That's a great question. As far as accuracy, that's a hard one because unless you are spending a LOT of $$ on gauges that have been calibrated against standards, it's hard to say how "accurate" it is.

So with that thought, repeatability is I think more an issue, especially when dealing with lower pressures. I faced something similar because I run low pressures here (18 or so psi) on the muddy, rocky, rooted jungle stuff we ride here often. Granted I used enough volume with my tires and will air up when speeds get higher.

So my old Blackburn pump had a little gauge mounted down low that went up to 150 psi. I got rid of my "off-dirt" bike years ago so I never air up that high anymore anyway. So I drew up a little project and built something like this:

This is what it looks like from up top. It's 3.5" mechanical gauge with 1/4" NPT fitting on the bottom. I plumbed it to a tee and a couple of barbed fittings that would adapt to the original pump hose. I could have gone digital but I wanted simplicity without and batteries.

Here's a link to ebay of the gauge I bought. $4.99.

NEW 0-60 PSI PRESSURE GAUGE 3 1/2" AIR OR HYDRAULIC GAGE 1/4" NPT THREADS | eBay

 

I only use the floor pump gauge and I don't really care about a separate high quality gauge.

I want dependable consistency in my pump gauge. That's all.

 

Well, the pressures I usually use in my fatbike tires barely register on either on my floor pumps (whose scales include road bike pressures). The scale on those gauges doesn't even start until 10psi, and I never inflate those tires that much. It's not accurate, and it's definitely not repeatable. So I got an inexpensive Meiser 0-30psi gauge. Its gauge has 0.5psi increments, which is good enough for me. And definitely repeatable. My wife also prefers using it. Her 27.5x2.35 tires get inflated to around 16psi, so the roadie gauges aren't too good for her, either.

Generally, overall gauge quality improves as the price of the pump goes up. So the gauge on a $25 floor pump won't be as good as the gauge on a $100 floor pump, or a $450 floor pump (yes, those exist....check out the new Silca pumps).

I am really happy with a Serfas floor pump I bought used. A shop used it for a season for customers to inflate their tires. I bought it after they wanted to replace it. MSRP was $80, IIRC, and I got it for $25. The gauge on it seems pretty good, but because of my low pressure tires, I only even look at the gauge on it when I'm inflating road bike tires.

 

As mentioned, repeatability/consistency is more important than accuracy if you always use the same gauge or pump. Having said that, I like the Meiser analog gauges and use them a lot. My new pump is quite high end and I confirmed that its onboard gauge (0-60 psi) correlates pretty much exactly with my 0-60 psi Meiser gauge in the middle of the gauges' ranges (~30 psi). But on low pressure side, it is off by a fair bit. So for fat bike pressures, I still plan on using my low pressure range Meiser gauge (0-15 psi)to achieve consistency.

https://www.amazon.com/Meiser-Prest...00GO4PZ5G/ref=sr_1_1?ie=UTF8&qid=1507045379&sr=8-1&keywords=meiser+presta+gauge

https://www.amazon.com/Meiser-Prest...00GO4PY3Y/ref=sr_1_4?ie=UTF8&qid=1507045379&sr=8-4&keywords=meiser+presta+gauge

 

I checked my 10 year old Spec floor pump against 2 decent quality auto gauges (older accu-gage and stetho-gauge), the floor pump is very-very close. Like Cleared2land said, consistency is most important. Just make sure to remember yours and not have to borrow or use a micro pump without a gauge.
I read some tests in a car magazine maybe 15 years ago, and the (then) super-cheap stetho-gauge got some of the best reviews, it was really cheap, I think I even got it from harbor freight, - looks like they're not really available anymore.

 

I see what ya'll mean..26 psi may not be truly 26 psi, but if it works for me then consistency of that 26 psi is what matters..gotcha. thx

 

Exactly!

That's why it doesn't matter to me as long as the gauge is dependably consistent.

 

I bought Performance's cheap tire pressure gauge $10 and calibrated it with my Lyzene floor pump. I know what pressure feels right. How accurate either of these is I don't know, but they both read same pressure which is all I care about.

 

I've been using the Specialized MTB Airtool with good results for a few years now. It's a lower pressure floor pump and it correlates spot on with my SKS Digital gauge.

 

Well surprisingly my floor pump was waaaay off. What I thought was 25 lb psi was only 17 lb psi. I had to show 38 lb psi on the floor pump to get 28 lb psi on the digital gauge..daaang..so much for going by feel.

 

Get a MTB type floor pump, made for lower pressure and pushing more air per stroke. It will be much closer to actual, if not actual. The pump you are using is a standard floor pump that's designed around reaching high pressure (think road tires)

The Specialized one that I have has been spot on. (MTB Airtool) I'm sure there are other brands that have similar, Topeak for instance, that you could give a look at.

 

When it comes to tire pressure repeatability is all that matters. As long as you always use the same gauge then you're fine. If you're aiming for 25psi and your gauge reads up to 150, then that's a bad setup. I have a calibrated Longacre tire pressure gauge that is super accurate. I have used it as my base line for years and test it every now and then. I have a floor pump at reads 5-7psi high and is hard to read that I use for the kids bikes.
I like my pressure to be within +-0.5psi so I built a digital setup and checked it to make sure it's calibration was good. Again I only use that one gauge for my tires. It's repeatable, accurate and it's consistent across all my bikes.

 

Yeah, have to say the digital MTB gauge (Topeak D2) is pretty right on. I used it on my car tire and also used a few other tire gauges and they read the same. Ha, for the longest time I've been reading extremely low pressure on my innertubes..crazy.

 

Does the Topeak D2 indicate increments of a PSI? Example... 18.3 Psi vs 18 psi only

 

Years back, I had a Joe Blow Digital that I totally loved. I remember that gave tenths of pounds increments. I do wonder in retrospect how accurate it was. I wore that thing out. Took what felt like a million pumps to get up to road pressure when it was on its last legs. Topeak did send me a replacement smart head for it though, which was nice.