porous wheels?

[Bretty]

So the k&n filter got a clean today and the bikes running nice and crisp. It had been bogging down a little with throttle full open.

Anyway, I thought I would check my tyre pressures as they keep dropping. Over a 2 to 3 month period the rear will drop from 40psi to 15psi!! The front also drops but not as much.

Twice I've asked a mechanic to take a look, they've done the soapy water thing and said they can find no leaks (bubbles).. but suggested I could be a porous wheel.
Now I'm pretty sure I never had an issue with previous tyres, so just assumed these were badly seated, or the rim might be corroded.

So how do I find out what the problem is? Would filling the tyre with sealant make any difference (I assume that stuff only touches the tyre and won't migrate to the wheel or rim?!)

Anyone had this before? Any suggestions? I'm not on a budget although if you saw my bike you would understand why I'm not wanting to splash too much cash on it.

Thanks,

Brett

[unfazed]

Is the Valve ok?

[Frosties]

Is the Valve ok?

My thoughts also. A steel wheel isn't porous only alloy type.

[Bretty]

The valve passes the soapy water test? So I'm not sure?!

The bike is a 2000 fazer 600. I thought they were alloy wheels looking at the flakey paint. I usually run the chain through the wheels, it chips the paint.

[Fazerider]

Several months to go down? With that rate of leakage you’d be lucky to spot bubbles during the soapy water test.
I’ve always been surprised tyres seal as well as they do. When you examine a new loose tyre there are usually bits of flashing from the moulding process still attached to the bead. I trim them flush to give a better chance of a good seal.
It's worth checking the condition of the rims next time you get the tyres changed, the alloy can corrode and cause leaks.

[celticdog]

it's all about osmosis, (you can google it) you can expect to loose a few psi over a month. Any more than that then there's something else at play.

[tommyardin]

Had a similar thing with my front wheel when I first purchased my FZS600 it turn out to be a very small leak between the alloy wheel and the rubber valve stem, I had a new valve fitted and Darren of A Force Motorcycles did a great job of cleaning the bead on both the tyre and the wheel rim, never had any other problem with it.
The tyre was loosing about 4 psi a week. I know that's not a lot but I thought it was only going to get worse and that one day it might fail when 50 miles from home or when Cornering at 70mph. The leak was only showing when sideways pressure was applied to the valve.

[darrsi]

That's quite annoying.
I've got the slimy stuff in my rear tyre, but i did find a very thin nail in it so it was the right thing to use in my opinion as the tyre's about half way through its life, and it will protect it now until i get my next one. It'll most certainly do the job for how i use the bike. But you're right in saying that although it remains runny it will only touch the main tread area of the tyre, or however much you lean the bike, but it won't really go anywhere near the rims.
I would be inclined to take the wheel to a reputable place, explain the issue with someone experienced in handling bike wheels and get them to take the tyre off, clean up the rim of any dirt or rust, then reseal the rim on refitting with whatever they use. Try not to let them give your wheel to a trainee though, been there, done that, and they generally mess your wheel rim up.
Probably cost you about £20-£25 at a guess if you take the wheel in off the bike.

[BBROWN1664]

Believe it or not, the newer the tyre, the quicker they lose pressure as the oxygen can weep out through the tyre (osmosis) leaving the bigger Nitrogen molecules behind. The longer the tyre has been on there and the more you have topped it up, the less oxygen there is to weep out meaning pressure drops are reduced.

My guess is it is a dodgy valve though or valve stem.