Re: Adjusting to a lighter DH tube



T

The Munieer

Guest
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.


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The Munieer - AKA Teachndad

Rod Wylie



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The Munieer wrote:
> * 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
> *

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


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unidad wrote:
> *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.
> *
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.


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I think your new wallis cf handle is thowing you off. You should sell
it, $25 sounds like a fair price.


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these " splitting hairs" on tiny weight differance threads you make are
the greatest :D

new thread " Helium in the tube"

i think the 4 months off is the reason here though. keep the lighter
tube in there and enjoy the portage.

PS, im a Drastic rider too now ;)


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The Munieer wrote:
> *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. *


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 :)


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maestro8 - Mad Scientists for World Domination

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maestro8 wrote:
> *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.


--
tholub - Kinetic Sculptor
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jagur wrote:
> *these " splitting hairs" on tiny weight differance threads you make
> are the greatest :)
>
> new thread " Helium in the tube"*


Jagur,
Yeah, I busted up when I read that. As a matter of fact, does anyone
know how I could put helium in the tire?;)

(serious)I was even going to weigh a 26" standard tube that you had
suggested in another thread, just to see if I could save another ounce
or two.


I pronounce my self as - King Weight Wienie


--
The Munieer - One for the...Off Road

Rod Wylie - King Weight Wienie



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jagur wrote:
> *these " splitting hairs" on tiny weight differance threads you make
> are the greatest :)
>
> new thread " Helium in the tube"*


Jagur,
Yeah, I busted up when I read that. As a matter of fact, does anyone
know how I could put helium in the tire?;)

(serious)I was even going to weigh a 26" standard tube that you had
suggested in another thread, just to see if I could save another ounce
or two.


I pronounce my self as - King Weight Wienie


--
The Munieer - One for the...Off Road

Rod Wylie - King Weight Wienie



'MountainUnicyclingLA.com' (http://www.mountainunicycling.us)
'Greater Los Angeles Area Trails - Images' (http://tinyurl.com/4otql)
'Greater Los Angeles Area Trails - Descriptions'
(http://tinyurl.com/6h8zn)



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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.


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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


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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
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Klaas Bil wrote:
> *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 modifcation.

Scott


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