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[twiglet]

I know this has been mentioned before, but I can't find it... 

I have a 3.2 Auto Elite Estate, and this weekend it will be loaded up with 2 people, a boot full of stuff, and towing a 25ft caravan!!

What would the OOf recommendation be for front and rear tyre pressures please? 

[Glyn]

40psi front.
48psi rear

Glyn

[dad1uk]

                                 Pressure with                  Pressure with
                                               up to 3 persons                  full load
Engine      Tyres            Front      Rear                  Front      Rear

Y22XE      195/65 R15      2.1      2.3                   2.8       3.3
Y22DTH      205/65 R15
Y25DT      225/55 R16
      235/45 R17

Y26SE      205/65 R15      2.1      2.3                   2.8       3.3
      225/55 R16
      235/45 R17
      195/65 R15 (M+S)


Y32SE      205/65 R15      2.1      2.3                   2.8       3.3
      225/55 R16
      235/45 R17
      195/65 R15(M+S)


Measurements in bar. 
1 Bar + 14.5 psi

[sticka_v8_init]

40psi front.
48psi rear

Glyn

Don't forget to check the max pressure your fitted tyres will take 

[twiglet]

Cheers guys! 

[Andy B]

I always used to up the pressures on my tyres when towing, but then thought that, the tow hitch is only getting another 75(-ish) kg which isn't much different from another passenger in the car, so I don't alter tyre pressures any more. In the last fortnight I've driven 1850 miles, most of which with a caravan on the back, & have had no problems. 

(NB Before we went to French France my wheels were all off for various checks etc & if anything, the rears seem to have been a little over inflated ie more tread on the sides of the tyre than in the middle. 32psi on 235-45x17 tyres)

[twiglet]

I always used to up the pressures on my tyres when towing, but then thought that, the tow hitch is only getting another 75(-ish) kg which isn't much different from another passenger in the car, so I don't alter tyre pressures any more. In the last fortnight I've driven 1850 miles, most of which with a caravan on the back, & have had no problems. 

(NB Before we went to French France my wheels were all off for various checks etc & if anything, the rears seem to have been a little over inflated ie more tread on the sides of the tyre than in the middle. 32psi on 235-45x17 tyres)

Hi Andy,

I have noticed exactly the same. I run 30psi front and 33 psi rear usually on 235/45x17 tyres and most of the time it's just me an SWMBO in the car. My last set of rear tyres definately wore quicker in the middle than at the edges. I have recently had a full WIM setup and new rear tyres, so I am watching things closely!  :-?

Now that I think about it 40psi/48psi does sound alot!  :-/

[feeutfo]

I always used to up the pressures on my tyres when towing, but then thought that, the tow hitch is only getting another 75(-ish) kg which isn't much different from another passenger in the car, so I don't alter tyre pressures any more. In the last fortnight I've driven 1850 miles, most of which with a caravan on the back, & have had no problems. 

(NB Before we went to French France my wheels were all off for various checks etc & if anything, the rears seem to have been a little over inflated ie more tread on the sides of the tyre than in the middle. 32psi on 235-45x17 tyres)

ime the rears tend to go that way anyway, opposite to the fronts.

[Entwood]

The "reason" for increasing tyre pressures for high load/high speed has nothing at all to do with tyre wear... but everything to do with preventing tyre blowouts.

With higher loads the tyre will deform slightly more, the "bulge" at the bottom will be slightly bigger, even though the tread remains "square" to  the road. As the wheel rotates the position of the "bulge" on the tyre remains at the bottom, but the tyre has rotated so to the tyre the bulge has moved and that part of the tyre no olnger "bulges" .. it "flexes" back  to flat.

This constant flexing of the tyre is not constant within the tyre walls, the different "layers" have to move different amounts. Thus the layers "rub" against each other and cause heat.

Heat causes the tyre materials to soften. The tyre then "bulges" and "flexes" more, so the friction between the layers increases, the tyre gets hotter .... etc etc etc. The temperature can rise far enough that a catastrophic failure of the tyre wall occurs .. a blow out..... 

High speed motoring for continuous periods has the same effect eventually, the normal "small" bulge causes a small amount of heat build up initially which then starts to increase rapidly.

This can be proved quite simply. Leave your tyres at "normal pressures" and do a quick 50 miles at high speed, stop, feel the tyres. You will be VERY surprised.

The higher air pressure supports the load, "strengthens" the tyre wall, and reduces flexing, all of which reduces the heat build up.

It is a pain adjusting the tyres everytime  .. but I change mine every time I tow. Then drop them back for normal driving.

Manufacturers would not put the information about increased load/speeds in the handbooks if it was not neccessary

Not worth the risk of a tyre blowout on the motorway at 60 mph with the 'van on the back .... which could get a tad interesting ... NOT... 

Just my thoughts .. nowt else 

[Andy B]

The "reason" for increasing tyre pressures for high load/high speed has nothing at all to do with tyre wear... but everything to do with preventing tyre blowouts. .....

I know that, but as most of my Omega's use these day involves towing I thought the fact that the rear tyres have been generally over pressure had relevance. Hitch weight of 75kg is only the weight of a person on the back seat, and would you increase your tyres to the upper pressures just for one extra passenger? 

[Kevin Wood]

Regardless of the increase in load from the hitch when towing, I find the combination is a good bit more stable with a little extra air in the car tyres - very noticeable with a 1600kg trailer getting on for 10 metres long.

I wouldn't go the the full load pressure generally, but 38-40 PSI all round is a good plan if towing, IMHO.

[YZ250]

I do inflate mine as per handbook for towing the van but was considering not bothering next time until I read Entwoods explanation.


Think I'll stick to doing it now though just in case. 

[Auto Addict]

The "reason" for increasing tyre pressures for high load/high speed has nothing at all to do with tyre wear... but everything to do with preventing tyre blowouts. .....

I know that, but as most of my Omega's use these day involves towing I thought the fact that the rear tyres have been generally over pressure had relevance. Hitch weight of 75kg is only the weight of a person on the back seat, and would you increase your tyres to the upper pressures just for one extra passenger? 

I could be wrong, but, as far as I am aware, the 75kg limit is nothing to do with carrying passengers, it's more to do do with the stresses the towbar puts on the bodywork.

[Auto Addict]

The "reason" for increasing tyre pressures for high load/high speed has nothing at all to do with tyre wear... but everything to do with preventing tyre blowouts. .....

I know that, but as most of my Omega's use these day involves towing I thought the fact that the rear tyres have been generally over pressure had relevance. Hitch weight of 75kg is only the weight of a person on the back seat, and would you increase your tyres to the upper pressures just for one extra passenger? 

I could be wrong, but, as far as I am aware, the 75kg limit is nothing to do with carrying passengers, it's more to do do with the stresses the towbar puts onto the bodywork.

[Entwood]

The "reason" for increasing tyre pressures for high load/high speed has nothing at all to do with tyre wear... but everything to do with preventing tyre blowouts. .....

I know that, but as most of my Omega's use these day involves towing I thought the fact that the rear tyres have been generally over pressure had relevance. Hitch weight of 75kg is only the weight of a person on the back seat, and would you increase your tyres to the upper pressures just for one extra passenger? 

I could be wrong, but, as far as I am aware, the 75kg limit is nothing to do with carrying passengers, it's more to do do with the stresses the towbar puts onto the bodywork.

Agreed.

Plus the fact that 75 kg ON THE TOW HITCH is a far greater force on the AXLE than a single person sat in the rear. The towhitch is some 2 feet BEHIND the axle.. so has a fairly significant "lever arm" causing the rear to "pivot" about the rear axle. A single person sat on the rear seat is actually slightly IN FRONT of the rear axle, so is BETWEEN the axles. This will cause the car to "squat" rather than "pivot" and so the load is spread more evenly between the front/rear axles....(if that makes any sort of sense)....

Thus the weight on the towhitch will, IMHO, cause a far larger "deflection" of the tyre wall ... thus leading to the increase in heat already discussed ...

Just my views .. nowt else ..