They basically work like air filter indicators and will show yellow or red when the tires drop below 10% of the desired pressure. Here is an example:
http://www.amazon.com/Quick-Pressure-PSI...lve+stem+cap+40
Has anyone ever tried them? I was thinking about purchasing some for my 2000 Focus (that doesn't have a TPMS system) so that I could quickly see when my car needs more air in the tires. The only downsides I can see are that they may stick out a little farther than a regular valve cap, and they are pretty pricey.
http://www.amazon.com/Quick-Pressure-PSI...lve+stem+cap+40
Has anyone ever tried them? I was thinking about purchasing some for my 2000 Focus (that doesn't have a TPMS system) so that I could quickly see when my car needs more air in the tires. The only downsides I can see are that they may stick out a little farther than a regular valve cap, and they are pretty pricey.