advice on aquaplaning is incorrect and not thought through well at all.

Here are some points to consider:

1. Aquaplaning occurs when the road surface is flooded with water after a heavy downpour or after a culvert has overflowed and directed water onto the roadspace to the point where as a vehicle's wheels pass through the flooded area the tyre actually sits up on top of the moisture and "floats" rather than penetrating the water, clearing the roadspace and retaining its ordinary contact grip with the road surface
2. This occurs for a number of reasons and it's nearly all to do with speed. Firstly a tyre is designed to act like a pump on a wet road. The network of tread blocks and their channels direct the water to the outside edge of the tyre to disperse the moisture away from the tyre's face. The sipes (the small "cuts") on the tread blocks squeegee the bitumen to give the face of the tyre something to grip to. If you seek out the speed rating of the tyre you will see that different tyre types as fitted to different vehicles, have differing speed ratings to suit the likely maximum speed of the vehicle. Typically Australian vehicles have speed ratings between N (140kph) and H (210kph), which are well in excess of the maximum highway speed posted in this country. Makers when arriving at these maximum speed capabilities factor in the effect of wet-weather on their tyre's grip ability and design the tread patterns to accommodate a certain amount of moisture at that maximum speed, the faster they go the faster they must pump the road dry. If the road surface is too flooded, or the tyre is worn, or the vehicle is being driven too quickly, or turning too sharply, the wet-weather grip formula will be overtaken and a loss of control/grip will result.
3. Tyres with less than 50% tread will be affected in the wet. Tyres worn down to the TWI (Tread Wear Indicator) may as well be bald in downpours, bald tyres are a disaster waiting to happen wet or dry! Tyres that are over or under-inflated will be affected too, check that your tyres at least match the recommended pressures seen on your tyre placard.
4. From my experience and the experience of colleagues both here and overseas, these aquaplaning moments are usually brief and can catch a driver by surprise. Sometimes you can see a roadspace that is flooded and can anticipate the situation before you get there and make the necessary speed adjustment, but more often than not the moment happens in an instant, lasts a few seconds and settles almost as quickly. In a worst-case situation the effect on the vehicle can be dramatic and potentially life-threatening if the driver reacts poorly.
5. The advice you've provided is a sore point here. What a driver is looking to do is regain control of the vehicle. The first response is to get off the accelerator. This will achieve two things, deny wheelspin and regain some traction.
6. The second response might be to apply some corrective steering (if the vehicle has deviated from the chosen path) and possibly apply some subtle braking. In non-ABS vehicles that will require some disciplined "threshold" braking to manage the pedal pressure avoiding a lock-up (consistent pedal pressure - no pumping of the pedal please), whereas in an ABS vehicle the driver can confidently apply any amount of pressure to the pedal to achieve the retardation required and the electronics will work out what to do without a skid/loss of grip.
7. If the vehicle had the new technology of VSC (Vehicle Stability Control) there'd be a pretty good chance the vehicle would have been able to mostly sort it out itself. By selective braking one or more wheels and automatically decelerating the engine the vehicle can correct some oversteer and understeer situations despite what the driver is doing.
8. In all cases the transmission should be left in gear and always engaged, manual or automatic!
9. The correspondent recommends depressing the clutch on a manual and on an automatic applying the brake. This is inconsistent and will create confusion amongst drivers.
10. In a manual if the clutch is depressed the transmission will be disengaged and the vehicle will "free-wheel" (this traditionally has been called "Angels" gear as it usually means a loss of control and a quick trip to heaven) and initially the vehicle will appear to accelerate as load is taken from the transmission and no resistance courtesy of engine braking is applied. It is always better to leave the clutch alone, lift off the accelerator and let the engine slow the vehicle ensuring it will track truly rather than free-wheel and possibly start to rotate and spin, requiring more of the driver to correct. If need be corrective braking (see 6) may be applied. Engine-braking and ordinary braking together will always slow a vehicle faster and more predictably than pushing in the clutch in concert with the brake pedal. Leave the clutch alone!!!
11. In an automatic lifting off the accelerator might be all that's required, supplemented with some braking and corrective steering as well if need be.
12. Emergency situations always require drivers to take a cool, calm and measured response that is uncluttered with panic or unnecessary or less important considerations about preserving the vehicle and its parts. The driver and other human occupants are the important things. The first focus is to restore grip and control and to do it without taking your eyes off the road so you can concentrate on finding an escape route, accompanied by the measured responses in steering and braking. Get that right and you'll live to tell the tale.
13. Nearly all of us in our pre-licence days were told by our teachers that when you had to brake you apply the clutch at the same time so as to save the engine from stalling. I'd agree with that around town when normally pulling up at a set of lights in the right fashion. I'd additionally supplement that deceleration with down-changes in the gears, coming off the clutch each time and using engine braking as well, pushing the clutch in just prior to rolling to a stop. Many people are quick to push the clutch in, in an emergency, but this is counter-productive and will only extend braking distances. You won't have time in any emergency to fumble around changing gears so it's best to stay with what you've got gear-wise and concentrate on pointing the vehicle the right direction with all of the previous recommendations in tow.

Hope that helps!

Regards,

David

Answer

I mentioned on Saturday that there were some gains to be had by improving the suspension of the Vitara and seeing if there was a replacement tyre that too could offer some benefits.

The problem with standard shocks and springs is they are set for light to median loads and in the case of AWDs and light duty 4WDs such as yours, bitumen road comfort is the key parameter they tune their targets on. That satisfies 90% of owners as there's only around 10% of us who go bush. In your case with great aspirations to explore what this great country has to offer the standard set-up is too light and may fail in difficult conditions. In the first instance with your suspension the benefits with the right system will be a subtle increase in ride height which improves ground clearance, more wheel travel to soak up the lumps and bumps better, a less "floaty" feel with the suspension at higher speeds, surer steering, better load carrying. I have put through a call to Michael Davis local manager of ARB to ask whether there is an Old Man Emu suspension kit for your vehicle and will advise when I know. In the meantime I've noted that Pedders Suspension offer in their Trak Ryder range a kit that might work. My first preference would be the ARB OME system.

On the tyres I hadn't realised how problematic that would be. Since the introduction of 17" and 18" wheels tyre choices for off-road usage have become tricky. The safety advantages of bigger brake diameters is what has driven bigger wheels, but tyre makers are loathed to invest heavily in narrow focus tyre types, hence reducing our options. You're right in looking at Bridgestone's range, we've used it since we started and have great faith in their product. I think you've already selected the standard size D694 225/65 R 17 with the 102 load index for the pair of replacement tyres you needed recently. I think a better choice that's still legal would be the D694 225/70R17 with the 108 load index.

Load index is the key to tyre strength and the difference between the 102 and the 108 is a healthy 15% increase, 850kgs compared to 1000kgs carrying capacity. You'll also pick up some extra ground clearance under the vehicle (12mm), which is handy. Unfortunately these tyres are not Light Truck offerings, but reinforced Passenger tyres, so to avoid the puncture potential you'll need to be really vigilant with your pressure regime (per our advice on Wednesday night). I searched a number of other tyre makers offerings to see if there was a Light Truck alternative but alas they were all too big and likely to foul on your bodywork and be illegal and cause speedo inaccuracies.

I think you'd mentioned to Drew that you wanted a bullbar on the car too, which is good for remote area work and ARB certainly make the best products out of steel in that regard. If you do get one the suspension will be necessary to carry the extra weight, particularly over the front axle.

So to rework the tyres on the vehicle contact Laurie or Anthony at the Bridgestone BSelect store at North East Road at Windsor Gardens, phone 83691045. They too will be able to source the suspension if ARB can't assist.

Regards,
David

Answer follow up

Alistair,

Got the response back from Michael and yes there's a spring kit for it, details below:

• Front OME623 (offers 20mm lift)
• Rear OME625 (offers 20mm lift)

ARB is at Regency Park, phone 82445001, if Michael's busy one of the sales team should be able to oblige. Make sure you let them know you're a VIP customer of ours. The lift in height is modest which is good, as you don't want to create a top-heavy vehicle, but what it will do is transform the vehicle into a far safer handling and steering machine. I've done this to every single one of my 4WDs over the last twenty years and it makes a positive difference.

Regards,
David

Answer

Sent 10/6/10

Jorge,

Unfortunately you have a very difficult wheel size to manage. As the braking evolution of 4WDs has revolved around bigger brake rotor diameters requiring bigger wheels, increasing in line with passenger car design, vehicles have been stopping in shorter distances, which is good, but not without some drawbacks. Its also been trendy to fit bigger wheels and low profile tyres to vehicles from an aesthetic standpoint, but hardly a practical one. I have numerous Land Rover Discovery 3 & 4 clients running 18" wheels with the same dilemma as you, wanting better security from punctures when they go bush. Eighteen-inchers aren't going to do that.

I've searched high and low for uprated tyres in this size and I can tell you there's nothing. Any other tyre makers building that size will only be offering exactly the same Load Index and likely Speed Rating as that that came with your vehicle, which confirms that they are merely high speed passenger tyres and wholly unsuited to gravel roads. No better than what you've currently got.

If you wanted to make a change that works, pick up a set of steel 17" wheels and fit a set of LT265/70R17 rubber or LT275/65R17. The rolling diameter is identical or very close to that you currently have but the big difference is Light Truck construction, thicker tread depth (13mm compared to only 9mm) and a much higher Load Index which is the only true barometer for puncture resistance and longevity. In that size there's two really good products, the Bridgestone D694LT in the LT275/65R17 with a 118 load (1320kgs) or the Toyo OPAT in a LT265/70R17 with a remarkable 121 load (1450kgs). In each case that's either a 25% increase for the Bridgestone or 37% increase with the OPAT. The D694 measures 790mm, the OPAT 802mm, your existing 18" combo rolls out at 802mm.

I'd suggest calling Laurie or Anthony at the BSelect (Bridgestone) store at Windsor Gardens phone 83691045 for advice. They'll be able to ascertain the wheel offset and PCD measure for the wheels, cost it and install with a wheel align. Laurie is one of my part-time trainers and a great bloke.

On the subject of ride quality you won't be making any sacrifices at all as from my experience standard tyres are usually crap. With these new products gone will be the vague steering, the floaty almost disconnected feel from the road, with much better stopping distances and the previously mentioned benefits in puncture prevention and longevity (expect 80,000kms instead of maybe 35,000kms).

Re locations to visit, YP doesn't have a lot to offer as much of the Peninsula is owned freehold. There's a couple of sandy tracks out the back of Port Victoria and that's about it. Eyre Peninsula is a whole lot different, give that a visit some time.

Regards,

David

Answer

Zoe,

Here's the info for you.

1. The SA Road Traffic Act states that "no part of the tyres and wheels of a vehicle may protrude beyond the vehicle's bodywork". The width of your new tyres currently does do that.
2. The tyres fitted by your retailer are 265/70R16 which are OK for the GXL and Sahara 80 series Land Cruisers of the day (that was their standard size mid way through the vehicle's model life) because they have wheelarch extensions to cover the tyre, but not for the commercial model that you've got which does not.
3. The placard on the vehicle lists the traditional tall skinny, a 7.50R16. I'm not a big fan of that tyre size as it only offers up a very limited product and pattern range, typically the original Dunlop Road Grippers and they were junk.
4. The nearest equivalent to the 7.50 is the more common these days LT235/85R16, which is what we've used for years on a number of our vehicles with great success and the same size we recommend to our clients in SA Government on their LandCruiser 100 and 70 series vehicles. It's also used by BHP at Olympic Dam courtesy of our recommendations on all of their full-size Toyota fleet. This tyre size also will fit on your existing rims as the design rim width codes allow 5.5" - 7" wheel widths when fitting up a 235.
5. The only potential wheel problem you still might have is with the offset. The centre of the wheel is welded to the rim at a particular position per vehicle to accommodate the individual brakes/hub size and to allow the wheel to fit under the guard comfortably without any body contact. I'm hopeful the original owner did his/her homework with the wheel selection and that once the new tyre size is fitted, the narrower profile of the tyre will then sit inside the guard, as is required by law. If they don't you better let me know before you go buying new rims.
6. My favourite 235 is the Bridgestone 661 Desert Dueler. This tyre has an extraordinary reputation in commercial circles, as it has an impressive 120 load index = 1400kgs carrying capacity.
7. The higher the load index the better for a 4WD going bush, because load index is a good indicator of puncture resistance/tyre strength. By way of a comparison the 265s you currently have have only a 112 load index = 1120kgs and an "S" speed rating (180kph) which immediately tells me they're a Passenger car tyre, not Light Truck (the devil's in the detail) and are no good for rough bush tracks, better suited to the bitumen.

Cleverly I haven't got the pics with me today I took on Saturday that show just how much your tyres stick out from the guards and I also took a pic of the placard that clearly states 7.50R16 as the standard size. These are good for a reference so I'll send them across via email to you, but the info above should be enough ammunition. Tyre brands to avoid in my humble opinion include Cooper, Mickey Thompson, Hankook, Kumho. Let me know if they're confusing you?

Regards,

David

Reply

24/4/10

Hi David - I had a quick look on the Goodyear website - these are the tyres with a 120 load rating - speed rating Q (160) and R (170), Wrangler MTR Kevlar, Wrangler Duratrac, Wrangler Silent Armor, GrandTrek AT3
Cheers, Zoe.

Answer

24/4/10

Zoe,
Thanks for doing the detective work, I reckon the Silent Armour is the go, the MTR is way-too aggressive and will be noisy, the Duratrac marginally quieter, Grand Treks are junk.
See how you go?
Regards,
David

Reply

30/4/10

Went there this morning to meet with the rep, ended up FOUR blokes looking at my tyres and me just looking at them shaking my head. I stood my ground on the fact they were illegal and I should have been advised, plus they were unsuitable for what I had in mind driving wise, and all of them said to me that they still don't think that they're defectable, and that the tyres would have held up in most 4x4 situations... geez how stubborn are some people! Long story short they changed them over today to the Silent Armours and 235 85 R16 and what do you know, almost perfect fit! Thanks for your help you were right all along and I didn't deviate from what you said and they did what I wanted, good lesson for me. And all at no charge, bet they were glad to see me leave.

Happy adventures!
Zoe.

Answer

Rob,

Thanks for your mail and I am very pleased you gained some benefit from the training. It was a good day!

On the subject of your tyres here's some advice that'll work. On Pajeros and Prados we've had great success with either the:
1.Bridgestone 694 Desert Dueler in a 275/65R17 LT (275mm wide, 65% aspect ratio (height of sidewall), Radial, 17" wheel diameter, Light Truck construction), 118 (Load Index of 1320kg), S (Speed Rating 180kph) 790mm diameter or a
2.Toyo OPAT 265/70R17 LT (265mm wide, 70% aspect ratio (height of sidewall), Radial, 17" wheel diameter, Light Truck construction), 121 (Load Index of 1450kg), S (Speed Rating 180kph) 802mm diameter
Challenger is near identical to Pajero so I've no doubt that these tyres will work for you too. Both of these offer a significant improvement in puncture resistance courtesy of the enhanced load index and deeper tread depth. The boys at Bridgestone at Windsor Gardens here in Adelaide could sort this out for you pretty speedily, contact Anthony or Laurie on 08 83691045.

Regards,

David

PS Have a look at what I thought of the D694LT at www.bridgestone.com.au

Answer

Folks,

Thanks for your kind words we appreciate your patronage and look forward to hearing instalments from the journey.

On the tyre pressure you'll remember we asked everyone to locate their tyre placard on their vehicle and use those pressure settings as a starting point when fitted with OEM (original equipment manufacturer) tyres. This will be good for the bitumen. Once on the dirt we recommended a pressure reduction of 20%, accompanied by a speed reduction of 20% (now no faster than 80kph). I haven't got a Prado placard in front of me but I think it said 29psi front, 34psi rear (if you could please verify that for me), but remember that was for those standard passenger tyres.

With your OPATs in a LT265/65R17 with 121S, I've consulted the TRA manual and at my best guess for a fully laden Prado at approximately 3,000kgs, with 1200kgs over the front axle and 1800kgs over the rear, it suggests 36psi front and 42psi rear for the bitumen. That sounds right to me based on past experience, so use the 20% formula on those, namely 29psi front and 33psi rear @ 80kph or less. Now where corrugations are particularly unpleasant (and I reckon Gibb River will be up there), a further reduction is warranted, because if we can get some flex into those sidewalls it'll soak up the initial impact, leaving the suspension with less work to do. Try another 10%, namely 26psi front and 30psi rear @ 70kph or less. Remember that this is for a fully laden Prado, if you carry less than GVM you may not need these starting pressures. The only way you'll find out is to get the car set-up as it would be for the journey and run it over a weighbridge three times. First the whole vehicle for GVM, then the front axle only, then the rear axle only. Armed with that we can consult the charts.

Glad to hear we've been instrumental in getting people together, it's a great way to travel and share experiences!

Happy to help,

Regards,

David

Reply

17/4/10

G'day David,

Thanks for your reply but I have thrown a spanner in the works and had LT265/70R17 121S fitted so I guess this will need more calculating. Our placard recommends 190kpa front & rear.[28psi by my calculations] .If you don't mind giving me a new starting point for the higher profile tyres, I can work the rest out from your previous information.
Sorry to be a pest but I appreciate your help.

Cheers,
George.

Answer

Sent 11/3/10

Ben,

Thanks for your email and glad to hear you're on the trail and it sounds like having a good time!

Firstly an apology. I think you had Drew and Laurie in attendance for your training sessions with us? Since I've received your mail I spoke to both of them and asked if they could recall the conversation and it appears that Laurie had noted that the sidewall on your Cooper stated "A/T" which is all-terrain, a throwaway bit of sidewall branding that really means very little these days as the real truth is whether it's a light-truck (LT) specification and additionally what the load index is. He didn't cast a glance to the index and construction and assumed it had the right LT value. Not so it would appear!

As your Cooper only had a load index of 112, it is essentially only a passenger car tyre and no better than the factory fitted tyres on originally.

With that in mind the Nissan's tyre placard is correct, 29psi front and maximum of 36psi rear.

Now that you have true light truck tyres on with a very healthy 123 load index (that's 1550kgs compared to only 1120kgs before, a 40% increase in capacity and therefore strength), we need to reassess the pressures.

The only accurate starting point for this is the Tyre and Rim Association Manual and it states the following for your previous rubber, P265/70R16 112S: Max inflation 250kPa or 36psi which is consistent with the Nissan placard. As I'm waiting for my new 2010 version of the TRA bible I can't give you the light truck equivalent from the charts, but the size you are running is identical to that I'm using on our Navara with great success in a Bridgestone 694LT.

Assuming the car is fully loaded and at maximum GVM which is around 3050kgs for Patrols with a likely 35/65% split front to rear, 36psi is plenty for the front and 50psi for the rear. Remember this is assuming there's around 1050kgs on the front axle and 2000kgs on the back and whilst driving on the bitumen. This might sound excessive for the rear but is accurate for bigger loads on full-sized wagons as from my experience they're nearly always overloaded.

When you go onto well-made dirt tracks try a 20% reduction in pressure and accompanied by 20% reduction in speed, 29psi front and 40psi rear, now no faster than 80kph (and don't forget to use HIGH range 4WD). You may find that when you get to significantly corrugated dirt roads that have sharp rocks a further reduction is warranted, say another 20% to 23psi front and 32psi rear and no faster than 60kph.

Of course on your genuine 4WD tracks whether they be sandy or muddy, getting down to between 15-20psi is highly recommended, but again reduce your speed to between 25-50kph and at the lower end of the pressure scale make sure your turns are wide and gentle. Excessive speed may cause the tyre to pop off its rim.

There's too much hoo-ha written about pressure creep due to the ambient temperature and speed/friction. To keep it simple set your primary pressures at the start of the day when the tyre is cold. Make all your adjustments at the time you need to make them and at what the gauge is showing you at that time. When you've done with the off-road elements and it's time to return to higher speeds on bitumen, pump them up again to the above on-road recommendations. Next morning check/adjust/reset again once cold.

Hope that helps, send us a pic of you and the car somewhere exotic and an explanation note of where it is and what you got up to???

Regards,

David

PS I'm not a big fan of mud-terrain tyres in any other environment other than mud... Be very careful on bitumen roads at high speed that are wet and make sure you rotate them every 5,000kms, those big tread blocks go out of round very quickly!

Answer

Sent 11/3/10

Christine,

Firstly to the 2WD Vs 4WD argument.

The Pajero is both a PART TIME and FULL TIME 4WD wagon and I reckon probably one of the best in our local marketplace as it is VERY safe.

To summarise:

• The only mid-full size wagon to be built on a monocoque platform with proper crash deformation zones
• Has a full complement of electronic safety features even in its basic model right through to the top of range see list below
• Those features include ABS brakes - anti-lock braking systems prevent wheel lock up under heavy braking and ensures steering control
• ETC - electronic traction control ensures that when grip is compromised or lost both on and off-road, traction can be regained swiftly without driver intervention
• VSC - vehicle stability control enables a driver to regain control of an oversteering or understeering vehicle at higher speeds via the vehicle electing to brake one or more wheels and/or decelerate the engine irrespective of what the driver is doing – it is a very clever car!
• With respect to the debate about using 4WD or not let's look at the Pajero's driveline.

It offers a multitude of options for the driver to select and the brilliance of the Super Select transmission as Mitsubishi call it, is that as the roadspace becomes progressively more difficult the driver simply shifts up through the range to gain more and more grip and capability.

Here's an overview:

• 2H is recommended for city driving on DRY and WELL-MADE bitumen roads at slower speeds 0>80kph - 100% of drive goes through back wheels only (no good on dirt)
• 4H is the FULL-TIME or CONSTANT 4WD mode recommended for all other bitumen situations especially when the road is wet, bumpy/patchy, and/or at speed over any distance (this makes the Pajero behave like a Subaru with its all-wheel-drive system AWD) and makes the car very safe on the highway or around town. The drive split is 70% to the rear, 30% to the front (OK too on those rare hard-packed dirt roads like you see in the SE). There will be no appreciable difference in fuel used nor will there be any transmission damage when used on the bitumen!
• 4HLc is the PART-TIME 4WD mode only to be used on loose surfaces - any dirt or gravel, sand, mud, rocks that you'd find on rural and outback roads. If you use this mode on bitumen you'll WIND UP the transmission and potentially DAMAGE it. We always say NEVER to use it on high friction surfaces - bitumen, concrete or paving. The drive split is even, 50/50% front and rear and provides the surest stability on gravel roads at speed.
• ALL of the above modes can be engaged on the move back and forth dependent on the road surface (see detail) at speeds up to 100 kph - although we have stipulated drivers should not be driving at speeds in excess of 80 kph on the dirt!!!
• 4LLc is another PART-TIME mode; again it cannot be used on high friction surfaces, but is ideal in difficult terrain where momentum is hard to find (mud, slush, deep sand and steep gradients). Engagement should be done whilst stationary (automatic transmissions need to be left in neutral before changing the transfer lever into 4LLc). Drive split is again 50/50%, but ground/travelling speed is significantly reduced.

We make it clear to our attendees that safety in the field should take precedence over any meagre cost disadvantage, every time. As stated previously the Pajero diesel used in the 4H (Constant 4WD) mode is particularly fuel-efficient and will not cost the organisation a noticeable amount more than if you ran in 2H all the time on the bitumen. However the enhancement in vehicle control is considerable and well worth exploiting. Remember Mitsubishi are not alone here, Subaru, as well as all other AWD makers, Toyota Prado and Land Cruiser 100 & 200 series, Land Rover Defender, Discovery and Range Rover, Nissan Pathfinder and others enjoy the benefits of a constant 4WD system with significantly less risk to rollovers and without a great cost in fuel consumption. As 4WDs account for nearly 60% of rollovers at speeds over 100kph on rural roads it is important to have as much safety at your disposal as possible.

So in answer to your second-last question, no I don't believe 2WD usage should be encouraged, as this vehicle offers a safety advantage that should be used. I think you'd find that there would be greater fuel savings across your vehicle fleet if drivers paid weekly attention to maintaining their tyre pressure at the placarded levels, as under-inflated tyres use considerably more fuel than just about any other operation with perhaps the exception of using a roof rack.

If punctures are a big problem there's a couple of ways to mitigate the issue. The first attack is to get the drivers to reduce their pressures (20-40% depending on terrain) and speeds when driving over surfaces likely to impact on the tyres, I suspect in your case the sharp gravel roads and those times you venture onto properties that are strewn with rocks and timber debris (don't forget to pump them up when the speeds return to bitumen road running – refer tyre placard for pressures). The "standard" Passenger tyres that makers fit to their vehicles in stock form are pretty ordinary for people who have a true commercial application for the vehicle.

The "truck" Light Truck tyre is a much better proposition in terms of durability and longevity and will likely save the agency a reasonable amount in running costs. In your case to opt for the Light Truck alternative you'll either have to as an agency buy the tyres outright out of your own operating budget or put a business case to your fleet managers to have them consider your request, done so on a case-by-case basis. In comfort terms I doubt you'd notice the difference, but in steering terms it'll be so much better you won't believe it!

I hope that helps and please contact me if there's anything else I can add.

Regards,

David