Manufacturers chose tyres based on a huge number of factors from testable criteria to subjective ones. Noise, response, balance, feel, bump absorption, and on and on are the things that mater at the point the car is signed off for production. Cost is a minimum factor as the manufacturer will be dictating the price for which supplying companies will have to conform. A given model of BMW for instance may come on a Michelin, Continental, Hankook, Pirelli or Goodyear. Whilst I’m not in the purchasing department, it is highly improbable that there would be any difference to the delivered cost of these tyres from any of these manufacturers as that would affect the overall economics of production.
Then, a tyre may be tweaked between manufacturers. An OE Michelin Premacy tyre on a Ford Puma may have a different carcase and rubber compound to one for a Citroen Aircross, and both different to the “standard” Premacy tyre offered at KikFit.
The testing that is performed, cannot account for all situations and senecios either. Testing is lengthy and expensive. Testing a car’s performance at different tread depths yields little relevant data for a vehicle manufacturer relating to the showroom, that side is down to tyre manufacturers. The priority of the engineers at Hiroshima to understand the wet performance of a OE tyre 4 years after the car was originally sold is likely to less than their concern for the drinks in the vending machine being the right temperature.
All tyres are compromises. In F1, where you are never more than 100 seconds from a 2 second tyre change, tyres are picked for the situation. We don’t have that option so must accept a compromise. Fitting All Season tyres to a car from new is always going to be one of those compromises to any manufacturer. You would be selecting a tyre based on what? Are people living on the South Coast worried about the same climatic conditions as those in the Scottish Highlands? The ultimate question is at which point does one tyre become the better option than another one and is there a penalty for running one tyre all year round compared to another? We have all experienced or seen RWD cars particularly, struggling for grip, to the point some can’t even get off their drive, once snow has fallen. On that basis alone, if you need your car and you expect to have to drive in snow, "non winter rated” tyres are not suitable and therefore not suitable for all round use, where as it is quite possible to drive on a Winter or AS tyre all year, even in a heat wave. So what are the down sides? Winter rated tyres, the three peaks and snowflake symbol, so that includes full Winter and AS tyres, use different rubber compounds, usually having a higher natural rubber content, than Sumer tyres. While you will not notice this to the touch, their compounds are softer and composition different, so their chemical grip, the actually sticking to the road, and mechanical grip, the bending and locking into the features of the surface, are optimised for lower temperatures. They also have a more cut or siped tread pattern allowing the tread in the contact patch to move around more under load and provide traction and by association, braking in snowy and freezing weather. There is no question that these type of tyres offer far superior performance in these conditions. The downside are very much when you are not in these conditions. Apart from a very small number of outliers, the wet performance of AS and Winter tyres is one to two levels of wet braking performance lower that the equivalent summer tyre. That is 4 to 8m longer stopping distance from 50mph, and given that most of the speed comes off in the last part of braking, you would still be going 20mph when the A rated Summer tyre has stopped. Is this the same in cold conditions? Much is said about a Summer tyre being limited to 7 deg, but what does this actually mean? Air temperature, surface temperature or something else? It actually refers to temperature of the rubber in the tread and carcase, and is considered the point where performance starts to reduce. It does not suddenly fall off a cliff. Summer compounds are harder, at a given temperature than Winter ones, they like a bit of heat or temperature to allow them to grip and flex. However, the act of driving will heat the rubber. The movement of the tyre, the constant flexing of the sidewall and tread produce heat within the rubber. On a dry road, even if it was minus 2, after 3 or 4 miles your tyre rubber will be capable of gripping well. It is water, and snow, that will suck the heat out of the tyre. But even then, if it is 4 or 5 deg a decent Summer tyre is still going to have very good performance and still possibly better braking performance than an AS and Winter tyre. It all comes down to tyre condition though. All these performance figures are derived from new tyres. Few MK3 drivers complained about their tyres when new, a 4 year old Bridgestone RE50 could be a spiteful thing though.
So basically you need to decide if AS or Winter tyres are appropriate for your driving need. In the dry, particularly in the summer, that soft, flexible tread can be imprecise, lack feel and communication and ultimate grip, you will notice understeer on a winter tyre. And if pushed, wear surprisingly quickly. They will wear faster in just general like for like driving anyway, but the final considerations are that they are generally more expensive than a comparable Summer tyre, typically require replacing at 5 years even if not being used and all winter rated tyres should be replaced at 3mm tread depth. If you need them though, they are priceless.