The Strangest Question Ever Asked About A Tire Gauge

General Discussion
1

The Strangest Question Ever Asked About A Tire Gauge…!

I’m sure all most of us here own a ‘dial/clock-style’ tire pressure gauge, or at least knows what one looks like.

My question concerns the two types of zero stop, or zero rest, employed in the design of tire and other pressure gauges:

  1. Zero pin - Where the pointer rests, lightly, against a metal pin sticking up from the dial. See Accu Gage below.

  2. Zero field - A small slice of the total gauge sweep dial where the pointer resides when reset, or not reading pressure. See Longacre Racing gauge below.

My two questions are: Which design is better, and in the case of the gauge with no zero pin, how important is it, with regards to accuracy, for the pointer to be as close to the middle of that zero zone, at rest?

image
image

2

Normally, with a gauge, I would prefer no stop pin. This is so I can see any offset error in the gauge. However, when it has a range like shown, versus a definitive zero point, it loses all value to me. Regardless, I am not measuring zero or anywhere near it. I normally prefer a gauge with a range where the region of interest is around 50% of the needle sweep. As long as it accurately reads the normal, expected values within advertised tolerance, I’m good.

1 Like
3

I suppose what I could do is to ask a local auto parts shop if I could test two or three of a Pro Products gauge they sell, with a zero box similar to the above Longacre.

If a gauge where the needle rests ‘high’(over the Z or E in ZERO in that box) also reads tire pressure higher, then I have validation of my theory.

4

All gauges are inaccurate near zero. I don’t care where the needle rests for that reason. If there is a question, borrow another known good gauge and use both to check accuracy.

6 Likes
5

My gut feel is what jtsanders said. I think the accuracy near zero is far enough off that the position won’t be related to the accuracy at normal pressures.

I have three good gauges, one in each car and one in the garage, so I can be pretty comfortable of the accuracy when they all match.

6

Note that the zero stop pin is at 3 psi on that gauge. At zero pressure all the mechanical slop in the mechanism comes into play, making it inaccurate, so either approach is fine.

7

As a general rule, as I was taught, gauges are only accurate in the middle 60% of the scale. The top 20% and the bottom 20% are in the most “non-linear” area and therefore are not accurate.

The reason is that most mechanical gauges use either a spring or a diaphragm. A gauge that uses a spring may have say a compression of one mm for every pound applied. That will vary as you go off center, but not by an appreciable amount for the 30% of either side. But as the spring exceeds this area, it may take either a lot more pressure per mm of compression or a lot less pressure per mm at the fully expanded end of the scale.

Springs and diaphragms are inherently non linear devices.

Edit: some higher end gauges will have a non-linear scale to compensate for the non-linear spring/diaphragm.

8

The simple gauges used by fishermen to weigh fish seem pretty accurate and produce repeatable measurements. Just a spring and a pointer. It seems like the closer you can get to that configuration, the more accurate and repeatable the reading. They all have to hold air pressure, so air leaks on any style will cause incorrect pressure readings. The dial gauges tend to use more complicated linkages. The pencil types, less complicated. So it seems like a well-made pencil type is the best compromise. Have to remember to hold it in a horizontal orientation is all.

9

Pencil gauges typically don’t get good reviews for accuracy the last I knew.

1 Like
10

  1. Fishing scales. I still have my old man’s, I don’t remember where I kept it. The brand name or model is “DeLiar” :rofl: :rofl:

  2. Stick/Plunger-style tire gauges. I have a couple of Milton’s model S921, 5-50PSI I think.

Occasionally my newer Milton gives me a ridiculous high reading, like 43 or 47, but after 2-3 additional attempts I get a reading within 2psi of my ginormous Longacre Magnum series dial gauge.

1 Like
11

Unless you are racing, +/_ 1 psi is more than enough.

12

Agreed.

Even if a gauge tends to read 1psi low, if it reads so consistently, it’s all good.

Also, it’s more important to make sure pressures in all tires match. So if I gauge them all to 33psi, or Honda’s 32psi, I’m experiencing something eighty percent of other drivers around me are not.

Typical driver’s tire pressures, assuming 32psi door pillar spec: 33, 29, 34, 37!

And don’t get me going on Porsches, and other cars with a large front rear pressure differential(front 36/ rear 42 for instance). I’ve gauged $150,000 Porsches with 40psi in all four tires! I wouldn’t want to drive NEAR that, let alone ride in it.

Me: All between 32-33psi! Because I take the time, and use a quality gauge.

13

Not true. Many vehicles require different front and rear pressures, especially when loaded. There have been several posts showing door stickers showing just that.

The most important thing is to not be significantly high or low or different side to side.

14

I apologize if I was unclear in any way:

Allow me to rephrase. If a car, such as my Honda or wife’s Toyota, requires the same cold tire pressure in all four tires, then I make sure of that, to the best of my ability and that of my gauge. Honda: (psi)32, 32, 32, 32. Not 29, 35, 31, 37. Toyota: 30, 30, 30, 30. Not 27, 32, 29, and 35.

And to restate the Porsche example in my previous reply: 34, 34, 43, 43. Not 34, or 40, or whatever, all around.

Corvair: (bias ply) 15, 15, 26, 26. (radial) 25, 25, 35, 35.

If you go back and re-read my previous post, this is what I have been suggesting and aiming for. Again, apologies for any vagueness.

1 Like
15

The truth is most of us have no way of knowing whether the gauge is correct, whether it’s a dial, a pencil or digital. Long ago I decided the exact number is an absurd goal and what I want is that the tires are inflated proportionate to the numbers the manufacturer of the car posts on the door frame. If the car feels wrong I adjust the pressures.

1 Like
16

I just had a rental car that should have been at 33 PSI that was actually at 36, 42, 44, and 46 PSI. That explained the harsh ride at first. I spent the first two days carefully letting air out.

1 Like
17

Your situation is actually typical.

18
  • Pencil gauges (or stick gauges) are small, inexpensive, and easy to use. They can be just as accurate as any other type of gauge. The downsides to pencil gauges are that they can be easily lost and may not offer advanced features such as showing several types of readouts (such as barometric pressure, psi, and kPa).
19

It’s interesting how Auto Meter and Longacre Racing products consistently never appear on those annual 5 best Tire Gauge things.

Is it their price? Possibly, but I do know that a couple of Intercomp’s gauges sell for north of $100 a piece. So I don’t know. I own several of Longacre’s gauges, analog and digital, and can certainly vouche for their quality and accuracy.