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martyn668

Tyre inflation - non-standard

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Thanks Red 90. I wondered why Land Rover have a 28 psi:40 psi split as standard. 

 

Hi Eightpot. I could have put metric tyre pressures as well, but that doesn't change the equation. I left it in imperial because most people probably still inflate to inperial pressures. (Strangely I use imperial on the Defender, and metric on my Honda Civic! Just earsier figures to remember). The GVW is indeed 3050kg for a 90. The 5520kg is the maximum load that 4 x BFG 255/85s can run at, inflated to max pressure. However, I fully take your point that different tyres of the same size from different manufacturers would have different load ratings, so if we use the calculator on the Legacy forum cited above, then you would have to vary the pressure depending on who made your tyres. That also seems logical to me. A 10 ply carcass will be stiffer than a 3 ply carcass, so should be inflated differently.

 

I've never seen the theory of inflating different ply / load rating tyres differently, so perhaps I'm over-thinking this.

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Where's that GVW from?! I'm sure the GVW of a 90 is only 2400kg and 2500kg for the later ones. :unsure: 

I know mine was miss-plated from the factory and I had it corrected (to avoid the need for a class 7 MOT). The GVW will be the sum of the front and rear max axle weights. 

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So, I wasn't too worried about GVW, because that doesn't come into the calculation. The calculatuon is maximum load capable of being supported by 4 the tyres, divided by  the actual all-up weight of the vehicle.

 

But since someone mentioned GVW, I looked it up. The official Land Rover manual for the Td5 90 (from https://workshop-manuals.com/landrover/defendertd5/general_specification_data/eec_vehicle_kerb_weights/ ) gives this:

image.png.e9dcdebecb3853609d0063a90c600c81.png

image.png.445fb476420c74087a5d63f5e4faa2d3.png

So with me in it, I'm at 2,300kg already as per the weighbridge. With the wife and two kids, I have about enough load carrying capacity for a toothbrush! I've upgraded the suspension to genuiine LR HD springs, which I think (hope) increases the GVW!

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Retroanaconda posted this on another topic on here back in 2009!

image.png.e64462503ad491bdc89b79f24c9714c2.png

That's bad news. Looks like the 2550kg is already the HD sprung max GVW. The wife and I will have to lose some weight, and the kids will have to stop growing.

 

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With a weekend of camping gear and two people, I got 2270 kg.  1120 front, 1150 rear.

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My 18 foot long 110" Range Rover ambulance converted to a camper, with double bed, fridge, cooker, sink, 5mm crash-winner bumpers and expedition kit is only 2200kg without passengers! 

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There is a method used widely in Australia and also popular here in NZ known as the 4psi rule. Basically you measure cold pressure, drive for 20-30mins or so and measure again warm. The pressure gain due to tyre carcass flex should be about 4psi. If more than 4psi increase, the starting pressure was too low. If less than 4psi increase the starting pressure was too high. 

Andy

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