Tyre Pressure Drop

[curlylegend]

This has got me puzzled...?

My 1991 3VD TDM850 had been parked up in the garage for seven days after a 200km run and apart from the battery being put on charge nothing had been done to it.

Without fail, every time I take my bike out, I give it a fairly thorough check-over.  Lights, chain, etc, and especially tyres, including pressures.  So, I was a bit disgruntled to find my rear showing 0.85 bar instead of 2.70 bar !  Seven days previously the bike had handled faultlessly especially on the twisty section just before home.  I assumed I had picked up some sort of penetration on the last few kilometers and resigned myself to a close examination of the rear tyre to find the damn thing and if possible to effect a repair.

I reinflated the tyre, a Battlex BT023 with on average 6mm tread, to 2.70 bar and then carried out a meticulous check for a nail or screw or whatever.

Found nothing !   

I dismounted the wheel to check for bubbles while immersed in a bath of water.

Not a single bubble !

The valve was new with the tyre about a year ago and the seating at the rim showed no signs of leakage. So I left it as it was and checked the pressure the next day,  exactly 2.70 bar.

I gave it another 24hours then another pressure check showed absolutely no pressure loss. I remounted the wheel, went for a very brisk local run, and rechecked the pressure on return, which was now 2.85 bar but this morning, cold, was back to 2.70 bar.

 

Was I imagining this ?  Don't think so because I had to inflate the tyre with a floor pump and my shoulders protested for a bit afterwards.

 

Any thoughts ?

[Pedro]

Sometimes, just sometimes, the core in the tyre valve can unseat itself and not seal properly. Pumping it up again would have moved it an maybe re-seated it. It may be a good idea to remove the core and give it a clean. It has happened to me on a car. Either that, someone was messin' with ya!

[curlylegend]

Sometimes, just sometimes, the core in the tyre valve can unseat itself and not seal properly. Pumping it up again would have moved it an maybe re-seated it. It may be a good idea to remove the core and give it a clean. It has happened to me on a car. Either that, someone was messin' with ya!

I remember reading years ago that Schrader made a specially strong racing spring for valve cores. It was thought that a high enough centrifugal force could overcome the spring pressure and unseat the valve. Just like you said.   However, honest guv, I never went that fast !

Good point though, I'll take out the core and give it a close inspection, maybe even replace it. 

[Studley Ramrod]

Is it possible you could have gotten a false reading when it showed 0.85 bar ?

[curlylegend]

Is it possible you could have gotten a false reading when it showed 0.85 bar ?

Don't think so.  I checked the front at the same time and got a reading of 2.50 bar as expected.  I then re-checked both tyres with my analogue gauge, same readings...front 2.50 bar, rear 0.85 bar.

[ChrisG]

Private garage rather than a communal one where someone could have tampered with it?

[curlylegend]

Private garage rather than a communal one where someone could have tampered with it?

Decidedly private !  And I'm living here on my own, my wife has been in the Untied Kingdom for the last two months.  

[marko67]

It's much easier if you use your foot to pump it up. Having said that I bet you can do a lot of press ups.

 

+1 on a valve rattling around. Make sure it's properly screwed in.





 " I had to inflate the tyre with a floor pump and my shoulders protested for a bit afterwards.



 

Any thoughts ?"