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short valve stem tubes(16 posts)

short valve stem tubesdoug m
Apr 15, 2001 9:05 AM
I have a pair of original spinergy spox with the carbon hubs and they are great except that they are light enough that standard stem tubes throw the front a little out of balance. I was curious if anyone knows if there is a tube out there with a short valve stem. I have regular stems in there now Thank you for reading this Doug
I call BSd-man
Apr 15, 2001 2:35 PM
there is no way that bike wheels spin fast enough that such a small difference in weight- a few grams- can make a difference... did you buy the wheel used or something?
True, but...Brian B.
Apr 15, 2001 4:05 PM
There are definately some wheels where, if spun freely on a stand, the valve stem will end up at the bottom. I really doubt this is noticeable at speed, though. The solution, at least for a front wheel, is to mount your computer magnet opposite to the valve stem hole.

-Brian B.
what ifHeybraniac
Apr 15, 2001 6:21 PM
your front wheel has fiber spokes, like Spox or Xaeros? or if you have a Trispoke or Spinergys?
My maintenance standLazy
Apr 15, 2001 9:15 PM
My experience is that the higher the speed, the more affect this would have. I have a HED DEEP rear wheel which takes a 60mm stem and a valve extender. This is obviously an extreme case of imbalance, but when I'm adjusting derailleurs and stuff and I get the back wheel moving at a pretty good pace the imbalance will really start to shake the whole bike and stand.
My maintenance standImbalance Myass
Apr 16, 2001 5:35 AM
Hey braniac, EVERY bike shakes on a stand.
No......Really?Lazy
Apr 16, 2001 7:08 AM
Attach a little weight to your wheel and spin it. Then remove it and spin it at the same speed. Which one shakes worse?
I call BSdoug m
Apr 15, 2001 10:45 PM
d-man They were purchased new. When the wheel is spun without tube or tire, the wheel does stop with the rim low point that appears to be random, however when the tube and tire are mounted, the wheel always stops with the stem at the lowest point. The question is legit and I respectfully disagree, I do believe that it does spin fast enough to make a difference, The wheel magnet is mounted opposite, however since the spox wheel has a bigger spoke the magnet is the same as the rolf and is very small and light.
Balancetommyb
Apr 16, 2001 12:04 AM
In a well designed wheel, the extra mass of the valve stem should be offset by two things: the missing mass of the rim where the hole was drilled, and by the extra mass in the seam in the rim which should be 180 degrees away from the valve hole. Given that, most wheels will still stop spinning in a stand with the valve at the bottom, and with the valve hole on top if no tire is mounted. This is a sign of good bearings in the hubs. I, for one, have never, ever felt this imbalance while riding. If a computer magnet on the opposite side doesn't balance it perfectly, I would still be hesitant to go to a shorter valve stem, as it would make pumping up the tube on the side of the road that much harder.
balance the wheels with lead?Dog
Apr 16, 2001 8:26 AM
I don't think there are short valve tubes.

But, you can balance a bike wheel just like a car wheel. Get some stick on lead weights; they come in strips that you can cut to get the size/ weight you want. You get it at auto supply stores, or get even smaller lead strips at golf supply places (they make stick on lead to go on golf clubs). Then, stick them on to you rim. Experiment and see what happens.

You might consider using a larger computer magnet, or placing it further out toward the rim, too.

Doug
Careful....grz mnky
Apr 16, 2001 9:06 AM
Static ballancing is NOT the same as dynamic ballancing. Wheels can be perfectly ballanced staticaly (Torque = Force x Lever Arm), but when things are rotating the moment of inertia and the square of the distance enters into the equation and the results can be quite different. Your ballance problem may or may not be caused by the valve stem. To be sure it is a factor, but it may not be the only one.

You could try using short valve tubes with a removable valve stem extender. The speed of our bike wheels does make the ballance a factor, but I'm not too aware of a dynamic ballancing rig out there like there is for car wheels.
dynamic balanceDog
Apr 16, 2001 12:55 PM
I was thinking of sticking the lead on, give the wheel a big spin, and see what happens. If it smooths out, it might be working.

But, if car tires are analogous to bike tires, the tires, and presumeably tubes, too, can have even greater imbalances than the wheels. When I drove and worked on race cars, we tried balancing wheels naked, first, so that balancing them with tires would require less time and lead. But, it didn't work. Car tires would be far more imbalanced than the wheels, so you essentially had to rebalance any time you changed, or even removed and replaced a tire. The same thing may apply to bike tires. You might have to rebalance every time you removed a tire or replaced tube. Also, I've see car tires go way out of balance from one big flat spot from skidding. I suppose the same thing might happen on a bike.

You some may perceive as a wheel imbalance could be the tires or tubes. I'd change them and see what happens. Also, I'd never try to balance wheels using Slime tubes -- they will certainly be off balance, and will be constantly changing.

Doug
dynamic balancegrz mnky
Apr 16, 2001 2:04 PM
Can't hurt to try - unless your crash in the process.

Problem is you're really just guessing and although the intent might be right, the results can be inconclusive or just confusing. Gettng it right would be a matter of luck.

It is a lot like car tires - no difference really except for the top speed and acceleration. It stands to reason that in the elite racing circles people should be looking at this (RAAM, TdF, etc.).

Wonder how long before we've got a tubeless road wheel from Mavic - they tend to introduce a lot of the new technology in the MTB world then bring it over to the road world (i.e. Ksyrium).

How do you like your Spin Skins so far?
Reliability more and moreDog
Apr 17, 2001 6:41 AM
The more I ride, the more I want reliability, vs. super light weight (except for the dedicated climbing bike, with full support), and comfort.

Thus, the experiment with the Spin Skins. Their promise is great, but, wouldn't you know it, I got a bad tire cut the very first time I used them with Michelin Axial Pro Lights, about 130 miles into the ride. Now, I doubt anything may have stopped the bad slash I got. Also, they made changing the tube roadside more difficult, such that I had to yank it out and stuff it in my jersey pocket. It got so crumpled up that I had to trash it. Since, I got some Vittoria Open Corsa's, which have a kevlar mesh, and no flats since. But, I've not yet ridden them enough to have any real significant experience to tell whether they work better or not. I still have the Spin Skins in two other wheelsets. It may take a while to tell if they help or not.

I have no doubt that sooner or later we'll have a tubeless road wheel and tire. The Ksyrium would work for this right now, if the tire were available. I'm sure it will take years and years to develop, though. BTW, what do you do when you get a flat with a tubeless? I suppose you patch it from the inside, but how do you find the hole? What if you have a big cut?

Doug
Tubeless Road systems,TJeanloz
Apr 17, 2001 9:14 AM
The last Bicycle Retailer reports that Alex Rims announced a tubeless road system at the Taipei cycle show. The UST system took Mavic 4 years to figure out, who wants to bet that a system designed by the lowest-end rim manufacturer (Alex) won't work?
If you get a flat with tubeless, you...biknben
Apr 17, 2001 9:59 AM
...put a tube in it and continue. The tubeless system will still work with a tube. You just have to take the valve out of the rim.

Most MTB racers I see with Tubeless don't carry any spares or patches. If they flat, they are done. Some just carry CO2 because it's not uncommon to have the tire roll off the rim if running really low pressure. Then there are those who carry a tube and air and will add a tube to a tubless system if they flat.

A few of my teammates have flatted with tubeless. Rock punctures and sidewall cuts are still a concern. Pinch flats are no longer a problem for them. I guess it is similar to a tubular road tire when it comes to flats.

The tubeless MTB system are heavier than their tubed cousins. I don't expect to see a road version of this technology any time soon. But who knows?