littleArnold

I was told by a guy at a bike shop that tires will inflate more in hot weather? So don't inflate it close to the max air pressure recommended on the tire instead keep the pressure lower? Otherwise the hot weather will pop the tire?

Since I was reading that on pavement if you inflate your bikes tire more to the upper end of specified tire pressure that this should result in lower roller resistant. So I have a Trek Fx2 if I usually only have it inflated to around 65 PSI, but the tire says 65 - 95 psi. So If I inflate it to 95 PSI it should in theory have a lower rolling resistance on pavement? But in hot weather doing that can be dangerous because the hot weather will cause the tire to inflate even more than 95 psi and will cause the tire to pop...according to a guy at a bike shop I was talking. He said he would really be careful about inflating it on the upper end to 90-95 PSI, like 70-80 PSI in very hot muggy weather would be better he told me because then the tire won't over inflate and pop.

So if I got more a road tire that required 100 PSI, inflating it to 100 PSI would be a very bad idea ... instead I would like to inflate it to like 85 PSI because the hot weather will increase the PSI from 85 - 100 PSI ? I am just going by what this guy at this bike shop was telling me... things I wasn't aware of?

ofajen

The part about pressure increasing with temperature is true. To the extent the air in the tire operates under the ideal gas law, pressure would be proportional to absolute temperature in Kelvins. Going from 68F = 20C= 293.15K to 104F= 40C = 313.15K is a 7% increase in absolute temperature. So if you had it at 95 PSI at 68F it could be around 102 PSI at 104F.

The part about rolling resistance and tire pressure is way more complicated because you need to consider not just the energy dissipated by the tire deforming, but also include the energy dissipation in the bike and rider caused by vibration from the roughness of the road surface.

A lower tire pressure will dissipate more energy in deforming, but may reduce vibration energy losses, so you may end up with the same or better use of your energy and more speed. Feel free to experiment with this.

Otto

woodcraft

1. Highly inflated tires left in a hot car- possibly.

2. Max pressures on tire sidewalls are conservative.

3. Lots of bikes & tires out there. If it was a thing, you would have heard the pops.

4. The theory of higher pressure = lower RR is in disfavor. You'll probably go faster & will certainly be more comfortable with 65psi than with 95psi.

Mista Sparkle

I had a wheelbarrow I was borrowing from a neighbor on a hot day, he must have inflated the tire to 120 psi on a 60 psi rating, he was that sort of guy...

It was sitting in the sun while I was working on something and BOOM!!!!! I though he was setting off fireworks or something to be an ass, I nearly had to change my underwear... I went to use the wheelbarrow and half of the tire was torn to shreds.

The weaker tire as a result of heat and the higher pressure caused it to pop, so yes, it is possible.

I doubt that with the volume of a skinny bike tire it will result in the same sort of failure, especially on a "good" tire, but if there's an underlying issue, you may discover it in an unpleasant fashion...

cyccommute 

Guy-Lussac law. At a constant volume, P1/T1=P2/T2. T is in Kelvin. Solving for P2, the equation becomes P2=P1T2/T1. Let’s say that T1=293°K (20*C or 70°F), P1 = 100 psi, and T2= 313°K. Plug and chug to get 107psi. Pretty close to ofajen’s estimate.

Now let’s assume that the absolute maximum pressure...the blow off point...is 150 psi. How hot would it have to get to reach that pressure? This time solve for T2. T2=P2T1/P1. Plug, chug and T2 is 440°K or 166°C or 330°F (for the metrically challenged). If it gets that hot, you got other things to worry about!

raceboy

Minimal effect. When I raced shifter karts, tire psi would only elevate 2-3 psi during a race. And you could barely touch the surface of the tire after a race because the soft rubber was hot and gooey. Bike tires don’t generate high heat like that.

Test it out. Check your psi before a high speed descent. Check them again at the bottom of the descent to measure the difference.

Kabuki12

Once I had a cheap ten speed many years ago and thought if I pumped the tires up until they were rock hard , the bike would roll better. The bike felt faster and I rode that thing until my legs got tired. I stopped to rest on a nice sunny day and as I was relaxing in the sun BANG, it damn near stopped my heart! Yes , the hot weather will increase tire pressure. It only becomes a problem when you over inflate to begin with. Stay below max pressure rating and you should be fine.

Phil_gretz

Post #2 answered this question correctly and to the point. Post #5 adds the ratio method and solves for the burst point temperature. Nice.

All other discussion beyond these two is simply a lot of extra air...

/close thread

jpescatore

I'll give my version of my short answer: in hot weather and on hot pavement, tire pressure will go up sometimes as much as 5 psi per tire. The tire is very unlikely to pop because of that.

But, riding on real roads, there is never any need to get within 5 psi of that highest pressure rating anyway; You can look at charts like the in this article to pick a reasonable tire pressure for your weight and tire size and not come close to those max ratings.

Troul 

A the tire that has been exposed to punctures; I personally would not run it at the higher PSI limits when using a tube in a 700x28 or 700x32 tire.
My personal experience has determined that if the tube is able to push against the inside of a tire with previous punctures that may not need an inner patch, that tube may try to squeeze itself into that hole. If that tire has multilayers & one of those layers contains a sharp edge, the tube can rupture when it is trying to force through that crevice.
I've had tubes "pop" when I ran the PSI at the higher threshold with a tire that contained a puncture. The blowout of the tube was aligned to that tire's faulted area. After putting a patch inside on the tire & installing a new tube, I was able to inflate the tube upto the higher PSI without follow-on issues.
I tried lowering the PSI lower without putting a patch on the inside of the tire, but I was having pinch flat issues.

My experiences were/are with:
Pirelli Cinturato Velo 700x32C
Schwalbe Marathon HS 700x32
Continental Touring Plus Reflex 700x32
Vittoria Zaffiro Pro IV 700x30
Continental Ride Tour E-Rated 700x28

YMMV based on rider weight, tire size, & terrain conditions.

Ubie

Anecdote time: I used to live in a desert in the American Southwest and kept our bikes in the shed out doors. My brother had a Trek 1000 at the time and would blow a tire in storage any time the outside temp was above 100*F or so (goodness only knows how hot inside the shed, 140*F+ ?). To solve the problem he finally bought a higher quality tube and then reduced the PSI by about 10-15lbs. Not sure exactly which one solved the problem, or a combination of the two.

rydabent

Inflate a tire to max in the cool of the morning, and then riding on pavement too hot to touch can raise the pressure a great deal. Then add in riding rim brakes down a long pass, there can and has been big bangs.

Miele Man

Inflating a tire to maximum pressure can lead to an unnecessarily harsh ride on certain road surfaces such as chip seal or with surfaces that have lots of cracks in them. I found that out the hard way. Had a bike with tires at 120 psi and riding it felt like Mohammed Ali was punching me in the kidneys. I had to turn around quite a bit short of my destination. I thought I might have to walk part way home the pain was so bad. Later I dropped the pressure a fair bit and the ride was much more comfortable. Sort of counter intuitive. Sometimes more is NOT better.

Cheers

shelbyfv

Now that you only have one wheel https://www.bikeforums.net/general-c...-fx2-bike.html your risk of mishap is cut in half!

CliffordK

My one Continental Gator Hardshell blowout was on a hot day.

I installed a brand new tire and inflated it to maybe 110 PSI during the cool evening before my ride.

Then about 70 miles into the ride, early afternoon, generally HOT, and BANG, sidewall blowout, bead blown off.

Whew, what a pain to boot a bead separation for the 20 mile ride to the nearest bike shop.

I can't say what caused the blowout. As above, I calculated that I should have been well within any reasonable pressure safety range.

Nonetheless, I've taken a little extra care since then.

pdlamb

Similar to above, but using Rankine (degrees Fahrenheit + 460). T starts at 520°R (60°F + 460), heats up to 120°F (= 580°R). Start with P1=100 psi, P2=T2*P1/T1 = 112 psi. If that's enough to blow your tires, you've got a tire problem and shouldn't have started so high (or had that tire on your bike to begin with).

Call me lazy, I've subtracted 32 instead of adding it or multiplied by 5/9 instead of 9/5 too many times to care.

Kapusta

When doing the above calculations, if you want to be more accurate, you need to use the actual pressure inside the tire, which is the pressure you see on your tire gauge, plus the ambient atmospheric pressures (around 14psi at sea level). The pressure you see on the gauge is actually measuring the difference between the pressure in your tire and the pressure outside.

As it turns out, when you are talking about high pressures (like 95 psi as we read it on our gauges) the effect on the results is negligible. But at very low pressures (like fat bike in the snow at 2-3 psi) it make a significant difference.

Pop N Wood

Tires heating up seems to be a thing on the internet these days. Can't say I've ever adjusted pressure based on ambient temperature and I've never had an issue either.

I've had tires blow off the rim when inflating them. Guess I could come up with an equation to sound cool but pretty sure heat had nothing to do with that.

cyccommute 

It’s not enough of a difference to matter if the pressure is gauge or absolute. It would make a difference if you are pumping the tire up and then changing altitude but that’s not what most people are going to do. The ambient pressure at a specific location will vary only a little. To use your fat bike example, a tire going from 3psi at -5°C (23°F) to 0°C (32°F) would see a pressure change of 3.1psi. Using the absolute pressure (17psi), the pressure change is 3.3psi. The change is small enough that it can’t be measured by bicycle gauges currently in use.

If the temperature change is from 0°C to 15°C (60°F), the pressure change is 3.2 psi gauge and 3.9 psi absolute. Not enough to make a difference.

Kapusta

I am not recommending trying to find a gauge that measures absolute pressure. It is the relative pressure difference that pumps and gauges measure that is the relevant number for how the tire feels and functions. My point is that the more accurate way to calculate the effect of temp on pressure is to use the absolute pressure for the calculation. As long as we are plugging numbers into formulas, I am simply pointing out a more accurate formula. While in most situations the difference is insignificant, there are some for which it is significant.

To your example, from personal experience I would argue that the difference between 3.2 psi and 3.9 (I get 3.2 and 4.0 when I calculate and round) in a fat tire actually IS significant and noticeable, but here is an example of an even bigger difference:

Pump a fat tire to 4 psi in a 70F house, and then take it riding at 10F. Let's calculate that using just the measured pressure vs converting to absolute for the calculation:

First, lets look at the calculation NOT using absolute pressure P2 = (P1*T2) / T1 (as you mentioned earlier)
T1 = 70F = 294.3K
T2 = 10F = 260.9K
P1 = 4psi (as measured)

P2 = (4 * 260.9) / 294.3 = 3.5 psi

Now, do the calculation using the absolute pressure for the calculation. In this case, you need to add ~14 psi to P1 and P2. So now you get

P2+14 = (P1+14)*T2 / T1

Solve that for P2....

P2 = ((P1+14)*T2 / T1) - 14

So,

P2 = ((4+14) * 260.9 / 294.3) - 14 = 2.0psi

In practice, he difference between 2.0psi and 3.5psi on a fat bike is very significant, and very noticeable..

Sy Reene

Unless there's some special setup.. the simple act of checking tire pressure will usually remove a few psi from the tire.. so if you're doing this measurement and finding the tire a few psi higher than you started, in actuality before you checked it could have been 6-8psi higher.

raceboy

It seems to be like that would be more or less a "constant. Whether it's before, after, or during your ride, every time you check your pressure you're going to drain off a few psi. My guess is that the narrower the tire (operates at a higher psi pressure), the more pressure you lose with each check.

Another worthwhile test, though time consuming, would be to see how many tire pressure checks it takes on your bike before the tire loses all of its air! I'll reserve that one for thw winter season. Now is the time to ride!

velojym

I had an Axial Pro explode in the back seat of my then girlfriend's car. It was a hot day, no tint on her windows, and my bike was laid across the back seat, tires at max sidewall pressure.

I had to do the club ride on a borrowed 'spare', which was showing thread. 5 flats on that ride. I usually let out a little air nowadays, if I'm leaving a bike in the car for more than a few minutes, in the heat. I carry a floor pump with me anyway.