I saw these valve caps for cars, set at 2.4 bar:

enter image description here

Is there something similar for bicyles? it would help less careful riders when it's time to pump more air in them.

  • There is the Quarq Tirewiz if you need a smartphone app to tell you to put air in your tires every time you ride. Dec 17 '18 at 18:15
  • I think the concept with the Tirewiz is that it syncs to your bike computer and gives you a continuous readout of pressure, so you know if you've got a leak, or how much pressure a tubeless tire burped out on that last bump. Admittedly this will have narrow appeal.
    – Adam Rice
    Dec 17 '18 at 18:31
  • It's easy to know when it's time to check and possibly pump in more air: Are you about to ride? If yes, then check and fill. If no, then you don't need to check or fill. Dec 17 '18 at 20:58
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    @Todd if a bike is issued for utility purposes, commuting etc., taking your comment literally would mean checking the pressure several times a day when it only needs topping up every week or so. That seems over the top
    – Chris H
    Dec 18 '18 at 6:52
  • @ChisH I check every day at least. More than once I’ve gotten a pinhole on a ride but didn’t know it only to discover a tire is suspiciously low the next day. The first time that happened I just filled it and rose and had to fix the flat in the field. Now I know better but my point is that you risk having to make field repairs by not checking at least every day. If I rode multiple times as day I would certainly use fingers to check before each ride. And the pump/gauge every morning. Dec 18 '18 at 14:02

These types of valve cap gauges aren’t recommended - either for cars or bikes. They work by bypassing the schrader valve in the tire and using a cheap spring-based pressure gauge in the cap.

First, they’re wildly inaccurate even on cars. By the time they show red, you’re riding on your rims.

Second, they’re cheaply made and a significant second point of failure. If the cap is just a bit loose, the o-ring gets just a bit of dirt in it, or the valve cap gets knocked the wrong way, they will start bleeding air. This is most likely why they aren’t sold in the higher pressures that bikes would need.

Finally, as @Argenti noted, many riders adjust their tire pressure depending on the road or trail conditions or their desired degree of ride comfort. Most bike tires can take a wide range of pressures, unlike cars which have a very narrow band.

Conclusions: I’d just get used to squeezing your tires (for the lower pressure of mountain bike and comfort bikes) and/or topping off regularly (especially if you have a road bike).

  • 2
    Plus bike tires use a wide range of pressures, so you need lots of different ones with different pressure settings; and they'd get lost easily. Dec 17 '18 at 18:13
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    (+1) And once you've done the squeezing/topping up process a few times you'll get a rough idea of how long your tyres hold. On the 2 bikes I use for commuting, and pumping up to within the ratings but harder than I'd choose, I get at least 3 weeks; on one of them that means pumping up before a big ride is nearly always enough
    – Chris H
    Dec 17 '18 at 18:29
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    I’ve found that pressing the whole bike against a sharp corner (e.g. kerb) lets you gauge pressure pretty accurately. If you manage to hit the rim it’s time to top off.
    – Michael
    Dec 17 '18 at 20:17
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    @Michael having had my first ever pinch flat recently, in a 32mm tyre at 75-80psi, I reckon hitting the rim in that test would indicate desperately low rather than "time to top off".
    – Chris H
    Dec 18 '18 at 6:48
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    Or just inflate whenever you feel that your ride is getting softer than it's supposed to be. Dec 18 '18 at 8:24

I think RoboKaren's answer is on point about avoiding those cheap gauges which will probably cause more problems than help. For completeness sake, I point to the fact that the only "bike-specific" tire pressure monitors on the market appear to be high-end wireless digital versions that send data continuous monitoring data to a smartphone.

From the press release:

Quarq, SRAM’s data and digital technology brand, today announced the launch of TyreWiz, the first-of-its-kind tire pressure sensor for road and mountain bike riders. The real-time monitoring device – designed to help riders reduce tire wear, improve compliance, and boost speed – is being debuted at Sea Otter this week and will be available on June 1 exclusively on Quarq.com. The two-sensor package will retail for $199.

It does have a pass/fail indicator lights, with the threshold pressure set by the smartphone app. The application is definitely focused towards "pros" who want to finely tune pressure or monitor it during events (e.g., gravel races).

Once installed, TyreWiz relays tire pressure data to a cycling computer or a smartphone every second. The TyreWiz app provides personalized recommendations and pressure alerts. For the first time, riders will have the ability to use highly accurate real-time information to make decisions that can affect rolling resistance, traction, tire wear, and rider comfort.

The real time continuous data stream suggests they are only intended to be run for events not as an everyday, day in an day out monitoring device. The "long" run times are 300 hours, or 12.5 days of continuous monitoring.

I think the easier option will be to pump your tires up to your desired pressure, give a thumb press to see how hard they resist and occasionally conduct a "squeeze test" as suggested by RoboKaren.

enter image description here

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    TPMS for bikes. I can’t think of a stupider application of technology....
    – RoboKaren
    Dec 18 '18 at 1:24
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    @RoboKaren that's a bit harsh. It would be more useful if it brought up a notification on a bike computer like a Garmin. The idea makes sense for events like gravel races, which are long affairs (sometimes over 10 hours) where you often push the boundaries of how low a pressure you can safely run the tires. After 10 hours maxed out, early warning signs of impending pressure doom can be easily missed. The concept has merit, the current implementation is meh.
    – Rider_X
    Dec 18 '18 at 6:28
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    These things sure do make your wheels look terrible. Also the thought of paying a fortune for the aerodynamics of a 454NSW then putting one of these gizmos on is quite funny.
    – Andy P
    Dec 18 '18 at 9:43
  • @AndyP: I'd say that not only the looks are a problem but the valves are usually not meant to receive additional side forces at a longer lever... The serious TPMS for car tires are put at the inside of the valve and are thus at a well protected position. Dec 18 '18 at 15:20

These now exist:

https://www.worldwidecyclery.com/products/quarq-tyrewiz-air-pressure-sensor-for-presta-valve-pair (smart pressure sensor)

They talk with your head unit or smartphone.

They have LED lights that tell you too low/high as well.

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