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Discussion Starter #1
Just wondering... You have to admit; sometimes the 29er bandwagon sounds a lot like a political convention.

Actually, I do want to understand how a 29er wheel can have a bigger footprint, better traction, and less rolling resistance -- as has been claimed more than once in this forum. And for the life of me I can't understand how the heavier 29er wheel and tire (and it has to be heavier than a standard sized wheel and tire) would ever allow you to climb better, particularly on climbs lasting for tens of minutes.

I was all set to join the 29er parade, but then my wife (probably motivated by the thought of saving that $2k I was ready to sink into the new bike) asked how could a bike with heavier wheels possibly serve me better in the type of races I like and excel at (100 mile mtb races with big, long climbs). As she knows, in these races it's all about climbing -- not about the descent or the technical issues. I had even justified to her the need for expensive light wheels and tires by droning on and on about how mtb racing was all about having to constantly accelerate back up to speed due to the technical terrain, so she immediately pointed out the inconsistencies in my pro-29er arguments.

I like to spend money and accumulate new toys as much as the next guy, so I need someone to provide me with a logical, sound argument to counter my wife's point (no bs here, she has a PhD in Biochemistry and is far too smart to be fooled by lame technical arguments).

Thanks!
 

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My gloves stink
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No, but 29ers will find Osama Bin Laden

PeT said:
Just wondering... You have to admit; sometimes the 29er bandwagon sounds a lot like a political convention.

Actually, I do want to understand how a 29er wheel can have a bigger footprint, better traction, and less rolling resistance -- as has been claimed more than once in this forum. And for the life of me I can't understand how the heavier 29er wheel and tire (and it has to be heavier than a standard sized wheel and tire) would ever allow you to climb better, particularly on climbs lasting for tens of minutes.

I was all set to join the 29er parade, but then my wife (probably motivated by the thought of saving that $2k I was ready to sink into the new bike) asked how could a bike with heavier wheels possibly serve me better in the type of races I like and excel at (100 mile mtb races with big, long climbs). As she knows, in these races it's all about climbing -- not about the descent or the technical issues. I had even justified to her the need for expensive light wheels and tires by droning on and on about how mtb racing was all about having to constantly accelerate back up to speed due to the technical terrain, so she immediately pointed out the inconsistencies in my pro-29er arguments.

I like to spend money and accumulate new toys as much as the next guy, so I need someone to provide me with a logical, sound argument to counter my wife's point (no bs here, she has a PhD in Biochemistry and is far too smart to be fooled by lame technical arguments).

Thanks!
I agree that the pro/con 29er debate is at times entirely emotional. For the most part, people don't look at the facts and make a rational decision with this or anything else. They go with their gut and then look for rationale to justify their decision. The mind justifies the choices of the heart.

I wouldn't presume to argue with someone with anything more than a grade skool education, let alone someone with a PhD. However...

Any argument that can be made against the 29er by comparison with a 26 inch wheel bike could also be made against a 26 relative to a 24 inch wheel. Why would anyone want a heavy 26 inch wheel when they can have a lighter 24 inch wheel? Why not even smaller?

Similarly, a case could be made for putting the skinniest tires on your bike that you can find. Hey, reduced weight and reduced drag, right?

The answer, of course, is that there's more to a wheel than how much it weighs. Back in the days when Gary Fisher visited this forum, he claimed to have spreadsheets showing that the flatter angle of approach of the larger wheel created less loss of momentum on bumpy terrain.

I don't think 29ers climb better in conditions that are relatively smooth, with relatively good traction. They climb better in the nasty stuff, due to the bigger footprint and lower tire pressure.

I have no direct experience on this point, but I would think the less-punishing ride afforded by the bigger wheels would pay off big dividends fatigue-wise in an endurance ride.

Just my non-technical 2-cents worth.

~Appendage
 

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Discussion Starter #4
Long climbs are about weight...

Appendage said:
Any argument that can be made against the 29er by comparison with a 26 inch wheel bike could also be made against a 26 relative to a 24 inch wheel. Why would anyone want a heavy 26 inch wheel when they can have a lighter 24 inch wheel? Why not even smaller?

Similarly, a case could be made for putting the skinniest tires on your bike that you can find. Hey, reduced weight and reduced drag, right?
I would actually say that the skinniest/lightest tire or wheel actually does improve performance on a long climb. I can climb virtually any dirt track faster on my cyclocross bike with 32c knobby tires than I can on my mtb. If it's loose and rocky that's not necessarily true, but then I might well be able to run up it faster anyway. The only real difference between the two bikes is 300 g more of tire and a bigger contact patch on the mtb. However, I can't go down the trail on the cyclocross bike much faster than I got up it (pinch flat issues if nothing else) so it's not the bike of choice for most of my off-road epics. It's taken me years of experimentation to find the happy medium of tire width and tread style to maximize my performance on long climbs and descents.

I would love to see the technical arguments/spreadsheets for "angle of attack" of the 29er wheel that Gary Fisher claimed to have. I saw the "10% decrease in rolling resistance" mentioned in the FAQ, but I don't know how much of that percentage is reality and how much is hype. Testimonial/anecdotal evidence only works for me when it's my testimonial or my anecdote...
 

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29ers are the key to perpetual motion.

Fisher used to have this on his webpage (back in the 2002 archives)

*The concept is simple. If my skateboarding son hits a 1" stone with his 2" diameter wheels, the board stops hard and Nick goes flying – The small wheel's angle of attack on the stone is so severe that it cannot roll over the rock

When I used to have a 26er steel hardtail and my 29er aluminum hardtail, I was amazed by how much smoother the 29er bike rode over the same surfaces.

The bigger wheels do take more energy to get going, but once they get rolling they do hold their speed much better. There isn't too much of a difference in the weight of the wheel/tire combo.

I agree that if you can get the skinnier tires to hook up they would be the faster setup, however, if you need the extra air volume of a bigger tire for rocky terrain you may need to compromise. I tried running Mutanoraptors on my 29er, and although the bike was much more nimble, there just wasn't enough air volume to cushion out the rocks.

Isn't your cyclocross 700c (or essentially a 29er)?

If you're ever out in AZ bring the cyclocrosser, and we'll swap for a ride. I'd love to try a cyclocross bike!




PeT said:
I would actually say that the skinniest/lightest tire or wheel actually does improve performance on a long climb. I can climb virtually any dirt track faster on my cyclocross bike with 32c knobby tires than I can on my mtb. If it's loose and rocky that's not necessarily true, but then I might well be able to run up it faster anyway. The only real difference between the two bikes is 300 g more of tire and a bigger contact patch on the mtb. However, I can't go down the trail on the cyclocross bike much faster than I got up it (pinch flat issues if nothing else) so it's not the bike of choice for most of my off-road epics. It's taken me years of experimentation to find the happy medium of tire width and tread style to maximize my performance on long climbs and descents.

I would love to see the technical arguments/spreadsheets for "angle of attack" of the 29er wheel that Gary Fisher claimed to have. I saw the "10% decrease in rolling resistance" mentioned in the FAQ, but I don't know how much of that percentage is reality and how much is hype. Testimonial/anecdotal evidence only works for me when it's my testimonial or my anecdote...
 

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Not faster on smooth climbs

I doubt there's any noticeable difference on a smooth climb. Perhaps the extra pound or so of weight on the 29er will slow you down a few seconds on a long climb, but it's going to be basically a wash. But as has been pointed out already, a 650c wheeled road bike with no big chainring and 19c tires would be best - if it's smooth enough. Sounds like a 29er with ~40c cross tires might be ideal for you, or perhaps 1.9" mountain bike tires. Provided, of course, that you actually want to try one.

Keeping in mind that this is a mountain biking forum, however, 29ers have enough advantages in terms of handling for *many* people to prefer them. I honestly don't think there's much of a speed differential on short distance rides - the reports many people were posting about doing 20% faster times on their favorite trail and such were baloney, IMO. But, all things being equal (meaning, both bikes are hardtails, both are using approximately the same tires, etc) a 29er will beat you up quite a bit less in even moderately rough terrain - which means that for really long races or rides, there's probably a small advantage on the 29er side.

Most people ride the big wheels for handling reasons, not for performance reasons. Though I think there are performance benefits to be had.

-Walt
 

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Walt's post reminded me... somewhere on here, someone posted a thread about a road bike (or cyclocross) winning a MTB race.


Walt said:
I doubt there's any noticeable difference on a smooth climb. Perhaps the extra pound or so of weight on the 29er will slow you down a few seconds on a long climb, but it's going to be basically a wash. But as has been pointed out already, a 650c wheeled road bike with no big chainring and 19c tires would be best - if it's smooth enough. Sounds like a 29er with ~40c cross tires might be ideal for you, or perhaps 1.9" mountain bike tires. Provided, of course, that you actually want to try one.

Keeping in mind that this is a mountain biking forum, however, 29ers have enough advantages in terms of handling for *many* people to prefer them. I honestly don't think there's much of a speed differential on short distance rides - the reports many people were posting about doing 20% faster times on their favorite trail and such were baloney, IMO. But, all things being equal (meaning, both bikes are hardtails, both are using approximately the same tires, etc) a 29er will beat you up quite a bit less in even moderately rough terrain - which means that for really long races or rides, there's probably a small advantage on the 29er side.

Most people ride the big wheels for handling reasons, not for performance reasons. Though I think there are performance benefits to be had.

-Walt
 

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29ers vs 26ers

I agree with some of the discussion here, but like it has been said. Borrow one, ride it, and see for yourself. I did just that. I was completely blown away with what I have found. I climb much better/faster on the 29er. Despite the terrain being smooth or rocky. Also, I find that they roll a lot faster on flat surfaces with little or no effort. I had a race this last summer where it had a lot of flat sections in it. I found that I was dropping people on their 26ers in those sections. If there is technical stuff like rock gardens, than I generally just point the wheel and go through it without trying to choose the best line. The bigger wheels just seem to float over stuff much better. The only downside thus far for me, is that I find it a little more difficult to manuveur the bike in tight technical sections like a switchback or something.

So, find a 29er, if you can, and try it out for yourself.

Also, there is a FAQ thread on 29er's on this board. Search for it and read it. You should be able to get all of your questions answered there.

Love the 29er. I don't ever see myself going back to a kiddie bike.
 

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To me the issue is rolling resistance. My hardtail 29er weighs in at 23.9 w/ a cx-1. Plenty light enough. I think wheel weight is a myth. The issue is just plain ol’ weight. Wheel weight vs acceleration is an issue for hot-rods and motorcycles, things that put out lots of power and undergo dramatic acceleration. A biker just doesn’t make enough power to really worry about wheel weight (any more than any other form of weight). I run super light weight wheels because I want a light bike not because I think that rotating weight is more important than any other type of weight. Although if you want to argue that wheel weight is more important than other weight the real issue isn’t acceleration but sprung vs unsprung weight. Second any increase in weight (wheel or otherwise) is more than offset by less rolling resistance. I also like long rides and races, the 29er is faster hands down. On road smooth surfaces a road bike will always be faster, but on bumpy off-road riding the 29er benefits kick in.

I find the 29er generally climbs faster and on longer rolling climbs the benefit is enhanced. Again the issue is rolling resistance. The 29er will hold its speed better so it rolls faster with less effort from the rider. This is crucial, especially if you are doing 100mile races or longer because by the time you load yourself down with gear (assuming the race is self supported) you are on a heavy bike anyway so you need it to roll as best as possible. In a race like that the advantage is not so much weight as your ability to move the weight smoothly and efficiently over the terrain. A 29er means you can carry more food, but will need less of it

I also think the bigger foot print issue is a bit of a red herring. All things being equal a 2.1 29er tire and a 2.1 26er tire at the exact same pressure will have the same footprint BUT the footprint will be shaped differently. The Foot print is a result of tire pressure and the way a tire deforms at pressure you should have the same amount of tire on the ground, BUT the 26er tire will be squished out and deformed wider than an 29er tire. Also, all things are not really equal because 29ers can run lower pressures, because of the high volume tire so that is where the bigger footprint idea comes from, lower tire pressure. Again the issue is rolling resistance less tire deformation equals less rolling resistance. The key is in changing the shape of the foot print.

Check out "Bicycling Science" from the MIT press. It is full of reasons why rolling resistance is a huge issue in biking, and will impress the PHD spouse. There is a whole chapter on why bigger wheels are better than smaller wheels. So that’s my rant. Rolling resistance is more important than weight so 29ers are better (in general I’m not saying that a 30lb 29er will beat a 22lb 26er but that my 23.9lb 29er is faster under me than a equal or slightly lighter 26er). Try one and see for yourself, also if you do ride one post back here with your thoughts.

Good luck

Adam


QUOTE=PeT]Just wondering... You have to admit; sometimes the 29er bandwagon sounds a lot like a political convention.

Actually, I do want to understand how a 29er wheel can have a bigger footprint, better traction, and less rolling resistance -- as has been claimed more than once in this forum. And for the life of me I can't understand how the heavier 29er wheel and tire (and it has to be heavier than a standard sized wheel and tire) would ever allow you to climb better, particularly on climbs lasting for tens of minutes.

I was all set to join the 29er parade, but then my wife (probably motivated by the thought of saving that $2k I was ready to sink into the new bike) asked how could a bike with heavier wheels possibly serve me better in the type of races I like and excel at (100 mile mtb races with big, long climbs). As she knows, in these races it's all about climbing -- not about the descent or the technical issues. I had even justified to her the need for expensive light wheels and tires by droning on and on about how mtb racing was all about having to constantly accelerate back up to speed due to the technical terrain, so she immediately pointed out the inconsistencies in my pro-29er arguments.

I like to spend money and accumulate new toys as much as the next guy, so I need someone to provide me with a logical, sound argument to counter my wife's point (no bs here, she has a PhD in Biochemistry and is far too smart to be fooled by lame technical arguments).

Thanks![/QUOTE] :) :)
 

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PeT said:
Just wondering... You have to admit; sometimes the 29er bandwagon sounds a lot like a political convention.

Actually, I do want to understand how a 29er wheel can have a bigger footprint, better traction, and less rolling resistance -- as has been claimed more than once in this forum. And for the life of me I can't understand how the heavier 29er wheel and tire (and it has to be heavier than a standard sized wheel and tire) would ever allow you to climb better, particularly on climbs lasting for tens of minutes.

I was all set to join the 29er parade, but then my wife (probably motivated by the thought of saving that $2k I was ready to sink into the new bike) asked how could a bike with heavier wheels possibly serve me better in the type of races I like and excel at (100 mile mtb races with big, long climbs). As she knows, in these races it's all about climbing -- not about the descent or the technical issues. I had even justified to her the need for expensive light wheels and tires by droning on and on about how mtb racing was all about having to constantly accelerate back up to speed due to the technical terrain, so she immediately pointed out the inconsistencies in my pro-29er arguments.

I like to spend money and accumulate new toys as much as the next guy, so I need someone to provide me with a logical, sound argument to counter my wife's point (no bs here, she has a PhD in Biochemistry and is far too smart to be fooled by lame technical arguments).

Thanks!
If weight was everything, we would all be rollerblading up rocky single tracks.
 

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No but they can ...

... help heal a broken heart ;)

Take a look at:

http://www.electric-bikes.com/physics.htm

With calculator in hand you can calculate the power required to ride.
up a grade at some speed with some tire rolling resistance.

Coefficient of rolling resistance according to the page is:

0.008 for a 700c road bike
0.020 for a mountain bike tire
0.040 for a 9 inch scooter tire

Power to overcome rolling resistance is like going up a 2%
grade. So lower rolling resistance reduces the grade ...

-r
 

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PeT said:
Actually, I do want to understand how a 29er wheel can have a bigger footprint, better traction, and less rolling resistance -- as has been claimed more than once in this forum.
Guess it's time to trot out some old links:

http://www.precisiontandems.com/artbillwheelsize.htm

http://www.gtgtandems.com/tech/700-26.html

-------------------------------------------------------------------------------

Pasted from the precisiontandems site:

WHEEL SIZE 26 vs 700C

Testing 26 vs 700

By Bill McCready, president Santana Cycles, Inc.

A Posting from Bill at Santana

Because of an aol software problem we lost a week of postings and only caught the tail end of the most recent 700c vs 26" battle.

Many of the comments were on-target and should be amplified.

First, the physics of the 26vs700 discussion are only meaningful if we standardize the other variables: rim width, tire width, tread pattern and inflation. To perform comparisons here at Santana we used two diameters of otherwise identical Avocet tires mounted to two diameters of otherwise identical Sun rims. We installed these wheels in frames built from identical tubesets. The frame geometries differed only to the degree that the resulting bottom bracket heights were equal. Components other than the wheels were identical. We inflated the tires to 115psi.

Between 700c and 26" there is no difference in the AREA of the contact patch. "Pounds per square inch" means just what it says. If we know the loaded weight of a tandem and the inflation of the tires we can accurately predict the area of the contact patch. Actually, if we know any two of three variables (weight, inflation and the size of the contact patch) we can calculate the third. Tire diameter has no effect.

Tire diameter does, however, effect the SHAPE of the contact patch. Because the 26" wheel has a diameter that is 11% smaller (559mm vs 622mm bead seat diameter) the resulting contact patch or footprint of a 26" tire is both 11% shorter and 11% fatter.

The shape of the footprint affects handling. With all other things equal (especially fork rake and bottom bracket heights) the rounder contact patch of a 26" front tire dramatically improves low speed maneuverability. Conversely, high speed stability is enhanced by the longer and narrower footprint of a 700c front tire. While the two tires will feel different in a hairpin curve--the smaller tire corrects quicker and the larger tire holds a smoother line--because cornering speed is a function of area and grip, maximum speed through a sharp turn is the same.

If they both corner at the same speed, is either wheel size more efficient? Yes. Because of its smaller diameter, the 26" tire is forced to deform more to apply its equal-area-yet-fatter contact patch to the ground. When we put the same weight on both bikes it's easy to observe more "bulge" in the sidewall where the 26" tires meet the ground. Greater tire deformation (sidewall flex and tread squirm) equals greater internal tire friction; the leading cause of rolling resistance.

Why not compensate for the extra rolling resistance by inflating 26" tires to higher pressures? While many of us fear blowouts, the leading justification for lower pressures (and wider tires) is COMFORT. Because the smaller wheels start with a comfort handicap (smaller wheels are less compliant), higher pressures won't be a popular option.

If rolling resistance effects speed, why do leading triathletes use 26" tires?

For certain events (triathlons, track pursuits and time trials) rolling resistance is less important than the frontal area of the tire--in these no-slipstreaming events a solo bike with 26" wheels has an advantage. But for pack cycling events (criteriums, sprints and road races) the aerodynamic advantage of the smaller wheel is not great enough to offset increased rolling resistance.

Is the wheel efficiency equation different for tandems? Yes. Compared to a solo bike, a tandem tire's frontal area is roughly half as important (twice as much power to push each tire through the wind). Further, a tandem's doubled weight can make sidewall deformation and rolling resistance twice as critical. Subsequently, there are no on-road races where a tandem with 26" wheels will be faster.

If a 700c tandem is faster, why does Santana offer nearly twice as many models with 26" wheels?

Even though a 700c wheel is actually slightly heavier than a 26" wheel, the difference in "bash-strength" (the ability to survive impacts) is enough to render a 700c wheel damned near useless for rutted jeep trails and urban curb-hopping.

If you want one tandem that does it all, 26" is the only wheel size that makes sense. While a 26" mountain tandem can easily be converted into a pavement scorcher that will keep you abreast of the fastest roadies on their solo bikes, a tandem with 700c wheels is too fragile for real mountain biking.

And even if you never plan to venture off pavement, the "bigger is faster" argument is limited by the size of the riders--tandems built around 700c wheels are inefficiently tall for captains shorter than about 5'7".

Prove it to yourself section:

Because one or two netizens might (again) find it easier to malign the messenger than to attempt to understand the accuracy of the message, I've included the following quick and simple experiments to allow everyone to test the verity of this posting.

Experiment 1: To confirm identical contact AREA and differing footprint SHAPE use an ink pad, a sheet of paper, a bathroom scale and a pair of different diameter wheels with similar width rims. Install similar-width smooth tires--worn out tires from the discard pile of a local bike shop work great. Inflate both tires to the same pressure before testing.

Experiment 2: To determine that tire deformation effects rolling resistance attach any bike to a wind or magneto trainer. After riding a bike for a couple of minutes, overtighten the adjustable roller (or lower the chainstay support pad) and try it again. Where does all that extra energy go? If you can stand to ride the "tight" setup for a few minutes you'll confirm that a bulging tire converts energy into heat.

Experiment 3: To discover the diameter-dependent differences in stability and handling visit a Santana dealer and ride a Visa & Vision, or Arriva & Fusion, or Sovereign & Encore back to back. These three 700c / 26" model-pairs have the same tubesets, neutral handling characteristics and identical components (except rims and tires). Experienced tandem riders will easily note the differences in crawl-speed maneuverability and high speed stability. If the dealer is willing (most are) bring along your cyclo-computer and tape or tie-strip it to each model before coasting down the same hill to determine the speed difference.

Happy trails

Bill

----------------------------------------------------------------

Pasted from the gtgtandems site:

700c vs. 26": Testing Reveals Best Choice for You

by Bill McCready, President of Santana Cycles
Santana sells similar numbers of tandems with both wheel sizes and has no ax to grind.

Four years ago a respected bike designer confidently predicted the impending demise of 700c tandems. While this was not particularly frightening to Santana (we had designed and promoted 26" road tandems as far back as 1983), it also didn't ring true. I've watched as hundreds of customers tested both sizes before making a decision --- was it possible the majority who chose 700c tandems were mistaken?

Many people who advocate one size over the other insist on comparing fat 26-inch tires and skinny 700c tires. Some make recommendations based on the availability of a particular tread pattern. Others confuse the issue by comparing 700c tandems designed for pavement with 26" tandems designed for dirt. Santana's question was simple: if you were to eliminate the differences in tread width, tread pattern, inflation pressure and frame geometry, is a 26" wheel superior to a 700c wheel strictly on the basis of its diameter? If yes, why? In an attempt to discover the truth, we prepared some test tandems and asked a number of teams to evaluate them.

To reduce extraneous perceptions our test bikes used identical tubing and direct-lateral frame style, 26" and 700c rims produced from the same extrusion, and tires with the same width and tread pattern inflated to the same pressure. The honest attempt was to discover the best size --- after all, life here at Santana would be a whole lot simpler if we could standardize on 26" wheels.

But first, some background. The argument over wheel size did not start with tandem riders. Alex Moulton of England produced pro racing bikes with 14-inch sew-up wheels in the late-'60s. In the mid-'70s, Tarn Cycles of Chicago built a series of Campy-equipped full-race singles (and at least one tandem) with 20-inch wheels. In the early-'80s California's first production mountain bikes, built by Victor Vincente, were equipped with 20" wheels. All of these builders argued that bikes with smaller wheels would be superior due to lower weight, stronger wheels, quicker acceleration, and less wind resistance.

Critics of these designs claimed bikes with smaller wheels were slower and less stable. While slower was difficult to prove, some organizers banned small-wheeled bikes from racing (where they might have disproved the "slower" argument) fearing "diminished gyroscopic effect" would inevitably lead to crashes in pack racing events.

Fred de Long, Technical Editor of Bicycling, disproved the "gyro" theory in the late '60s when he assembled a unique bike with side by side front wheels --- a normal front wheel plus an identical counter-rotating wheel slightly above and to one side. The second wheel (which rotated at the same speed but never touched the ground) offset the gyro effect of the first. His finding: a bicycle's gyro-stability is a myth. He postulated (and I agree) that all us cyclists remain upright by continually steering through/across the path of our imminent fall. (You can quickly prove this to yourself by riding a bike with an over-tightened headset --- the results are extremely convincing).

Three years ago there was yet another resurgence of interest in road-racing bikes with smaller-than-700c wheels. For a time you could buy road racing bikes with 26-inch wheels from many serious builders including Serotta and Paramount.

While a few large-frame time trial and triathlete bikes are still built around a pair of 26" wheels, the designers of these bikes are admittedly chasing tiny aerodynamic and weight advantages that will be lost on a tandem (where doubled power reduces the significance of these advantages by 50%).

So what did we learn during Santana's testing? Our panel of testers uniformly found 700c tandems were more stable at higher speeds. Most testers also believed the tandems with 700c wheels were faster. The difference in "feel" was substantial enough so that an envisioned follow-up "blind" test with carefully shielded-from-view wheels was deemed unnecessary.

Why were 700c tandems clearly more stable? At the time of the testing, none of us had a clue. I later developed a theory, first published three years ago, that the answer was due to the shape of the tires' contact patch (footprint). If the same mass is supported on tires inflated to the same pr essure, the area of the contact patch must also be the same --- this is, after all, the meaning of p.s.i. or "pounds per square inch." The difference in wheel diameter causes the footprint of the bigger wheel's tire to be more elongated than the footprint of the tire on the smaller wheel. I reasoned a longer footprint would provide greater directional stability at high speeds (as is the case with longer skis, surfboards, and skates). Until someone comes up with an alternative explanation, this theory not only explains the increase in high speed stability, it also explains why off-road riders might reasonably prefer 26-inch wheels --- the rounder footprint provides less steering resistance and easier maneuvering at low speeds.

While my original "footprint" theory explained stability, it didn't explain the perceived difference in speed. I originally thought it probable our testers were mistaken about a speed advantage for 700c wheels. If they actually rode faster with 700c wheels, I felt certain it was an ephemeral result of enhanced rider confidence. Put simply, if riders on 700c test tandems felt more confident at higher speeds (because of stability resulting from the shape of the footprint), this confidence might allow a temporary increase in performance. If there was an enduring speed difference, it seemed likely to me the lighter and smaller 26" wheels would have the advantage.

Some of you might think the difference in diameter between 26" and 700c is too small to matter. Actually, even though we all know 700c rim is slightly smaller than 27" rim, a 700c rim is a full 2-1/2 inches larger than 26" rim.

Two-and-one-half inches?! How can difference between 26" and 27" exceed 2-1/2"?! Answer: a ridiculous tradition dictates that sizes of bicycle wheels --- unlike car and motorcycle wheels --- indicate the nominal outside diameter of the TIRE, and not the actual diameter of the rim. While the out side diameter of a traditional 26-inch "balloon" tire is about an inch smaller than the original 27-inch "racing" tire, the rim is nearly 3 inches smaller. The same tradition exists in Europe where there are no fewer than 4 diameters of rims that accept "650" tires (labeled 650-A through 650-D). To compare the "real" size of a rim or tire you must know the "bead seat diameter." Fortunately, this number is found molded into the sidewall of most tires. The real size of a 27" rim is 630mm (about 24.8"), a 700c rim has a bead seat diameter of 622mm, and the "26-inch" rim found on tandems a nd mountain bikes is only 559mm (a mere 22"). If matching width tires are installed, the outside diameter of a 622 (700c) tire is 63mm (2.5") larger than the outside diameter of a 559 (26") tire.

I've since realized the testers who reported faster speeds on a tandem with 700c wheels were correct --- and here's why:

Remember that the area of a tire's contact patch (or footprint), because it is purely a function of weight and inflation, owes nothing to the diameter or width of a tire. It follows that our test tandems with 11% smaller wheels produced footprints that were exactly 11% shorter and, therefore exactly 11% wider. Shorter explains the stability difference and wider explains the speed difference.

Why is wider slower? To apply the extra width against the pavement, the tread and sidewall of the smaller yet equally-wide tire is forced to undergo a great deal of additional contortion --- and tread and sidewall squirm are the primary causes of rolling resistance.

Is the difference in rolling resistance enough to produce a significant difference in speed? Because rolling resistance is a much smaller factor than wind resistance, until a few months ago I would have guessed no. Today I'm convinced otherwise --- whereas aerodynamic and weight differences are probably only half as significant for tandems (because of doubled power), internal tire friction is probably twice as critical (because of doubled mass). Even if 26" someday proves itself the superior size for road racing singles (it hasn't yet), the optimal wheel size for a racing tandem will always be larger.

While determining an exact difference in rolling resistance would be fairly easy, the effect on speed is difficult to ascertain. My best current estimate is a 26" tandem with equivalent rims, tread width, tread pattern and inflation will be 2-4% slower than a 700c tandem. While this will be a small difference for those who want the flexibility of using their tandem off-road, those interested in ultra-fast pavement rides might expect a cruising speed difference of up to one mile per hour (or a century finishing time difference of 5-10 minutes).

A couple of final thoughts about ultra-fast road rides on a 26" tandem. To achieve the same gearing as a 700c road tandem with a 54 tooth chainring, a 26" racing tandem will need a 60 tooth ring --- which is incompatible with the curvature of modern front derailleurs. And when you want to stop, because braking power is a squared function of effective brake radius, a rim brake on a 26" tandem is 19% less effective than the same brake on a 700c tandem.

Does this mean 26" tandems are stupid? Hardly. If you want to conquer the toughest terrain, 700c wheels simply aren't strong enough. And if we built a 700c frame with sufficient clearance for as-yet nonexistent 2.5" knobbies (700x63), captains shorter than six feet would have a hard time straddling the top tube.

If you want a tandem for tackling rugged trails or rutted fire-roads, a 26" tandem with clearance for wide knobbies is the only choice. If you can limit your off-road excursions to graded dirt, a good 700c tandem is adequately strong and will always be faster on pavement.
 

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I think you should start with the Krebs cycle

You've gotta show her this diagram

http://www.people.virginia.edu/~rjh9u/krebs.html

and tell her how the Krebs cycle is like a 29" bicycle. It's great! . Now you explain that a 26" bike is llke a the Krebs cycle without the citrate. It just not great! This is the reason that you need a 29" wheeled bike and the real reason that they are better.

So, back to the original question, no it won't cure cancer but it is responsible for the function of the Krebs cycle!
 

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Maybe not Cancer...how about heart disease

In the 15 months since I purchased my Gary Fisher 29er, I have have lost a fairly substantial amount of weight, lowered my cholesterol, triglicerides and blood pressure. I found out I have a very bad family history of ateriolschlerosis(sp?) and I riding my 29er has definitely increased my lifespan. Sure, any biking could have done this, but my 29er fits so much better, is so much more comfortable that I went from riding 3-5 times a month to 5-7 times a week! I even bought a road bike so that I could ride when the trails are too sloppy. I have so much more fun riding this bike than any other bike that I have ridden (a lot) that I just can't imagine just NOT riding it.
 

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Discussion Starter #18
Fastskiguy said:
You've gotta show her this diagram

http://www.people.virginia.edu/~rjh9u/krebs.html

and tell her how the Krebs cycle is like a 29" bicycle. It's great! . Now you explain that a 26" bike is llke a the Krebs cycle without the citrate. It just not great! This is the reason that you need a 29" wheeled bike and the real reason that they are better.

So, back to the original question, no it won't cure cancer but it is responsible for the function of the Krebs cycle!
Hey now, all biochemists know the Krebs cycle is more akin to a unicycle. If you want a bicycle, you need something like the combined Krebs and Glyoxylate cycle, or even the malate/aspartate shunt. But I do think you're on to something...
 

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Discussion Starter #19
Now this is useful ammunition!

jpre said:
I read the responses above and have gone through the FAQ more than once and, frankly, it's mostly fluff and hyperbole. The material in jpre's post on the other hand is thought provoking and informative -- this should be in the FAQ, or some version of it. Time to go hone my arguments for the wife...
 

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Other advantages besides better climbing...

Dunno if these points were mentioned above or if it will help convince your wife that bigger is better in the case of bicycle wheels. Other than the larger footprint and lower volume tire, another rarely mentioned advantage of a 29" bike is that the bottom bracket is better protected due to less distance between the front wheel and large chain ring. Check out my cheesy diagram below. The bikes are both Gary Fisher Sugar's, one a 26", the other a 29".

Notice the EXTRA distance (BLUE BOX) between the large chain ring and front tire on the 26". The added distance increases the chance whacking that new $100 XTR chain ring and thus getting stuck in the deep stuff. The big wheels close this gap and allow you to BLAST over just about anything in your path. Also, notice that the 29" wheel bike is longer (RED lines on left and right) even though the frames are the same size. The larger diameter wheels extend the wheelbase thus providing increased stability. Combine this with the increased momentum of a 29" wheel, the shallower angle of attack and you've got the ultimate climbing machine when the terrain gets nasty.

Another fine attribute of a 29" bike is that the bottom bracket center of gravity is LOWER than that of a 26" bike. The (GREEN BOX) box shows this clearly. One of the first things people notice when they ride a big wheel bike is the superior stability. Wes Williams describes the feel of a 26" bike to be more of a swaying back and forth (skittish) motion when descending, especially at high speed. This is a result of the bottom bracket being equal in height (or very close) to that of the hubs, thus a higher center of gravity. Due to the larger diameter 29" wheel, the bottom bracket drops below the hub axis. This brings the overall center of gravity lower which results in more stable and surefooted handling. Conversely, some would argue this makes a big wheel a less responsive in the handling department. I say ride one then decide. And don't listen to those who have not tried it. Like most of us here, your 26" stuff will probably end up on Ebay.

Cheers,
James
 

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