Tyre pressure loss!!

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NewBoots1

NewBoots1

Joined
Jul 25, 2007
Messages
1,827
Location
Northamptonshire, England
Just a quick one....has anybody experienced a loss of pressure from the front tyre, particularly after a 'spirited' session on the bike. I've had a problem intermittantly since I got used to the bike and particularly recently (probably as I'm now finally up to speed !!!no pun intended). This morning was a case in point, after a ride the other night front tyre very low on pressure...went to inflate (this is a virtually new tyre) and when i took the valve cap off it virtually flew out of my fingers from the air pressure behind it!
Sharky had a similar problem which was cured by a 90 degree valve, just had one fitted today so not had a chance to check it's effectiveness...but wondered if it's a wider issue rather than soemthing to do with the water/air in Northamptonshire!:devious
 
That happened to me a while ago not had any probs since the 90 degree valve was fitted
 
NewBoots said:
and when i took the valve cap off it virtually flew out of my fingers from the air pressure behind it!
:devious
Click to expand...


Sounds like your valve is not sealed or tightened properly. Try fitting a new valve. You can buy them from Halfrauds in packs of four. Also get a valve fitter thingie (technical term) which lets you tighten up /slacken them. After that try a 90 degree one. My first option is very cheap.
 
When it happened to me the tyre was deflating when i went over 140 mph the centrifugal force was sucking the valve in so causing the air to leak out 90 degree valve soon cured that
 
Okeleydokelay, it appears the fix I've finally got round to:90 degree valve should work...I'll keep my eyes crossed in hope (my fingers will be too busy with those handlebar thingumyjigs)
 
sharky said:
When it happened to me the tyre was deflating when i went over 140 mph the centrifugal force was sucking the valve in so causing the air to leak out
Click to expand...

Hey Sharky, what's that funny smell? Oh yes, it's BS!
 
sharky said:
When it happened to me the tyre was deflating when i went over 140 mph the centrifugal force was sucking the valve in so causing the air to leak out 90 degree valve soon cured that
Click to expand...

"centrifugal force" force's things out:confused doesn't suck them in is some one being a silly:thumbup
 
I had this prob last month, it was a dodgy valve. Only happened if i was really flying... took it back and a new valve put in. No probs since.:thumbup
 
MSmilleR said:
"centrifugal force" force's things out:confused doesn't suck them in is some one being a silly:thumbup
Click to expand...

centripetal force sucks things in, which is equal and opposite to centrifugal force. That said, i think its just a **** valve.
i thought you guys just fitted 90 degree valves to enable you to blow the tyres up at the petrol station, find my discs obscure the valve on the 07 front and since they are not the rubber flexy type ones, they go down instead of up until you force the little f****rs on. did notice i lost 6lb front and rear last time out and worried now............... that stand isnt going to be great with flat tyres. Has anybody experienced significant pressure loss during winter storage?
 
Loss while laid up is normal, tyre pressures should be checked weekly and 90 degree valves stop the centrifugal force depressing the valve at high speeds, they are also handy for easier access
 
B o B said:
Hey Sharky, what's that funny smell? Oh yes, it's BS!
Click to expand...

No f#*king ******** atall.It happened twice and both times after going over 140 mph the tyre deflated once in the uk on a private road and the other time in belguim ,When it happened in Belguim.
When I got it back to the UK I took it back to Forza Italia at Silverstone,After they had tested it they said it was caused by the speed of the bike sucking the needle up into the valve causing the air to leak out.
If thats centrifugal or centripetal whatever! but if anything is spun fast enough the centrifugal force will take it to the outside same as a valve on a wheel.
So if you want to smell the BS again B o B go to Silverstone!
 
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Anyhow........whatever the reason: centrifugal force, the Moon's gravitational pull on the Earth, ****** tyre valves, Mr Burns' shoes, The Brazilian Economic system, Arnold Schwarzenneger's inability to speak English........the pressure problem seems to have been resolved with the 90 degree valve.....MANY THANKS for all the responses, they've all been helpful!
 
sharky said:
No f#*king ******** atall.It happened twice and both times after going over 140 mph the tyre deflated once in the uk on the A5 milton keynes and the other time in belguim doing 155 mph,When it happened in Belguim I stopped on the hard shoulder right outside a motorway police station and a very nice copper helped me get the bike back there and blew it up.
When I got it back to the UK I took it back to Forza Italia at Silverstone,After they had tested it they said it was caused by the speed of the bike sucking the needle up into the valve causing the air to leak out.
If thats centrifugal or centripetal whatever! but if anything is spun fast enough the centrifugal force will take it to the outside same as a valve on a wheel.
So if you want to smell the BS again B o B go to Silverstone!
Click to expand...

Oh dear, I seem to have hit a raw nerve there Sharky. I genuinely thought you were joking.
I would be very worried if a tyre deflated at speeds it was designed to do. I do know that valves sometimes can give problems as I posted. I have a greaty deal of respect for Forza Italia and their mechanical knowledge & experience but cannot take that theory seriously and nor do my tyre suppliers. Why don't all tyres have this problem? Track days would be littered with flat tyres. Don't tell me they all have 90 degree valves. The valve is depressed inwards to allow air in, it springs upwards & outwards to seal. Centrefugal force forces it upwards & outwards.
 
BoB not wanting to butt in here fella, but Sharky is right, the centrifugal force of the spinning wheel will force the needle valve within the tyre valve itself towards the outer part of the tyre, i.e away from the wheel's centre, causing a very small amount of air to escape through the valve. Imagine a big fairground ride where you are strapped into a chair and spun around. You are being forced away from the central point of rotation. The reason it happens i suspect is due to manufacturing tolerances in the tyre valves in particualar the needle valve itself. Top quality ally dust caps have an o ring seal inside that stops this problem occurring by forming an air tight seal over the end of the tyre valve.
 
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