After rotating my tires and checking tire pressure at a local gas station, the air pump dial read 36psi, with new air in tire my gauge read 38, then a station's mechanic's $50 gauge read 40. Where and how much to pay for an accurate gauge? And how long does it remain reliable? George
Sears item #02875114000 Mfr. model #75114) pictured below. I really like it. It's portable and easy to use. That triangular part on the top removes from the base unit and has the digital tire gauge. So when I'm checking my tires I can just remove that part and go around without having to lug the entire unit. I keep it in my cargo hold at all times and have even used it at various meet-ups to help top off other people's tires.
Rebco 0-45 pound gauge at Summit Or just find a cheapie digital gauge that measures in 1/2 pound increments... Price doesn't always mean accurate...
<div class='quotetop'>QUOTE(TonyPSchaefer @ Aug 15 2006, 08:59 AM) [snapback]303451[/snapback]</div> IF you get one of these, make sure the prius is started and in ready mode so you don't end up with a dead 12v battery.
<div class='quotetop'>QUOTE(syncmaster @ Aug 15 2006, 08:40 AM) [snapback]303475[/snapback]</div> :huh: I own and use one of these; no problems with my 12-volt battery whatsoever. You don't need to have it in "Ready" to use the inflator; you just need to have the 12-volt system turned on. Unless you're inflating an 18-wheeler, you won't zap the battery.
<div class='quotetop'>QUOTE(tnthub @ Aug 15 2006, 09:12 AM) [snapback]303459[/snapback]</div> Neither does digital though.. Virtually all "digital" gauges have at their core a small plastic mechanical movement like a balance lever; the electronics simply translate this miniscule movement into a digital reading.. The movement vs. pressure is very small and due to this, the degree of both accuracy and precision from a "digital" pressure gauge is significantly *less* than that of a good dial gauge, but the digital readout tends to make people believe that it's the other way around.. The dial gauge mechanism multiplies the tiny movements made by the air pressure on a Bourdon tube so that a movement of a fraction of a millimeter is translated into a large needle movement that you can see- depending on the size of the dial gauge, the multiplication may be as much as several hundred times. The digital gauge on the other hand relies on a linear position sensor or a strain gauge to measure the miniscule changes with comparatively little multiplication (a fraction of a millimeter to perhaps a few millimeters worth of travel), so the accuracy of a reading is actually much more limited than with an analog dial, and you're subject to the limits of digital resolution, despite the nice digital display, your actual precision is not any better than one of those pencil style gauges that you have to eyeball the stick.. The only real benefit of a digital gauge is the ease in reading the display- no more counting the ticks on a stick or a dial, the number is right there for you.. If the only problem with digital gauges was a bit of inaccuracy and imprecision, it could be lived with, but digital gauges all tend to have a common flaw: I've tried a wide variety of them, cheap and expensive and looking at the patent #s on the back of the package, they all use the same basic microcantilever mechanism and they all have the same very poor valve mating- whereas even the cheapest "pencil gauge" tends to mate positively with the tire valve every single time, these digital gauges hiss and bleed air unless you're extremely lucky and make a perfect connection, so you always end up doing a number of measure/add air cycles because every time you measure.. If you go through the reviews of digital gauges, say on Amazon.com, a common theme with virtually all digital gauges is their poor valve seal.. Finally, in terms of how long a gauge maintains its accuracy? A good quality dial gauge provides the best accuracy and precision, but like all good measurement tools, such a gauge needs careful handling and regular maintenance and calibration.. The $50 mechanic's dial gauge may be perfect out of the box, but if it gets knocked around and just tossed in the toolbox or glove compartment, it will go out of calibration very quickly.. Even if you baby such an instrument, it will still eventually need recalibration, and this is another area where the digital gauges tend to give you false security- they have an auto-rezeroing function before they turn off, but this does nothing but reset the zero point the way that turning the dial does on a dial gauge, it doesn't address initial miscalibration, scaling, temperature effects (which digital semiconductors are much more sensitive to than a big chunk of brass in a dial gauge), so even though a digital gauge may always have a proper zero reading, it doesn't do anything to help the "at pressure" readings, which may be out as much or worse than the purely mechanical gauges.. And where a high quality mechanical gauge may be re-calibrated, this is not the case with a typical consumer grade digital gauge..
<_< Shortly after our Prius "came to live with us," I purchased a high-quality accurate analog tire pressure gauge from Racer Parts Wholesale (on line) and a 12v mini-compressor (Campbell-Hausfeld) which reside in the left side storage bin in the cargo area. As I recall, the gauge cost about $25 and the compressor about $20 at WallMart. The pressure gauge has a bleed valve which assists in setting the exact desired tire pressures. I run mine at 40 psi front and 38 psi rear. I got a tire gauge that reads to 60 psi (needed for the spare). This same information is also found in the "Care, Maintenance and Troubleshooting" section of Prius Chat. [attachmentid=4501][attachmentid=4502]
I agree with the last two posts, a good quality analog gage is best. Take good care of it, don't drop it, and it should last a lifetime. It doesn't need batteries either.
So what do you do? Switch back and forth between the gauge and the compressor until you hit it right? Sorry, if this sounds stupid, but I've just never bothered with tire pressure this much before.
I recently ended up with 3 gauges - my old (40+ years old) stick, a new dial (came with compressor) and another stick (came with tyre fittings). Taking a reading on a tyre using the 3 gauges gave 38, 40 and 42 psi. Went to a tire shop and had my tyre pressure checked on their master gauge (by law, Assie tyre shop must have a calibrated master gauge). Then I tried my gauges. The only one that was accurate was the old stick gauge. FWIW, the shop owner took one look at the new stick and threw it in the trash can. He said that particular type of gauge was useless. I agree.
