Please stay on the trail.

FAQ and threads for those just starting to hike the Colorado 14ers.
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madbuck
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Re: Please stay on the trail.

Postby madbuck » Mon Oct 01, 2012 4:36 pm

Dex wrote:
So, to lessen the PSI on the ground all a mountain biker needs to do is decrease the psi of the tire inflation to 25psi or even 20 psi?


Actually, yes.
Bigger contact patch from a "flatter" tire gives you the same force spread out over a larger area. Think about riding on sand or snow.
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Re: Please stay on the trail.

Postby Average Joe » Mon Oct 01, 2012 4:41 pm

madbuck wrote:
Dex wrote:
So, to lessen the PSI on the ground all a mountain biker needs to do is decrease the psi of the tire inflation to 25psi or even 20 psi?


Actually, yes.
Bigger contact patch from a "flatter" tire gives you the same force spread out over a larger area. Think about riding on sand or snow.


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I have no idea who's right but couldn't resist.
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Re: Please stay on the trail.

Postby TallGrass » Mon Oct 01, 2012 4:43 pm

tlongpine wrote:Bean is talking about the PSI within the tire while you are talking about PSI upon the ground.

So the "50-100+ psi" ...
Bean wrote:A hiking boot (as tends to be worn by anti-bike troglodytes) with a raised heel will be less, but close enough (I'll make up the difference in average hiker weight incl. gear). At 200lb all geared up, that's 2psi standing perfectly still, 4psi on one foot, and 50-100+ psi when stepping forward. Meanwhile, 30psi in a bike tire is 30psi. A fatbike can go as low as single-digit air pressure.

is not referring to pressure upon the ground, but... within the boot? :-s
tlongpine wrote:The discussion isn't a question about what is causing the erosion, the question is how to mitigate it.

So we have to mitigate erosion without understanding the cause(s)? How does that process go?

Better still, who'd want to volunteer their time to work this as a CFI project? Wouldn't organizing something like that have the best impact?
Not sure if I'll do more 14ers. The trip reports are too tiring. :wink:
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Tiredness is the shortest path to equality and fraternity - and sleep finally adds to them liberty."
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Re: Please stay on the trail.

Postby planet54 » Mon Oct 01, 2012 4:53 pm

Science: Science does not produce wisdom. While the insights of science can help us to change our world,only human thought and concern can enlighten us about the path we should follow in life.

In other words,science can help fix this problem, but it will take people that give a damn to get it done.
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"Climbing K2 or floating the Grand Canyon in an innertube;there are some things one would rather have done than do." Edward Abbey
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Re: Please stay on the trail.

Postby Bean » Mon Oct 01, 2012 5:16 pm

Dex wrote:So what you are telling us is that if the max pressure on the tire is 50 psi, then the max pressure it can a bike with 400lb rider can put on the ground is 50 psi?
Seriously?

Yes. The contact patch will increase in size. There may be slight pressure changes as the tire deforms but that will be insignificant. Assuming a square contact patch, all you'd need is 2" x 2" (per tire) at 50psi to support 400lb.
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Re: Please stay on the trail.

Postby Bean 2 » Mon Oct 01, 2012 6:18 pm

Bean wrote:
Dex wrote:So what you are telling us is that if the max pressure on the tire is 50 psi, then the max pressure it can a bike with 400lb rider can put on the ground is 50 psi?
Seriously?

Yes. The contact patch will increase in size. There may be slight pressure changes as the tire deforms but that will be insignificant. Assuming a square contact patch, all you'd need is 2" x 2" (per tire) at 50psi to support 400lb.


Dex, at the end of the day all of this physics talk is insignificant. The point is that walking downhill is for hiking boot wearing troglodytes (yes, that's right, troglodytes) and mountain biking/skiing is the way to go. If you are looking to build muscle (you can always use my calves for a good example of built muscle (my calves (which are gigantic FYI) can be seen in multiple threads and trip reports on this site)) you can always take up mountain biking and skiing, as they are most definitely NON-troglodyte methods of travel. With the aid of my physics textbook I can talk PSI and other such concepts all night but let's get to the bottom line here; and that is building muscle in it's finest form (my calves for example (which happen to be huge)) is not related to physics or trail design. Ergo this PSI conversation is more or less irrelevant...
gdthomas wrote:

Bean, you're an idiot 2.

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Re: Please stay on the trail.

Postby Bean » Mon Oct 01, 2012 6:20 pm

Bean 2 wrote:Dex, at the end of the day all of this physics talk is insignificant. The point is that walking downhill is for hiking boot wearing troglodytes (yes, that's right, troglodytes) and mountain biking/skiing is the way to go. If you are looking to build muscle (you can always use my calves for a good example of built muscle (my calves (which are gigantic FYI) can be seen in multiple threads and trip reports on this site)) you can always take up mountain biking and skiing, as they are most definitely NON-troglodyte methods of travel. With the aid of my physics textbook I can talk PSI and other such concepts all night but let's get to the bottom line here; and that is building muscle in it's finest form (my calves for example (which happen to be huge)) is not related to physics or trail design. Ergo this PSI conversation is more or less irrelevant...

Image
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Re: Please stay on the trail.

Postby Bean » Mon Oct 01, 2012 6:37 pm

Dex wrote:
Bean wrote:
Dex wrote:So what you are telling us is that if the max pressure on the tire is 50 psi, then the max pressure it can a bike with 400lb rider can put on the ground is 50 psi?
Seriously?

Yes. The contact patch will increase in size. There may be slight pressure changes as the tire deforms but that will be insignificant. Assuming a square contact patch, all you'd need is 2" x 2" (per tire) at 50psi to support 400lb.


No it won't, it is a tire - too much pressure and it will blow.

You are equating internal psi with external psi on the ground.

Where is Bean2 when you need him.

I just checked and my tires suggest 35-65psi (35 is too much, 65...lol) which means they could easily support our friend.

We're rapidly approaching an "airplane on a treadmill" level of discussion.
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Re: Please stay on the trail.

Postby Bean 2 » Mon Oct 01, 2012 6:56 pm

Bean wrote:
Bean 2 wrote:Dex, at the end of the day all of this physics talk is insignificant. The point is that walking downhill is for hiking boot wearing troglodytes (yes, that's right, troglodytes) and mountain biking/skiing is the way to go. If you are looking to build muscle (you can always use my calves for a good example of built muscle (my calves (which are gigantic FYI) can be seen in multiple threads and trip reports on this site)) you can always take up mountain biking and skiing, as they are most definitely NON-troglodyte methods of travel. With the aid of my physics textbook I can talk PSI and other such concepts all night but let's get to the bottom line here; and that is building muscle in it's finest form (my calves for example (which happen to be huge)) is not related to physics or trail design. Ergo this PSI conversation is more or less irrelevant...

Image


The Fonz approves, building muscle in its finest form :

suns out guns out.jpg
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Bean, you're an idiot 2.

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Re: Please stay on the trail.

Postby mtnfiend » Mon Oct 01, 2012 7:20 pm

Well, all is right with the world.....it seems Bean is correct. It's not intuitive or obvious at first, but I had to put pen to paper to convince myself or loose my sanity (I mean honestly, Bean can't be right, can he??).

90 kg person+bike (~200 lbs). I weight about 165lbs and my bike is roughly 35lbs (heavy I know, but it's old and I'd rather spend my money on ski gear).

Since Newton was the pimp-daddy of math and calculus: F=ma; so 90kg*9.8m/s^2. = 882N.

P=F/A, rearrange to solve for area; A=F/P. I measured the pressure in my rear tire at 18 psi (124,105 Pa).

Solving for area; A = 882N/124,105N/m^2 = .0071 m^2 (~11 in^2).

I'll admit, when I first ran the calc, 11 square inches seemed absurd especially since the width of my tire is roughly 2" (meaning the contact length would need to be about 5.5 in). I know tires deform, but that much seems ridiculous, right??

I sat on my bike with as much weight on the back tire as possible (the calc above assumes 1 tire is carrying all the weight) and had my wife mark the contact length on the garage floor (slid a straight edge under the front and back of the rear tire until it touched the tire, then marked the location with a sharpie).

Measuring the distance between the 2 marks yielded 5.75 in. - means good enough for government work.

Now that we've got that solved, we can go back to ridiculing people for not staying on the trail........or bean can keep posting topless photos of himself (I'd wouldn't post that kind of stuff on the interwebz if I were you, but that's your deal). [-(
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Re: Please stay on the trail.

Postby HikerGuy » Mon Oct 01, 2012 7:24 pm

Dex wrote:
Bean wrote:
Dex wrote:So what you are telling us is that if the max pressure on the tire is 50 psi, then the max pressure it can a bike with 400lb rider can put on the ground is 50 psi?
Seriously?

Yes. The contact patch will increase in size. There may be slight pressure changes as the tire deforms but that will be insignificant. Assuming a square contact patch, all you'd need is 2" x 2" (per tire) at 50psi to support 400lb.


No it won't, it is a tire - too much pressure and it will blow.

You are equating internal psi with external psi on the ground.

Where is Bean2 when you need him.


Internal PSI = External PSI. Simple physics, opposite and equal forces. Bean is correct in the example he uses. The pressure in a tire does not change due to load.
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Re: Please stay on the trail.

Postby RckyMtnWildman » Mon Oct 01, 2012 7:35 pm

Please stay on the trail," should state: "please stay on one of them trails." Like June Carter tells Johnny Cash: "Y'all can't walk no line!" Doesn't mean the chosen path is wrong, it just deviates. I'm all for preservation, treading lightly, and keeping our mountains pristine; but if I see that beautiful summit lurking in the distance, the shortest path is a straight-line and that path will be taken as long as the obstacles concur.

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