jessestylex

Do you guys go by the max ratings thats marked on inner tubes? I have 700cX32 tires that came with the bike and a inner tube from academy sports. Once i hit the inner tubes max PSI it still seems to low as when I sit on the bike the back rear tire flattens out a bit from my weight.

Can i put more air in it without blowing the tire or inner tube? I would like a more rounded tire so that it rolls faster with less drag.

zukahn1 

Typically you can safely run slightly higher pressure than what the tires are rated for. So go ahead an put some more air in the tires. On slick streat tire I typically run as much pressure as I can get with a hand pump.

FBinNY 

I've never seen an inner tube with a pressure rating.

In any case it's irrelevant since the inner tube is just a balloon with a valve. At anything above 5 psi or so it'll stretch to fill the tire or whatever else is holding it in. It's the tire that provides all he structure, which is why tires (tubes) blow out if the tire isn't seated right or has a cut.

So it's he tire's pressure rating that counts, but even here there's generous margin for error.

bikeman732

Inner tube PSI rating? I have never seen it.

ultraman6970

+1... never seen it either.

as for the tire getting flat like if it had less air pressure than the max, well, it depends a lot of the clincher tire, the inner tube has nothing to do with that at all. No idea what clincher are you using but some do exactly what you are saying.

2 wheeler

I haven't seen a tube psi rating either. Post a pic of the tube box with the rating.

DX-MAN

At work, dealing with big-box crap, we routinely send 35max-psi-tired bikes to the sales floor with 50+(almost 60), and when we find problems with them, it's ALWAYS a faulty tire bead.

gregjones

I was doing well.

Now, I am lost.

DX-MAN

Okay. Follow.

Tubes don't have a PSI rating, TIRES do.

You CAN exceed the rated pressures printed on the tire, just remembering that if you do, ANY tire warranty is null and void. Real life, things don't always go by an expected limit.

I would recommend that you not exceed the rated limit on the tire by more than about 10-15%, though.

JanMM

OP: When you sit on the bike, the tires should flatten out just a bit (15% tire drop) but I suspect you mean considerably more than that.

rebel1916

Why? The minimum needed to avoid pinch flats might be a better rule of thumb.

cxwrench

This makes no sense to me. Why don't you inflate the tire to the pressure that gives the ride quality you want for the 99.9999% of the time you're not pinch flatting? And then keep your eyes open for pot holes and rocks...and if you miss one every now and then, oh well...a flat or 2 a year are acceptable to most people. I see no reason to over-inflate my tires by 10-20psi to avoid something that might happen .0001% of the time I'm riding.
If your normal roads are bad enough that pinch flats are a constant concern you need to be riding bigger tires.

rebel1916

^^^^^Uh yeah, thats the point I was making to a guy who said his method was to inflate the tires as high as he possibly could.

jessestylex

Sorry guys, you may be right. I got the tire psi mixed up with the inner tube. I just didn't want to be 15 miles out and my tire pop off the rim and blow the inner tube cause I have too much air.

I added about 12psi over the tire limit this morning and it did ok, I did notice it hit a bit harder on road bumps but it looks right and rides a bit smoother now.

FBinNY 

I'm glad you worked it out to your satisfaction. Here's a guide to optimal tire pressure based on weight and tire width.

IME, more width is better than more pressure, so I use 105-110psi as my ceiling and use wider tires rather than go higher. My road bike has 25mm tubulars and I ride it at 105/95 rear/front. My commuter has big fat 1.9" tires and I ride that at 60/50.

One benefit of wider tires is higher rim to ground clearance. This makes the wheels much more forgiving of potholes, and other hard impacts which is why I use fat tires for urban riding, especially at night where I don't always see potholes in time.

davidad

The tire pressure on the side wall is 1/2 the pressure needed to blow the tire off of the rim. Proper pressure is a function of rider and bike weight and tire width.
https://docs.google.com/spreadsheet/...hl=en_US#gid=0

seely

What tire are you running, and what are the min and max pressure?

bradtx

The rear tire is the main load carrier. Try reducing the front tire's pressure to reduce the vibration.

Brad

Kimmo 

IME even the crappiest tyre in the world can handle 10-15% over max pressure no problem.

Because I'm pretty sure most of em can handle 50-100% over, at least for the minute or so it takes to pop a stubborn bead into place.

Also, I recall reading in a thread here a few months back someone saying max pressures are half what it takes to blow the tyre off the rim.

This sounds plausible, given how engineers do things, not to mention the possibility of any given tyre being mounted on a rim-braked tandem or loaded tourer, which can send the PSI up pretty dramatically on a long descent.

cxwrench

How much do you weigh?

Bill Kapaun

Try that on a straight wall rim.

bobotech

Just how much do you weigh? What brand and size of tires are you running?

I am a big guy (350 pounds roughly) and I run my tires at max PSI or more just because I'm so big. I generally run 700x23c or 700x28c tires lately on my current to go-to bikes. The charts recommend super high PSI ratings for people my size with tires that thin.

Kimmo 

Well that's obviously outside spec.

Who uses those anymore, anyway? Odds-on anyone still running em knows the deal.

FBinNY 

My commuter has straight side rims, and I trust them completely to hold tires so they don't blow off. In fact, I'd bet that I can crack the flange before the tire lifts and blows off.

As far as I'm concerned, there's no reason to inflate tires above the max rated pressure. If you think you need more pressure, you really need a wider tire. If you need a wider tire and lack the fork or stay clearance, you bought the wrong bike.

SharpCarp

+1

Also, many rims/wheels have a max pressure which may be lower than the tire max. It's not wise to exceed the wheel's max pressure.