Thread: D4 Axle Load Tyre Pressures and Bridgestone Dueler A/T d697 LT 265/60r18 114s

After discovering the sidewall damage (photos) on both rear tyres on our D4 I have learnt a few thing about D4 axle load and tyre pressures and am after any advice or feedback or points of view regarding our choice of tyres and loading and if there are better tyre choices out there please.

D4 SDV6 3.0L 2011 with no added-weight modifications except roof rack carrying 4 Maxtrax, one spare wheel and one spare tyre - 2 adults, 2 dogs, recovery kit, 80L fridge, tools, bits and pieces

On leaving Sydney a year ago we fitted four new Bridgestone Dueler A/T d697 LT 265/60r18 114s to existing Compomotive wheels and have covered around 16,000 km towing about 95% of the time a 2.5 tonne (fully loaded) hybrid camper. Mostly sealed except for Cape York, Savannah Way, Oodnadatta track and we’re currently located in Perth doing maintenance before heading to northern WA.

The rear tyre sidewall damage (photos) was discovered by chance when the wheels were off and it is weirdly only on the inside faces of the sidewalls, not on the outside faces (someone may have insight as to why this is).

Before leaving Sydney, we had weighed both D4 and camper and were comfortable with total vehicle weights but on discovering the tyre damage we have re-weighed axles individually and this is what we found.

Firstly tow vehicle and camper hitched together to reproduce actual towing conditions and each axle weighed separately (all fully loaded including people, dogs, fuel, water, etc)

	Actual.	Handbook max.	Difference
D4 front axle	1250 kg	1450 kg	-200 kg
D4 rear axle	1970 kg	1855 kg	+115 kg	(6% over)
Camper (single) axle	2310 kg
Total all three axles	5530 kg	6740 kg	-1210 kg
Tow ball weight	250 kg	350 kg	-100 kg	(10% of camper)

Secondly Vehicles weighed separately and unhitched (the D4 is a bit out because the driver was jumping in and out)
D4 2920 kg
Camper 2530 kg

So the D4 rear axle is 115 kg over by 6.4%

We had been running tyre pressures against the placard.
Sealed Unsealed
D4 front 36 28
D4 rear 43 30
Camper 50 30

Bridgestone tell us that for the rear axle load we should have been running 51 psi on the rear tyres sealed and wouldn't be drawn on unsealed. Front pressure were ok.
Apparently this information about load and pressures is not published anywhere?
And we didn't suspect how marginal we are with D4 rear axle loading not that we are assuming anything will break as a result?

We don't seem to have many other options - unlike conventional caravans, redistributing weight in the camper doesn't offer much as it’s a 4WD design with the axle well to the rear and a long nose extended drawbar and the tow ball weight is about right as it is anyway. Maybe move the fridge forward, chuck out some tools, put spare wheel on the bonnet, put the people on a diet and send the dogs home?

So to continue using these tyres we need to go to 51 in the rear and maybe a modest reduction on rough roads

IMG_0537.jpgIMG_0539.jpgIMG_0541.jpgIMG_0540.jpgIMG_0538.jpg

I base my tyre pressures from axle load and tyre max load/pressure. Weather its right or not who knows, but I find it works as a good starting point. The tyre max load and pressure information is on the sidewall. Use single tyre max load not dual obviously.

(Max tyre pressure / Max single tyre load) * Axle load /2(divide by 2 as the max tyre pressure/load is for a single tyre and that second part of the equation is for axle load so 2 tyres)

Therefore in the OP's example, (with a tyre max pressure of 80 psi and max load of 1450kg per tyre) = (80/1450)*1970/2 = 54psi. Thats fairly close to Bridgestone's recommendation of 51 (although Im not sure of the OP's tyre load - my calc was for a load rating of 121)

** edit, just reread the first post - load rating 114 = max load of 1180kg per tyre:
80(Im assuming the max tyre pressure is 80 here)/1180 *1970/2 = 66psi