rbrides

I’ve not previously taken tire pressure after a ride. But I just put new Perrelli P-Zeros 700x28. Since it was the first ride I measured tire pressure and found they had both increased 5 LBS.

That is a surprisingly high increase.

how common is that?

zipp 303 wheels
new perrelli p zeros running tubeless
170 lbs rider
85degree air temp
70 mile ride @ 19 mph.

Crankycrank

I'm not a pneumatic engineer so don't know the exact formula but assuming you're using the same pressure gauge the 85 deg temps might account for the higher pressure if say you took the original pressure reading in temps well below that. Also plenty of room for errors trying to find correct tire pressure in multiple attempts with high pressure tires. Hopefully a more educated poster will chime in.

Iride01 

Like Crankycrank said.

If you topped it off in the cool of your airconditioned home and then took it out in the 95°F (35°C) and in the hot sun where it could be more inside, then maybe that's where it came from. But I'm not a pneumatic engineer either. <grin>

I don't check my tires pressure after a ride so I'd have no idea how common that might be.

Perhaps the needle on your gauge is loose and never gives the same reading twice.

Bill Kapaun

What's the temperature of the pavement? Probably much higher.

BCRider

In addition to the day warming up after you set the pressure there's also the fact that tires get warm when ridden. 5PSI worth? Probably not on a bicycle. More than that on cars or motorcycles.

Probably mostly the day's temperature warming up from the start to end of the ride. Got up to 85 by the end of the ride? What was it when you pumped and checked? If it was down around 70 and warmed to 85? That could be the 5PSI.

The other option is if you used the same gauge for both measurements. Different gauges often give different readings. I'm thinking same gauge though since we're creatures of habit.

GhostRider62

As common as PV = nRT

Expect about 2% increase in tire pressure for each 10F. Garages and houses are cool, pavement is hot. Tubeless and hookless? NB

curbtender

You using a tire pump gauge or a dedicated gauge? At work we had a preset test valve to calibrate our gauges. Seems the act of checking pressure would drop it by a pound or two. Anyway, at least it's not losing air.

rbrides

yes, tubeless and hookless.

rbrides

same gauge before and after. The Topeak digital gauge.

rbrides

What is most interesting to me is, I don’t recall anyone posting or advising about tire pressure increases. Back in my motor sports days, sports car and stock car racing, we obsessed about it by constantly checking tire diameter to manage to the best growth.

with all the constant chatter about “correct” tire pressure for tubeless bike tire setups, it’s curious there is no conversation or research into increasing pressures.

Crankycrank

Yes, used to road race motorcycles so correct psi after warming up the tires could make a huge difference. Bikes not so much and people have different requirements for their tires such as best cush or least rolling resistance, best traction, best pinch flat resistance and different weight riders will use different psi for the same bike. So much personal preference it's hard to have a definitive discussion about it but there are kind of ballpark suggestions I guess for someone to experiment with and tweak to suit themselves.

easyupbug 

5 PSI in a passenger car and absolutely in high pressure tires for heavy vehicles is not unusual for large swings in temperature, added radiant heat from the Sun, and from driving on them, etc. That's why all passenger vehicle's recommended tire pressure is its cold tire inflation pressure.

KerryIrons

If we assume you inflated to 90 psi at 70F, then if the temp rose to 91 F you would see 95 psi. Of course this assumes that your pressure gauge is accurate, precise, and reproducible so that you really did see 5 psi. For example, if you checked your pressure several times and saw a 3 psi variability, then maybe your pressure only rose 2 psi after your ride. And if your gauge is only precise to 2 psi (even though it shows to 1 psi) then there's another "maybe.

KerryIrons

How about high school chemistry? As noted by another poster, PV = nRT. All you need to do is ratio the temperatures (in either Kelvin or Rankine) to get the % pressure increase. Kelvin = celcius plus 273. Rankine = F + 491.

Bill Kapaun

Maybe try high school PHYSICS?
Celsius
Apparently you were afraid to try Fahrenheit?

cyccommute 

You can get there with the Ideal Gas Law but it’s the long way round. Guy-Lussac’s Law is a better way to do the calculation: P/T= k. In the Ideal Gas Law will give the same thing if you consider that the volume, n and R are all constant.

That said, the influence of temperature isn’t all that great on pressure. If the tire were filled at 70°F, the temperature would have to be raised to 95°F to get a 5 psi increase. Possible but unlikely. I’d suspect error in measurement more than temperature increase. To check, I’d measure again when the tires are at the same temperature as when it was pumped up. The problem is that there’s a bit of the Heisenberg Uncertainly Principle and Schrödinger’s cat with the pressure measurement. Measuring the pressure changes the pressure so you can’t know the pressure until you measure it but it’s no longer the pressure.

Troul 

Put a tire pressure sensor that reads out live data (via BT usually) onto the stem & see what the findings are.

GhostRider62

Sampling error(s) aside, slight overpressure on hookless rims can be disastrous because the safety margin is much, much lower than crochet rims. I did a mini gage r/r, the error is never upwards. 1-2 psi is lost when measuring. 5 psi difference is well within capability.

I am not sure why you consider a 2% per 10F increase unlikely. It is common form the differential from inside to outside temp to exceed 20F and the temps on the pavement are much higher still.

DiabloScott

Agreed that measurement error is the biggest unknown, and most likely explanation.
But we do not even HAVE a measurement of temperature, either before or after the ride.
This comes up a lot in the "heat from braking blows tire off rim" threads.

So - temperature MIGHT explain it, but if you want to be sure, you have to run a real experiment multiple times and measure everything... not just rely on intuition and a couple data points.

Camilo

What you're probably seeing is the difference between cold pressure and warm pressure. As you probably know, any tire pressure spec (cars, bikes, etc) is based on cold pressure. This is to make that pressure reading fairly uniform. Because, as as soon as you start driving or riding, the tire temperature - and therefore the pressure - will go up. Friction from the road, heat from the road, braking, air temp, etc. I'd be surprised if the pressure of your tire didn't go up with use. I've never checked a bike, but I do know that the pressure of my travel trailer tires goes up substantially as soon as I start towing (the pressure monitoring system also measures temperature)

An interesting question to me would be - after you ride, and the tire has cooled to the temperature at which you took the original pressure, what is it?

GhostRider62

On a short ride, I can say for sure mine will measure 1-2 psi lower everytime. Taking a sample of air (volume) to measure will lower the pressure with all else equal.

Take ten or twenty pressure measurements. You will not get a normally distributed curve. I lost 1.3 psi on average with ten pressure checks done consecutively. If after a ride, one measures 5 psi increase, the actual is more like 6 psi

sweeks

Are you sure you didn't accidentally install one of these?

Iride01 

Maybe this should be a poll. How many cyclist check their tire pressure immediately after a ride?

I'm thinking the OP is the only one! But I might be wrong.

GhostRider62

Maybe he listened to Silca's Josh Poertner who said tires blew of the hookless rim at a mere 80 psi. Think of how many use 75 psi. And how accurate is that 75 psi? (not very)

How many take an infrared gun out to test the carbon rim temps after a long hard descent? I know one.

Iride01 

Oh geez's. Just when I'm thinking I might venture into tubeless tire realm you give me another reason not too.

So do you stop every other switch back on the way down to check the rim temps? I admire your dedication to being safe! Though actually I hope carrying the IR thermometer is just in the interest of gathering data to help with the dogma.