No mention of "going straight" in your initial comment that I replied to, but you later inserted it to suit your point? But I've seen the results of drivers losing control at lower speeds than that, and they generally haven't tried that hard at all, since the end result was never their intention to start with. There are many more variables involved than simply speed.
Not at all. Fitting the tyres with the best grip to the rear may increase the overall stopping distance, if the front tyres have less adhesion in the conditions encountered. But the vehicle will generally remain more stable in all conditions, rendering its handling safer overall, and particularly at the extremities of its capabilities, which could again be absolutely vital in an emergency situation.
But if the tyres to the rear have substantially less grip because they are more substantially worn, because they are of a different type which provides a lower level of adhesion in certain road or weather conditions due to the tread design, compound, difference in construction, different slip angles etc. there will be many occasions where the vehicle is likely to be less stable and could be downright dangerous, particularly in an emergency situation that is not the normal day to day driving conditions that the vehicle and driver normally encounter. There is no inconsistency.
You realise that all season tyres are designed to cope with a range of conditions outside of the scope of a dedicated summer or winter tyre, and as such are generally a compromise? A good summer tyre will often perform better in non-adverse conditions above about 7C. Similarly a good winter tyre will generally perform better in colder conditions. What an all season tyre is good at, is performing moderately to well in a much broader range of conditions, avoiding in some countries the legal necessity to otherwise change between summer and winter tyres at different times of the year.
From that, you may have realised that there are likely to be certain conditions in which the location of different tyres may not matter too much, but in general, in conditions where tyre adhesion is likely to be seriously affected, such as loose, slippery wet or greasy surfaces, it is generally far safer to have the tyres that will provide the best grip at the rear of the vehicle. In comparison to normal, or what are now termed summer tyres, all season tyres have a genuine performance advantage in those conditions. Their tread patter is specifically designed to perform well in those conditions, and they generally have a deeper tread, better able to disperse water and increase grip in wet conditions, compared to a summer tyre.
If you have gone to the thought and trouble of fitting all season tyres, you have obviously done it for a reason. If you can only afford two such tyres, surely it is better to fit them in the location where they provide the best advantage and greatest safety margin, in the type of conditions you probably envisaged buying them to counter? But for the maximum advantage provided by the tyres, it would be inherently safer to fit them to all of the wheels, rather than just one axle, which is generally the situation with any type of tyre.
There is no specific legal requirement, as you have said, but it is a matter of what is safest. You can legally drive a motor car on a road with only 1.6 mm of tread depth across the central three-quarters of the breadth of the tread area, and around the entire circumference. Is that as safe as having say, 3 or 4 mm of tread as a minimum across the whole breadth of the tread area? Of course it's not, and there are likely to be conditions encountered where tyres worn to their minimum legal tread depth could seriously compromise the handling of your vehicle and its safety. So as with many things, you have a choice between saying, "Well, it's legal" no matter what the outcome may be, or deciding that you want to be as safe as possible in any situation that you are likely to encounter.
If you have taken the decision to purchase all season tyres, you have probably done that for safety reasons. It surely makes sense then, to maximise their advantage if you can only afford two of them?
Oh, I'm done. I can see that I'm on a hiding to nothing. I posted because if the advice I gave helps top save a life, expensive damage or even another motorhomer finding themselves in a sticky situation, it will have been worth it.
Anyone reading the thread can make their own choices and decide weather to take notice of advice given by a professional with many years of experience and qualifications in vehicle technology, including vehicle handling and tyre examination, design and technology; who has worked with similarly qualified people, had his observations and conclusions peer reviewed and has given evidence as an expert witness on many occasions in both criminal and coroners courts, or the bloke whose arguments relating to the laws of physics apparently revolve around his preference for saving money.
I won't be replying again. I have other things to get on with
