TPI and Tire Performance
Tires with supple casings are faster, more comfortable and simply more fun to ride. Most cyclists know this, but how do you measure ‘suppleness’?
A measure that often is used to describe the quality of tires is ‘threads per inch’ (TPI). The idea is that tires with higher thread counts usually have finer weaves that make these tires more supple.
The reality is more complex, and TPI is of limited use when comparing tires. Here is why:
1. How do you measure? Ideally, you look at the TPI of the casing fabric before it is made into the tire. Casing fabrics vary between 15 TPI for coarse utility tires to 120 TPI for very high-end tires.
What about the tires with 300 TPI or more? These makers count every layer of the tire. Most tires have three layers of overlapping casing, so by that method of counting, a 100 TPI fabric will make a 300 TPI tire. So if a tire makers claims a TPI of more than 120, you have to divide the number by 3 to get the TPI of the fabric.
2. What is the diameter of the threads? The reason high-TPI tires tend to be 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—in effect cramming more threads into one inch—your TPI goes up as well, but you actually have a stiffer, less supple 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 it’s in fact the more supple, faster casing.
3. How much rubber? Fabrics with very thin threads are fragile. They need 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 120 TPI casing can be a lot less supple than another maker’s 120 TPI casing.
4. What material is used for the threads? With hand-made FMB tubulars, you get a choice of cotton or silk threads. The silk is more supple than the cotton or polyesters. It makes no sense to claim that a 90 TPI silk casing is less supple than a 100 TPI cotton casing. And especially among polyesters, there are great differences in the thread materials.
These are just a few of the factors that determine the tire’s suppleness. Let’s compare two hypothetical tires:
Tire 1 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. Yet the result is a relatively stiff and heavy tire.
Tire 2 uses a supple, superfine thread, woven into a relatively loose weave. The manufacturer keeps the rubber coating to a minimum. They count the TPI of the casing fabric, and arrive at a 90 TPI tire. This tire is among the most supple and fastest anywhere.
It’s easy to see that the Tire 2 above is superior to Tire 1, even though it has less than 1/3 the TPI. Suppleness, like so many important things, is hard to quantify, but you’ll notice it when you ride the tires. Needless to say, our Rene Herse tires (and the FMB tubulars we import) are made from the finest, most supple threads, with a minimum of rubber, to create the most supple tires you’ll find anywhere.
Further Reading:
Photo: Lauren de Crescenzo on the way to winning the 2022 Tour of the Gila stage race, riding Rene Herse 700C x 28 mm Chinook Pass Extralight tires. (Photo: Cinch Rise)
