500 Two-Stroke Tech

RZtuner wrote:New tires and 90 degree valve stems from Kurveygirl.

A word of caution on the 90 degree valve stems,...... have seen these fly off at high speed.Not a good idea.

Seen the same thing with fitting bling "skull" valve caps..... will rip the valve right out of the rim.

Please explain how the 90 degree valve stems fly off at high speed. The retaining nut on the inside of the wheel is the same as on straight valve stems.

Both, my Marchesini and BST carbon wheels came with 90 degree valve stems, and I've used 90 degree valve stems from Curvy Girl as well, with no issues.

I can see how in extreme cases a heavy skull type cap could push a rubber stem through the hole, but it would still have to overcome the tire pressure. If you calculate the centripetal force on the angled valve stem using the reasonable assumption that the offset stem portion weighs about a gram, at 300 kph (186 mph) the force on it is 17 N or 3.8 lbf.

I have heard cases of big (relatively heavy) fancy valve caps causing the rubber valve stem to bend over and touch the rim at high speed. Sharp edges of the rim valve hole can cause the rubber stem to tear and rapidly deflate. There was a craze years ago of fitting LED valve caps which caused these type of failures in extreme cases.....

steveho wrote:I have heard cases of big (relatively heavy) fancy valve caps causing the rubber valve stem to bend over and touch the rim at high speed. Sharp edges of the rim valve hole can cause the rubber stem to tear and rapidly deflate. There was a craze years ago of fitting LED valve caps which caused these type of failures in extreme cases.....

There are no rubber valve stems here.

The 90 degree valve stems under discussion are aluminum.

I don't understand how they can be ripped out of the rim, if they are properly installed.

I'd like to see an example of a relatively heavy valve cap.

How much do the LED valve caps weigh? Do you have any example of an extreme case?? Anything whatsoever to back up your claim?

I'd just like to know the truth.

Appreciate that the angled valves are aluminum, but I was responding to the comment about heavy 'novelty' caps on straight rubber stems.
I read about failures in some bike mags years ago.
Below is a link I just found though.

http://community.ebay.com/t5/Archive-Mo ... -p/1198131" onclick="window.open(this.href);return false;

Rgds.

Hi.
At 200 km/h, the rotation speed of a 17" wheel is nearly 40 rpm.
I'd like to see a valve fly off at this high rotation speed !

phildu31 wrote:Hi.
At 200 km/h, the rotation speed of a 17" wheel is nearly 40 rpm.
I'd like to see a valve fly off at this high rotation speed !

40 rpm?

Your math is WAY off.

Oups !!
40 rotation per second ...
Just 60 times more ...so 2400 rpm

We has an incident at Bonneville with a guy on a Kawa 750 running a 90 degree valve stem that blew out of the rim at high speed. Luckily it was on the rear wheel and he stayed on the bike. SCTA actually changed the rule book for the following year to "steel valve stems only" following this incident. I had a chat with the Kawa guy in the line-up the next day, said it scared the hell out of him!.... and after that I am always wary whenever I see 90 degree valve stems. That's why I gave you a heads up.

A good friend of mine runs a Suzuki dealership. A guy bought a brand new GSXR1000 of him last year and came back into the shop screaming blue murder because the rear valve stem had blown right out of the rim and wanted all the damage to the bike covered under the warranty. Examining the bike, he noticed a "Skull" valve cap was still fitted to the front wheel, and when questioned the bike owner admitted he had replaced the OEM caps with the heavy chrome skulls. Nuff said?

Possibly the nut on the inside of the valve was overtightened and started a crack that led to the failure? What kind of speed was he doing when it went? I am interested in this because my first thought when I saw the 90 degree stems was that it is now a little lever that can fatigue the base with enough cycles, but this might only affect high powered bikes running at high speeds regularly. Part of the the claimed benefit of them is that the centrifugal force cannot unseat the valve stem at very high speeds, with your Bonneville experience have you ever seen that happen?

nope, just the one incident with the 90 degree valve. That failed at 140+mph.

Quite a few guys have had tires go flat not running enough tire pressure and the tire lifting off the rim.

Seen production road race tires with soft rubber fall apart with just 1 run, most of the high speed Busa's and BMW's run hard touring spec tire.

RZtuner wrote:nope, just the one incident with the 90 degree valve. That failed at 140+mph.

Quite a few guys have had tires go flat not running enough tire pressure and the tire lifting off the rim.

Seen production road race tires with soft rubber fall apart with just 1 run, most of the high speed Busa's and BMW's run hard touring spec tire.

Whilst nothing like running at Bonneville, I took my standard Hayabusa to some top speed events and all valves and caps where checked carefully , the only caps we where allowed to use where tin(not alloy) items with a rubber seal, I didnt pay much attention to it until a couple of years later when my friend lost control of his bike due to a sudden tyre deflation on his R1 at speed, the cause? Tyre flies..

[url]

Whilst this "problem" wouldn't be common to the classic bike world, those going for ultimate speed are very aware of it.

Thanks for the responses to my question.

Hard to believe people are still using rubber valve stems in 2016, but that's another issue.

I have to call bullshit on the 90 degree valve stem failure.

As I mentioned, I have 2 sets of Marchesini wheels, BST carbon wheels, and Dymag magnesium wheels - which all came with 90 degree valve stems. These type of wheels have been raced as much as any wheels ever made, and I can't believe they would come with 90 degree valve stems if there is any issue.

I've been searching, and can't find examples of failure, with the 90 degree aluminum stems.

I agree that improper installation could cause cracking of the stem, or misthreading the nut could strip the threads - but the exact same thing could occur with straight valve stems.

Jorge's 2016 Yamaha. mmmmm. wonder why they went for straight, steel valve stems???

http://www.mcnews.com.au/wp-content/upl ... h-Bike.jpg" onclick="window.open(this.href);return false;

As interesting as this is, maybe you guys should move the discussion to another thread and not keep this debate going in geakins RG500 build thread.