Air Pressure Nuances

[Jay51]

I had a set of new Bridgestone Battalax T31 GT Spec tires installed about 1500 miles ago.
The shop also installed some right angle valve stems.

The tires are sturdy and fantastic in all road conditions. I am very happy with them.

I check the tire pressure weekly and notice that both front and rear lose about 3-4 pounds each.
I refill them to 42 psi and go about driving.

How much tire pressure loss per week would be considered normal?
The temperatures here in SoCal range from 50's-70s...

Jay

 

[naedlaen]

A twenty degree temp swing is marginal on air pressure. (20/(273+60)=6% times 40psi =2.4 psi) But this should vary consistently as the temp goes up and down, i.e., higher at 70 than at 50 and vice versa. I would check the base of the stems for a slow leak. (And the cores.) The rubber seals may not be squeezed tight enough around the stem to stop a low loss. The change seems to be the new stems and tires if you did not see this same thing previously.

On car and trailer tires, I seldom see pressure loss over a longer period as long as the temperature stays close to the same. When the temp drops 40 degrees in a short period, then I see the 4 to 10 psi loss.

Neal

 

[MarkyD]

My thought is a properly mounted tire and reliable valve stem system shouldn't lose any air; not even over weeks/months. If you measure in the morning one Saturday it should be pretty much the same the next Saturday if temps haven't changed by more than 10s of degrees (I think a 20° F change is about 2 PSI).

I had a new tire losing at that rate once and a 1/4 or 1/2 turn on the valve stem core fixed the problem. It was a tire I'd replaced and I had pulled the valve stem core prior to breaking the bead on the old tire so it was my reinstallation of the core that was at fault; which was part of the reason why I'd thought to try tightening it. I leave the valve stem cores in now and release air as I begin to compress the tire to break the bead.

Since it isn't a huge loss I'd call the garage once they reopen and see what others say before trying any messing around with the cores in the new valves.

Putting on angled stems is on my short list.

 

[dwalby]

3-4 psi per week sounds high, plus you've got new valve stems, doesn't seem like a coincidence to me. Do you or anyone you know have a swimming pool? Pull the wheel and dip it in the pool enough to cover the rim and look for bubbles. Also, a wheelbarrow filled with a few inches of water would probably also work. If you have a really fast leak you could probably spray soapy water on the valve stem and look for bubbles, but I'm not sure how reliable that method is with a very slow leak.

@MarkyD - every tire loses pressure over time, the air molecules escape through the rubber molecules.

 

[triospec]

Agree with dwalby that 3-4 psi/wk is high. I'd be suspicious of the tire bead/rim seal.

If the mounting process didn't include a thorough cleaning of the rim before mounting the tire, there's a chance of dirt/grime could sabotage the seal.

 

[roginoz]

We always check the valve core torque with one of these:

https://www.lislecorp.com/specialty-tools/valve-core-torque-tool

 

[SMSW]

Before I put my new tires on last year, the rear tire was losing about 2 to 3 lbs per week, and I was adding air before every weekly ride. Once the new tires were on and seated, the air pressure became pretty much constant and I add a little air maybe (maybe!) once a month. I check the air in the morning before leaving the house, bike is garaged, and temps are more or less similar from morning check to morning check. I never test air pressure at other times unless my Fobo says to. I'd look for leaks in this order - squirt a soap solution - or use a small paint brush to apply it - to the base of the valve stem. If no leak, loosen and tighten the valve core - just enough to blow air past the seal and then tighten it back up. Don't torque it till it screams. Wait and check pressures after adding air back to 42. If it is still losing air, then I would pull the wheel and use the wheelbarrow test - or take it to my fav garage and use my mechanic's tire tub to look for leaks while the wheel is dipped in water.

 

[Jay51]

Excellent Recommendations!

I performed the following before reading SMSW's post.

I applied very soapy water to both the front and rear valves. No bubbling at all from either.
I then, applied the soapy water along the edges of each tire and rim. Also, no bubbles detected.
I tested the core stems by seeing if they were loose. The back was tight and the front had a tiny bit of room to tighten more.
I then refilled them back to 42 psi.

The bike is garaged and I always test once I roll it out.

I will try loosening the cores and letting some air scream out!

 

[klaproth]

Although soapy water is good, it can be misleading because of the bubbles it has in it to start with. If you don't feel like taking the wheels off, try going to Home Depot and getting a bottle of leak detect for gas lines. It's in the plumbing area. it comes in ( I think) an 8 oz. bottle, with a dauber, and is blue. You smear it on the possible leak areas, and it has HUGE bubbles if there is a leak. I use it on gas lines, where it will detect VERY minute leaks.

 

[BakerBoy]

As mentioned, two likely culprits: 1) installer didn't clean rim bead-seating area before installing new tire, 2) right angle valve stems can leak at the core when the core is turned in too far (it easy to turn them in too far).

I've seen both of the above. Many tires that I've pulled off of other's bikes were surprisingly dirty at the bead seating area and the rider commented "yeah I've had to air it up often". I tossed a couple right angle valve stems due to poor machining (of both the core seat and the rim-mount threads) after having leaks from them on my ST.

A twenty degree temp swing is marginal on air pressure. (20/(273+60)=6% times 40psi =2.4 psi) But this should vary consistently as the temp goes up and down, i.e., higher at 70 than at 50 and vice versa. I would check the base of the stems for a slow leak. (And the cores.) The rubber seals may not be squeezed tight enough around the stem to stop a low loss. The change seems to be the new stems and tires if you did not see this same thing previously.

On car and trailer tires, I seldom see pressure loss over a longer period as long as the temperature stays close to the same. When the temp drops 40 degrees in a short period, then I see the 4 to 10 psi loss.

Neal

273 in above calc should be 460 (you've mixed Kelvin and Rankine).

 

[dwalby]

(20/(273+60)=6% times 40psi =2.4 psi)

273 in above calc should be 460 (you've mixed Kelvin and Rankine).

and while we're at it, 40psi (gauge) should be 55psi (absolute)

 

[Oldbikefixr]

My tire pressure 'behavior' varies with both of our Texas seasons. In our summer months, which include most of the year (high 70's to high 90's+) I add air every week or two.. During our winters (low 30's to high 60's usually) I check air pressure on cooler mornings and only have to top it off once a month or so.

 

[Andrew Shadow]

I was warned off angled valve as the rotational forces pull the valve stem outward - levering it downwards towards the rim and hence pulling on the seal. I haven't got a clue whether this was a theoretical observation, or something of real concern. I wanted to fit one on the rear, but I never have done because this thought is now stuck in my head.

B.S. unless you install some of those huge and heavy angled stems like those that are used on a tractor. If you use something that is intended for a motorcycle like these angled valve stems there is no cause for concern. I and many others here have quality angled valve stems installed and have never had any problem with them.

 

[paulcb]

B.S. unless you install some of those huge and heavy angled stems like those that are used on a tractor. If you use something that is intended for a motorcycle like these angled valve stems there is no cause for concern. I and many others here have quality angled valve stems installed and have never had any problem with them.

+1. I’ve been using these same angled valve stems for several years now with no issues. And they have TPMS sensors on them.