Tire Pressure: How to test for "too low"?
 

What's the limiting factor on low tire pressure? Obviously is the tire rolls off the rim when cornering, but beyond that:

1. "Feel" - responsiveness?
2. Getting flats?

Tech Details

• 2008 Specialized CF Roubaix, Mavic wheels, Mavic 700x25 tires, weight 235
• I pump the tires up to 90/100 and I don't pump again until I feel it's soft pressing hard with my thumb (usually after about 10 days, but sometimes longer!)
• When I pump up my "soft" tire, the pressure can read as low as 65 psi
• The winter causes pot holes, and I do hit one occasionally (maybe an average of once per ride (30 miles)

I'm old and slow (15 mph with 50' ascent/mile average is a good average speed!). I ride every 2nd or 3rd day when the weather is agreeable. I am somewhat insensitive to road feel except I notice the ride is harsher after I've just pumped up the tires.

Thanks.

PS - I would have ridden today, but I need to clear the 18" of fresh snow!

March has sucked so far in NE. Seems like every time the roads get good to ride, it snows again. I would say if you are getting pinch flats you are ok.

If you can pinch the sides in with our fingers, even just a little, it's no longer 90.

I don't really pay a lot of attention to the exact pressure. A quick thumb test sometimes when getting on the road.

At times a slow leak can be associated with a pinch flat. So, first one picks up something like a radial tire wire... then an hour later, pinch flat.

As far as detecting when it is really getting bad, there is a hard bumpiness when one knows it is time to pull over and check the tire. I have also had a strange rolling feeling, especially if hitting things like thick road paint, or a transition between road and gutter, which can indicate a low tire.

Um, maybe use a gauge?

Pump up before every ride. Why would you do anything else?

Soft tires first lead to pinch flats. If way too low you can get rim damage. It isnt’t worth the risk to neglect pumping before every ride.

Tire pressure that is too low can give you more pinch flats and less traction when cornering

I add [check] air..... need it or not.... every time I ride. It's just part of the process.

That's way too high tech, and doesn't have enough opportunity to get wrong. Do you have a method involving the angle of the sun in the sky?

I ride latex tubes in tubular and clincher.
You must pump each ride. But then if I was cycling for efficiency, I'd take a car.

I squeeze the sidewalls and lean on the tops of the tires (resting on the hard floor, not carpet). Then check with a gauge. When it seems like I've got a good feel for the right minimum pressure with any given tire, I'll sometimes just do the squeeze test before a ride.

Ditto when I try a new-to-me portable pump. I knew it took about 300-400 strokes with a Topeak RaceRocket HP to get my 700x23 tires up to safe riding pressure, around 80 psi.

Tuesday evening I had my first chance to try a new Blackburn Core Slim pump, which is a Presta-only high pressure road pump specific pump, a little larger than a mini-pump and a little smaller than a small size frame pump. After 150 strokes I couldn't do no more. The tire *felt* right. I checked it at the nearest bike shop within five miles. It was dead on 85 psi. Pretty reliable guesstimate.

But I can't really tell riding on a tire. I didn't have a puncture flat Tuesday. It was a slow leak from a previous nick in the tube caused by my own darned self almost five weeks ago installing the new tires and tubes. These were Continental Ultra Sport 2, ridiculously difficult to mount and I didn't have a bead jack. I nicked the new tube using a plastic lever to horse the bead across the rim. I didn't want to remove and redo it, so I filled the tube with 2 ounces of Slime for tubes. It worked for more than a month, about 500 miles, before it leaked.

When it happened it was so gradual I just felt something getting squishy. Then I looked down and realized I was riding on a completely flat tire. I thought it was be a lot more obvious. Probably depends on the tire. I know when my previous tires -- Schwalbe One V-Guards -- went flat, I could feel it sooner. Those Schwalbes had very thin sidewalls. But the Conti Ultra Sport 2 have thicker sidewalls and in 700x25 squished out across the rims enough to protect them from the pavement.

So I can't reliably judge tire pressure by how it feels while riding. I'm just not that picky. I can feel if it's harsh from over-inflation. But not if it's low.

If it feels spongy or you can see the tire deform when you push down on the bike, you need to put air in it. :)
I've been thinking lately about how, when I was a youth, I don't remember having to fix a flat but once, ever, and how putting air in the tires was something I rarely had occasion to do - only when the tire deformed from the weight of the bike alone - and it meant stopping by a gas station, because we didn't have a pump. Of course I never rode very far or very fast, but still, it seems weeks would pass.

I've a gauge on the pump itself. Don't know how accurate it is but I pinch it at whatever pressure it reads and note how hard it is. So before each ride I'll pinch it and compare the 'hardness' when I had it on the pump. Seems to work pretty good.

Depends on how you ride. For me that would require getting the pump out about 20 times per week when it's really only needed about once every two weeks.

go with feel.

seems like people are turning tire pressure management into a religion nowadays.

Once a day is proper for narrow road tires. The best rides are at your preferred pressure. Not so much plus or minus 20%.

Wow people are really all across the board here....

An important consideration though is tire size/optimal pressure.

If you have 23mm tires at 100psi+, you really should be checking them once a day. They can lose pressure quite fast.

If you've got 40mm+ tires at <50psi....yea you can go weeks. Probably a whole season and they'll still be perfectly rideable. There's a dramatic difference in both the rate of air loss due to existing pressure, and also the total volume of air in relation to tire size.

90/100 psi on 25mm tires with a ~260 lb system weight is already lower than I'd probably run. If you aren't getting pinch flats, consider yourself lucky. 28mm tires would give more of a margin if your bike can fit them, but as I remember 2008 was still skinny tires at max pressure. :)

IME the limiting factor is pinch flats. Of course it's possible to have some disaster before one hits something that might cause a pinch flat by simply being ignorant of your tires' current pressure. All this easily taken care of by pumping your tires, using a pump with a gauge, every time before you ride. Then the issue becomes what it should always be: what's my optimum pressure? Other than optimum, if you're pinch flatting, choose a higher pressure when you pump.

I sometimes pinch flat because I've had a slow leak which I didn't detect early enough. Then I find 3 holes in my tube.

Your "tech details" replicate mine pretty close.

I check tire pressure every other day and re-inflate my tires to 115. My tires lose a few lbs every other day and a couple strokes on my Joe-Blow pump followed by verification with a separate air gauge and I am good to go.

Buy a pressure gauge and check at least every other day, if not every day. I really dislike pinch flats.

It really really depends on your tire size...

For the tires I’ve had, the following are the timeframes for them losing significant pressure, assuming they started at a pressure appropriate for the size

23mm - every day
25mm- every couple days
28mm - twice a week
33mm - once a week
40mm - every couple weeks
45+/mtb tires - a month

Check your tires daily with the gauge of a floor pump. You'll figure out how often you need to inflate assuming your ride length is in a narrow range. I commute 28 miles a day and know that inflating every other day works well. I always pump after metric century day and if I haven't ridden for a couple of days. I have 25c (which measure 27mm when inflated) at 100 psi.

It's really not that big a deal to check at home with a floor pump. Don't forget to check tires for slices and cuts, too!

Sounds about right, but depending on what one considers appropriate and an acceptable range, one could extend those a bit. And it seems that would depend on the properties of the rubber - some tires seem to be leakier than others. It's been nearly a week since I pumped up the 25mm tires on the fixed gear to 100psi, and I just checked - they felt reasonably firm, and turns out they are still around 90, which is still fine in my book. Takes about a month for them to get as squishy as tubulars (also 25mm, pumped to 120psi) get after three days. Other tires are somewhere in the middle in terms of leakiness.

I also use the finger method. If I can depress the tyre appreciably in any direction with my fingers then it does not have enough pressure, so I pump it up to 115-120 again. I find that the higher the pressure the fewer punctures. I never get anywhere near low enough to get a pinch flat unless I already have a puncture.

My cushioned bars take care of most of the road vibration due to a hard front tyre.

Well 10psi is kind of a lot.

If they're fine at 90psi...I would just pump them up to 90 instead of 100. Only 1 is the best pressure...

I doubt any tire pressure gage is NIST certified & calibrated annually.
At best maybe +/- 10 psi
(10% at 100psi)

Get a good thumb squeeze feel for the inflation that works for you
Probably be +/- 10 psi
:)