Drop in Tyre pressure (normal?) - K-Bikes.com - Excellence in Motion
 
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post #1 of 9 (permalink) Old Nov 15th, 2007, 3:13 am Thread Starter
JIS
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Drop in Tyre pressure (normal?)

I have noticed that, whenever I check the tyre pressures (esp the rear tyre) every 2-3 weeks, that the pressure, instead of being 42psi at the rear, is more like 32-35psi.

I have Michelin PilotRoad2 tyres (which are marvellous) but the decrease in pressure seems a bit excessive. Of course, pump them up and they're fine again; for a while.

Thoughts? Is this normal?

John

John I. Stephen - Tunbridge Wells, Kent, UK
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post #2 of 9 (permalink) Old Nov 15th, 2007, 5:57 am
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Easiest thing to do is to start with the weakest link in the chain....replace the valve (you can check it by putting a soapy solution, or spit, on the opening and check for light bubbling). If you still get this constant drop....... thoroughly check the tire for an imbedded puncture (thorn, staple, nail, etc) that are easily hidden, but still partially seal the hole allowing only a small amount of seepage.

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post #3 of 9 (permalink) Old Nov 15th, 2007, 8:02 am
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I've had this happen some. Some tires seem to hold their pressure just fine. The next, often the same needs to be checked before every ride to be sure. Could be valve core, bead area or a slightly more porous carcass. Keep the pressures up and ride it.
I don't think being a Michelin has a whole lot to do with it. I've run them for a decade and have seem both sides of the coin.

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post #4 of 9 (permalink) Old Nov 15th, 2007, 11:03 am
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Quote:
Originally Posted by JIS
I have noticed that, whenever I check the tyre pressures (esp the rear tyre) every 2-3 weeks, that the pressure, instead of being 42psi at the rear, is more like 32-35psi.

I have Michelin PilotRoad2 tyres (which are marvellous) but the decrease in pressure seems a bit excessive. Of course, pump them up and they're fine again; for a while.

Thoughts? Is this normal?

John
IMO 1-2lbs every 2 weeks is normal. Also gauges are not all that accurate and if you use more than one that could throw it off. Hot and cold tires, and ambient temps also factors, but 8-10lbs in 2 weeks is sure to mean a slow leak somewhere.

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post #5 of 9 (permalink) Old Nov 15th, 2007, 11:16 pm
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Drop in Tyre Pressure

A sudden and marked drop in ambient temp. will often lead to a pressure drop. I have found with my B'stones that a 10 degree temp drop can lower tire pressure 3 - 5 psi. Another good reason to check pressures prior to every ride.

NuKGT
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post #6 of 9 (permalink) Old Nov 16th, 2007, 12:35 am Thread Starter
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Quote:
Originally Posted by NuKGT
A sudden and marked drop in ambient temp. will often lead to a pressure drop. I have found with my B'stones that a 10 degree temp drop can lower tire pressure 3 - 5 psi. Another good reason to check pressures prior to every ride.
Interesting; yes it's my first start of winter (since returning to biking last Dec) and the temp have dropped markedly; especially in the early morning when I check the tyre pressure.

Anyway thanks; good advice and feedback. I think I'll check the valves though. There IS a small "flap" in the rear tyre where a small cut is evident in the tyre. I had it checked by the bike shop which fitted the tyres in the spring and he said that the tyre was fine. Mmm, perhaps I need to get it checked over again. Thanks !

John I. Stephen - Tunbridge Wells, Kent, UK
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Triumph Tiger 1050 (2008)
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post #7 of 9 (permalink) Old Nov 17th, 2007, 8:34 am
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Do you have the OEM valve stem cap?

The original cap in the rear only has two "O" rings in in to prevent air leaking out at high speeds. As you approach very high speeds the centripedal force will open the valve stem and air will leak out. That's why there is a different cap front vs rear. It's in your owner's manual. The front wheel valve stem is 90 degrees to the plane of rotation.

If that's your solution, you're a speedy fellow.

Dave

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post #8 of 9 (permalink) Old Nov 17th, 2007, 10:05 am
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I think that 1 or 2 lbs a week or so are normal. Seems to have happened on every set of tires I've ever had on any bike. Not on my truck though? Go figure.

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post #9 of 9 (permalink) Old Nov 21st, 2007, 4:48 am Thread Starter
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Quote:
Originally Posted by lost-boy
Do you have the OEM valve stem cap?

The original cap in the rear only has two "O" rings in in to prevent air leaking out at high speeds. As you approach very high speeds the centripedal force will open the valve stem and air will leak out. That's why there is a different cap front vs rear. It's in your owner's manual. The front wheel valve stem is 90 degrees to the plane of rotation.

If that's your solution, you're a speedy fellow.

Dave
I suspect not. I had the tyres changed by a local m'cycle workshop who simply changed the tyres. He never made mention of special or modified valve caps? I would have thought that he'd have simple reused the same ones as were there on the (former) Bridgestones...

John I. Stephen - Tunbridge Wells, Kent, UK
K1300 GT (quite superb ! )
Triumph Tiger 1050 (2008)
K1200 GT (2003)
R1150R (2002)
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