Deeper and wider circumferential grooves and lateral slits increase the “Void Ratio” (the amount of material taken away from a full slick) and improves hydroplaning resistance at the cost of contact patch size. Compounding has a big effect in terms of wet grip but increasing the void ratio is purely a tradeoff between standing water hydroplaning performance vs steering response and overall dry performance. This is why some of the fastest and most aggressive Cup 2s do not have the same hydroplaning resistance as more street focused Cup 2s.
Due to the differing demands between performing in the wet and dry, a tire acts like two tires in one. The inboard placement and location of the grooves enables a large outer shoulder (like a slick-type racing tire) to improve dry grip, cornering performance, and durability on track since it gets the majority of load and pressure when cornering.
Meanwhile the inboard grooves are mostly in play during straight line driving and especially in the wet, where the tire does not roll over and load the outer half of the tire as much because of the reduced grip. The inner half tire also greatly affects steering response and straight-line driving.
There’s a reason when you look at many of Michelin’s tires (from the Cup 2, PS4S, PSS, and going back to the older days of the PS2 and earlier) the tires essentially look like ‘street’ or ‘rain’ tires on the inner half and more aggressive slicks on the outer half. There’s also a reason many tires in this category have slowly shifted towards this philosophy and tread layout for UHP and streetable track-focused tires.
Outer Shoulder “Features” and “Sipes”
The outer shoulder can have a varying amount of what Michelin calls “features” (any lateral groove across the tire) that many, including myself, would incorrectly call “sipes”. This is not technically correct since “sipes” are the very small hairline cuts in a tread block that provide micro biting edges in the rubber that deform and open up to suck in water to remove it from the contact path surface. They are designed to increase grip in low friction conditions like heavy rain and snow type conditions, but are not conducive for performance driving. These lateral features also create a path for water to exit the contact patch laterally, further improving hydroplaning and wet grip. The effectiveness of these depends on their depth and number around the circumference.
These outer “features” slightly improve hydroplaning resistance, provides an aesthetic look to put tire in certain family, and also affect the tread-induced noise the tire makes. Upon closer inspection, Michelin uses 3-4 different ‘pitches’, or width & distance between ‘features’, that through programming, can optimize pitches to reduce drone and tread induced noise.
Many Cup 2 tires made for Mustangs and Corvettes have wear hole indicators that are commonly used on racing tires.
The lateral groove “features” can easily be mistaken as the thickness of the tread and once they’re worn away, are often (incorrectly) assumed to be worn out when in fact they are designed to be worn away, look like a slick, and still have plenty of life left in them.
Cup 2 R:
Cup 2 R’s have an extremely shallow of a tread depth and just enough features to meet euro ECE wet & DOT certified wet. They are a single focus tire: dry lap times.
Table of Contents:
Page 1 – Intro, My Background, Developing Bespoke Tires
Page 2 – TREAD DESIGN – Tread Depth
Page 3 – TREAD DESIGN – Circumferential Grooves, Outer Shoulder Features & Sipes, Cup 2R
Page 4 – COMPOUNDING – Compound Variation Across Tread & Tread Depth, Cup 2R
Page 5 – CONSTRUCTION – Carcass Profile/Shape, Width, Ribs
Page 6 – CONSTRUCTION – Sidewall Stiffness, Run Flat Tires, Cup 2 Connect
Page 7 – How Tread Design, Compounding, and Construction Come Together
Page 8 – Conclusion