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Old 01-08-12, 08:20 PM   #1
triggerracing
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Outfitting 29 inch wheels on 26 inch MB?

Been looking to purchase a 29er and came across an ebay listing where guy said he had replaced front tire with a 29, claimed better handling as far as going over rough terrain, roots, etc. Any opinions on this, pro's and con's opinions, what all would have to be done. Just curious, and if this has ever been discussed maybe someone could post a link, I couldn't find anything in a search.
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Old 01-08-12, 08:30 PM   #2
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http://forums.mtbr.com/650b-69er-new...se-292315.html
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Old 01-28-12, 08:13 PM   #3
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Typically, it's not a great idea. 29'ers are designed with very specific geometry to handle the 3" larger wheels. I'm guessing the guy who said it handled great might not really know what a great handling bike is. Ride your 26" bike, then if you could ride a Niner Air9, Specialized Camber, Marin NailTrial, Giant XtC, etc.

If your terrain is conducive to a 29er, a dedicated 29" bike will work wonders - roll over rocks and roots better, climb really well with those larger contact patches, descend confidently, etc.
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Old 01-29-12, 10:18 AM   #4
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A 26in wheel with 2in tires is about the same diameter as a 700 series rim with a 700 x 28c series road tire. Bigger than that and you get onto tire/fork arch safety clearance issues so a real 29er uses a larger fork size than a 26in MTB.700 series rims and tires are really only suitable for 26in frames if you restrict your tires to narrow road or cyclocross tires.
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Old 01-30-12, 09:52 PM   #5
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Typically, it's not a great idea. 29'ers are designed with very specific geometry to handle the 3" larger wheels. I'm guessing the guy who said it handled great might not really know what a great handling bike is. Ride your 26" bike, then if you could ride a Niner Air9, Specialized Camber, Marin NailTrial, Giant XtC, etc.

If your terrain is conducive to a 29er, a dedicated 29" bike will work wonders - roll over rocks and roots better, climb really well with those larger contact patches, descend confidently, etc.
I think you're full of s*it. There isn't one shred of scientific proof that 29" MTB wheels outperform 26" wheels. Sure, they perform differently, but whether that difference is better or worse is up the the rider and their preferences and riding style.
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Old 01-31-12, 12:16 PM   #6
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I think you're full of s*it.
I like your style.
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Old 02-01-12, 09:28 AM   #7
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If your terrain is conducive to a 29er, a dedicated 29" bike will work wonders - roll over rocks and roots better, climb really well with those larger contact patches, descend confidently, etc.
29ers don't have larger contact patches. The size of the contact patch depends entirely on the tire pressure, not on the size of the wheel.

They are a different shape, however.
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Old 02-01-12, 10:54 AM   #8
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I like where this thread is going. I think we're going to get some new ideas & original thoughts out of this for sure.
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Old 02-02-12, 09:48 PM   #9
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You would need to get a 29er fork, preferably one with less travel than the original fork. (A 29er wheel will hit the fork brace on most forks designed for 26" wheels). If you were going to spend that much money, you might as well spend a little more and just buy a complete 29er instead.
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Old 02-03-12, 06:33 PM   #10
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You would need to get a 29er fork, preferably one with less travel than the original fork. (A 29er wheel will hit the fork brace on most forks designed for 26" wheels). If you were going to spend that much money, you might as well spend a little more and just buy a complete 29er instead.
Or just a 26'' rigid front fork adjusted for 80mm of travel. thats just like a zero suspension corrected 29er fork. same ac height of 430+/-

that'll work.

I agree though, just go with a 29er or a 69er.
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Old 02-03-12, 06:40 PM   #11
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29ers don't have larger contact patches. The size of the contact patch depends entirely on the tire pressure, not on the size of the wheel.

They are a different shape, however.
Wait a minute . . . if the contact patch is longer, then, for the same width of a given tire at the same psi, wouldn't it stand to reason that the contact patch would be physically larger in sq in?
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Old 02-03-12, 08:32 PM   #12
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Wait a minute . . . if the contact patch is longer, then, for the same width of a given tire at the same psi, wouldn't it stand to reason that the contact patch would be physically larger in sq in?
Well... do the math. For a given tire pressure in pounds per square inch, the area A of the contact patch in square inches is the weight W on the tire divided by the pressure:

A = W / P

This does not depend on the shape of the tire. So, as long as P and W stay the same, if you make the contact patch longer, you also have to make it narrower, so that the area stays the same too.

A 700x32 tire at 60 psi will have exactly the same size (i.e. surface area) contact patch as a 26x2.1 tire at 60 psi, or a 24x1.75 tire at 60 psi.
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Old 02-03-12, 10:29 PM   #13
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Some of that makes sense except that a 700 x 32c tire isn't a 29er. It's Imperial measurements are actually only 28 x 1 1/4 inches. Even a 700 x 50 isn't a 29er. It's actually only 28 x 2.00 inches. Something in the order of a 57-622 would give 29 x 2.25 inches.


The other thing is that I can't think of any good reason to run any tire width of over 1 1/2in at 60PSI. Anything from 25 to 45 would be more reasonable.


So yeah, in similar tire widths and with similar tire pressures, a 29er would definately have a slightly greater contact patch. It's probably debatable if that's of any real advantage though. The flip side is that a smaller rim is naturally stronger and more rigid with a similar spoke count.
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Old 02-04-12, 06:25 AM   #14
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Some of that makes sense except that a 700 x 32c tire isn't a 29er. It's Imperial measurements are actually only 28 x 1 1/4 inches. Even a 700 x 50 isn't a 29er. It's actually only 28 x 2.00 inches. Something in the order of a 57-622 would give 29 x 2.25 inches.
I picked those numbers at random to make the point that the width of the tire is irrelevant to the size of the contact patch.

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So yeah, in similar tire widths and with similar tire pressures, a 29er would definately have a slightly greater contact patch.
No. The surface area of the contact patch depends on two things, and two things only:

(1) The weight on the tire
(2) The inflation pressure of the tire.

People typically run fat tires at lower pressure, which gives a larger contact patch, but that is because of the lower pressure, not the geometry of the tire. Fat tires do make it possible to run low pressures: try running a 700x23c tire at 30 psi, and you'll pinch flat as soon as you sit on the bike.

It also seems reasonable that frame geometry is going to have an effect on the distribution of weight between the front and rear tires, and therefore things like rear-wheel traction on climbs.
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Old 02-04-12, 10:05 AM   #15
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The surface area of the contact patch depends on two things, and two things only:

(1) The weight on the tire
(2) The inflation pressure of the tire.
I'm calling shenanigans on that one!

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Old 02-04-12, 11:21 AM   #16
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Old 02-04-12, 12:33 PM   #17
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I'm calling shenanigans on that one!
OK. Believe what you wish. Physics doesn't care.
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Old 02-04-12, 01:04 PM   #18
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OK. Believe what you wish. Physics doesn't care.
I think your physics is book 'in a vacuum' physics not out in the real world physics.

Are you saying that a 700x25 tire at 60psi has the same contact patch as a 700x60 tire at 60psi?

unpossible. I don't care that your Physics doesn't care. I think your Physics has been hitting the pipe too long.

the next thing you'll be telling us is to clean our brake rotors with moose piss.
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Old 02-04-12, 05:32 PM   #19
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OK. Believe what you wish. Physics doesn't care.
Yeah - you're right - physics doesn't care. Problem is there's a lot more forces at work in a tire than just load and tire pressure. And the general laboratory statement that usually accompanies this kind of claim is : "All other things being equal."

But change the tire profile, the sidewall construction, the rubber composition or the material and none of that's straight forward any more. Because the "All other things being equal" part just went out the window.

It's all been tested in the real world and confirmed that tires are sneaky, unpredictable little critters that don't always behave according to the laws of physics we'd like them to.

http://www.performancesimulations.co...on-tires-1.htm

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Old 02-05-12, 10:14 AM   #20
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But change the tire profile, the sidewall construction, the rubber composition or the material and none of that's straight forward any more. Because the "All other things being equal" part just went out the window.
Sure. A rigid sidewall could carry part of the load on the tire, which would make the contact patch smaller than it would otherwise be given the pressure. Likewise, elasticity in the tread might make the contact patch a little larger than it might otherwise be. So two different tires on the same rim at the same pressure will have slightly different contact patch sizes, depending on the details of the tire construction. None of these things changes the underlying physics a bit, and none of these things have anything at all to do with the "29ers have a bigger contact patch" myth. Equilibrium demands that the total force pushing up on the wheel be equal to the total force pushing down on the wheel. Period.

If you really want to believe that tires are magic objects capable of defying basic physical constraints, I really don't know what to say. This is the same kind of logic that leads people to buy $100 digital cables for their home audio system.

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Old 02-05-12, 10:42 AM   #21
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Sure. A rigid sidewall could carry part of the load on the tire, which would make the contact patch smaller than it would otherwise be given the pressure. Likewise, elasticity in the tread might make the contact patch a little larger than it might otherwise be. So two different tires on the same rim at the same pressure will have slightly different contact patch sizes, depending on the details of the tire construction. None of these things changes the underlying physics a bit, and none of these things have anything at all to do with the "29ers have a bigger contact patch" myth. Equilibrium demands that the total force pushing up on the wheel be equal to the total force pushing down on the wheel. Period.

If you really want to believe that tires are magic objects capable of defying basic physical constraints, I really don't know what to say. This is the same kind of logic that leads people to buy $100 digital cables for their home audio system.
I'm thinking you didn't read the article I linked to.
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Old 02-05-12, 10:59 AM   #22
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I'm thinking he hasn't read anyone's entire comment except for mine. Makes sense though, my argument totally carries the most weight here
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Old 02-05-12, 11:44 AM   #23
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I'm thinking you didn't read the article I linked to.
The pressure on the contact patch multiplied by the area of the contact patch is equal to the weight on the wheel. This is Newton's Third Law. It is a basic law of the universe. It is true for bike tires, for car tires, for train wheels, for wagon wheels, for the tires on a 747, and for the wheels on a rickshaw. It is true whether the tire is made from rubber, or steel, or marshmallows, or granite, or unobtanium. It is true on Earth, it is true on the moon, it is true in orbit, it is true on Jupiter, and it is true in the Andromeda galaxy.

Anybody who claims to have measured differently either measured wrong, or doesn't understand his measurements. I suggest a $1000 HDMI cable to go with those magic tires.

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Old 02-05-12, 04:30 PM   #24
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But the shape of the tire is irrelevant
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Old 02-05-12, 06:52 PM   #25
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Sure. A rigid sidewall could carry part of the load on the tire, which would make the contact patch smaller than it would otherwise be given the pressure. Likewise, elasticity in the tread might make the contact patch a little larger than it might otherwise be. So two different tires on the same rim at the same pressure will have slightly different contact patch sizes, depending on the details of the tire construction. None of these things changes the underlying physics a bit, and none of these things have anything at all to do with the "29ers have a bigger contact patch" myth. Equilibrium demands that the total force pushing up on the wheel be equal to the total force pushing down on the wheel. Period.

If you really want to believe that tires are magic objects capable of defying basic physical constraints, I really don't know what to say. This is the same kind of logic that leads people to buy $100 digital cables for their home audio system.
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The pressure on the contact patch multiplied by the area of the contact patch is equal to the weight on the wheel. This is Newton's Third Law. It is a basic law of the universe. It is true for bike tires, for car tires, for train wheels, for wagon wheels, for the tires on a 747, and for the wheels on a rickshaw. It is true whether the tire is made from rubber, or steel, or marshmallows, or granite, or unobtanium. It is true on Earth, it is true on the moon, it is true in orbit, it is true on Jupiter, and it is true in the Andromeda galaxy.

Anybody who claims to have measured differently either measured wrong, or doesn't understand his measurements. I suggest a $1000 HDMI cable to go with those magic tires.
Nawwww .... Newton's third law is : The mutual forces of action and reaction between two bodies are equal, opposite and collinear.

You're just assuming that the forces at work are entirely limited to what you've listed. Typical difference between theory and reality.

Even based on your own oversimplified analysis you've overlooked a little detail. A larger wheel has more metal in it and a larger tire and tube have more rubber in them so a 29er wheelset using the same build components and tires would weigh more than a 26er. That alone would change the load on the tire with the same rider and result in a larger contact patch. Even using your own slightly linked view on things.


PS: Why do I suspect you yourself got sucked into buying those digital cables you're whining about?
'Nuff said - think I've already wasted too much time on this thread.

Last edited by Burton; 02-06-12 at 04:14 AM. Reason: Simple info added for the benifit of tunnel vision scientifics
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