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[05omegav6]

Braking is one obvious example of when an axle, and therefore the tyres, might become momentarily overloaded, but cornering is the other scenario... a sweeping bend is another and the higher the speed, the greater the weight transfer, and therefore the greater the load on the outer tyres.

Yes the numbers might be conjecture, but braking a fully laden car mid corner due to external factors could see a third of the cars weight (or more) over acting on the outside front wheel. So using my example, that's around 760kgs, so potentially overloading a 94 rated tyre by 100+kgs.

Generally speaking the tread will probably wear out before the sidewall, but even the most careful driver will encounter potholes, kerbs, bumps on and off driveways, and speed humps, all of which have the potential to weaken the structure of the tyre.

[Marks DTM Calib]

The Max permissible weight of my estate is approximately 2300kgs iirc, split 1100 kgs on the front axle and 1200 on the rear.

If I fit 93 rated tyres, that allows for a total of 1300kgs per axle... under heavy braking, the centre of gravity will move forward. How far forward do yo think it needs to move to overload the front tyres?

Ok you might say that this is an extreme example, but overload them, even for a moment, repeatedly and you'll run the risk of fatiguing the tyres, possibly to the point of failure.

Which actually is a nothing test sadly Al as going on that basis, even the max rated tyre will be overloaded and hence they are rated to much higher peak side wall loadings.

The tyre wall will not explode or fatigue under short term excess load, its all about continual flex of the tyre wall due to excess load which will result in a side wall blow out, similar to an under inflated tyre. 

[05omegav6]

As demonstrated by the relatively low failure rate of car tyres...

Trouble with tyres is that there are so many variables which affect their behaviour and performance...

Failure of the sidewall is more likely at lower pressures, not only as as that generates heat which softens the rubber, (great for grip, and perceived performance Tb/Chris), but it allows greater flexing of the sidewall, which could accelerate the fatigue effect on the reinforcement. A combination that lends itself to sidewall failure...

[TheBoy]

But that's not scientific, more coincidental I think. But load rating will affect handling I suspect...   ...and not always for the better (or worse)

I see where the "tyres are subjective" argument comes from now. Its only subjective if discussed in a subjective manor, as here. A factual approach is needed here I think.

Lazy bloody admin. Facts please

Ahhh, but we know the facts. Fit Dunlop Sport Maxx TT, and all your grip and stability problems go away .  Shame they aren't made any more 

[TheBoy]

As demonstrated by the relatively low failure rate of car tyres...

Trouble with tyres is that there are so many variables which affect their behaviour and performance...

Failure of the sidewall is more likely at lower pressures, not only as as that generates heat which softens the rubber, (great for grip, and perceived performance Tb/Chris), but it allows greater flexing of the sidewall, which could accelerate the fatigue effect on the reinforcement. A combination that lends itself to sidewall failure...

Aside from Mrs TB driving too far on a tyre rapidly losing air, I've never had sidewall damage on any Omega.  I've always managed to "get my money's worth" from the tread first.

I'm sure GM specced it to leave enough headroom, even 4 up with luggage.

[chrisgixer]

As demonstrated by the relatively low failure rate of car tyres...

Trouble with tyres is that there are so many variables which affect their behaviour and performance...

Failure of the sidewall is more likely at lower pressures, not only as as that generates heat which softens the rubber, (great for grip, and perceived performance Tb/Chris), but it allows greater flexing of the sidewall, which could accelerate the fatigue effect on the reinforcement. A combination that lends itself to sidewall failure...

Aside from Mrs TB driving too far on a tyre rapidly losing air, I've never had sidewall damage on any Omega.  I've always managed to "get my money's worth" from the tread first.

I'm sure GM specced it to leave enough headroom, even 4 up with luggage.

Given the attention they paid to the set up figures, I wouldn't bet on that. Al all, personally.

[TheBoy]

As demonstrated by the relatively low failure rate of car tyres...

Trouble with tyres is that there are so many variables which affect their behaviour and performance...

Failure of the sidewall is more likely at lower pressures, not only as as that generates heat which softens the rubber, (great for grip, and perceived performance Tb/Chris), but it allows greater flexing of the sidewall, which could accelerate the fatigue effect on the reinforcement. A combination that lends itself to sidewall failure...

Aside from Mrs TB driving too far on a tyre rapidly losing air, I've never had sidewall damage on any Omega.  I've always managed to "get my money's worth" from the tread first.

I'm sure GM specced it to leave enough headroom, even 4 up with luggage.

Given the attention they paid to the set up figures, I wouldn't bet on that. Al all, personally.

The designers and bolt-em-together peeps have different agendas 

[Auto Addict]

The important thing is that the load rating matches or exceeds that which the manufacturer specifies. 

Towing etc. should not result in the manufacturers spec being exceeded (for example, the max nose weight on the tow bar is circa 75Kg which is bugger all extra assuming the pikey wagon/trailer brakes are working correctly.) 

Totally agree ... but there are a few additions .... many folks will have 2 adults + 2 kids in the car + a boot full of stuff when towing .. so the tow bar load is additional to the "normal" weight, and has a degree of "leverage" given the position of the towbar.

In my case .. and the "worst case" scenario ... off to France so the roof box will be on and full , around 60 kgs, 2 bikes - another 20 kilos, LPG tank full - 40 kilos and then all the other crap we take .. BBQ, coldbox, awning, poles etc etc etc on the back seat as I prefer to have a heavy(ier) car and light(er) van when towing.

All this plus driving for 4-5 hours in (hopefully) warm conditions will put extra stress on the tyres, so I choose to use XL purely as a precaution ...

Yes but as said, the load ratings for the tyres are based on the manufacturers max load calculations (e.g. fully laden) which will have already considered those factors including the nose weight 

Interesting, Blackcircles recommend XL on mine, but the tyres fitted (original factory) are not XL - confused.com

....but the handbook gives tyre pressures for both....

[chrisgixer]

As demonstrated by the relatively low failure rate of car tyres...

Trouble with tyres is that there are so many variables which affect their behaviour and performance...

Failure of the sidewall is more likely at lower pressures, not only as as that generates heat which softens the rubber, (great for grip, and perceived performance Tb/Chris), but it allows greater flexing of the sidewall, which could accelerate the fatigue effect on the reinforcement. A combination that lends itself to sidewall failure...

Aside from Mrs TB driving too far on a tyre rapidly losing air, I've never had sidewall damage on any Omega.  I've always managed to "get my money's worth" from the tread first.

I'm sure GM specced it to leave enough headroom, even 4 up with luggage.

Given the attention they paid to the set up figures, I wouldn't bet on that. Al all, personally.

The designers and bolt-em-together peeps have different agendas 

The designers think up to 2.45 camber is in tolerance, iirc. What's that to do with assembley ?