On Sunday, I swapped out my 24" IRC downhill tube that weighed a little over 15 oz. for a Specialized DH tube that was 6 oz less. The IRC tube has the all metal valve stem and I rode it with the lock nut and washer on it. The Specialized has the rubber valve stem
Going to the lighter tube has proved to be interesting. When I appoach a drop, I am having difficulty getting the timing right for the drop. I can’t seem to set up right. I think it is the lack of weight from the tube and the heavier valve. I think that valve creates a pulse in the tire that helps in the timing or maybe not.
Has anyone had a similar experience? I haven’t ridden in over 4 months due to injuries, so that may be the problem, but I am not sure.
I’m guessing but the alll metal stem would probably be a prest and the one that looks like a car valve stem is schrader.
I don’t think that the tube weight would have much if any effect, except a slight difference in rotational weight.
Not sure what difference 6 o.z. would have on hopping. Perhaps more pinchflatting due to thinner tubewalls, unless you switched to latex instead of butyl.
Jeff
IRC tubes are schrader and are threaded the length of the valve. Most likely because they are made for DH use. Getting used to the weight reduction will take time. I went from a tube to tubeless and felt like I was starting over on the H36.
Think about the ratio of tube weight to spoke + rim + tube + tire weight. We’re talking a fraction of a percent. Even less in the case of the valve. Your wheel’s moment of inertia changes in direct proportion to its mass, so there is a fraction of a percent change here too. Splitting hairs indeed!
For a concrete test, tell us this. Tape a dime (weight, 2.5g) to your rim, anywhere you like. Go for a ride. Do you notice a difference?
I’d agree that the solution to your dilemma involves a lot more riding, including many drops. After enough practice you won’t even have to think about the set up. With the weight you’re saving from your tube you could put on a few more ounces of armor for those drops
We’re talking about 6 ounces here; almost 200 grams. That is a significant amount of rotating weight. (Try 80 dimes instead of one). Thinner tubes also have different deformation characteristics; they’ll bounce differently.
Still, I’m sure it’s just a question of getting used to it.
On a rtecent Santa Cruz ride we speculated about alternative inflations for tires, and the general consensus was a hydrogen/helium mix. The helium would help deter combustion, and the hydrogen would be less dense.
I like the idea of cutting weight, but I only do it if it’s reasonable. I won’t spend an extra $50 in order to cut 2 oz. If it takes me an extra 10 minutes at the mill to cut 1 oz of material, by all means, I’ll do it. For me, time is free.
Drilling holes in your seatpost, crankarms,pedals, seat frame,uniframe. Shave extra knobbies off the tire then shave down the importants ones. Grind excess materials anywhere that you can find it. Pull one bearing out of yur pedals and hubs.
Or take a dump before you ride.
Jeff
On Wed, 16 Mar 2005 14:40:30 -0600, “The Munieer” wrote:
>As a matter of fact, does anyone
>know how I could put helium in the tire?
From a helium bottle. These are commercially available at a pressure
of 200 bars. I have it at work.
The gas volume of a typical 24 x 3" tyre is on the order of 8 litres.
Let’s assume you run your tyre at 1.5 bar (that’s above ambient
pressure). The mass of air in the tyre would be about 26 grams. The
mass of helium would be about 4 grams. So you save a mere 22 grams.
(With 100% hydrogen you could save another 2 grams.)
Note that (any) gas in the tyre does not effectively count as
/rotating/ mass. Yes, if you ride at a constant speed the gas will
eventually rotate with the tyre, but for any speed variation the gas
will adjust amazingly slowly.
Also note that tubes are not designed to hold helium. The helium will
leak off a lot faster than air.
Klaas Bil - Newsgroup Addict
people who unicycle are shyly exhibitionistic - GILD
Rod,
Don’t forget to use a vacuum pump to evacuate all the air from the tire before filling with helium, to get the most weight reduction. I want to be sure you get the full unperceivable benefit of the modification.
