ChrisAlbertson

Short version: I want a GOOD and ACCURATE tire pressure gage for shop use for road bike. (presta valves, up to 100+ PSI)

Long Story:
I had a flat yesterday. The tube blew on the inside of the tube in a long slit. The rim tape is good. My guess was I've been over inflating tires. It blew at the bottom of a hill. Figured by rim brakes cause heat. But today I blew up the new tube on my driveway. It seems the gage on my 20+ year old Silca floor pump reads 20 PSI low so it reads 90 and I had 110 pounds. Seems I've been riding with 110 pounds in tires that say "inflate to 100" I ride mostly on smooth pavement

Botton line is I want a gage I can 100% trust for use in the shop and to double check my floor pump.

dsbrantjr

Meiser Accu-Gage or other high-quality Bourdon tube gauge

Sy Reene

Sounds more like it's time to trash the old floor pump than to buy a separate gauge. If it's 20lbs off, what would you be double-checking?
If you really want a gauge, one of these works well -- very simple and within 1-2 psi of my floor pump. There are cheaper options out there, but this works pretty well.
Topeak D2 Smartgauge

Bill Kapaun

All you need to do is check your pressure against a good gauge and then see what your gage reads.
OR
Just inflate your tires 20 PSI low.
I would say most of us inflate to a pressure that works good for our conditions and THEN use that number for future ref.

BTW- Over pressure would have blown the tire off, not slit the tube, unless you "almost" blew the tire off.

Iride01 

I think you are letting your imagination run wild. I've never had a tube blow in a tire from over inflation until it was at least 150 PSI or better. I have burst a few new tubes because of me not checking that they weren't caught under the bead of the tire.

Not saying that you didn't. I wasn't there.

But an accurate tire pressure gauge for the average consumer at a price we are willing to pay...... I think you won't find that till big-foot is caught. <grin>

So just get what makes you feel good that will give a repeatable result even if it's not actually the correct exact PSI.

ARider2

I am ready to replace my 12 year old Topeak Smartgauge with a new one as it started being difficult to switch between presta and schrader. It still reads accurately and I will keep using it but after many years of shop use I need a new one and I will get another Topeak.

cyccommute 

I think you need to go looking for another reason for your flat. Far too much is made about temperature impact on tire pressure. Far too many electrons are spilled over tire pressure in general but I’m only going to concentrate on the temperature relationship. Let’s say you had 110 psi in your tires when you started your ride and assume the temperature was 70°F. If you heated the tires to 100°F, you’d gain 6 psi or 116 psi total. That shouldn’t be enough of an increase in pressure to blow the tires off the rim.

If you heated the tires to 212°F, the pressure would be 140 psi which is closer but the tube should just “split”. Over pressure of the tire should result in the tire pushing off the rim so that it actually blows out. You won’t mistake a blowout for a “flat”.

On a side note, how do you know that your pump is off by 20 psi? If the gauge is broken, such as the needle being stuck, get a new gauge. Replacements are available and are relatively easy to replace. If you are just “guessing” that the gauge is off, what are you measuring it against? If you have another tire gauge to measure the difference, why not use that to measure the tire? How accurate do you really need the pressure to be? Being off by ±5% isn’t going to make that much of a difference anyway.

Frankly, I’d question the quality of the tube before blaming the pump.

Koyote

As others have written, your tubes likely didn't fail due to overinflation.

And how do you know the gauge you were using is inaccurate? That seems easier than figuring out what is really going on.

But for what it's worth, I use a Meiser gauge, as recommended by dsbrantjr . Inexpensive, and consistent.

dwmckee

So many answers other than your question, but I have to agree that the tube split for another reason. And the Silca is an excellent pump and the gauges are reasonably accurate. I have one that is 32 years old and I have rebuilt it several years ago with a new gauge that is bigger and easier to read tha the old one. If the gauge is that bad, I'd just replace he gauge in the pump and maybe the check valve and leather washer with it. The gauge just unscrews and you screw a new one in with a dab of thread sealer... Silca gauges and rebuild kits are available on their web site. There are a ton of folks that will pay a good price for your old pump so they can rebuild it themselves and pass it on to the next generation.

ChrisAlbertson

To answer a few questions...

The tire did not blow off the rim. In both cases the tub ripped. The rip was facing the rim and parallel to the long dimension of the tube. Rip was about 1 or 1.5 inches long.

I suspected the floor pump gage error so I compared it to some other gages I had. They all vary by a small amount but the Silca that I normally used turned out to read about 20 low compared to the others. In other words the slice reads "80" when the others read "100". Before a ride I usually pump the tires up to 90 pounds. But with the bad gage I must have been filling to 110. The tires say "inflate to 100" on the side

This is a classic bike. 27" wheels. I have road slick 27 x 1.25 (about 30mm if they were metric) tires and the old classic single-wall aluminum rims

I got two flats in a row Friday after a downhill and toda (Saturday)y in my driveway before getting on the bike with a new tube.

Tires now have 80 PSI in them as measured by a different pump and there is a huge difference in hardness.

I checked the rim tape too. I push fingers in the rim and check for anything sharp, It is all clean and smooth.

So what else other then to much air causes a tub to split on the rim side.

ChrisAlbertson

I've had a blow out last year the tire sidewall blew with close to 100 PSI. I was one beach bike path going slow and EVERYONE heard it. The tire was just old and the fibers win the sideway gave out. This was less dramatic. But in BOTH cases there was a slit 1 inch long on the part of the tub that faces to rim.

Friday afternoon I replcedthe tub while on the side of the road and used CO2 to some low but ridable pressure. Let's guess 65 PSI. Thetire felt softer then normal but I hade no gage, just the CO2 and a tube. The new tube never used but year old. Then this morning I deflated the tire to nearly empty then pumped it with the Silca pump to 90 on the gage but 110 actual. 5 minutes later the tub split just like it did Friday while riding down the hill.

How do I kknowthere is a 20# error? I used the Silca to inflate some other tires to 80 PSI then checked tire pressure with some gages I have and they mostly said "100 PSI"

It has rained here recently. In So Cal this is really unusual, I mean it NEVER rains. I think water got in my pump from being left on the porch. I will buy a parts kit from Silca

But it still might be some other reason for the flats.

Moe Zhoost

Improper mounting. Tubes are not stressed much by over-pressure because expansion is resisted by a properly mounted tire. If the tire mount fails, the tube expands at that point and fails as well.

Trakhak

Check the sidewalls of the 27" rims. If the rims are old enough, they might be straight-side rims, without an inner lip to hold the tire bead. If that's the case, the limiting factor is not the maximum pressure specified by the tire manufacturer, it's the rim. Some rim/tire combinations with straight-side rimes won't reliably hold a tire at pressures much above 70 psi.

And, yes, as others have noted, a lengthwise slit along the inner side of a tube (or any other side of a tube) in what you'll see with tires that blew off a rim because of improper installation or excessive pressure.

cjenrick

thus is weird, i have a Serfas FP-200 fllor pump with gauge. it is probably not the best pump around. the pump head really sucks, it lets about 10 psi out during disconnect probably since i have to jam it on so deep to get it to stay on, thus depressing the thingy that you tighten back up when done.

so to get rid of the crappy pump head, i cut it off and put on a silca pump head that was laying around. what a difference! i no longer have to top of every day as the silca head lets out no air.

however, the first time i used the silca pump head before a ride, i felt a bump-bump-bump rom the front tire wtf?

turns out the front tire had about a half foot blow off. lucky i caught it before losing the collar bone.

so i thing the silca head is putting more pressure in the tube, why/ i do not know, maybe a physics geek could explain it, i am thinking it might have to due with the age of the pump head that has been sitting around for 20 years, possibly a constriction of the rubber has caused the narrow passage to allow more pressure.

needless to say, we backed off about 5 psi on our gaige and it is now time to get a new gauge for a second opinion so thanks for the recomendation(sp).

ps: we are running Araya 20-A red label which has a rep on some vintages for tire blow off but we have not had a problem since reducing pressure.

ChrisAlbertson

I think this is what happened. The tires might be oversized for my rims. I can actually change them with no tools. But also I've verified my Silca pump has a bad gauge on it. I've reduced pressure and it's working again.

I think the root cause was leaving the pump outside in the rain. Rain is so rare here that you never expect it and the pump has left on the porch and it was blowing atomized water out the hose. The 30 year old Silca pump was due for a rebuild anyways.

I had planned to buy a bicycle before the COVID thing ended that plan. I figure I can wait until 2022.

70sSanO

I'm not suggesting that you buy these pumps...

I have an SKS Rennkompressor floor pump for my road bike. It works quite well and have not had a reason to check the pressure.

I also have a Spin Doctor higher volume floor pump that I use for my mountain bikes. Since I want to run close to the lowest pressure, I bought a Meiser Accu-Guage to check it at different pressures; but you can buy whatever seems best. The pump is off by about 3lbs.

In addition to the pump and separate gauge, I have a black Sharpie. Rather than buy a new pump, I have written the actual checked pressure variance on the side of the pump so I'll know what pressure I need to go to using the pump's gauge. And I occasionally check it. So far I have not had any issues with the Sharpie.

John

DaveSSS 

I bought a winters glycerine filled gauge with a much larger face from Amazon for about $21. Choose 0-100 or 0-160 psi. It requires a short 1/8 inch pipe nipple, a 1/4 to 1/8 reducer and a 1/4 elbow to connect it to the pump.

https://www.amazon.com/Winters-PFQ80...4028010&sr=8-5


Improved Silca pump

scottfsmith

This thread prompted me to get a digital gauge and I learned that my 25-year old floor pump (Performance brand I think) with the standard circular gauge is reading 15 psi too high.. ouch! 25 years of riding at lower pressures than I though I was.

Now I know why I kept not quite getting those KOM's, it is so obvious now! :grin:

Anyway I have started to just add 15psi to my target and aim for that reading on the floor pump gauge and it seems to work pretty well.

2_i 

I replaced the analog gauge in my Zefal Husky floor pump, that I could hardly decipher, with the replacement digital gauge for a Lezyne floor pump. There were some challenges in matching the threads for the gauges, but all is good now.