1. "At 50 cents a piece, [the pressure gauges are] hard to resist. At this price, I don't mind giving them away to friends and family." Definitely not a math major.
2. "Are they 100% accurate? I don't know, I don't have a calibration kit. Do my tires feel really firm when the gauge says 65psi? Yes. That was my way of 'calibrating' them." If gauging tire pressure by feel works well enough for you, why bother with the pressure gauge?
Do you use a small tire gauge for your bike tires? I use the pressure gauge built into the floor pump.
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I, too, use a floor pump gauge. Is it accurate? I can only hope so. I've often thought of getting a hand guage to confirm, but it seems so silly to have two.
So, are floor pumps fairly accurate? Mine is a Giant Control Tower 3.
Yes, I have a tire gage, but I use the gage on the pump mostly. (SLIME, available in Presta or Schraeder) I always buy a pump with a gage, as you lose pressure every time you check it. By all means compare it to a KNOWN accurate gage at some point.
Amazon prices change all the time, sometimes by a lot. Very plausible that this product was 50 cents each when the reviewer bought them. If you are patient, maybe the price will return to that level in the future.
I use my floor pump to inflate my tires before every ride, a Joe Blow floor model, and have a dial gauge in my saddle bag to verify my inflation should I have to use my hand pump on the road. Why ride 90psi when I can ride 110. Seriously, leave your mp3 player home if you want to save weight, it will also make you a safer rider.
I'm not sure it begs the question but it certainly raises it. Sorry to go all grammar-nazi on you but somebody has to. :)
I'm pretty sure these types of gauges can't be calibrated. You can use a reference gauge to establish a known, desired pressure then calculate the offset of this gauge at that pressure and use that in your measurement.
I have an inflator that I know is 4 psi low at 40 psi so I pump my car tires to 44 psi on that gauge. Works like a charm.
Fritz.. I am a car nut and a bike commuter. I have a bunch of pencil gauges, and I have one of the planet bike ones as well. I also have some dial-gauge ones, as well as the one built into my Park Tool Floor Pump.
Most automotive gauges and ALL of the pencil gauges I own do not go past 50PSI. The planet bike one hits 100, which is good because my schrader-equipped tires all run between 55 and 85 PSI.
There is, indeed a difference between the PBike gauges and the ones you find at car parts stores.
The planet bike gauge reads a little lower than the one in my floor pump, perhaps 3 PSI.
I use my floor pump before heading out and then just go by feel out on the road. I've considered carrying a pencil guage in my bag but knowing the exact pressure isn't all that important to me. Just so long as I have enough air in the tire to keep it from rolling off the rim...
Regarding the lower pressures that are typically registered on auto tire gauges -- the pencil gauge I have is for truck tires, come to think of it. I bought it specifically because it can go to higher pressures.
Thanks for all the feedback -- I pretty much assume the gauges are off but never worried about accuracy. How important is 10 lbs in a bike tire, after all?