For Anyone Who Owns a Digital Tire Gauge

[RidingOnRailz]

Hi!

I need some recommendations for a digital tire pressure gauge. I'm getting the dropsies in old age and do not have the budget to keep replacing my clock-face analog bleeder models from Slime and Accu-Gage after dropping them only from the height of a tire, and finding out they are no longer accurate from even such a short fall onto pavement.
My priorities are:

1. Must read down to 1/10th - not 1/2, not a whole - but one-tenth PSI, IE: 32.7 or 29.2psi (yes, it matters!)
2. Have a bleeder valve as my clock-face gauges all did.
3. Price: approx $$$ on a scale of $(cheapo) - $$$$$(military pentagon grade).

Any suggestions, models you have had good experience with?

Thanks!

[RidingOnRailz]

Come on!

I'm not asking about how far apart to plant geraniums here, lol!

[shorod]

I don't own this one, but Amazon reviews suggest it's pretty good. It's probably a bit on the inexpensive side of your required price scale (considering I work on military grade components and know how expensive such trivial items can cost). It fits your other requirements, but unfortunately you didn't mention what the full-scale accuracy needs to be. It reads to 0.1 psi resolution, but with a full-scale accuracy of 0.5% which apparently is good enough to be considered "professional racing accuracy standards."

From a quick search I didn't find anything that provided a lower full scale AND also listed the full scale accuracy.

FWIW, finding out the recommended distance to plant geraniums from one another is much easier to find.

-Rod

[RidingOnRailz]

Getting the tire pressures this precise could help eliminate them in cases of pull or drift to one side or another, or unequal steering effort on one side, etc, except in hopefully rarer cases of conicity - tires with different tread circumferences from one sidewall to the other.

[shorod]

So you're looking more for consistency and resolution more so than accuracy. In that case, the one I linked to seems like it should check most of your boxes.


-Rod

[RidingOnRailz]

Originally Posted by shorod

So you're looking more for consistency and resolution more so than accuracy. In that case, the one I linked to seems like it should check most of your boxes.


-Rod

Actually, both: Higher resolution, RE: Having all four tires read precisely 32.7PSI(just an example!) is easier to achieve than trying to eyeball such with a dial or stick gauge.

[shorod]

Right. My accuracy comment pertains to the 0.5% full scale accuracy. Since that particular unit can measure up to 200 psi, that translates to a 1 psi accuracy. Your readings may be off by as much as 1 psi, but as long as the reading is consistent with 0.1 psi resolution, the accuracy is less important to you. If you wanted accuracy as well, you'd want to find one with either a lower full scale capability or better than 0.5% accuracy.

-Rod

[RidingOnRailz]

Originally Posted by shorod

Right. My accuracy comment pertains to the 0.5% full scale accuracy. Since that particular unit can measure up to 200 psi, that translates to a 1 psi accuracy. Your readings may be off by as much as 1 psi, but as long as the reading is consistent with 0.1 psi resolution, the accuracy is less important to you. If you wanted accuracy as well, you'd want to find one with either a lower full scale capability or better than 0.5% accuracy.

-Rod

So, if hypothetically, I adjust all my tires to indicate exactly 32.0PSI, one tire might actually have 33, another one 31, and so on?

So how do I know if the gauge is indicating low(causing me to overinflate) or indicating high(resulting in underinflation)?

By "lower full scale capability" do you mean, buying a 5-60psi gauge vs a 5-100 model?

[RidingOnRailz]

Bump!

[shorod]

Originally Posted by RidingOnRailz

So, if hypothetically, I adjust all my tires to indicate exactly 32.0PSI, one tire might actually have 33, another one 31, and so on?

So how do I know if the gauge is indicating low(causing me to overinflate) or indicating high(resulting in underinflation)?

By "lower full scale capability" do you mean, buying a 5-60psi gauge vs a 5-100 model?

I would expect the gauge to be consistent, it just might be consistently high by as much as 1psi or consistently low by as much as 1psi. I would not expect it to read high 1 reading and then low on the next though.

Regarding lower full scale capability, yes, you interpreted my comment correctly. For a gauge that can read up to 100 psi, 0.5% full scale would be 0.5 psi. For one that has a 60 psi full scale, 0.5% would be 0.3 psi.

-Rod

[RidingOnRailz]

Originally Posted by shorod

I would expect the gauge to be consistent, it just might be consistently high by as much as 1psi or consistently low by as much as 1psi. I would not expect it to read high 1 reading and then low on the next though.

Regarding lower full scale capability, yes, you interpreted my comment correctly. For a gauge that can read up to 100 psi, 0.5% full scale would be 0.5 psi. For one that has a 60 psi full scale, 0.5% would be 0.3 psi.

-Rod

Thanks! I know it's just tire pressure, set & forget, come back in a month, but, it's my F-18- I mean, Hyundai! And I just want things as evenly set as possible.

By the way shorod, there's a set of calculations out there that I learned, that returns a set of front and rear cold pressures even more exact than the ones listed on a car's b-pillar load sticker:

It involves knowing the max load and inflation pressure of the original tires, and the front and rear GAWR(gross axle weight rating).

IE: The load sticker on my 2015 Hyundai recommend 33psi cold, front and rear.

Plugging the information about my car and the tires in, and the formula returns 35psi front and 32 rear - to account for the front weight bias in a typical front wheel drive econo-sedan. The car really sticks to the road in turns, smoother ride, and 1-2mpg better highway mileage. Same for my wife's 2004 Toyota:

Recommended: 30psi all around. Calculated: 32psi front, 29 rear. She says she presses the gas less, and the brakes more! Fuel economy improved too.

For a friend's 2005 Legacy GT sedan however, the calculated pressures made ZERO sense: 48psi front, 49 rear! WT... ?! Sound more like TRUCK pressures, ehh?

Actual recommended pressures on that Subaru's sticker: 35psi front, 33rear. I think she will stick with those! lol

It's tires are 45-series 17" wagon wheels, vs my Hyundai's - 65-series normal tires. That might explain why I got the wonky figures on the Subaru.

Ordinarily, most vehicles I've done it for are predictable: They add 1-2psi for the heavier GAWR axle, and reduce 1-2psi for the lighter axle.

[CapriRacer]

Originally Posted by RidingOnRailz

……. By the way shorod, there's a set of calculations out there that I learned, that returns a set of front and rear cold pressures even more exact than the ones listed on a car's b-pillar load sticker: …..

Do you mind sharing? As a tire engineer who has been told how the vehicle tire placard values are calculated, it would be interesting to know what other methods exist.

[RidingOnRailz]

Originally Posted by CapriRacer

Do you mind sharing? As a tire engineer who has been told how the vehicle tire placard values are calculated, it would be interesting to know what other methods exist.

1. Obtain the following information(mostly on the tires, and stickers on vehicle door frame):

GAWR(gross axle weight) values for front and rear axles.

Max. cold pressure and USTA max load rating from OEM tire, if possible. *Some replacement tires, even with exact same size, speed-rating letter code, and maximum cold pressure as the OEMs, might have a different USTA max load stamped on them. Use it in those cases.

2. Divide both front and rear GAWR/2 - remember: you want final pressure per tire, not per axle!

3. Plug figures into following formula:

Front: [(GAWR/2) /USTA max load] * Max Cold Pressure from OEM tires.

Repeat for Rear axle.

My 2015 Hyundai example: The B-pillar sticker specifies 33psi cold, front & rear - nice n easy for average Schmoe consumer to remember and set their tires to!

B-pillar Front GAWR: 2,160lbs. Rear GAWR: 2006lbs.

OEM Tires: 44psi Max cold, USTA max load 1,356lbs.


So for front tires:

Half of front GAWR = 1,080. Half of Rear GAWR = 1003

(1080/1,356 )
= 0.7964601 * 44 = 35.04psi

For rear tires:

(1003/1356)
= 0.7396755 * 44 = 32.5psi(I rounded down to 32psi for convenience!)


35psi front, 32 rears.
Or alternatively(for summer): 34 front, 31 rear - as long as that difference is maintained.


Essentially it calculates GAWR/2 as a percentage of the USTA maximum load
(in my case, 1,356lbs) per tire. 1080lbs = 79% of max load for the front tires, and 1003lbs = 73% of max load for the rear tires.

It does not work for all vehicles! Like I said previously, the formulas above returned some ridiculous figures for my friend's 2005 Subaru Legacy.

Your mileage - and pressures - may vary

[CapriRacer]

Thanks,

OK, that's not a new one for me - however, it is one I debunked quite a while ago. Here are the flaws:

1) The max pressure on the tire is NOT related to max load - at least for P type tires.

US regulations say that the max load and the max pressure must be imprinted on the sidewall of any tire that is to be used on the street. Usually it is expressed this way: Max Load XXXX at YY pressure. Notice the relationship. This is the way pretty much the way every tire is done except for P type tires.

For P type tires, it is usually expressed this way: Max Load XXXX, Max pressure YY. Notice that no relationship is expressed - and there's a reason for that. The pressure where the load maxes out for Standard Load P type tires is 35 psi (or if using metric units, 36.3 psi), but it is permissible to use higher pressures for certain conditions. The values specified by The Tire and Rim Association are 44 and 51 psi. I show where those values come from here (about 1/3 the way down): http://barrystiretech.com/loadtables.html

2) The load curve is NOT proportional to the inflation pressure, nor is it linear. So the formula won't match what the tire manufacturers (through The Tire and Rim Association) publish.

3) Nowadays, it is common practice for the GAWR's to be 85% of the load carrying capacity of the tire at the placard pressure. This is a change that result from the Ford/Firestone situation back in 2001.

The net effect is that you won't get what the vehicle manufacturers specify. The fear is that you will get a value lower than what the vehicle manufacturers specify and that could be dangerous.

Plus, the spring rate of a tire is relatively proportional to its inflation pressure, so the vehicle will handle differently if a different pressure is used.

[RidingOnRailz]

CapriRacer wrote: "The net effect is that you won't
get what the vehicle manufacturers specify."

I wasn't expecting it to!

"The fear is that you will get a value lower
than what the vehicle manufacturers specify
and that could be dangerous."

I did - on both mine and my wife's car -only for the rear axle tire pressures.

My wife's Toyota load decal specifies 30psi both front & rear. So easy a caveman could set tire pressure

The formula yielded 32psi front and 29 rear.


My Hyundai load decal specifies 33psi front & rear - easy for the masses to set.

The formula yielded 35front and 32 rear.

We both like the way our cars steer, handle, and roll with cold pressures set accordingly.
Notice that for both of our cars the formula successfully took into account the front-end weight bias - lowering the tire pressure a tad in the rear and adding some in the front.

My friend's AWD 2005 Subaru calls for 34psi front, and 35 rear.

However, for reasons yet unknown, the formula returned suggested cold psi of 48 front and 49 rear!

The only thing I could possibly think of, is, even though the tires currently on her Subaru match the size on the door placard, they might not be the same speed or USTA load weight rating. That could be throwing things off in her case.

At any rate, it shows that Subaru appreciates that its customers love to drive, and took the time to calculate and recommend the exact front and rear pressures for tires on their vehicles - not just an average pressure for both front and rear - as in mine and my wife's cars cases.