Tyre pressure/speed opinions for loaded D90

**Lagerfan** · 21st August 2013, 07:35 AM

Tyre pressure novice here so any advice much appreciated!

Will very shortly be taking our D90 on its maiden outback tour up to Alice via Oodnadatta and have been checking out Adam Plate's (RIP) guide to tyre pressures on dirt (http://www.pinkroadhouse.com.au/Pink...essure-pdf.pdf). He suggests 26-30 psi on rear loaded, which of course we will be with all our camp gear, bikes, jerrys for water/fuel etc. etc.

I thought the rule of thumb is you should adjust your speed by the same amount you adjust your pressures. So for our Goodyear MTRs (235/85R16) on the 90 the "sticker" pressure is 48 psi loaded. So some maths tells me running 30 psi back there means we shouldn't do over about 70km/h? I'm happy with that (we're on hols after all) but thought I'd tap the experience of this board for some opinions.

Cheers,
Heinz

**Tote** · 21st August 2013, 07:45 AM

Different experience here as I have a D3 with 60 series tyres but we did the same trip a couple of years ago.
On the dirt I was running around 30-32 PSI rear and 28 front on the dirt with no issue (and no punctures).
This was with heavily loaded vehicle as well. On Bitumen I was running 36 front and 45 on the rear. I had a tyredog monitoring system and heat buildup was not an issue. I was doing up to 100KM/h on good quality dirt and slower as neccesary

Regards,
Tote

**87County** · 21st August 2013, 08:34 AM

There are many conflicting opinions about tyre pressures on rough roads - different experts, different opnions.

And it will, to some extent, depend on how heavily your load the vehicle.

FWIW IMHO your placarded pressures are way too high for comfort and you would really appreciate somewhere about 30-32 all round much more comfortably.

Pressures can be dropped to the 20-25 psi level but heat build up does start to become an issue and your 70kph at this pressure would be about right for long distances IMHO.

The heat build up & increased flex can lead to tyre failures.

Why not try pressures in the 25-32psi all round while you're on the tar and see how it feels, and see how hot they get.

**KarlB** · 21st August 2013, 08:36 AM

Tyre pressures are critical in a D90 for comfort and handling. In mine, with camping gear including a 50 litre fridge, 50 litres of water, total fuel of 140 litres and two people, I run tyre pressures of 32 psi (2.2 bar) all round on the highway, and travel comfortably at 110 kph. On dirt roads I will go lower. You should not be carrying any where near the max payload of 935 kg (ie nearly a tonne). Your heavy items are: people (~200 kg), water (~50 kg), extra fuel (~50 kg); and all your camping gear and food should total less than 200 kg.

Cheers
KarlB

PS I am running Goodyear Wrangler MT/R Kevlar tyres, so very comparable to the tyres you are running.

**Leroy_Riding** · 21st August 2013, 01:20 PM

I run 35psi all round on my D90, drop them to 25-30 for general offroad use and sand, (probably should go lower on sand though?) I did egg one of my tired in some rocky patches so think I would go lower again if I was playing with rocks. . . generaly offroad my D90 has myself and another person 45ltr fridge, 20kg toolbox (to help the broken toyotas

) 10ltr water for a day trip and recover gear. have not done 'long touring' yet, but for 2000+km trip on black top I ran 38rear 35 front with a tandem axel car trailer in tow and the back loaded with a fair what of stuff (would still have been under 400kgs int he back though) and it was comfortable, a little 'bouncy' but comfortable

Leroy

**Naks** · 21st August 2013, 04:54 PM

horses for courses

There is a definitive way of calculating what tyre pressure one should use, the formula is: (Max Pressure / Max Weight) * (Measured Axle Weight /2)

For this to work, you will need:

1. The tyre rating off your tyre: there should be a max load/pressure rating on the sidewall
2. The weight on each axle of the vehicle (you can get it weighed at the weigh bridge)

Using a thumb-suck example of a tyre with a pressure rating of 4 bar at a maximum weight of 1500kg:

Let's say your axle weights are: Front - 1000kg and Rear 1200kg.

Front Tyre pressure: (4 / 1500) * (1000 /2) = 1.33
Rear Tyre pressure: (4 / 1500) * (1200 /2) = 1.6

When venturing off tar, I deflate between 20-40% for gravel and down to 1 bar for sand.

Friend of mine who overlands a lot uses this rule:

We found managing tyre footprint in terms of % pressure reduction much more useful. E.g. after playing around a bit we discovered that for our vehicle deflating tyres by 50% from their current pressure works brilliantly on gravel, rock and in mud. And this you can do either when the tyres are cold or warm, because you are reducing the amount of air inside the tyres by 50%. If you do this when cold, once warm the pressure will be what it would have been had you deflated the tyres to 50% when warm ;-). And vice versa.

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