Thank you chaps. Some good comments. I think I will play safe and have new tyres fitted including the spare which has not been used. Black Circles don't offer caravan tyres it seems but I will trawl around and find someone who can supply and fit.

I agree that safety first is best, they tyre tread is your only contact with the ground after all.

Cheers Concrete

Let's not be ageist about tyres. Like people, they can deteriorate with age with hardening of the tread and not quite so much grip on reality. But a bit of surface cracking is immaterial. I put new Goodyear tyres on my TR7 in 1988 at 45,000 miles and, although their tread was well above the legal limit, I changed them in 2011 at 65,000. They are coming up to ten years old but have only done 6000 miles. I do not plan to change them soon.

The point about exposure to light is a good one. The TR7 is mostly in the dark. I once had a small boat which lived on a trailer by a reservoir, along an east/west axis. The south facing tyre was all cracked and crumbly but the north facing one looked as good as new.

If the OP is worried about the unlikely event of a blow-out, he should inflate them to at or just above the maximum pressure indicated on the sidewall and look for bulges. I suspect most caravan blowouts are from carelessly neglected low pressured tyres getting too hot on a sunny M5.

In the (hopefully unlikely) event of it being needed is it likely to be serviceable?

In a word, yes. It's spent its life in the dark, and you have topped up the pressure occasionally. The spare in my equally-old Pug has done the same and still looks as good as new. I used it for the second time last month to take one of the other wheels to ATS for treatment.

His explanation was when tyres are used they obviously flex and this keeps the rubber nice and subtle. Let a tyre stand too long and its not just the fact its older, a person with no exercise results in stiffness etc, with a tyre this lack of use can result in cracking when its used.

You must mean supple, Skidpan, there's nothing subtle about a racing tyre ... :-) Joking apart, of course all tyres age with exposure to air, but I would guess that a 10-year-old tyre kept in the dark will be in a similar state to a 2-year-old one on a vehicle. As an ex-photochemist I know that UV triggers slow oxidation of hydrocarbons.

<< Cars live outdoors and spend most of their time parked. >>

But they usually turn a wheel (all of them) every few days - caravans may not move for months. Not good for tyres which slowly lose pressure.

That exactly, my caravan has not moved since October. Will be March at least before it can come out and play.

If the club(s) recommend 5-7 years that would be good enough for me.

I don't think I've ever ridden a motorbike on anything else, so I've yet to learn how rubber softens with youth.

If youve ever ridden a motorbike on old tyres in the wet you'll soon learn about how rubber hardens with age.

Indeed, and as the Space Shuttle Challenger disaster of 1986 showed, rubber doesn't work very well when it gets cold and is far less compliant.

People have to realise that just because a tyre is not cracked, it doesn't mean it's perfectly fine.

I do also agree that a fixed 'lifetime' isn't the way forward either - I just have used those I've been given as a general guide to when to expect issues to start arising, so I can monitor how the car behaves in the cold, wet, snow and ice.

Most commercial vehicles have twin rear wheels so less of an issue with a single tyre failure.

A commercial vehicle starts from something like a Fiesta or Corsa van and goes right up to the biggest trucks. Twin rear wheels only become commonplace on vehicles with a GVW of more than 3.5t, so there are significantly more commercial vehicles with single rather than twin rear wheels.

If blindspot meant LGV (large goods vehicle, which used to be called HGV for heavy goods vehicle), then that does make more sense with regards to what you said, as there are virtually none with single rear wheels.

Still doesn't make much sense in my mind though. If you take a 12 tonne (GVW) lorry as an example, unladen, with a basic dropside body, that will weigh around 6 tonnes unladen, split between the two axles. Put the 6 tonnes of payload in the back, and while the front axle will bear some of that, most of it is being supported by the rear axle. So there is going to be a fairly equal amount of strain on all 6 tyres on a hard working truck.