TYRE PRESSUES

[Meister]

Hope someone can help.

The owners handbook of my car tells me that I should increase the tyre pressures when towing a caravan.

I have read somewhere on this site (and on other forums) that people increase the tyre pressure when towing so:

If I am towing with a noseweight of 75Kg and just myself and my wife in the car WHY would I need to increase the tyre pressures ??

It makes good sense to do so IF my car were loaded (with awning etc etc) but not otherwise.

I would appreciate the thoughts of you experienced caravanners please.

Thanks

Steve

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I started out with nothing & I still have most of it left.

 

[Meister]

I should add that I would not increase tyre pressure if carrying a 75Kg (11 1/2stone) passenger in the rear seats.

Steve

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I started out with nothing & I still have most of it left.

 

[RogerP]

dont think its to do with the 75kg weight of a rear passenger more to do with the forces a caravan would excert on the towbar / suspension / tyres.

After all your 75kg passenger wouldn't change weight(much) whilst travelling say down hill but effectively the caravan would or at least the forces it excerts on the car would.

My hand book states that

for driver and passenger 32psi.

for 3 rear passengers and luggage 39psi

for towing 39psi ,

oddly it says nothing if i had 3 rear passengers , luggage and was towing?

 

[Bri-C]

Hi Steve..

Time me thinks to get a bit techy "SORRY"

If you put 75Kgs of little people on the back seat of your car then their weight is forward of the rear axle and as such the weight is shared between the front and rear axles, probably around 25% front 75% rear. 75 Kgs in the boot will go onto the rer axle. But the towball is outside the vehicle and a considerable distance behind the axle so therefore 75Kgs here actually relates to around 100+Kgs of extra axle load depending on the ratio of wheelbase to rear overhang, as it actually lightens the load on the front axle when you hitch up.

When you accelerate, a lot of the vehicle weight is transfered to the rear axle towing or not !!

When towing the aerodynamic drag on the front of the van increases the noseweight considerably. When you hit a bump the rear axle now has to lift the front of the van as well as the rear of the car and as for when the caravan brakes apply then the drawbar is forced towards the road probably increasing the noseweight to a couple of hundred Kgs maybe more ..

Poor tyres !!!!

Tyres overheat when the sidewalls contiually deflect with load so increaseing the pressure inside the type reduces the deflection..

I hope that this helps.

Regards Brian....

 

[Meister]

Hi Brian,

Thanks for the reply.

It makes sense and I now understand the reasons for the extra tyre pressure so will ensure I carry my mini compressor when towing.

Steve

----------------------------------------------------------

I started out with nothing & I still have most of it left.

 

[Bri-C]

Hi Steve...

Your more than welcome good sir..

I opted for the shortform responce rather than the detailed one as that could run into several pages... But I'm sure that somewhere out there will be a Maths teacher who would love to put some numbers togeather. You will however be amazed at the level of forces that move about you vehicle when towing... quite scary really..

Interestingly enough though you don't often see people reducing their tyre pressures when they arive for their two weeks holiday or increasing them again for their return trips... Often thought that the sites could supply an air line for the use of visitors. Or would it simply dissappear overnight..

Regards Brian.....

 

[Meister]

Hi Brian,

Thats the very reason I purchased a portable compressor which plugs into the 12v socket in the car .......... to use before I leave the camp site as I will have reduced the pressure on arrival.

No problem at home as I have a large compressor.

Thanks again.

Steve

 

[Woody3]

This is one of those oddities. We recently got an Octavia Mk1 which indicates 39psi for fully laden, so that is what I put them to the first time I towed. Nearly died of fright - it wallowed like nothing I've ever had before. Dropped the pressure to 36 then to 34 (normal is 32) and everything was hunky dorey. (Octavia ball weight is 60Kg max)

I found the same with a couple of other cars - Astra estate, Vectra estate, but curiously not on a Montego estate where the rear wheels are much closer to the back end.