Because of this, the tire requirements of a rear-engine Porsche are significantly different than a front-engine and front-heavy Mustang. Despite both cars running a similar sized rear tire, the Porsche tire has far more rear weight and loading that goes into the sidewall, and using a bespoke Mustang tire may hurt the performance and feel of the tire. The same could be true if trying to use a Porsche front or rear tire on a Mustang.
Tires are complex machines in and of themselves. They are not a part “ON” the car, but an integral part “OF” the car as a whole, especially when optimized for a specific car. Tires are one of the most complex and engineered components on a car.
Having said that, selecting the right tire is not complicated or scary even if all of the technical details that we have covered were overwhelming. While there are A LOT of small details and magic that goes into creating tires, both the-off-the shelf and bespoke tires operate in the same “performance envelope” that the family of tires (PS4S or Cup 2) represent. This means that while there is some variation in performance and feel, you’ll never be out in left field by choosing any tire within a given tire model. And let’s face it, 99% of drivers cannot get within a few seconds of a tire’s limit, so a second difference between one tire and another won’t be noticeable. It is important not to mix tires from different applications without a lot of knowledge on how those tires were designed. For example, fitting a high grip compound tire from a Mercedes application on the front with a moderate grip compound for a Porsche on the rear just because they were both PSC2 and sizes were convenient could result in poor handling characteristics.
When looking for a UHP tire like the PS4S for a car that did not come with them from the factory, or if you are upgrading from a UHP tire to the Cup 2, you can’t go wrong with selecting a tire that fits your application. Going from a PS4S to a Cup 2 will outright give you better dry and track performance. It’s important to know that if there is more than 1 tire listed for your size, it’s important to look at the actual ‘tread width’ of the tire (like we learned in the How to PROPERLY Select and Size TIRES for PERFORMANCE article, where tread widths can vary despite the same nominal width on the tire) and select the one that best fits your wheel.
If your car came with PS4S or Cup 2 tires from the factory, it is probably best to stick with that exact model when it’s time to replace the tire. This is because a lot of work goes into developing bespoke tires from a handling and electronic programming standpoint, the subjective feel and performance is optimized for the car, and they often use a more aggressive and performance-oriented compound than standard off-the-shelf tires. Because of this, swapping out a bespoke PS4S or Cup 2 designed for your car to a wider off-the-shelf tire can actually make the car slower and hurt both the subjective and objective aspects of the car. If you decide to go with a different model of non-factory tires, even if it’s the same size, it’s important to swap all of your tires out and not mix and match one off-the-shelf tire with bespoke tires.
Now if you are considering the track-focused Cup 2 R, it’s important to know that it is not recommended to use these tires on the street, especially in cold weather. The Cup 2 R is a motorsport race compound and they should be treated like a race tire: with respect and with the knowledge that there is significantly less grip in ambient temperatures and they need to be warmed up to even make the same grip as a normal Cup 2 or PS4S on the street. But once warm, the Cup 2 R delivers world-class grip and is designed for the heat and abuse of turning some of the fastest production car lap times out there.
At the end of the day, there is far more that goes into tires that most people realize. They are highly complex machines but most of the magic that goes in to their creation is rarely ever known. Hopefully this article shed some light on the effort that goes into creating these tires behind the scenes and for particular cars and how important the symbiotic relationship between car and tire really is.