Tyre deflation
 

Renewed tyres and innertubes on my Trek DS with Bontanger wheels.
Both front and back tyre deflate 10 psi and 15 psi after every ride. Valves are shaudler.
Why is this happening so often. Is it the valves I wonder
I am concerned when doing my first bike tour this year, I will be spending every other day trying to inflate with my small pump which wont reach the 75 psi of recomended tyre pressure.
I have checked for faults on tyre, tube and protective ring to wheel, but all seem OK.
Totally baffled!
Please ...any ideas out there.:(

How long between rides? What SIZE tires?
At your pressures, you might expect to lose that much in a week, but not a day.

I just mounted a 622-23 tire on a new rim yesterday and it dropped from 100 to 80 in less than 24 hrs. That's not abnormal. A "fatter" tire should drop less.

Something has to be wrong for that amount of leakdown, especially with a starting pressure of 75psi. Shraeder valves are very reliable but it is possible for the core to be loose. Any bike shop or service station should have a tool to tighten the core. A bit of very soapy water in the stem with it pointed upward will easily show if it's leaking. The odds of that on two random tubes is very low. I would recommend inflating the tubes quite a bit and putting them into water to check for leaks.

It's also not clear what you mean by "deflate 10 psi and 15 psi after every ride." I would not want to see that much in 24 hours but it's conceivable - from beginning to the end of a ride is a whole different matter. I am assuming here that you are using standard tubes, not ultralight and certainly not latex.

Finally, how are you measuring pressure? If you attach your tire to a pump with a reservoir part of the air in the tire will go into the pump reservoir, giving an artificially low pressure.

Check your tubes as suggested above, by all means. As Bill Kapaun says above that level of leakage may or may not be reasonable depending upon the time between rides.

"Any bike shop or service station should have a tool to tighten the core."

There are also metal valve caps which have the tool built in, I get mine from my local car parts store. They will keep debris out of the valve as well as acting as as secondary seal against loose or leaky valve cores. Nice to have on a tour, I carry spares as they are easily lost.

As to your inadequate pump, check out the Topeak Road Morph G. Don't go on a tour with a known crappy pump.

if your pump will only get you to 75psi, you need a better pump.

for 'at home' inflation, I highly recommend getting a decent floor pump... they are inexpensive, last a long time (I've had my specialized air tool 15+ years), and a decent one will pump a skinny-bike tire up to like 120 or 140psi in a matter of a few pumps, and a big fat tire to 60 or 70 or whatever in a few more.

the little shorty pumps they sell for emergency use are nearly useless. you need about a 2' (60cm) long stroke to get sufficient air compression.

You're doing worse than average, but not much worse if you have 25mm wide tires. These tires have very little volume, and so the normal blled that happens through the tubes walls, has a bigger effect on these in comparison with a wider tire.

I ride tubulars, and topping off the tires is the first part of every day's ride. Also consider that if you use a tire gauge, there's a good chance you're losing 5 or more psi every time you take a reading.

OTOH- there may be a problem, test to valves by putting a drop of water (spit) on each and watching for bubbles. But in all fairness I suspect that you won't find anything. If one tire loses pressure faster than the other, it's a leak of some kind, but if both tires lose pressure, it'smost likely normal bleed, since the odds of two tires having the same slow leak are too low.

BTW- if you're planning a long tour, get a reliable full length pump, and get used to using it. Flats are too common, and the chore of topping off will make you miserable unless you have a good pump.

I doubt he has 25mm tires, not at 75psi, unless he weighs something under 40kg. 75psi is typically used with like 35mm tires.

We don't have to guess, the OP can read the sidewalls of his tires. As I said earlier, this is at the high end of normal bleed (if overnignt) but not unheard of, if you add in the 5psi loss to the gauge.

One leaky tire is a leak, 2 identical slow leaks is most likely just the way they are.

I don't know if this would be safe but I'd suggest taking the valve core out, filling the tube with water, and seeing if water is leaking out. You could also take out the tube, inflate it to around 10 psi or until it get somewhat fat( just don't explode it) and pouring water around the tube. Any leaks will appear instantly. If you don't find any holes, replace the tubes and get some with the green slime.

I never heard of putting water IN a tube to detect leaks, but certainly, pumpnig a tube up til its a bit fatter than normal, and using soapy water to find leaks is common practice. its nowhere near 10psi, though... more like 2-3 PSI.


first, tho, I'd do the spittle over the valve stem while its still on the bike, thats the most common source of a slow leak.

Gee, why do things the hard way. You can put 6" of water in the bathtub, stand the wheel in it, and look for bubbles. Or remove the tube, inflate it to 1-1/2 normal width and submerging it.

Unfortunately, a 10psi / 24hours leak will produce bubbles slowly, you you'll have to be patient.

#1: :eek:

#2: OP wrote something about 75psi. From what I have read, Slime won't seal if the inflation pressure is over 60psi. Feel free to try...........I won't see the mess on my porch.

Thanks guys for advice. yes tires are 700x 35c. I use at home a car foot pump with gauge before each ride (say one 25 mile trip every three or four days). My pump is an emergency mini pump (i suppose useless really), so will look for a new one. (any recommendations?). Bye the way..I am interested to now what OP abbreviation is in some of the replies. Thanks again guys!

OP, that's you, as in Original Poster.

For you pump, using a low volume (car) foot pump for high volume bike tires is never going to give you the best results.

For the mini pump, don't discount it too quickly, you don't mention what make it is, but many out there now are now very good.

OP=Original Post.

Topeak Morph. Great pump. Do not go on tour with a pump that will not pump to recommended inflation pressure.

OP can also refer to the person who put up the original post. You'll know which by the context.

Do you mean that the car foot pump will not give the correct pressure?
The mini pump is a Beto. Is about 10" long folded, with a barrel lenght of I would say 5". I got it has an emergency pump, which so far has worked for local rides till I get back home. But is really hard to get up some decent pressure. But just enough to get me to a garage I feel.

When I was looking for a "travel" pump this Topek Road Morph came out on top of all the thread searches that I did:

http://media.nashbar.com/images/nash...-NCL-ANGLE.jpg

It's light, has a swing out step at the bottom and a tee handle of sorts on the rod to make pumping easy. And..........what I found in recommendations to be a big deal, a hose. The hose lets you connect the pump to the valve stem and not break the stem off while pumping the tube up. I've never done it myself but I guess its a bit of a day wrecker to fix a tube then rip the valve stem off trying to pump it up.

Around $30-35.

Seeing as car tyres are generally run at much lower pressures than bike tyres (especially skinny ones like 25s), it may not be able to generate enough pressure. I'm surprised you managed to get 75 psi out of one, to be honest...

Thanks again guys. I went to my local bike shop and they informed me that my shrader valves were the cause. (Not suitable for high pressure, ie in my case 75 psi for touring tyres). So I bought some Presta valve tubes (recomended). Also got new BBB Windrush mini pump to pump upto 100 psi. Its actually smaller than my existing mini pump, so I hope I have made a wise purchase.
Tyres should now not deflate as before...I hope.
My stock of shrader valve tubes will now have to go in to store, till I next put on low pressure tyres.

Gee, we all must have been extremely lucky to get through the 70's and 80's, and even now with high pressure tires and schraeder tubes. My Motobecane Grand Jubilee had shraeder tubes and 90 psi tires and I rode literally 10's of thousands of miles without any air pressure problems.

Pure, unadulterated falsehood, promulgated most likely by some young snobbish neophytes who don't want to bother with figuring out a problem other than deciding it's because a part is "old-fashioned."

Did you get the washers used to fit Presta valve tubes to rims drilled with the larger holes for Schraeder valves? Shop should have them.

This.

+1
The pressure drop I mentioned was on new wheels that used Presta.
My previous wheels were equipped with Schraeder and had a slower pressure loss, but with slightly larger tires. (more air "available" to leak)
It's my feeling you get more "seepage loss" by using undersize tubes than anything else.