TPI and Tire Performance

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)

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Comments (19)

  • rabausten

    Currently enjoying the Extra light Barlow Pass. Running them on the new Pacenti SL25 rims (20mm internal width) at about 40psi front/45psi rear. Even at these low pressures they sit at 37-38mm wide. They replaced a pair of Challenge Strada Bianca, which I really liked, but a new frame gives me the option to go wider, so I took it.
    Beautifully smooth!

    January 5, 2015 at 5:01 am
  • Ron

    Love your posts about the “science” of cycling…. so informative. I’m not riding as much these days but still drop by your site often just for all the great posts and pictures. Keep up the great work !

    January 5, 2015 at 7:43 am
  • Xavier

    This is fun because there is exactly the same situation with suits fabrics.
    For suits fabrics there is a scale of S numbers (Super 100’s, 150’s, 180’s, 200’s, and so on). It comes from the worsted yarn count system where the worsted count was the number of 560-yard lengths of worsted yarn that 1 pound of wool yields. The finer the wool, the more yarn and the higher the count. The super S system derivates from this count and defines the S number by correlation to the maximum fiber diameter. For example, 80s must have maximum fiber diameter of 19.75 micrometres or finer and 90s, 19.25 micrometres or finer. (
    This system has led to an arms race to finer and finer fiber diameter (And therefore higher and higher S numbers). But at the end of the day the fiber diameter is only a component of a fabric quality and you can have stupendous fabrics in 80s and the other way around: Another good article but in french only:

    January 5, 2015 at 7:44 am
    • Jan Heine, Editor, Bicycle Quarterly

      arms race to finer and finer fiber diameter

      Interesting that in suits, you see a similar focus on numbers that can be misleading. It seems that the real world rarely can be expressed in a simple number.

      January 5, 2015 at 8:05 am
  • Pete

    My passion is cycle touring on roads. I’ve no interest in randoneuring(?) Currently I’m using 700c x32 Panasonic RiBMos which are a definite improvement on the holy Marathons, they last a long time and are relatively flat free, the last one I replaced had worn down to the threads and I hadn’t had a flat in 2000 miles. Would I see improvements if I switched to say Stampede Passes?

    January 5, 2015 at 8:32 am
    • Jan Heine, Editor, Bicycle Quarterly

      It depends on what you are looking for. If you value long life and flat resistance, the Stampede Pass won’t be any better (and probably not worse, either) than the Ribmos. However, if you are after comfort and a spirited ride (not just the speed, but also the feel of the bike), give the Stampede Pass a try. The fact that you consider the Ribmos an improvement over the Marathons makes me think you may want to move further in that direction.

      January 5, 2015 at 8:50 am
  • ahongo

    Will there be a 650x54ish Compass tire in time for this year’s Oregon Outback?

    January 5, 2015 at 8:38 am
  • Michael

    So, if I understand correctly, a tire is a bunch of threads embedded into rubber, and a tread put on top. That’s an oversimplification, of course, but just trying to visualize all the parts.

    January 5, 2015 at 11:04 pm
    • Jan Heine, Editor, Bicycle Quarterly

      Yes. You have a woven (not knitted) fabric that looks like the fabric you see in linen, which is impregnated with rubber. This is the casing. It gets folded around the beads (which are cables similar to brake cables, either made from steel or kevlar), then overlapped over the top of the tire. Now you have the “carcass” of the tire. A strip of rubber is placed on top for the tread. If you want puncture-proof belts, they get placed on the carcass before the tread goes on.
      Then everything gets placed in a tire mold and heated up. The heat fuses the parts together (vulcanizing is the technical term), while the mold impresses the tread pattern on the top and the writing on the sidewalls.
      Hand-made tubulars are made the same way, except they don’t vulcanize the parts, but just glue on the tread.

      January 6, 2015 at 5:25 am
  • John Hawrylak

    Can you compare the Compass standard and extralight casings? From this Article and Comments & previous artcles, a starting point would be
    Xtralight: 120 TPI threads, material Unknown, spaced at 90 TPI, 3 layers, minimum rubber, 3.5 mm thick tread

    January 6, 2015 at 5:55 pm
  • thebvo

    I can’t wait for the next round of roll down tire testing! Hopefully the Resist Nomad 700×45 will be on your list as well as some lovely tires designed by a small company in Seattle. They are called Compass and they haven’t been tested yet. Maybe they are as fast as they claim… 😉

    January 7, 2015 at 5:18 pm
    • Jan Heine, Editor, Bicycle Quarterly

      The Resist tires have such poor grip in the wet that we cannot recommend them. (I once broke a thumb in a crash on a test bike equipped with these tires.)
      We do plan to test more tires eventually, but we need perfect conditions for testing first… Since we test outdoors, we must control variables such as wind (none) and temperature (constant) to get meaningful results.

      January 7, 2015 at 7:19 pm
  • Pete

    Thank you for all the research on tires, I have found it all very enlightening. I am wondering if in your research you have made any comparisons on outside diameter of the tire and how it effects the relationship between rider input and performance output? I know in the automotive world tire diameter is a big factor. Larger tires take more power to accelerate and rob a car of gas mileage. Some individuals that care about such things will change gear ratios to compensate. I recently put Barlow Pass tires on my bike that had 700 x 35 previously. In result I have noticed a change in cadence when in a similar gear, I find myself pedaling in different gears than I used to. (I commute so I ride the same route 100’s of time a year, you get pretty used to how your bike “feels”, any change no matter how subtle is detected) Have any studies been done regarding overall tire diameter and the effects it has on acceleration speed and power output on bikes?

    January 8, 2015 at 3:17 pm
    • Jan Heine, Editor, Bicycle Quarterly

      Taller tires will change your gearing, so you’ll be in a smaller gear at the same speed and cadence. However, the small differences on bicycle tires (3 mm in extra width and height is only 1% of the wheel radius) gets lost in the performance difference between tires. For example, when I switched to Extralight tires (from the standard casing), I often found myself in a larger gear than usual. (The tires are the same size.)
      We tested whether taller tires roll better, and found that they don’t, not even on relatively rough roads. We also tested whether bigger tires make the bike handle differently, and yes, they do stabilize the bike, which can be good (more stable) or bad (reluctant to adjust line in mid-corner).

      January 8, 2015 at 3:42 pm

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