The NT05’s carcass is also designed with ultra high performance in mind. The tire's casing is made of two plies of polyester with a high end turn-up. The turn up refers to the turn of the plies as they go around the bead of the tire and back up the sidewall. High turn up means that the termination of the plies is higher on the sidewall than normal giving the sidewall 3-4 plies of stiffness from the bead to the tread from a two ply casing. This stiffens the sidewall in the bead area, improving handling by quickening response to steering input while still allowing the sidewall to flex a little in the tread area for smoother ride and layout of the tread to the ground plane for better grip by reducing sensitivity to tire shock.
The NT05 has two steel belts that increase puncture resistance and reduce tread squirm, helping keep the tread flat on the ground without lifting under side load when the sidewalls distort. A spiral wound aramid (aramids are super strong synthetic fibers like kevlar) cap ply prevents tire growth and tread center bulging at high speeds, reducing heat build up and improving the tire's speed rating. The spiral winding eliminates the need for the typical way of joining the cap ply, a lap seam which is a weak spot under load and an area of differing stiffness that can cause problems at high speeds.
A big part of the R&D testing for the NT05 involved dialing in the composition of the NT05’s unique tread compound. The compound developed for the NT05 uses a lot of silica and a special blend of polymer additives to create a flexible and resilient tread material that is very good at conforming to micro irregularities in the road surface. This tread compound works exceptionally well in both wet and dry conditions and is a big step forward in grip capability when compared to the long wear biased compound used in older Nitto tires. The NT05 has two large circumferential grooves to resist hydroplaning while the large tread blocks with narrow grooves on the sides of the tires give good lateral grip.
We chose a 245/40-18 tire for our car. The larger tires on our aggressively wide wheels really fill our wheelwells, especially at the low ride height that our Tein Flex-Z coilovers allow.