tire pressure
 

i have another post about my rims being dented and someone recommended that i keep my tubes at less pressure than recommended. The recommended is 120, so if i keep my tires at 100 wouldnt that result in pinch flats?
I know that if i dont pump my tubes every other day i get flats, which i assumed was because of loss of pressure.

What should i do? I dont mind decreasing pressure but i dont want flats.

I keep my tires at 90-100 psi ... and that pressure does not result in pinch flats, nor do they go flat every other day. It's actually a very comfortable pressure.

To some extent it's going to depend on what you weigh.

^And the size of the tire. I'm 160 and go to 95(f) and 100(r) max on my 23C tires. Road biked over 5000km last year and had one flat (not roadside, but discovered when pulling bike out for next ride). Cobbles, pavers, road debris and all.

Disclaimer: I do know how to bunnyhop when the situation dictates.

Opinions certainly vary but I have found the info on this sheet quite informative. Seemed like a bunch of hocus pocus when I first read it but I tried it anyway. Pretty darn accurate in helping me achieve my personal comfort level. :thumb:

by this pdf the only thing that matters to tire pressure is wheel load and tire size. Doesnt the type of tire matter as well? For instance, a slick racing tire vs a knobby cyclocross tire of the same size?

Most bikes would ride like garbage at such a high pressure. The pressure listed on the side of a tire should be considered the maximum inflation pressure, no matter what they say. You would only need that much pressure if you weigh enough that you need it.

It depends on your weight, and nothing else. I've always found the tire pressure chart provided by Michelin quite satisfactory. You can find it on their website, in the bicycle tire section.

Why would the type of tire matter? The size (and the volume of air that fits inside) would be the same regardless of tread pattern.

Seems strange that you would point out that the required pressure is weight dependent then claim "Most bikes would ride like garbage at such a high pressure" ?

Maybe you should amend that to say "Most bikes would ride like garbage at such a high pressure - FOR MY WEIGHT" ?

I've never found a good reason to run any tyre below it's maximum pressure - but that is my experience and I may well weigh more than you :)

At my 215, I always run at max pressure. If I was back at fighting weight, I would certainly dump that down to keep the ride comfy.

I only had a pinch flat once. It was on my mountain bike, after rain on clay soil. Very very slippery - the only way I could get traction over one section was to drop the tyre pressure to 12 psi. I got a pinch puncture bungling a curb hop a couple of weeks later, having left the tyre at 12 psi for 100 miles or so. At my usual 30ish psi I rarely flatted, except on thorns which would go through anything.

i thought it was very important to keep tire pressure up because if i dont pump my tubes every other day i get flats... which i assumed were pinch flats. Thats why I thought having very high tire pressure was good. Keeping tire pressure down scared me because i thought it would just lead to more of those flats.
Does tire pressure drop drastically just from bleeding out? Maybe it makes sense that after two days my tire pressure is down to ~60psi and then it gets flat but 90psi will work fine?

If you are so heavy that you need to inflate to max pressure, that is the point when you should consider a wider tire so you don't have to do that. Riding with a tire at maximum pressure is almost like riding solid rubber.

Call me an idiot, but I don't understand the chart.

That isn't entirely true, changing to a wider tyre will usually result in the wider tyre having a lower maximum pressure, so nothing is gained, you'll still be at maximum pressure just on a different tyre.

Riding with a tyre at maximum pressure might almost be like riding solid rubber - for you.

I can guarantee that it isn't for me, on any of my bikes regardless of tyre width.

:)

No, tire pressure does not drop that drastically. I pump my tires up about once every 2-3 weeks and they haven't lost much at all in that time. If you are getting flats every other day, I would really wonder why:

-- are you changing the flat properly?

-- have you found the bit of glass or wire that caused the flat?

-- do you watch where you ride and avoid riding through glass and other debris?

-- have you checked your rim tape lately?

According to this, I should keep my 32-mm tires at 35-40 psi. I've actually done that a few times, though not on purpose, and I must say I didn't enjoy riding them like that at all. The biked moved like molasses.

sorry, my bike and I wiegh 200lbs together. I have 700x25c which puts me at 90psi on that chart in the pdf.

I have checked my tire/tape etc many times. Its just that for the most part I will only get a flat if I dont repump my tubes every other day. I heard that many people repump them every day so I didnt think i was doing anything wierd. It is the only thing I have found to reduce my occurences of getting flats.
And Ive been riding it at ~120 for a year so it doesnt phase me at all, solid rubber or not.

Ok, NOW we have enough info to go on, thanks! :) Whew (no known tire size and ALL this good advise? what?)

I'd not go under 100 lbs if you're worried about the wheels. With your weight and that tire size, that seems like about the limit to me.

Let me try to explain it this way:

On my bike, I use either 23 or 25 mm tires, and I have had 28 mm tires on it (700c). With the 23's, I use 95 psi, with the 25's 85 is about right, and with the 28's, I think I used around 80-85 psi. None of those tires are at max recommended pressure, because none of them are too narrow for my weight. But all in all, there's a significant difference in ride between the 23 and the 25. The latter feel a lot smoother over typical inner urban streets, without compromising handling in any way that I can notice. The 28's are smoother still, but they feel vague in handling. But because I have some way to go before reaching the max pressure, I can decide to go harder if I want to go faster vs having a smoother ride. If you already are having to ride your tire at max pressure, you don't have any leeway to play with, plus, as I said before, it's going to make for a pretty hard tire (we're talking road bike tires here, where max pressures can be like 120 or even 140 psi, not low pressure mountain bike tires). I'm in no way suggesting a person can't ride that way, only that one might at least consider the next wider size.

There's no point in explaining it another way - everything you have said is relevant to your weight

What do you weigh ?

You can't expect your experience to hold true for someone who is much heavier or much lighter.

I ride 23s and have them at max - carefully checked with a proper gauge. I have had 25s on the same wheels and ran them at max pressure. My tourer has 2.1" tyres, again, I run them at the max pressure.

Same goes for my MTB (1.6" tyres) and tandem.

My experience is anything less than max pressure feels soft. My experiences aren't any more or less relevant than your's, they are just mine.

If I advised everyone to ride at max pressure that would be as pointless as you advising everyone to ride at 70 - 80% of max.

Changing to a wider tyre is never going to allow a heavy rider to get away from max pressure as the wider tyre will be lower pressure anyway, so they will just run max pressure on the fatter tyre.

I'm not saying your experience isn't valid or that your advice is poor.

I'm saying that it only holds true for a rider of your weight, is that so difficult to grasp ?

fwiw some people prefer to ride on harder tyres and I've used wired on tyres with a max pressure of 125 and run than at 110% on the basis that there has to be some margin available, so that's 138 psi.

Anyway, I guess you weigh a few piounds less than me ?

:)

People might top them up every day (or in my case, once every couple weeks). They don't pump them up from flat every day!! I pump mine to somewhere between 90 and 100 psi ... and a couple weeks later when I check, they're down to maybe 75-80 psi, so I top them back up to somewhere between 90 and 100 psi.

By flat, do you mean flat? As in ... no air? Or do you mean ... ever-so-slightly squishier than the were a couple days ago?

If your tires are going completely flat every day, there's a problem. If I were you I'd very carefully change the tubes and tires.

Yes, it is a function of rider weight (and load if touring). I'm pretty sure I said that from the very start. We all have tires on our bikes, and we all weigh something, don't we? It doesn't matter if you weigh more or less than I do. The concept remains the same.

Erm...that depends what 'it' is.

If 'it' is the same 'it' we were talking about - that is having the correct tyre pressure - then rider weight really does matter.

:)