Tyre Pressures

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This seems to be quite a common issue, I did quite a lot of digging in other forums and sites and found that many people drop the pressures by 10 - 20 psi as the manufacturer figure of 80psi is a "safe"  figure, but the tyre manufacturers will sometimes give a lower figure if you supply them with the axle weights. 

Personally I've reduced my fronts by about 15 and my rears by 10 and the ride is so much better.

There is of course one other thing to check, and that is the springs, make sure you're not running on the bump stops due to the spring being almost fully compressed, a common issue with Ducato's and the converter not up-rating them (More of a problem with A class to be fair). I up-rated my fronts and it's a different vehicle.

Still awaiting to hear back from Continental, but on putting all the relevant details into the Tyre Safe calculator, it gives 53psi for the front, and 80psi for the rear.

You should tell them actual axle weights not the ones on the plate by going to a weighbridge and getting both axle weights as well as overall weight.  Good exercise as well to make sure you re not over the limit!!

Ok, I have heard back from Contintental (very helpful as has been mentioned)

As suggested here, I have just had the vehicle weighed. Full water tank, and full tank of fuel. but no passenger, or driver.

The total weight of the vehicle is 2960kg.

The front axle weight:  1280kg

The rear axle weight:  1680kg (total weight minus front axle weight)

This means that without us, clothing, and food etc, in the van, we are 540kg under the 3500kg max.

Going by the chart (attached) from Continental, it would seem that Fiat/Bessacarr's 5.5Bar all round, is excessive, and unnecessary.

 

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A roughcalculation, adding our combined body weight, brings the front axle weight to 1430kg.

Adding this to the weighbridge total weight, brings it up to 3110kg. 

This leaves 390kg of remaining payload before reaching the 3500kg limit.

A guestimate would be that any of this extra 390kg will over, or behind the rear axle, and so adding this to the weighbridge given rear axle weight, takes it to 2070kg.

Continental's chart doesn't go down as low a 1430kg for front axle weight, but erring on the higher side for the rear axle, a weight of 2130 gives a recommended level of 65.3 for the rear tyres.

I am going to try 55psi for the fronts, although this is way above what the chart would indicate.

Now have 55psi front, and 65psi  rear.

Visually, the tyres don't sit any differently on the ground, so certainly not looking under inflated.

Took the vehicle out for a short run, and didn't notice any additional body roll on cornering.

Need to try it at speed 65mph, to see if the steering still feels like driving on marbles, as someone described it. I suspect that it won't.

Need a more extensive run to confirm, but it does feel a more comfortable ride, and not like diving on solid tyres, as it did.

Dave, if your 3500kg MH is based on the 'light' chassis (more than likely) then you have an issue...

the front axle weight limit is 1850kg (no problem) but the rear is 2000kg and your guesstimate is 2070kg...not good.

ok, a couple of points.....some good, some not so good...

firstly, the extra weight of driver and passenger will not just be loaded to the front axle....it will be split around 70/30...so some effect in the rear axle.

similarly, any weight added to a garage (rear storage behind the rear axle) will add MORE than the nominal KG value, due to the fulcrum effect.

so, 390kg added to a garage may add approx 450-500kg to the rear axle but remove that same extra 60-110kg from the front axle...

any overall 'upgrade' of MTPLM to (say) 3650kg will NOT increase any axle limits, of which the rear will always be the Achilles' Heel...

i strongly suggest you do the whole operation again, as in DDs earlier post, and FULLY load the van with everything you intend to carry, including full fuel, full water, gas, driver, passenger, bedding, bikes, BBQ, chairs, tables, tools, electrical items, books, clothes etc, etc

this is the only way to get an exact weight of both axles.

good luck.

 

 

An interesting input BB input. Thanks for taking the time to put it together.

I can understand the fulcrum effect, but hadn't considered this.

If as you say, its something like 70/30% split, front to back, then I guess the it works both ways, back to front.

From the weighbridge results, I know that the front axle weight is 1280kg. Taking the 70/30% split into account, our combined body weight of 150kg, adds 105kg to the front axle, taking it up to 1385kg.

Whilst adding the remaining 30%, 45kg to the rear axle, taking this to 1725kg.

1385 + 1725 = 3110kg., which leaves 390kg, before reaching the 3500kg limit.

If all of this 390kg, was added the rear axle loading it would of course now take it to 2115kg, so over the 2000kg limit you refer to.

However, if we assume assume that only 70% of this 390kg is loaded onto the rear axle, and the remaining 30% applied to the front axle, then 273kg would be added to the rear axle loading, and 117kg added to the front axle.

So now we have a calculated front axle weight 1502kg, and a rear axle weight of 1998kg. Close to, but not exceeding 2000kg.

1502 + 2000 = 3502

Realistically, we are never going to load 390kg of clothing and food into the van, and so not going to get anywhere near to the full 3500kg.

The only thing missing from the van when it was weighed, was me and the wife, clothing and food.

Chairs, TV toiletries etc, etc, were all onboard. Fuel and water tanks both full. No rear garage, and we don't carry bikes.

When we do go off for more than a day trip,loaded with clothing and food, I'll say to the wife, "I've just got to go to a weighbridge on the way"