I just got a Meiser PSI gauge w 60 psi max. It looks like it should be great for my CX tires. Nice big number lettering all around 20-40 psi.

My Joe Blow Sport pump says my tires are 30/35. The Meiser gauge says they're 22/24. I weight 180 but I've felt no wallowing, no hitting rim. Such low numbers are "europro" style for skinny people. Hmmm...

So I pumped a 25mm road tire to 60 psi by the floor pump. Feels pretty firm. The Meiser gauge says 45.

How to find out which one is wrong? I'm guessing it's the Meiser. How could a brand new gauge be so wrong? I guess it is a cheapy. But people say they're good. I was looking forward to using it!

I mean, yeah, it's all relative as long as I use the same gauge. But I'd like to get a LITTLE closer to reality.

(DIGRESSION: I heard an interview w Sanne Cant on CXMag.com. She said she used "1.6" pressure for her race in WI last Sunday. Is this atmospheres stuff really more convenient for ppl than PSI? I forget, is the atm measured in kPa? or is that something else.)

Does it matter? Pump tires to the pressure you feel gives you the right ride properties, the use either gauge to duplicate that in the future.

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Heck, I use this method with a pencil gauge. It takes up less room in my seat bag.

If you are serious about calibrating your gauges you can use the "dead weight method".

You already have most of what you'll need in the form of the floor pump.

Start by measuring the ID of the cylinder. Use the formula to convert that to the area, then apply the formula weight / area = Pressure. You'll want to calibrate near the center of each gauges scale, ie. 30psi for the Meiser, and mid scale for the built it, so you'll need dead weights of the right weight.

The built in gauge can be calibrated simply by plugging the end of the hose, or leaving it on a tire and pumping to just shy of the test pressure. Assuming (for here) a cylinder area of 1 sq. inch, you'll need about 75#s to calibrate a 150psi gauge. The easiest place to find that is to recruit a child to sit on your pump handle. If they can't balance they can put a foot down on a bathroom scale, but you'll have to subtract that.

For the Meiser, 2 gallon milk jugs full of water will do the trick.

Yes.

IMO most people approach the entire pressure and gauge question backward. They use some kind of chart or formula, or the tire markings to decide on what should be the right pressure, then think they need a precise gauge to check that the tire is filled to spec.

IMO, What matters is the ride, or performance, and the numbers are just a way to get close, then experiment to dial it in. So precise numbers don't matter in the end. OTOH, If it's about the ride, one can use crapshoot estimates, then dial it in. Now the ride itself has determined the right pressure, and it's only a matter of duplicating that on demand. It no longer matters what the gauge reads, you simply put a red dot in the right place and the right pressure is "red dot psi" and it doesn't matter what that actually is.

Within limits.. There are conceivably potential safety issues with tires that are too under-inflated over-inflated.

Yes, and I assume that anyone who's trying the method can get into the ball park without help. In case they can't find the ball park, they should at least be able to find the city, and that's good enough to start.

So, not to get too far OT in this thread, but I believe that many folks use a calculator to find the city that holds the ballpark. eg. like this one:
Bicycle tire pressure calculator

However, to illustrate a potential problem. Here are 2 returned results for different weight riders. These results presumably provide a mathematically calculated optimum combination of speed and comfort. All fine and good, except for example, my Michelin Pro4 Endurance tires have a sidewall rating of 73-109psi. What I don't know really though, eg. Would 60psi in front tire for the 180lb scenario feel and ride great? Would this however, really be dangerous? Same question for the 119psi in the rear tire for the 220lb scenario?

Atmospheric pressure can be measured in any pressure units. Typically, in engineering we'd use a weight/surface area type pressure like pounds per square inch, or Newton's per square meter (which is a Pascal). I'd guess the "1.6" would be in bar (which equals 100 KPa, or you can say that 1.013 bars is one atmosphere). Bars are used because they're about 1 atm. But 1.6 bar would be pretty low - only 24 psi or so. So Im not sure what pressure unit Sanne was talking about.

Yes, bars. That's what the Euros use. Hard to believe that makes for easy chatting about tire pressure.

24 is firm for Sanne.

As I posted at the start, I understand it's all relative. Doesn't matter. Still... once one declares that they've made a precision gauge and they put numbers on it... It's hilarious. This is the most precise gauge I've ever bought. What should be the most suited for the task I need. ...And it is apparently by far the least well-marked I've ever seen. It might be a third off! It is lame as heck to sell a "precision" gauge that reads 45psi while a cruder gauge reads 60.

JeffOYB, I agree. It would bother me... I wouldn't sleep at night.
Start checking it with other cheap gauges ( I think Meiser is cheap at $15).... then send it back where you bought it.
Spin Doctor for $10......reads the same as my JB Sport floor pump.
https://www.performancebike.com/webap...ssociationsCmd

Jeff,
That shows how little I know. I haven't ridden on 24 since ... never.

I remember reading an article on the accuracy of tire pressure gauges in Popular Science or Popular Mechanics back in the late 60's or early 70's. Whether pencil gauge, dial gauge or other, whether high price or low, there were wide variances in accuracy among all even when comparing the same to the same.

47 years later, and it's still the same. I use both pencil and dial. Some I trust, others I don't. Just fill the tire to where you feel comfortable with the gauge you trust the most. Continue to use that gauge to adjust your ride to what ever pressure gives the combination of ride comfort and cornering and rolling resistance you want.

I agree with you that for the price you pay for some gauges they should be more accurate. But I gave up looking for the perfect gauge 30 years ago. After using them for a while and comparing, you'll know which to trust.

I look for gauges that are patented

OTOH, it might be spot on.

In fact, if I had to bet, I'd put my money on the Meiser over your other one. I'm very familiar with them, and know they're quality instruments rated to be accurate to within 3% of the scale, or within 2psi on a 0-60psi scale. When they go bad, they err high.

Also, keep in mind that gauges are calibrated at the center of the scale, and are most accurate there, and less accurate towards either end.

But, you're like the guy with two watches who can never be sure of the time. Either check your gauges as I explained earlier, or check against a number of other gauges to see which best matches the average, or simply stop worrying about it, and use either to consistently duplicate whatever pressure you feel rides best.

Actually, bars/atmospheres* are a very intuitive measure of air pressure. It's just a multiple of atmospheric pressure at standard conditions. And for those of us who think in psi, 1 bar is close enough to 15 psi that it's easy to do a conversion one way or the other that is close enough for tire pressures.


* Yes, bars and atmospheres are not exactly the same unit, but again, are close enough for our purposes to be used interchangeably.

I would argue that the calculator is the city, and once in it, the user (whose brain is the product of millions of years of evolution) should be able to find the park. The articles upon which the calculator are based are very explicit that if you find yourself exceeding the max pressure ratings, you should consider using larger tires.

As for going under the mininum pressure rating, I'm not sure there is a front tire in my collection that is over the minimum rating, if there is one. I'm a happy rider just the same.

That's fine. But now to apply to the OP's situation. His floor pump may be telling him his 25mm tire is at 80 psi which is all well and good. But suppose the meisser would say it's 60 psi. Taking the simple advice to ride what is comfortable might mean he's riding around at a real 60 psi which is the theoretical ideal comfort/speed blend but which is potentially unsafe.
All in I'd say the best advice is to do whatever is necessary to identify which tire gauge is trustworthy, and not rely on feel.

I think then it goes back to Francis's point in post #2. If the tires pooch out too much and get pinch flats with a certain pressure, use more and then mentally calibrate yourself to whatever the gauge reads at that pressure. So if the Meisser says 100psi for a real 80psi, the OP can just make a note to fill up his tires to "100."

I don't actually know if my old Planet Bike pump is accurate anymore, but since the Berto suggestions result in neither pinch flats nor harsh riding on my bikes, I'm not too concerned.

I've done comparisons between pump gauges and external hand gauges. For me it is more about having some degree of confidence in being close to being an accurate measure when using various pumps and not just a blind guess.

Between a couple of floor pumps, and frame pumps (which is usually just a get enough air to feel okay on the road), I would not want to be off by 15psi and not at least know which is off.

I've inflated car tires and checked with different gauges, and used a bike pump gauge to compare. I was able to use a hand gauge after our daughter's low pressure indicator when off on her car. While they can be notoriously problematic, when I got to the correct minimum psi on the hand gauge the indicator went off. For me that is close enough to use that hand gauge as a baseline. From that, my pumps are probably within a few psi of the gauge.

Back to the 15psi difference, I would hate to be running car tires at 20psi or 50psi instead of 35psi because the and gauge is off that much. That would bother me more than bike ride comfort.

John

This talk of calibrating gauges (especially cheap ones) reminds me of the woodworking axiom:


Measure with a micrometer, mark with chalk, cut with a chainsaw.

lol I have the most interesting time cutting lumber for ppl at a leading home improvement store "please cut this 4' 6" & 5/8ths but it doesn't have to be accurate ... drives me crazy

I agree. Life was so much easier when we were ignorant and simply pumped our tires "melon hard". I rode for years and 10s of thousands of miles checking the pressure in my tubulars by the sound when I flicked my fingernail against them. Or by how hard I had to push on the pump handle.

My "pressure gauge" was built into my saddle, and knew when the tires were low (they don't magically get over inflated).

IMO all this obsessing about the "right" pressure, based on formulas and precise gauges is BS of the first order.

Here's an example of why I say there's no "right" pressure to be found by formula.

On my daily commute there's a small steep hill of about 100' vertical rise. It's annoying, and I prefer to simply sprint it, gearing down only as I near the crest according to whether breakfast kicked in. Unfortunately, the pavement was a patchwork of repaired potholes, and the bumps greatly increased the climbing effort at speed. So, this one hill caused me to drop tire pressures 10psi, which made the bike a hair slower for the rest of the 12mile round trip, and anything else I rode on that bike.

Finally, they repaved the road, and as soon as I realized that I could climb with higher pressure, I changed back to my "normal" pressure for that bike.

For the record, at home I rely on the gauge built into my floor pump. I have no idea how accurate it is or isn't but I don't care. I pump to the indicated pressure that has proven itself to be "right" based on experience.

My advice, stop obsessing and ride your bike. If it feels right, it probably is. If it feels off, adjust according o how it feels off, until it feels right.