ZZR600 front tyre problem - dangerous!

calum17 · Brolly Dolly Joined: 25 Oct 2007 Karma :

Hi everyone, I'm after a bit of advice on a problem i've had on my ZZR 600. it's an E1 model ( L reg).
a while ago i took the bike to work, like most days in this nice weather, and whilst going down the motorway for a change and running late i opened it up a bit - as far as 125 and when i go to my junction i pulled off the motorway and then as i learnt it into the bend the bike wouldnt go - i knew straight away my front tyre was flat. so i struggled the bike the last mile or so to work and it was fine after pumping it up - no problems again (i didnt go that fast again either though)
now, i ave had a new tyre fitted - BT014 (the old tyre was a BT010) and when coming home from a trip away recently i opened the bike up more again and hit an indicated 140 and then as i leant the bike over for the junction (after slowing down ofcourse!) i noticed the same problem with a flat front tyre, but after re-inflating it i have no problems.

now, why could this be happening?! it's fine unless i go over 120 and then it seems to just release most of the pressure in the front tyre - not the back which is also a BT014. i run slime in the tyre which should seal up any leaks but i can understand it not being able to work that quickly at high speed - but i dont even have any trouble with the pressure dropping any other times not even over long periods of time. so far as i dont even check my tyres with a gauge that often anymore cos i'm confident they are ok - i just squeeze them a bit before i go out on the bike as a brief check.

so, why is this happening ? plenty of bikes do over this speed on a regular basis and no one i have asked, mechanics and other people seem to know why it could be cos there isnt a constant air leak which is made worse by speed, but its only once over a high speed. and probably more importantly, how do i stop this happening - other than just keeping my speeds down and/or carrying a pump at all times in case i open it up obviously?

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

My first guess would be a dodgy tyre valve. Getting to a decent speed and the centripetal forces are pushing it open.

Also possible there is a puncture and the slime is failing at speed, although then I would expect to see the slime coating bits of the back of the bike. That kind of stuff can do a good job of disguising a puncture until you go fast enough for it to be dangerous.

All the best

Keith
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nightshaddow · Nearly there... Joined: 18 Feb 2008 Karma :

ok basicaly it could be one of 3 things that i could think of, i used to work for ATS the tyre place in york and had this a few times on cars and not at that speed though, sometimes the valves can weaken due to the heat when the tyre was replaced did they fit a new valve?????

also 2 and 3 can be interlinked i beleive they have alloy wheels and sometimes these can decay and leve small gaps betwwen the rim and vibration and heat can make the air escape, did they ballence the wheel when they fitted the tyre to cut vibration,

as you probably know gas expands when it gets hot and creates more presure so when you hit high speed the gas escapes through the gaps left by decay,

my advise get the wheel cleaned (normally done whith a wire brush to remove any deposits) and recealed (instead of using tyre soap or lube they use an adhesive compound soap on the tyre bead) and have a new valve and wheel ballence

hope this helps
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"WHAT DO YOU MEAN 100 MPH THATS IMPOSSIBLE Its chinese OFFICER."
Current rides CB 125 TDE(the next project) NS125RK ( now on the road ) CB125TDC (soon to be project 17) melody ( the nephews )

calum17 · Brolly Dolly Joined: 25 Oct 2007 Karma :

thanks for both of the replies.

im pretty sure that they did fit a new valve, but if i get a chance this week i'll call down to the shop and just ask if they fit new valves as standard, or if i can i'll go see the same mechanic and ask him if he did.

Kickstart, wouldn't the force push outwards on the valve - from the rip out to the tyre and therefore not push the valve open as it works in by pressing the valve in and not pushing it out?

the wheels are alloy i think as they were polished before i bought it, and now the front looks a bit naff cos i just haven't been able to keep on top of making sure it looks good - the back is fine but the twin discs on the front and lack of paddock stand make it a nightmare job! so i guess it is possible that it's escaping from there.
as for the heat being generated and then escaping, i rode the bike for 5 hours with only stopping for petrol last bank holiday weekend and it was fine, same when i was coming home - but it was after 4 hours this happened. wouldnt the temperature be already that high from the long time riding on hot roads and at high speeds (80 a lot of the time unless in towns or on back roads with limits)

if i had this problem a few times wouldnt the slime seal the tyre properly anyway - as it would fill the problem gaps which seem to only be a problem when doing these high speeds? im just thinking i could take a pump and do a few speed runs with stops to re-inflate the tire so that the problem stops - not ideal but if it works then its ok. just, after fitting a new tyre i dont have the money to take it off and clean the wheel etc - especially when the problem is only above these speeds and not all of the time, when it would be more serious if it happened daily or something.

oh, yes the wheels were balanced when the new tyre was fitted, but slime could cause extra vibration? though it shouldn't cos it stays as liquid in the tyre until 'needed'.
i dont think it is a puncture in the tyre itself which the slime is hiding then causing problems at speed, because this is the 2nd tyre it has happened on and both times the speeds were higher than normal.
i know the valve is tight because i put the slime in myself and made sure that i screwed the valve up properly.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

The valve is only pushing against centrepetil force by the light pressure of the spring. It is not uncommon for valve to leak on top speed runs due to this (and probably why some bikes have valves that point sideways).

The force on the valve is exactly the same as the force you would put with your finger to let air out of the valve.

The slime will seal a puncture, but isn't that good. Know of someone who had the stuff in for ages after getting a puncture only for it to spew out and let the tyre down when they went at speed.

All the best

Keith
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calum17 · Brolly Dolly Joined: 25 Oct 2007 Karma :

thanks again kickstart.
you say about the 90 degree valves. would an adaptor work or does it have to be the whole valve - it was mentioned to me to try one of those and metal valve caps with O-rings - but i already have them on the bike. though im not suer if the O ring has been pushed too far upwards in the cap and so hasnt sealed as much as it should of / could of.

thanks

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

The metal valve caps with the O ring seals can greatly help, just don't use alloy ones (they have a bad habit of seizing in place at inconvenient moments).

DO NOT use the adaptor. From experience they add a load of weight to the rubber tyre valve. Had a value split at about 60mph with a pillion almost certainly due to leaving one of those adaptors in place.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

calum17 · Brolly Dolly Joined: 25 Oct 2007 Karma :

ok thanks. i dont think these are alloy - but they might be, they look like pistons and had rubber seals around the outside for effect, but they have all come off now.

that's quite worrying about the adaptors, i was told they can unbalance the tyres too so i'd have to fit a whole new valve and get the wheel re-balanced. but i just dont have the money for that now because this isnt a constant problem but only when at high speeds which i dont do very often anyway. but obviously it's nice to know i can cos with this problem i know i cant safely do it and keep riding unless i have a foot pump with me!