Valve Stem Failure

Some time ago I read of a near-fatal experience someone had when the tyre valve stem fractured leading to an almost instantly deflated tyre.

At the time it was noted that the bike was fitted with right angle extensions on the valve stems to making pumping up the tyre simpler due to the lack of space.

I had also fitted these adapters and removed them once I heard about this experience.

A few days ago on the CBR650 forum, a member reported an instant tyre deflation when the valve stem fractured.

His bike is only new so the valve stem was new also. He had fitted fancy valve dust caps which may have exacerbated the problem.

Thinking back over a few years I think I had new tyres fitted on many occasions but just left the old valve stems in place.

Time for some theories

1. Could the valve stem harden over time which could lead to it fracturing?

2. Are valve stem manufacturers using inferior materials in the manufacture of valve stems?

3. Could adding heavy tops to the valve stem cause it to flex?

From now on my solution at each tyre change will be new valve stems at $1 to $2 each

I also use a 150mm flexible extension when inflating my tyres so I don't wrench on the valve stem to get the air chuck on.

The same CBR650 forum member has found Pirelli sell aluminium valve stems to replace the traditional rubber ones

These are the ones I've got. No problems with them so far. They are, or appear to be a cast alloy construction. Very short so I would think they wouldn't flex much.

ebay link



Unlike this type which looks to be just bent tubing

I use a type that is similar to the second ones you have shown MM. But I do not leave them attached, ie I screw it on to inflate then remove it. I only lose about 1 psi removing it so I add that bit extra to allow for that. These adapters are not meant to be left installed.

I got one of these from Pashnit when I bought some other tyre tools, this is what they clearly say about it on their website:

*Note: These extensions are only meant to be used while inflating the tire, they should not remain on the tire. If you leave the extension on the tire it will cause an unbalanced condition, it may damage the valve stem, and it may cause sudden loss of tire pressure!

barry_mcki wrote:I got one of these from Pashnit when I bought some other tyre tools, this is what they clearly say about it on their website:

*Note: These extensions are only meant to be used while inflating the tire, they should not remain on the tire. If you leave the extension on the tire it will cause an unbalanced condition, it may damage the valve stem, and it may cause sudden loss of tire pressure!

I use what Barry uses for fear of what Dave describes
Short stems in line with the center of rotation sounds a safer option to me even though its a PITA to check pressures.
Centrifugal forces can be calculated by someone much smarter than me. Go!

I have the alloy ones and no problems so far. A friend however suffered front tire deflation after a valve stem failure. I put it down to the polish he was using on the rims causing the stems to perish prematurely. It was a scary moment for him on a heavy TL1000s

BTW bike biz sell them right angle valves for $30 

http://www.bikebiz.com.au/products/La-Corsa-Tubeless-Right-Angle-Valve-Stems.html

I had this type of valve failure on a GPX 250 a few years back. I'd only had the bike for 2 weeks and the right angle valve was on it already so I thought to leave it on.

As another member said, centrifugal forces at speed are quite large and having the right angle piece not in line with the valve will cause it to bend and eventually crack, especially if your on a nice bumpy country road.

I was fine doing 100kph on big open roads, but when i turned into the first corner on macquarie pass, the back tyre felt like it was made of jelly and was only about half inflated. When the wheel was stopped, the valve sat fine and actually sealled the gap in the rubber, so I removed the 90 degree bend and slowly rode back to the nearest bike store. $15 and a new tyre valve later i was good to go.

The forces on a wheel and in a bick can be quite large, especially the faster you go.

They say you should always have your valve caps on as at speed the actual valve can depress and release ana mount of air, a valve cap can reduce this problem.
It's similar to the MotoGP riders have cuts outs in the brake/clutch lever because at 300kph, the front brake can be forced on by the wind.
Cars don't have this probelm as much, as their valves come out of the rim on an angle or are parallel with the ground.

Little things can put out the balance of a wheel, thats why the lead weights are applied in small 0.5 gram increments, they are that sensitive.

Good balanced wheels and tyres can be the difference between a rough and smooth ride.

Final thought, don't use the 90 deg valve tops, get a bicycle style pump with the connection that gets pushed on and locked when inflating the tyre, they are pretty accurate with the pressure guages also!!

I think there are a lot of people leaving adaptors on their valve stems without realising the risks - I've been guilty in the past

One of the CBR650 forum members in the UK tells me that valve stems are always replaced whenever a new tyre is fitted. I'm not sure this is the case in Oz

This is the adaptor I used on the Bandit and now on the CBR.
This one is around 150mm long.
They should be available from truck tyre outlets.
They work great.

Note: like all safety messages these days and as ridiculous as they may sound "the green tape is not part of the item" (who writes this crap?)

I've done it.  Left the right angle extension on.  Caught me out once too.  Rapid rear deflation when the stem failed. No real dramas in the wonky stop.  (straight road, 175 kg bike)  No chance of tyre repair kit helping with this.  Now I have short, metal, 45 degree stems.  My tyre fitter ordered and supplied them.  They work a treat and do not perish, though the rubber seal might.  

It might or might not be significant that "back in the day" (70s) with tube type tyres, I never had a a problem.  Balanced the wheel with them on, left them on.  Tyre after tyre.  Seems the rubber in the stems of tubes is (or was) better than the rubber of tubeless stems.  That bike (Honda 750) frequently was ridden at licence cancelling speeds.  Never gave it a thought.  Now I do. 

Don't leave them on, you might be real sorry.

The MONO Racing RA stems as per madmax's post are absolutely dangerous.
These were fitted to my bike by the previous owner so I had no idea they were aftermarket.
Problem occured 2 days after I had front tyre replaced, I like to check pressures daily for a few days after having new tyres fitted, just to monitor for leaks.
Well the valve stem did not like all this extra attention, it seems that I may have been moving it slightly from side to side.
This nut must have been working loose for a while.
This allowed the nut to loosen and the inner rubber ring deformed, not instant deflation but 10 minutes into a 30 min trip I could not go around corners very well.
The tyre guy showed me the problem when he removed the front tyre.

The short stubby RA stems are probably a lot better, but anything with a long arm is trouble.
I don't trust anything that relies on a nut on the inside of the rim.
I have fitted standard rubber stems and use a flexible attachment on my air comp.