Tyre Top Up?

[mjr]

A bicycle's vibration cannot generate enough inertia in those light parts to make the valves bounce open. You seem to think that leakage comes from the valve itself.

Not only but Schwalbe Woods tubes lose less than Schwalbe Schrader ones in the same size (DV vs AV of the same numbered size IIRC) so what would you hypothesise?

 

[slowmotion]

It might possibly just be a temperature effect.....Boyles Law (or one of the other Gas Laws).....

PV=nRT

or something. Air expands when it's hot and shrinks when it cools. If you measure the tyre pressure after the tyres etc have cooled, you will get a lower reading than the one you would have got when the bike was hot. Leaks might have nothing to do with it.

Where's@McWobble when you need him?

 

[Pat "5mph"]

both bikes are kept in a plastic shed which in the Spanish sun can get over 90f inside.

I don't know about the pressure loss (I need to top up my hybrids every couple of weeks, fwiw) but be careful leaving your bikes in such a hot place: I had a tube exploding at the valve while parked in the sun on one of the rare summer days we get here.
Can't be sure if it was really the hot temperature or just valve fatigue, but it had never happened before in the cold, even with older inners.

 

[Yellow Saddle]

Not only but Schwalbe Woods tubes lose less than Schwalbe Schrader ones in the same size (DV vs AV of the same numbered size IIRC) so what would you hypothesise?

I won't hyothesise until I see some data. I have no idea if the two tubes are made of the same material in the same thickness.

 

[Yellow Saddle]

I don't know about the pressure loss (I need to top up my hybrids every couple of weeks, fwiw) but be careful leaving your bikes in such a hot place: I had a tube exploding at the valve while parked in the sun on one of the rare summer days we get here.
Can't be sure if it was really the hot temperature or just valve fatigue, but it had never happened before in the cold, even with older inners.

It was a latent defect and the failure was brought forward in time by the increase of pressure. That's a good thing. The other option is it happening away from home.

 

[Pat "5mph"]

It was a latent defect and the failure was brought forward in time by the increase of pressure. That's a good thing. The other option is it happening away from home.

Well, yes, it was at the coffee stop after about 35 hot miles.
The bike was stationary in the sun for a good 30 minutes.
@Fubar had his tube explode on a train once, don't know if it was a hot day

 

[Yellow Saddle]

Well, yes, it was at the coffee stop after about 35 hot miles.
The bike was stationary in the sun for a good 30 minutes.
@Fubar had his tube explode on a train once, don't know if it was a hot day

Tubes (and indeed all rubber) have a limited life-span. Apart from mechanical degradation (particularly rubbing at the valve and rubbing at the edges of things like tyre liners and rim tape, butyl rubber tubes also "outgas" and change chemistry. A tube that's stressed (I.e. inflated) will degrade more than one that's not.

If you lock an inflated tyre/tube in a time capsure and do absolutely nothing with it, it will eventually pop. Therefore the fact that they pop from time to time whilst just standing outside the pub minding their own business, in the sun or sleet, should not be surprising.

In other words, it is life, it happens.

 

[Jody]

Hi Jody, the Cube is a AMS 130 Pro full suspension bike and although I will ride it on roads in the area we are there are a lot of gravel 'off road' paths that I enjoy using, actually think I inflate to 70 psi not 75 psi

45-50 is more than ample for canal paths and road. Most MTB tyres will have max inflation of around 55psi. 70+ seems a little excessive.

Try it further down around the 35-40 region as it will still roll well but offer better comfort with a lot more grip.

 

[mick1836]

Tyres fitted are Schwalbe Marathon Plus 2" x 26" According to Schwalbes web site up & over 110kg tyre pressure should be 5.0bar ( 72.5 psi ) I'm just under that

(trying to loose more) so will go for 70 psi.

 

[Globalti]

I thought it was well known that tyres can explode if left in a hot car? A metal shed in Spain must reach a similar temperature. The rubber softens and expands and can come off the rim.

Try fitting latex tubes - they ride superbly and make a nice sound but lose 10 psi in two days.

 

[si_c]

I run my tyres at a reasonably high pressure (currently 28mm at 100 rear 95 front), as I'm a heavier chap. I have to top up the air once a week or so as I lose around 10psi. I have noticed that the loss doesn't appear to be linear decay, in that if I leave it 2 weeks, the pressure hasn't dropped 20psi, more like 15.

This leads me to believe @Yellow Saddle is correct in his assessment that loss of pressure is related to starting pressure and the thickness of the rubber tube. I see no reason why a schrader valve would be mechanically less useful than a presta valve, both operate in roughly the same way, except that the latter has a screw lock instead of a spring closure.

 

[froze]

Your need to fill the tires before every ride is right on! All tubes except the very thick heavy ones will need to be topped off before every ride especially the thin tubes used in road bikes, usually MTB's can be topped off every other day if it's being ridden every day. Tires have nothing to do with whether or not the bike will lose more or less air unless it's a tubeless tire, in a normal tire it's the tube that holds the air not the tire, and thus it's the tube based on thickness of the tube, and whether it's latex or butyl, will determine how much the tube will lose PSI.

The biggest question for you should be what is the correct PSI to use, so for that use this website: http://www.dorkypantsr.us/bike-tire-pressure-calculator.html Use the second one down from the top, enter your ready to ride body weight plus your ready to ride bike weight, enter your tire size, then enter the F/R weight distrubution factor, for a slight better ride use the 45%/55% catagory, if you want performance use the 40%/60%. For MTB's use this calculator: http://mtb.ubiqyou.com/ Both of these calculators will get you to within 5 psi plus or minus from being the optimum pressure for you and the optimum tire wear and handling.

Latex tubes do feel nicer but they are more fragile which means more flats, more difficult to repair, and of course cost more. They lose more than 10 psi in 2 days, much closer to 10 psi in 24 hours. They also should be talc, but that is true with any tube, but latex will get sticky and can get pinched flat easier if not talc'd.

 

[Alan O]

The biggest question for you should be what is the correct PSI to use, so for that use this website: http://www.dorkypantsr.us/bike-tire-pressure-calculator.html Use the second one down from the top, enter your ready to ride body weight plus your ready to ride bike weight, enter your tire size, then enter the F/R weight distrubution factor, for a slight better ride use the 45%/55% catagory, if you want performance use the 40%/60%. For MTB's use this calculator: http://mtb.ubiqyou.com/ Both of these calculators will get you to within 5 psi plus or minus from being the optimum pressure for you and the optimum tire wear and handling.

Alternatively, just pump it up hard and then let some air out until it feels right

 

[nickyboy]

I run my tyres at a reasonably high pressure (currently 28mm at 100 rear 95 front), as I'm a heavier chap. I have to top up the air once a week or so as I lose around 10psi. I have noticed that the loss doesn't appear to be linear decay, in that if I leave it 2 weeks, the pressure hasn't dropped 20psi, more like 15.

This leads me to believe @Yellow Saddle is correct in his assessment that loss of pressure is related to starting pressure and the thickness of the rubber tube. I see no reason why a schrader valve would be mechanically less useful than a presta valve, both operate in roughly the same way, except that the latter has a screw lock instead of a spring closure.

My limited common sense suggests that loss of pressure (ie egress of air from the tube) is proportional to the (square of the?) pressure gradient between the inside and outside of the tube. So as air escapes the pressure inside the tube reduces so the rate of air escaping reduces. Presumably in periods of higher atmospheric pressure, the rate of air loss will reduce too. It's a miserable low pressure day here so the good news is that I may not need to pump my tyres up as much. Conversely it's a bit cooler which will reduce pressure....oh dear, decisions decisions

Need a proper scientist like @McWobble

 

[Dirk]

Some time ago, you said that it was impossible for a tube to pop when it was constrained within a tyre, when I described one letting go.

........A tube cannot blow inside a tyre with a noise........

Now you say....

Therefore the fact that they pop from time to time whilst just standing outside the pub minding their own business, in the sun or sleet, should not be surprising.

In other words, it is life, it happens.