# Losing Tire Pressure, Normal?



## stevetheupsguy (Oct 31, 2008)

Hey, new to this forum, first post. 
I've been commuting 26 miles r/t to gym, work and home again, for about 2 years now. Just upgraded my bike to a Trek 1.2. I upgraded from a Huffy MTB, (Target Special). I shopped around and bought this bike, as it fit great, and weighed like 40lbs less than the MTB. 

My question is about tire pressure loss. I notice that after about 2 days I have to inflate the tires again. I'm running stock Bontrager tires/tubes. Running at 105psi at inflation. After 2 days it goes down to about 80-85psi. Any ideas?


----------



## bigbill (Feb 15, 2005)

stevetheupsguy said:


> Hey, new to this forum, first post.
> I've been commuting 26 miles r/t to gym, work and home again, for about 2 years now. Just upgraded my bike to a Trek 1.2. I upgraded from a Huffy MTB, (Target Special). I shopped around and bought this bike, as it fit great, and weighed like 40lbs less than the MTB.
> 
> My question is about tire pressure loss. I notice that after about 2 days I have to inflate the tires again. I'm running stock Bontrager tires/tubes. Running at 105psi at inflation. After 2 days it goes down to about 80-85psi. Any ideas?


It is normal to lose a little pressure each day but 20-25#'s in two days is excessive. I give my commuter tires a squeeze each day and pump them around twice a week. I usually only have to add 5-10#. I only ride my road bike once a week and it loses 10-15# during the week but has light tubes. IME, light tubes lose pressure faster.


----------



## rugger (Mar 1, 2005)

*Sounds a bit high*

I can't prove this, but I would expect that from a purely physics perspective, pressure loss rate would be higher for greater pressures. For example, if you are pumping to 120 psi, I would expect the pressure loss in a given time to be higher than if you were pumping to 60 or so, as the driving force is greater. Maybe it's imperceptible. 

The above notwithstanding, your loss sounds high, maybe a faulty valve. Assume you are using prestas? Be sure the inner and outer caps are closed down. Easy to check for a leak in a tube by pumping up and inspecting, or immerse in water.


----------



## Mr. Versatile (Nov 24, 2005)

How do you know they're losing that much pressure? Are you measuring with a Gage or with a Gage on a pump?


----------



## tarwheel2 (Jul 7, 2005)

High pressure, low volume tires lose pressure more quickly than big fat ones. Your experience is not unusual. I typically pump up my tires before every ride, even if I just rode the day before -- but I've got 700 x 23 or 25 tires on my bikes. When I used 700 x 28 tires for a while, I could go 3 or 4 days without having to pump up my tires. Pumping tires is a small price to pay for avoiding flats, and running tires on too low a pressure is the surest way to get a lot of flats.


----------



## tarwheel2 (Jul 7, 2005)

*tire pressure*

High pressure, low volume tires lose pressure more quickly than big fat ones. Your experience is not unusual. I typically pump up my tires before every ride, even if I just rode the day before -- but I've got 700 x 23 or 25 tires on my bikes. When I used 700 x 28 tires for a while, I could go 3 or 4 days without having to pump up my tires. Pumping tires is a small price to pay for avoiding flats, and running tires on too low a pressure is the surest way to get a lot of flats.


----------



## stevetheupsguy (Oct 31, 2008)

Mr. Versatile said:


> How do you know they're losing that much pressure? Are you measuring with a Gage or with a Gage on a pump?


I'm measuring with the gauge on a pump. I use the mechanics pump at work, same he uses for his pnuematic tools. I have presta valves and am running on 700x23, currently.
I ride about 5 days a week, should I use a regular guage instead, to get a truer reading?


----------



## jmlapoint (Sep 4, 2008)

I use 700x23 Tires and Butyl Tubes at 120 psi.
I pump them before every morning ride and never lose more than 4-5 psi overnight.
A 20 psi loss seems excessive.
If this occurs in BOTH Tires, it would be hard to explain on the basis of a defect or a tiny puncture in BOTH Tubes.
Are you using the same gauge to fill the tire and to check it for pressure loss?
This could account for the apparent difference.
I check my Tire pressure before every ride, and always use the same gauge.


----------



## wim (Feb 28, 2005)

stevetheupsguy said:


> I'm measuring with the gauge on a pump. I use the mechanics pump at work, same he uses for his pnuematic tools. I have presta valves and am running on 700x23, currently.
> I ride about 5 days a week, should I use a regular guage instead, to get a truer reading?


For that brief moment of attaching a pump to a Presta valve, you can easily lose anywhere from 5 -15 psi of pressure. In other words, all you're measuring with a pump gauge is tire pressure after you've just let some air out of that tire. It's a completely meaningless reading, and most people just ignore it. Attach the pump and pump to the pressure you want, done.


----------



## JohnnyTooBad (Apr 5, 2004)

I run 700x28 tires with slime tubes on my commuter. I pump them to about 100 lbs. I usually add air once a week, and the tires are usually down to about 80lbs after a week of riding. If I go 2 weeks, they will be down to about 70 lbs.

Oddly enough, I just started using slime filled tubes, but before, using regular tubes, they held air longer. One thing, is that I used to use tubes recommended for 28-35c tires in a 28c tire, so the tubes didn't strectch as much.

To lose that much air in 2 days is unusual. For commuting that far, I'd recommend 25c tires and thicker tubes that don't have to stretch as much. The more they stretch, the more air will leak out. They also won't puncture as easily.


----------

