All tires are made up of layers of fabric, which is known as the casing that serves as the foundation of a tire. A cord is the individual strands of fabric that construct the casing. The cord casing is covered in rubber and then the remainder of the tire is made around this casing. Threads per inch is a Unit for the density of the carcass fabric, measuring the number of nylon threads per square inch of casing material.

TPI/EPI Vs Quality of Tire

In general, the higher the EPI, the denser, more supple and lighter the casing is and thus the higher the quality of the tire. Lower EPI casing provides better puncture protection but makes for a stiffer and heavier tire. In principle, the more close-meshed a carcass is woven, the higher the quality of the tire. The idea is that tires with higher thread counts usually have finer weaves that make these tires more supple. A dense carcass is important for low rolling resistance and good riding properties. At the same time, puncture protection increases, because carcasses with a high strand density are difficult to puncture.

It is more complex in reality while comparing TPI and the following aspects have to be taken into consideration:

How TPI/EPI is measured? Ideally, you look at the TPI of the casing fabric before it is made into the tire. Some manufacturers count every layer of the tire to measure TPI. Most tires have multiple layers of overlapping casing, so by that method of counting, a 50 TPI fabric will make a 150 TPI tire. And if you added another layer for added puncture protection, you’d make the tire slower, but you’d bump up the TPI. So if a tire maker claims a higher TPI, you have to divide the number by the number of fabric layers to get the TPI of the fabric. Some companies measure TPI as a count for an individual layer in a casing. Other companies may give the total number of fabric threads of all layers in the casing construction. Be cautious when comparing EPI indications, as often the number of strands of all carcass layers are added together.

What is the diameter of the threads? The reason high-TPI tires usually are more supple is that the threads are thinner. If you keep all things equal, thinner threads will mean more threads per inch. However, if you make your weave denser, you also get more threads per inch, but a stiffer casing. The most supple tires use super-fine threads, but space them out a little further. That way, you get an even more supple, and even faster, tire. If you go by TPI alone, the best casing looks inferior, but in fact the more supple, faster casing.

How much rubber? Fabrics with very thin threads are fragile. They have to be handled very carefully during production. The factories that make budget tires aren’t equipped for that, so they compensate by covering the fabric with more rubber to protect the threads. This makes the casing stiffer and reduces performance and comfort. So one maker’s casing may be a lot less supple than another maker’s casing of the same TPI.

What material is used for the threads? With a hand-made FMB tubular, you get a choice of cotton or silk threads. The silk is more supple than the cotton (which already is more supple than most polyesters). Even among polyesters, there are great differences in the thread materials. It makes no sense to claim that a 90 TPI silk casing is less supple than a 100 TPI cotton casing.

These are just a few of the factors that determine the tire’s suppleness. Let’s compare two hypothetical tires:
Tire A uses a stiff and relatively large-diameter thread. The fabric has a super-dense weave and is slathered with rubber. The maker counts every layer of the casing, and thus arrives at a 300 TPI tire.
Tire B uses a supple, superfine thread, woven into a relatively loose weave. The manufacturer keeps the rubber coating to a minimum. They report the TPI of the casing fabric and arrive at a 90 TPI tire.

It’s easy to see that Tire B above is superior to Tire A, even though it has less than 1/3 of the TPI. Suppleness, like so many important things, is hard to quantify, but you’ll notice it when you ride the tires.