Ever wonder what tire pressure you should be running? Maybe you’ve heard that lower pressures are actually faster, while simultaneously being told by someone else that higher pressures are better? Regardless of what you’ve heard, the team at Silca has a massive amount of time invested in determining the ideal pressures for ProTour teams, Ironman Triathletes, plus Olympic and World Champions. Supposedly the calculator pulls from 4,000 data points from 150 athletes over the course of 5 years at 90 different events.

After the initial post, Silca’s President Joshua Poertner reached out to us to add some back story saying, “this calculator is the first in the world based on actual tire spring rate (which is very hard to measure) rather than something like tire drop which is much easier to measure. Because the algorithm is fully mathematical, it takes each pressure calculation and compares it to an energy required to bottom out the tire in an impact and then will also warn you about pinch flat risk if you are using too small a tire for a given surface… it will even give a recommendation for how much more pressure, or more tire width you might need for your weight/speed/surface condition.

The algorithm was built by curve fitting these 4000+ real world optimizations, so if you want to calculate Peter Sagan’s Roubaix winning pressure, you can just enter his weight/tire size and cobbles and you’ll get his exact pressures… same for Bettiol’s Flanders win, multiple Dirty Kanza winning pressures, and so on.”

Since there’s no single pressure that will work for every rider, Silca has taken that pressure knowledge and packaged it into an online tire pressure calculator that you can use, for free. The most basic form is the LITE version which limits you to inputs for the total system weight (rider + bike + gear) and the measured tire width.

The more comprehensive Pro version is still free – but you’ll have to cough up your email. After dropping my address in to check out the Pro version I received a sale notice via email just 18 minutes after receiving the welcome email, so it seems like even if you don’t add your email to the Pro form at the bottom, you’re still signing up for email notifications from Silca. If this bothers you, it’s easy enough to unsubscribe.

By adding your contact info you gain access to more detailed inputs to help you dial in your tire pressure even further. That includes details like the surface condition from indoor wood tracks to Category 4 gravel, wheel diameter, average speed, and the bike’s weight distribution or type of bike.

Curious to see what it would recommend for me, I punched in the numbers for my Why Cycles PR road bike. It’s currently running 700c x 28mm GP5000 tires that actually measure 30mm on the Zipp Firecrest rims, and I’m guessing my total system weight is somewhere around 172lbs. When calculated for Worn Pavement/Some Cracks and for the Fast Group Ride setting, it recommends pressures of 70psi for the rear, and 68psi for the front. That’s lower than I have been riding them, but not by much – I typically pump up to 75/74psi before each ride.

Time to drop some pressure for the next ride!

silca.cc

16 comments

  1. Dinger on

    ” tire spring rate”

    That is a beautifully simple way to describe the interplay between tire volume, construction and pressure. Wish I’d thought of that…

    Reply
  2. Paniagua on

    I don’t see the calculator accounting for construction, sidewall TPI, etc. which is a huge factor between brands/models

    Reply
  3. Joshua Poertner on

    Paniagua – Think of tire pressure as the spring rate in a suspension system and the tire construction as being the damping.. So tire construction plays a major role in rolling resistance and handling as it affects the dynamic response of the tire in rebound which can be critical to comfort, but as the casing of the tire is generally working in compression, the addition to spring rate of the tire is at most equivalent to fractions of a PSI of pressure increase. So if I take a GP5000 with butyl tube, GP5000 with latex and GP5000 tubeless tire and do a full optimization workup on them using field study, we will find that all of them yield the same optimal pressure result, but some of them are much faster due to reduced damping (hysteresis) as a result of tire construction.

    Reply
    • Panigua on

      Josh – I see your reasoning, but I’m not sure it applies “real world” I use different pressures for different tires, let’s make it really easy to understand with MTB tires as the example, DH casings vs. XC casings, the different sidewalls work better with different pressures even though the sizes can be the same. Is the derived pressure really “optimal” if some tires are “much faster due to reduced damping (hysteresis)” ?

      And…I really love Silca, I’ve had my pump for 38 years!

      Reply
    • Paniagua on

      Josh – I see your reasoning I’m just not sure it’s “real world”, an easy example are MTB tire casings, DH vs. XC same size tires will have different pressures. Using your spring rate analogy/explanation, is the “optimal” pressure really optimal if different tires are “much faster” at the same pressure?

      Huge Silca fan , had my pump for 38 years!

      Reply
      • Joshua Poertner on

        I have no experience or data on DH vs XC casing tires, but have lots of experience with otherwise identical road and gravel tires that have ‘race’ vs ‘endurance’ casings and the like and despite testing for it, have not seen these casing changes change the optimal pressure for a given surface. We just see that the slower tire is always slower, and that the curves for the slower tire are steeper either side of the break point. Of course, in many of these optimizations, we are optimizing down with a 1-2 psi range most of the time, so it is possible that there is a <1psi delta due to casing, but it hides in the data both from a data set size and test resolution point of view. This is another reason to run supple tires, the penalties for being too high or too low are less..

        Reply
  4. Beverly Drangua on

    Like the calculator, but don’t understand why avg speed input is in subjective categories instead of kph or mph.

    Reply
    • Joshua Poertner on

      Thanks Beverly,
      In beta testing we had the speed as a number input by the user and found that people were dramatically overestimating average speed which was both leading to overly high pressures and also was causing people to trip into the pinch flat warning too frequently due to over-estimating their average speed. So we used the Strava speed data to develop these categories which mathematically assume a distribution of speed around a normal value that then uses some statistical modeling to judge pinch flat likelihood. For reference, roughly half of the people using the calculator were entering their ‘average speed’ as being higher than the average speed of a ProTour race!

      Reply
      • Erik on

        LOL at the ridiculously over estimated average speeds people were entering!

        This looks like a neat tool. Just don’t give your actual email address

        Reply
  5. briannystrom on

    Their calculator gives me results for my road tires that are over 15 psi higher than the pressures I’ve been using for the past decade, with less of a front/rear differential (using the “Worn Pavement” setting). Given that I know the pressures I use work well, I don’t see any value in this tool, as is seems like it’s just continuing the old paradigm of road pressures that are much too high.

    For gravel, it’s only close if I select “Category 4”, but still slightly high

    Reply
  6. ed llorca on

    Seems to me if I use the recommended pressuers (20% loweer than I run I will be squirming my way right into a pinch flat.

    Reply
  7. George French on

    Interesting tool. I’m getting pretty low results from it on the road/gravel side and ludicrously low results on the MTB sizes, pressures that would see pinching and burping on even slightly uneven terrain and in my opinion too low even with DH casings and inserts. Would be interesting to see the underlying maths.

    Reply

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