[Bill]

If both the gauges work on your car tires but not your bike tires then I would suspect the tube stem core is faulty. The stem is designed the same way on both tires. So if the gauge works on the car then the gauge isn't faulty. The easiest check would be to see if air can be released from the bike tire. But even if it can I would still do the simple and cheap core replacement on the bike tires.

Cheers!