Valve Cap Tire Pressure Monitor

[Freewheeler]

I want to try these monitors for a few reasons.

1. The act of using a pressure gauge on a properly inflated tire oftentimes deflates it enough to require pumping. 
2. I want to be able to check my pressure "at a glance". If I'm heading out to run errands or just to grab a bite I have two choices; a commuter and a day tripper. If the monitor on my commuter shows that it's low I'll just use my much larger wheel and wait to inflate my commuter when I have more time.   

These monitors have three indicators. Green means that the tire is between 80.1% and 100%. Yellow is between 75.1 and 80%. Red is 75.0% of lower.

The problem is that an indicator rated at 34 PSI wouldn't trigger the yellow indicator until it's at 27.2 PSI or lower. This is WAY lower than an EUC rider would want to go before inflating. These are meant for cars that have a much larger margin of error. But, it's my belief that Excel spreadsheets can solve the world's problems and it was in that spirit that I fired it up and got to work.

Here's what I did. I charted the PSI levels of the indicators of every monitor. And what I discovered is that I could get a very useful range by choosing a monitor with a much higher rating.

GREEN still means "safe" (though it will only ever use the lower end of its range). YELLOW is the new RED. I will inflate at YELLOW. Red is only useful to show when it's ridiculously low. For example; a rider that likes 35 PSI can choose a 40 or a 42. A 40 will pop YELLOW at 32 PSI or lower. A 42 will pop yellow at 33.6 PSI or lower (a very tight tolerance). So, if you're okay riding down to 32 then go with a 40. If you want to know when you dropped 1.4 PSI then go with a 42.

The column that has target PSI is only my estimation; it is not my recommendation for you. Verify your choice by looking at the YELLOW column and determining the trigger that is acceptable for you.

Keep in mind that these work by depressing the valve stem and that removing or installing them can deflate the tire somewhat. So, this will explain why the pressure might be even lower than you expected when you go to inflate it. It will also explain why a monitor popped YELLOW just after you inflated your tire. For instance, if you ride at 35 and have a monitor that pops YELLOW at 33.6 then just putting these on can deflate them enough to pop it. Frustrating, but manageable. I just inflate to 36, knowing it will settle at 35 or so. With a little trial and error in the beginning you can lock in  a process that works for you every time.

Also, temperature affects PSI. In general, tires lose or gain 1 PSI (pound per square inch) for every 10℉ increase in temperature. Theoretically, your tires could gain 2 PSI over the course of the day if the temperature rises 20℉ - a real possibility in many parts of the country. The reverse is also true (a temp drop can decrease PSI). Check your pressure before riding and in the same environment you'll be riding.

Hope this helps.

Edited January 22, 2020 by Freewheeler

[EUCSTEVELA]

cool idea i like it 

[Denny Paul]

Bought a set of 4 rated for 44 psi (yellow indicator will pop at 35 supposedly). Pumped it up to 40psi, and the green indicator is still showing after some valve cap jockeying so as far as I can tell they work as advertised. 

It fits the Tesla no problem, and I’d anticipate that any angled valve stem similar to it you should have no clearance problems. They add about a centimeter and a half of length. 

It obviously won’t fit the mten3 or any other unicycle without a perpendicular valve stem. Sad, but I expected this.

I can tell already it’s going to put my OCD brain at ease! No more guesswork!

[Freewheeler]

22 hours ago, Denny Paul said:

Bought a set of 4 rated for 44 psi (yellow indicator will pop at 35 supposedly). Pumped it up to 40psi, and the green indicator is still showing after some valve cap jockeying so as far as I can tell they work as advertised. 

It fits the Tesla no problem, and I’d anticipate that any angled valve stem similar to it you should have no clearance problems. They add about a centimeter and a half of length. 

It obviously won’t fit the mten3 or any other unicycle without a perpendicular valve stem. Sad, but I expected this.

I can tell already it’s going to put my OCD brain at ease! No more guesswork!

Nice. I needed a slightly tighter tolerance. It may seem trivial, but with the chart I created above I can target 35 psi and be alerted at 32psi using the 40 psi cap. I agree that it's can eliminate a lot of guessing and unnecessary inflating. Happy and safe riding!

[Joao Campos]

I'm not from the US and I tried to find these from Aliexpress and the best I could find was some rated for 36 PSI. Finally after much searching I found a single seller on ebay with all the different pressures, maybe someone else will find this useful: https://www.ebay.com/itm/143329753520

You can probably ask him to do a combination (2 x 40 + 2 x 42, etc.).

Edited January 31, 2020 by Joao Campos

[LanghamP]

On 1/30/2020 at 11:21 AM, Freewheeler said:

Nice. I needed a slightly tighter tolerance. It may seem trivial, but with the chart I created above I can target 35 psi and be alerted at 32psi using the 40 psi cap. I agree that it's can eliminate a lot of guessing and unnecessary inflating. Happy and safe riding!

I'd suggest carefully checking wheel to valve clearance. I've taken off all my valves because on some of my wheels the valve cap catches and the wheel instantly stops.