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  1. #1
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    Lower vs Higher 29'' tire pressure issue...

    So...given the bigger tire volume/wheel perimeter + bigger contact patch of a 29er

    vs

    the lower equivalent of a 26er...

    ..when riding a 29er,trying to be in the same-or better-circumstances (traction,control,everything) as with a 26er,isn't it unreasonable that most big wheeled riders use lower pressures?

    Bigger contact patch/wheel perimeter means 'better',isn't it?

    Please excuse the simple minded way of putting it,maybe it is a rhetorical question of the moment,maybe ignorance,i really don't know what i'm missing and if,and i understand that now on a 29er we can have very low pressure as a possibility,but should we for some reason?

    ....when i was riding my 26er i had low pressure too,and it was traction etc that i had to achieve cause of the smaller perimeter/patch,and at that time there wasn't any 29er to compare.....

    so....Why lower and not higher????

    ...



    I appreciate your input,
    Kosmas.
    Last edited by Zaratustra; 06-19-2011 at 09:16 PM.

  2. #2
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    I like the stans rule of thumb, body weight + bike wight divided by 7. Anything lower than that is far past the point of diminishing returns.

    According to the rolling resistance article that was published by cyclingnews, 29'ers have a very comparable contact patch to a 26" tire. It's just longer than and narrower than the 26" counterpart.

  3. #3
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    Quote Originally Posted by Zaratustra View Post
    So...given the bigger tire volume/wheel perimeter + bigger contact patch of a 29er

    vs

    the lower equivalent of a 26er...

    ..when riding a 29er,trying to be in the same-or better-circumstances (traction,control,everything) as with a 26er,isn't it unreasonable that most big wheeled riders use lower pressures?

    Bigger contact patch/wheel perimeter means 'better',isn't it?

    Please excuse the simple minded way of putting it,maybe it is a rhetorical question of the moment,maybe ignorance,i really don't know what i'm missing and if,and i understand that now on a 29er we can have very low pressure as a possibility,but should we for some reason?

    ....when i was riding my 26er i had low pressure too,and it was traction etc that i had to achieve cause of the smaller perimeter/patch,and at that time there wasn't any 29er to compare.....

    so....Why lower and not higher????

    ...



    I appreciate your input,
    Kosmas.
    I generally use the same pressure for the same model tire, same width in 26" or 29".
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  4. #4
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    Same here.

  5. #5
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    Lower tire pressures will result in a short and wide contact patch, resulting in less rolling resistance (to a point of course). Higher pressures will give you a long and narrow contact patch, which has higher resistance. There was a thesis produced by a gentleman in Germany I believe where he tested this theory on grass, pavement, gravel/single track... Not sure if it's still able to be found, but it has a lot of good info and is what convinced me to go lower tire pressures when I was on 26" wheels.

  6. #6
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    That is a decision better made by your butt than your brain. Soooooo many things are a factor, trail, soil, bike, tires, rider experience and technique, personal preference.

    Find a length of trail, two miles or so long, that has as much variety as you can find, and represents the kind of trail you like. Set tire pressure and ride it out and back. Drop pressure a couple psi and repeat. Drop pressure a couple psi and repeat. Repeat. Repeat.

    Now try it with a couple psi higher and repeat, repeat, repeat. The answer will come clear. It will change with different tires, so you may have to do it again and again. As you gain more experience on different tires on different trails, you will find the sweet spot that works for you, based on each tire.
    Last edited by slocaus; 06-20-2011 at 09:37 AM.
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  7. #7
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    Quote Originally Posted by PHRANQUY View Post
    Lower tire pressures will result in a short and wide contact patch, resulting in less rolling resistance (to a point of course). Higher pressures will give you a long and narrow contact patch, which has higher resistance.
    False. Lower pressure makes the contact patch longer and wider. Higer is the opposite. Take your tire at high pressure and it may have 1 square inch hypothetically, and air it down and now its longer front to back and wider side to side. Now your contact patch is like 1"x3". Try it for yourself and look at the difference.
    Now rolling resistance, regarding low vs. high tire pressure, will be different on different types of terrain. Higher press on smooth path with be faster than low on smooth. Switch it around for terrain. Lower pressure will have less resistance than high pressure bouncing you all over the objects rather than conforming and flowing over.

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    Quote Originally Posted by hal0tw0 View Post
    False. Lower pressure makes the contact patch longer and wider. Higer is the opposite. Take your tire at high pressure and it may have 1 square inch hypothetically, and air it down and now its longer front to back and wider side to side. Now your contact patch is like 1"x3". Try it for yourself and look at the difference.
    Now rolling resistance, regarding low vs. high tire pressure, will be different on different types of terrain. Higher press on smooth path with be faster than low on smooth. Switch it around for terrain. Lower pressure will have less resistance than high pressure bouncing you all over the objects rather than conforming and flowing over.
    Tire width plays a huge factor as well. If you want to PM me your email address I'd be happy to send you the paper.

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    send me that paper...THX

    Quote Originally Posted by PHRANQUY View Post
    Tire width plays a huge factor as well. If you want to PM me your email address I'd be happy to send you the paper.
    PM me or just put it in this thread....THX

  10. #10
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    It's a PDF, so I'm not able to attach it.

  11. #11
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    Quote Originally Posted by PHRANQUY View Post
    It's a PDF, so I'm not able to attach it.
    Yes you are.

    Ronnie.
    Attached Files Attached Files
    The trouble with having an open mind is that people will insist on trying to put things in it.

  12. #12
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    Tube or tubeless? One man's high may be another man's low, what air pressures are we talking? FS, hardtail, rigid?
    Good thread.

    I ride FS and read that means a little more air pressure.
    Was not aware of the Stan's rule, interesingly, that's about where my tire pressure has evolved.
    dirtaoist

  14. #14
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    Quote Originally Posted by Zaratustra View Post
    no discussion of pressure.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

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    Now we start adding all the variables and its not apples to apples anymore.
    Do this test with the same wheel/tire set and play with your pressures on rocky vs. pavement. When you take your MTB on the road and ride to the trail head youre not airing down first. You air up to high pressure on pavement and then air down when you get to the trail. Why? because of the higher rolling resistance of that knobby tire with low pressure on pavement. It makes no sense if you just think about.

  16. #16
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    Fwiu...

    Quote Originally Posted by hal0tw0 View Post
    Now we start adding all the variables and its not apples to apples anymore.
    Do this test with the same wheel/tire set and play with your pressures on rocky vs. pavement. When you take your MTB on the road and ride to the trail head youre not airing down first. You air up to high pressure on pavement and then air down when you get to the trail. Why? because of the higher rolling resistance of that knobby tire with low pressure on pavement. It makes no sense if you just think about.
    If the surface is smooth, then higher pressure yields lower rolling resistance. If the surface is soft and uneven, the lower pressure yields lower rolling resistance. It has to do with the tire being able to 'envelope' the bumps rather than being deflected by them, and bouncing the whole bike up.

    Me, I found I could run lower pressure on my 29er in general than I could with my 26er. I tend to run as little as I can get away with.... without pinch flatting or with the tire feeling squirmy. For my 215 pound self, that is around 25/27 psi, with a few pounds more if I'm going to ride some place with lots of pointy rocks.

  17. #17
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    Quote Originally Posted by Maheoway View Post
    Tube or tubeless? One man's high may be another man's low, what air pressures are we talking? FS, hardtail, rigid?
    Good thread.

    I ride FS and read that means a little more air pressure.
    Was not aware of the Stan's rule, interesingly, that's about where my tire pressure has evolved.
    I've found I can get away with a little less tire pressure in my case, running a 29x2.4 tire on a 4" travel bike I've foudn the bike even felt comfortable, but on the edge of squirly, at 20lbs... 22-24lbs seems to work well. This is running tubeless though, so the tires react a little differently. On that note, on my previous HT with tubes I was still running 27lbs in a 26x2.0 last year, which is still pretty low. Then again, I also weigh 170lbs pluss the weight of a camelback w/ 100oz. of water and misc. spares/tools.

  18. #18
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    My initial thought was more theoretical,trying to have as objective answers as possible,out of what i or someone else does,which means more difficulty to explain all the personal factors etc...all caused because very often people are promoting low pressure (or it is my idea)...

    I mean..of course i'm experimenting with my pressure and i know,or i think i know what is better,for the present,for me,for my conditions.(HT,tubeless,similar to my ex 26'' pressure too.Nothing too different.27psi rear/23 front)

    But even this-my-personal situation constantly changes since our bicycling story is like travelling,it seems impossible to have a conclusion from time to time,from place to place,from person to person..

    On the other hand,my current 2.10 Pythons have the low limit at 29psi and the Maxxis over 30 if i'm not wrong.This again???Isn't too high?
    If i inflate over thirty my bike is dancing and nor rolling (i'm 70k/154lbs) + my LB mechanic insists that my pressure is unacceptable.He proposes what is written on the tire,even in the case of my gf = 50k/110lbs....i don't get it.

    ..but the conversation helped me to clarify some things.


    Thanks for the pdf and everything!!!

  19. #19
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    Quote Originally Posted by hal0tw0 View Post
    Now we start adding all the variables and its not apples to apples anymore.
    Do this test with the same wheel/tire set and play with your pressures on rocky vs. pavement. When you take your MTB on the road and ride to the trail head youre not airing down first. You air up to high pressure on pavement and then air down when you get to the trail. Why? because of the higher rolling resistance of that knobby tire with low pressure on pavement. It makes no sense if you just think about.
    One could argue it would never be apples to apples though. Ones riding style, weight, bike setup (rim width and tire width paly huge factors), terrain, environmental conditions (heat, rain) can all make a difference.

  20. #20
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    Quote Originally Posted by PHRANQUY View Post
    One could argue it would never be apples to apples though. Ones riding style, weight, bike setup (rim width and tire width paly huge factors), terrain, environmental conditions (heat, rain) can all make a difference.
    The original question proposed one variable: the wheel diameter. As close to apples-to-apples as you are going to get.
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  21. #21
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    Maybe the better answer then would be that the larger volume of the 29" tire allows the same amount of air to fill up the larger space resulting in a lower pressure then? Much like the fact that I run the tires on my truck @ 25psi compared to the 35psi that the factory tires were at.

  22. #22
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    Quote Originally Posted by PHRANQUY View Post
    Maybe the better answer then would be that the larger volume of the 29" tire allows the same amount of air to fill up the larger space resulting in a lower pressure then? Much like the fact that I run the tires on my truck @ 25psi compared to the 35psi that the factory tires were at.
    i can't make sense of this at all.

    for off-road use, the lowest pressure you can comfortably and safely run seems to be the best for traction, comfort & efficiency. 29ers seem to allow a lower pressure floor than 26" bikes, perhaps due to the angle of attack.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  23. #23
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    I've played with tire pressure at different places I ride. One place I can get away with 26 psi, others I need a little more to prevent rim hits. I normally ride 28 psi.

    The above equation works well to get you started - rider weight + bike weight divided by 7. This equation gets me to 29 psi.

  24. #24
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    Quote Originally Posted by frdfandc View Post
    I've played with tire pressure at different places I ride. One place I can get away with 26 psi, others I need a little more to prevent rim hits. I normally ride 28 psi.

    The above equation works well to get you started - rider weight + bike weight divided by 7. This equation gets me to 29 psi.
    Thanks,it gives me exactly the average that i use = 25 psi.

  25. #25
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    Holy crap. Does everything have to become some sort of quantified, scientific equation? Optimum volume ... ideal contact patch ... perfect rolling resistance ... maximum efficiency ... jeebus. I thought you were supposed to ride your mountain bike in the woods, not a physics lab.

    Just put some air in your damn tires. If they bounce you around, take some out. If your rims get banged up, put more in. Simple.

  26. #26
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    wow! if I use stan's equation I need to be running@ 40 psi.... Really on a 2.4? Normally I'm @ 20 up front and 26 outback!
    The most important thing is what God thinks about it. He will have the final say.” – Joshua Stinebrink

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  27. #27
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    Quote Originally Posted by ae111black View Post
    wow! if I use stan's equation I need to be running@ 40 psi.... Really on a 2.4? Normally I'm @ 20 up front and 26 outback!


    I use it as a guideline, not as a strict rule. A 250 lb rider will need a higher pressure than a 180lb rider (myself) to prevent pinch flats when running tubes and rim strikes when tubeless. If you can go lower great, do so.

    A larger sized tire has more volume, so lower pressure is needed to provide the same tire pressure. So a 2.2 wide tire with 30 psi will not support as much weight as a 2.4 tire with the same 30 psi.

    Example here - I used to run 23mm wide tires on my road bike at close to the max pressure to prevent pinch flats - usually around the 110 psi area on the rear. A switch to 25mm wide tires, I'm now running 20 psi lower on the rear with the same amount of pinch flat protection.

  28. #28
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    Quote Originally Posted by Godless Communist View Post
    Holy crap. Does everything have to become some sort of quantified, scientific equation? Optimum volume ... ideal contact patch ... perfect rolling resistance ... maximum efficiency ... jeebus. I thought you were supposed to ride your mountain bike in the woods, not a physics lab.

    Just put some air in your damn tires. If they bounce you around, take some out. If your rims get banged up, put more in. Simple.
    Before the Internet, that is what we did, rode and figured it out.

    Now we have to talk it in circles, talk it to death, have a couple flaming disagreements, then maybe we can ride........
    "The physician heals, Nature makes well" - real fortune cookie

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  29. #29
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    Quote Originally Posted by Godless Communist View Post
    Holy crap. Does everything have to become some sort of quantified, scientific equation? Optimum volume ... ideal contact patch ... perfect rolling resistance ... maximum efficiency ... jeebus. I thought you were supposed to ride your mountain bike in the woods, not a physics lab.

    Just put some air in your damn tires. If they bounce you around, take some out. If your rims get banged up, put more in. Simple.
    +1.......What he said

  30. #30
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    Quote Originally Posted by Godless Communist View Post
    Holy crap. Does everything have to become some sort of quantified, scientific equation? Optimum volume ... ideal contact patch ... perfect rolling resistance ... maximum efficiency ... jeebus. I thought you were supposed to ride your mountain bike in the woods, not a physics lab.

    Just put some air in your damn tires. If they bounce you around, take some out. If your rims get banged up, put more in. Simple.
    you mean... like... say... a gear inch calculator? same thing... and i think it's funny that you're ripping "quantified, scientific equations" with this holier-than-thou "go ride" purist BS while in the same day recommending gear inch calculators and specific numerical ranges for different types of riding. thanks for the laugh.
    Last edited by meltingfeather; 06-22-2011 at 07:21 AM.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  31. #31
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    Quote Originally Posted by meltingfeather View Post
    you mean... like... say... a gear inch calculator? same thing... and i think it's funny that you're ripping "quantified, scientific equations" with this holier-than-thou "go ride" purist BS while in the same day recommending gear inch calculators and specific numerical ranges for different types of riding. thanks for the laugh.
    See?????

    WhatdidItellya?

    Here starts the "Flaming Disagreements" part, just so you know where we are in this thread.

    (predictable - most times you can even anticipate the two or three posters who will get their knickers in a twist first and start calling someone else out on it)
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  32. #32
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    Quote Originally Posted by slocaus View Post
    See?????

    WhatdidItellya?

    Here starts the "Flaming Disagreements" part, just so you know where we are in this thread.

    (predictable - most times you can even anticipate the two or three posters who will get their knickers in a twist first and start calling someone else out on it)
    should i find that this forum twists my knickers i'll know that's a good point to restablish my priorities.
    you don't think it's funny for a guy to stop in on a thread to go off on a rant about equations and tell people to go ride right after he tells another guy to use a calculator and recommends numerical gear-inch ranges for him to use?
    i did.
    funny as in, "haha," not funny as in knicker twist.
    if it bothers him so much, maybe he should take his own advise.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  33. #33
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    Quote Originally Posted by meltingfeather View Post
    i think it's funny that you're ripping "quantified, scientific equations" with this holier-than-thou "go ride" purist BS while in the same day recommending gear inch calculators and specific numerical ranges for different types of riding. thanks for the laugh.
    I was just trying to help a new guy get started. Gear ratios are a bit more complex than tire pressure, and a hell of a lot more expensive to experiment with. Sorry if this perceived inconsistency offends you.
    Last edited by Godless Communist; 06-22-2011 at 11:15 AM.

  34. #34
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    Quote Originally Posted by meltingfeather View Post
    should i find that this forum twists my knickers i'll know that's a good point to restablish my priorities.
    you don't think it's funny for a guy to stop in on a thread to go off on a rant about equations and tell people to go ride right after he tells another guy to use a calculator and recommends numerical gear-inch ranges for him to use?
    i did.
    funny as in, "haha," not funny as in knicker twist.
    if it bothers him so much, maybe he should take his own advise.
    Stalker

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  35. #35
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    Quote Originally Posted by ae111black View Post
    wow! if I use stan's equation I need to be running@ 40 psi.... Really on a 2.4? Normally I'm @ 20 up front and 26 outback!
    My reaction exactly. At 220lbs. plus my bike (±28lbs.) plus my Camelbak (±10lbs. I suppose) I'd be pumping up to about 39psi. in my Nobby Nic 2.35 or Purgatory 2.4. Both of which I've been using at 24psi.

    I though I would take a look at where the fore mentioned formula came from. The following is cut and pasted from FAQs on the Notubes website:

    "What is the max air pressure I can have for my tubeless set up?
    Do not inflate over 40psi. Use this simple equation to figure out a strarting point when running NoTubes tires (2.0-2.2) with our ZTR rims use this simple formula.
    Rider weight in pounds divided by 7 = x
    x-1 = Front tire pressure in PSI
    x+2 = Rear tire pressure in PSI"

    Notubes is not recommending this calculation for anything other than their tires and rims. They also mention limited sizes. I don't know their tires but they look to me like they are targeted at racers and not trail riders.

    Ronnie.
    The trouble with having an open mind is that people will insist on trying to put things in it.

  36. #36
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    Quote Originally Posted by Godless Communist View Post
    I was just trying to help a new guy get started. Gear ratios are a bit more complex than tire pressure, and a hell of a lot more expensive to experiment with. Sorry if this perceived inconsistency offends you.
    didn't mean to come off as offended. i thought it was funny. i saw that thread and i guess i have a good memory. your username is memorable. perhaps the "BS" was a bit much... my apologies, but what do you really expect of people on a mountain bike forum if not to talk about mountain bike stuff they're interested in? and what reaction do you expect when you stop in to a thread to say nothing more than, "this discussion is stupid, y'all should go ride."
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  37. #37
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    Quote Originally Posted by slocaus View Post
    Stalker

    Do you check every users posts on this board to make sure they are consistent and valid, or just when they bother you and you want to catch them "screwing up"?
    i read that thread and there are a few usernames that are pretty memorable to me. it was yesterday.
    i rarely check users' posts, and i could give a sh@t about catching people "screwing up," whatever that means.
    i thought it was funny... like i do almost anytime somebody posts on an internet forum telling people to stop talking about bike stuff and go ride. in case you missed it, there's a bit of irony there.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  38. #38
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    Quote Originally Posted by meltingfeather View Post
    i thought it was funny... like i do almost anytime somebody posts on an internet forum telling people to stop talking about bike stuff and go ride.
    Quote Originally Posted by meltingfeather View Post
    and what reaction do you expect when you stop in to a thread to say nothing more than, "this discussion is stupid, y'all should go ride."
    Well, for the record, I never said either of those things. I simply suggested that one find their optimum tire pressure by riding their bike, instead of by reading a thesis by a German scientist or performing abstract computations.

    Peace on dirt,
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  39. #39
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    Quote Originally Posted by Godless Communist View Post
    Well, for the record, I never said either of those things. I simply suggested that one find their optimum tire pressure by riding their bike, instead of by reading a thesis by a German scientist or performing abstract computations.
    since we're establishing the record, maybe you can point out the post where anyone suggests doing as you say, even the referenced study.
    sorry to have used the quotes. i figured the go ride part was implicit in between the "put air in your damn tires" and "if they bounce you around."
    you stopped in for nothing more than to rant. what do you expect in reponse? that's another thing i think is funny... wait... nevermind.
    maybe i can remember that you're sensitive.
    ooh... was that too much?
    (sorry, couldn't help myself)

    oh... i thought the "jeebus" was funny, given your username.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  40. #40
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    Quote Originally Posted by meltingfeather View Post
    didn't mean to come off as offended. i thought it was funny. i saw that thread and i guess i have a good memory. your username is memorable. perhaps the "BS" was a bit much... my apologies, but what do you really expect of people on a mountain bike forum if not to talk about mountain bike stuff they're interested in? and what reaction do you expect when you stop in to a thread to say nothing more than, "this discussion is stupid, y'all should go ride."
    You continue to misrepresent my post. I never called the discussion stupid, I never suggested riding instead of posting, and I never took a "holier-than-thou 'go ride' purist" tone, as you accused me of earlier.

    My one and only point remains: when determining one's best tire pressure, experience is a better guide than a formula. You're welcome to disagree, but please don't put words in my mouth for the purpose of refuting them.

    Apology accepted.

    -- GC

  41. #41
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    Quote Originally Posted by Ronnie View Post
    My reaction exactly. At 220lbs. plus my bike (±28lbs.) plus my Camelbak (±10lbs. I suppose) I'd be pumping up to about 39psi. in my Nobby Nic 2.35 or Purgatory 2.4. Both of which I've been using at 24psi.

    Ronnie.
    For Situations that I'm gonna do any fast DH for a ride I will actually go as high as 40 in the rear to stave off pinch flats. I normally am not @ 250 lbs (I gained 20+ lbs after the birth of my twins) and am in the process of training again for weight loss.
    The most important thing is what God thinks about it. He will have the final say.” – Joshua Stinebrink

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  42. #42
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    Quote Originally Posted by meltingfeather View Post
    since we're establishing the record, maybe you can point out the post where anyone suggests doing as you say, even the referenced study.
    sorry to have used the quotes. i figured the go ride part was implicit in between the "put air in your damn tires" and "if they bounce you around."
    you stopped in for nothing more than to rant. what do you expect in reponse? that's another thing i think is funny... wait... nevermind.
    maybe i can remember that you're sensitive.
    ooh... was that too much?
    (sorry, couldn't help myself)

    oh... i thought the "jeebus" was funny, given your username.

    Meltingfeather: forgive me if I don't continue this conversation. You seem to have a personal agenda here that I'm not interested in fueling. Again, sorry if my posts offend you; that wasn't my intention.

    --GC

  43. #43
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    Quote Originally Posted by Godless Communist View Post
    Meltingfeather: forgive me if I don't continue this conversation. You seem to have a personal agenda here that I'm not interested in fueling. Again, sorry if my posts offend you; that wasn't my intention.

    --GC
    i'm sorry i hurt your feelings.
    HTFU
    i've got no beef with you and i'm not bothered.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  44. #44
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    ...don't misundertand me,but i find that everybody has a share of the truth.

    Nobody can do anything without trying it live,and nobody can have as much info as using all the available sources with common sense...i was just naive asking something that i knew that i have to try-more-for myself and not asking for some magic filter...there are sooo many different factors,but even the different opinions helped me to come closer to my answer.I really thank you for this,all of you!

  45. #45
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    Quote Originally Posted by Ronnie View Post
    My reaction exactly. At 220lbs. plus my bike (±28lbs.) plus my Camelbak (±10lbs. I suppose) I'd be pumping up to about 39psi. in my Nobby Nic 2.35 or Purgatory 2.4. Both of which I've been using at 24psi.

    I though I would take a look at where the fore mentioned formula came from. The following is cut and pasted from FAQs on the Notubes website:

    "What is the max air pressure I can have for my tubeless set up?
    Do not inflate over 40psi. Use this simple equation to figure out a strarting point when running NoTubes tires (2.0-2.2) with our ZTR rims use this simple formula.
    Rider weight in pounds divided by 7 = x
    x-1 = Front tire pressure in PSI
    x+2 = Rear tire pressure in PSI"

    Notubes is not recommending this calculation for anything other than their tires and rims. They also mention limited sizes. I don't know their tires but they look to me like they are targeted at racers and not trail riders.

    Ronnie.
    Well, my interpretation of the stans formula is that you should not add bike plus luggage. So you have 39 lbs too much in your calc. Then again, I might be keying too much on the word "simple". And I do see that this formula only applies to their tires and rims. I still run within 5 psi for the 10 or so different tires I have tried.

    Use this simple equation to figure out a strarting point when running NoTubes tires (2.0-2.2) with our ZTR rims use this simple formula.
    Rider weight in pounds divided by 7 = x
    x-1 = Front tire pressure in PSI
    x+2 = Rear tire pressure in PSI"
    "The physician heals, Nature makes well" - real fortune cookie

    CCCMB trail work for trail access - SLO, CA

  46. #46
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    post deleted
    Last edited by Godless Communist; 06-22-2011 at 10:45 PM.

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    FWIW I also use the ZTR "Formula" but only on 26" wheels with very good results in both Conti 2.2 Race Kings and Schwalbe Racing Ralphs on ZTR 355 rims.

    On 29" Wheels I have found this to be a bit harsh. I've dropped the pressures. In fact it does show a similar formula, except on 29" wheels my pressures resulted in a Division by 8. ZTR Crest.

    Thus 26" Wheels:
    Rider Weight in pounds DIV 7 = x
    Front PSI = x -1
    Rear PSI = x +2

    29" Wheels:
    Rider Weight in pounds DIV 8 = x
    Front PSI = x -1
    Rear PSI = x + 2

    In my case 26" wheels = F @ 21PSI, R @ 24PSI
    29" Wheels = F @ 18PSI , R @ 21PSI

    These are all tubeless pressures and only my own personal take on this and it works well with very good results for me.

  48. #48
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    Quote Originally Posted by customfab View Post
    I like the stans rule of thumb, body weight + bike wight divided by 7. Anything lower than that is far past the point of diminishing returns.

    According to the rolling resistance article that was published by cyclingnews, 29'ers have a very comparable contact patch to a 26" tire. It's just longer than and narrower than the 26" counterpart.
    I checked out the stan's site after reading your post, and I couldn't find anywhere that said that lower than the formula wieght was bad, just that the formula is a good starting point.

    It also said don't go over 40psi yet using the formula I should be putting 44psi in my front tire and 45 in the rear (I'm a clyde).

    ETA: I didn't read below the first reply. I didn't realize this thread became such a pissing match. Customfab, I realize you were just giving a good starting point and it might not apply to the more beefy riders. :quietly backing away from thread:

  49. #49
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    Quote Originally Posted by slocaus View Post
    Well, my interpretation of the stans formula is that you should not add bike plus luggage. So you have 39 lbs too much in your calc. Then again, I might be keying too much on the word "simple". And I do see that this formula only applies to their tires and rims. I still run within 5 psi for the 10 or so different tires I have tried.
    Well why would you not add additional load to the calculation. The load after all is on the tires. This from the tire pages on Notubes.com:

    "To determine a starting tire pressure when running mountain bike tires tubeless on our ZTR mountain rims use this simple formula:

    Rider weight (with gear) in pounds divided by 7 = x

    x - 1 = Front tire PSI

    x + 2 = Rear tire PSI"

    Ronnie.
    The trouble with having an open mind is that people will insist on trying to put things in it.

  50. #50
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    Ok, I don't run Stan's find or tires. I run a DT Swiss with captain control tires. And to me they feel great pumped up to about 37lbs. If i run lower than 30lbs I pinch out cause I'm running tubes. But if I wasn't they just feel faster pumped?

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