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This is from www.cyclingnews.com



Dave Harris' 26 vs. 29 inch challenge
By Steve Medcroft

Dave Harris contemplates the 26in vs 29in conundrum
Photo: © teamhealthfx.com
Twenty six or twenty nine inch wheels - which is the better format for cross country mountain biking? Endurance racer Dave Harris (Team HealthFX) decided to settle the question for himself by putting two of his own bikes to the test at the 24 Hours in the Old Pueblo (February 18 and 19, 2006). Armed with a Trek Top Fuel and a Salsa Dos Niner, Harris used a Power Tap integrated hub system to gather data about his performance on the mostly rolling desert course in Oracle, Arizona (about thirty miles Northwest of Tucson).

He got the idea to do the comparisons two years ago. "I'm a competitive racer and I take it seriously," he says. "Once I turned to racing endurance events, you can't help but notice the popularity of two-niner bikes; the Fisher team (Nat Ross and Cameron Chambers) do really well with them. I got intrigued. I looked around for some research to see if the claims I heard about their performance was true but all I found was an abstract from a study which provides no information about the conditions under which the study was performed and ravings on two-niner forums. But it's like going to the Catholic Church and asking if God exists so I bought two last year to figure it out for myself."

Harris says that after several months of riding he worried that he wasn't gaining in performance. "As an engineer [Harris works for a Virginia-based engineering consulting firm], I needed objective evidence to support what I was feeling" Which was? "I just didn't feel that my two-niners were as fast as my Fuel. They're more fun to ride but I was getting the sense that I was going slower." Which was a paradox. "Since that went against everything everyone said, I knew I couldn't just trust my perception. Since I've been training by power for a long time, I set up a 29in inch wheel with a Power Tap hub and decided to test my bikes side by side."

Harris says that although his was not a fully-funded scientific test, he took the experiment seriously enough to set the bikes up in similar ways. "Both bikes weigh 25.5 pounds," he says. "They both have Specialized Fast Trak tires." Because a two-niner wheel has a ten percent larger circumference than a two-sixer and front and rear cogset combinations would have produced different gear-inch measurements, Harris even tried to normalize the drivetrains. "I put a smaller middle ring on the Dos Niner."

The 24 hours in the Old Pueblo wasn't the first time Harris had done side-by-side comparisons of power measurements from his two bikes. In the first test - on a relatively smooth forest service road (a constant climb) in January - he gave the Fuel a slight edge. In early February, on a 3.2-mile competitive mountain bike loop at McDowell Mountain park in Fountain Hills, Arizona, he declared the competition a tie After careful analysis of some minor differences in the power meter readings between the two bikes (recorded five days apart) after the second test, he chalked up the better readings from the Fuel as his just 'feeling' better during the Fuel test run. Old Pueblo, with its constant conditions and multiple laps of data to analyze, seemed like a better laboratory for his experiment.

The day after he finished the Arizona 24-hour epic, Harris sat down with the power data from his daytime race laps (although he traded the lead with ultimate winner Tinker Juarez into the night, vision problems caused Harris to sit out the early morning hours so he dismissed night laps from the test) and created some scenarios on his computer.

"There were a lot of different ways to look at the data," Harris said about how he broke down the results. "But people have enough difficulty understanding power in general so I kept it simple and looked at lap time versus average power." Simply put, he wanted to kow how much power was required to drive each bike around the course and if there was a difference between the bikes.

Based on that data, Harris concluded that his Salsa required more average power to achieve the same lap times over the same terrain in the same conditions as his Trek (175 watts for the Fuel, 188 for the Dos Niner). He says that by his measure, if he rode both bikes at the same power output (presumably a limitation of his physique and fitness), Harris calculates that his two-niner lap times would be about two minutes slower. "I think I can attribute some of the difference to the power required to accelerate each bike," he says. But adds, "I can only base this on impressions. And my impression, my sensation, is that Dos Niner does not accelerate as fast as the Fuel."

Harris says he realizes that his test was about his performance on his bikes and not in indictment of the two-niner format. "I haven't tested the bikes on descents and technical, rocky terrain," he adds. "I think that if I do, the Dos Niner will shine on rocky terrain." But for now, the experiement at the 24 Hours of Old Pueblo has him wondering if anyone's looking to buy a Salsa Dos Niner with a Power Tap hub.

Forty year old Dave Harris is an ultra-endurance mountian-bike racer based in Durango, Colorado. He won the West-coast based Endurance 100 endurance series last year and plans to mount a serious challenge for the Trans-Rockies co-ed title with teammate Lynda Wallenfels. He writes a blog on his team's Web site at teamhealthfx.com.
 

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Questioning!

Now I need something at least as good to tell me 29" wheels are faster. I luv'em, no doubt. but 2 min. per lap? Give me some objective data and I'll be grateful. But this stuff is pretty good.


Let's see, in the trans-iowa if it takes 30 hours and you can save 2 min. per hour then the 26 wheel could give you ONE HOUR by the finish. See? Now that I've sold off all of my 26" stuff....
 

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I could be wrong but isn't that course pretty much connected service/county/BLM/pavement? Little to no sudden stops, turns, quick accelerations, etc. If this is the case I'd be running a super lightweight cyclocross setup with some fattie Tufo's.

Look at the records on the GDR...the most recent on 29"ers.

If I were that heavy into racing (read sponsored and had multiple bikes and a large budget with a full time paid mechanic) I'd have an arsenal of rides. For instance, the Winter Park MTB series. I'd do that on a 26"er (20 miles about max for the Expert races) - but on the longer endurance stuff where you are riding long doubletrack for hours on hours and don't have the sudden ups, downs, etc. I'd ride the 29"er probably all the time for the long stuff.
 

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ftp13 said:
"They're more fun to ride but I was getting the sense that I was going slower."
Hmm... I think he's onto something here. Maybe wheel size doesn't matter after all, and we ought to all just slow down!
 

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it seems to me that a test like that should be done on two more simillar bikes like two rigid singlespeeds with similar gear inches. I think that the technology that is put into the trek is a bit of an advantage. What kind of wheels were used in the testing? What kind of suspension did the trek have? If we had a pure bred carbon fiber FS race bike in 29" format I wonder how would the times compare? I appreciate the objectivity done in this study but I would like to see some kind of tests that could be done under stricter guidlines.
 

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whoa. that dude is a freak! cool that he did that, but there are some obvious issues...

i wonder how consistent of power he needs, even staying on the same bike, for each lap.

also, i always thought that power was only one part. if you use the brakes less on a DH, you go faster. power is all important only if you are pedalling all the time, like in a TT or something.

isn't it lap times that are important? he never mentioned that.

those bikes are sort of different, too. wonder what the pwer numbers are for a bunch of different 26ers...

does the powertap work on all size kegs? isn't watts a sketchy part of LA?

that dude's camp must have been quite the party between laps! good to see people out there enjoying themselves.
 

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2melow said:
I could be wrong but isn't that course pretty much connected service/county/BLM/pavement? Little to no sudden stops, turns, quick accelerations, etc.
Okay.

You're wrong.

There is zero pavement, some fire roads, and alot of very twisty singletrack thru the cacti. So twisty in fact, that one needs to accelarate out of tons of corners that are quite tight and loose.
 

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If the course is the same for both bikes, which makes it a fair test, then it takes the same amount of energy no matter what wheel he is riding. Right?

A perfect situation to compare the bikes would be the same course for both. Then lap times would be all that is needed to tell the difference.

Why did he need to do that powertap hub thing and change gears and what not? Just freaking ride the bikes and look at your time. It is not scientific, but it is simple.

Is there a 29" version of the Specialized Fast Track tire? Is that the one time deal where they had a few hundred Specialized 29er tires left over?
 

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Quasi said:
If the course is the same for both bikes, which makes it a fair test, then it takes the same amount of energy no matter what wheel he is riding. Right?

A perfect situation to compare the bikes would be the same course for both. Then lap times would be all that is needed to tell the difference.

Why did he need to do that powertap hub thing and change gears and what not? Just freaking ride the bikes and look at your time. It is not scientific, but it is simple.

Is there a 29" version of the Specialized Fast Track tire? Is that the one time deal where they had a few hundred Specialized 29er tires left over?
Nope, too many variables between laps. lap times will always flucuate depending on how you feel. Power output however is quantifiable, if lap times were virtually identical yet one bike required more power to do that lap you have taken the rider out of the equation.
 

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Quasi said:
...Is there a 29" version of the Specialized Fast Track tire? Is that the one time deal where they had a few hundred Specialized 29er tires left over?
Where have you been? Yes there is and no it is not.
 

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Agreed. Even with the same bike there were a couple sets of laps at about the same power level and a 1-2 minute time difference.
 

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standards

I could be mistaken, but I don't remember anybody making this big of an issue over efficiency and speed when full suspension XC bikes were introduced. As I recall, it was always sort of accepted that, "yeah, they're going to weigh a bit more, and yeah, they might not be as snappy off the start, but overall you'll appreciate the comfort and control and their ability to swallow the bumps." I don't see how 29ers are any different, really. But the 29er contingency is either choosing to, or being asked to, take the position that their bikes have no shortcomings, yet they provide all these benefits! Hell, that's the Holy Grail of bike design -- is it really fair to expect the 29er to deliver everything? Is it at all reasonable to assert that it does? Personally, I choose to accept these six propositions and be done with it:

1) A 3-inch-larger wheel diameter will make a significant improvement in ride quality and momentum, but probably not a miraculous improvement.

2) A 3-inch-smaller wheel diameter will have some drawbacks, but they probably aren't devastating drawbacks.

3) Bigger wheels maintain momentum and roll over things better.

4) Smaller wheels are easier to spin and to turn.

5) A 29er is a really good idea for tall people, and is a pretty darn good idea for a bunch of other people, but it might not be for everybody.

6) The 26er has served its purpose well for 30 years, and will continue to be a viable and sensible option for many riders, but not all riders.

It just doesn't seem that hard for me to acknowledge their weaknesses while I enjoy their strengths. I mean, they're different bikes, right? They're going to be different! I completely fail to see why anyone even has to take sides on this.
 

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Joe Sausagehead said:
I could be mistaken, but I don't recall anybody making this big of an issue over efficiency and speed when full suspension XC bikes were introduced. As I recall, it was always sort of accepted that, "yeah, they're going to weigh a bit more, and yeah, they might not be as snappy off the start, but overall you'll appreciate the comfort and control and their ability to swallow the bumps." I don't see how 29ers are any different, really. But the 29er contingency is either choosing to or being asked to take the position that their bikes have no shortcomings, yet they provide all these benefits! Hell, that's the Holy Grail of bike design -- is it really fair to expect the 29er to deliver everything? Is it at all reasonable to assert that it does? Personally, I choose to accept these six propositions and be done with it:

1) A 3-inch-larger wheel diameter will make a significant improvement in ride quality and momentum, but probably not a miraculous improvement.

2) A 3-inch-smaller wheel diameter will have some drawbacks, but they probably aren't devastating drawbacks.

3) Bigger wheels maintain momentum and roll over things better.

4) Smaller wheels are easier to spin and to turn.

5) A 29er is a really good idea for tall people, and is a pretty darn good idea for a bunch of other people, but it might not be for everybody.

6) The 26er has served its purpose well for 30 years, and will continue to be a viable and sensible option for a lot of riders.

It just doesn't seem that hard for me to acknowledge the weaknesses while I enjoy the strengths. I mean, they're different bikes, right? They're going to be different! I completely fail to see why anyone even has to take sides on this.
Rational, thoughful posts like your will not be tolerated in this forum, drink your Kool-Aide.
:D
 

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Taking sides

Joe Sausagehead said:
I completely fail to see why anyone even has to take sides on this.
If you could save 2 minutes per hour of racing with the same power output, that would be HUGE! I dig the big wheels, really feel good on'em, but 2 minutes per hour is HUGE! I don't wanna look like a gorilla on a tricycle anymore but 2 minutes is HUGE! Is it true? I don't know for sure but if it is, it's HUGE! :)

On the other hand, if 2 minutes per hour doesn't matter, then it just doesn't matter.

Heh, maybe a guy should train on his 29 and race his 26 ;)
 

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2 minutes per hour, I've finished mid-pack dozens of times with such time on the winner. I onder how much a world class athlete would lose on a department store bike rather than his super trick racing machine. Probably about the same :)
 

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nothing has been proved...

Fastskiguy said:
If you could save 2 minutes per hour of racing with the same power output, that would be HUGE! I dig the big wheels, really feel good on'em, but 2 minutes per hour is HUGE! I don't wanna look like a gorilla on a tricycle anymore but 2 minutes is HUGE! Is it true? I don't know for sure but if it is, it's HUGE! :)

On the other hand, if 2 minutes per hour doesn't matter, then it just doesn't matter.

Heh, maybe a guy should train on his 29 and race his 26 ;)
I think that it's foolish to make any conclusions based on this "study". Dave Harris is clearly a very competent bicycle rider and probably a damned fine coach and sports fitness technology user. But he hasn't designed a study to describe the difference across a broad range of terrain, rider size, bicycle type, tire pressure, etc. Nor has he controlled all the causal factors that could be affecting his outcome. Nor has he subjected his work to peer review. Etc. Etc.

Here's what he said about the data he produced and based conclusions on (from this thread):

hairball_dh said:
Thanks for the lesson, but I'm not a new scientist. My question is simple: which bike is faster for me, my Dos or my Fuel? Add to that question the constraints of differing types of terrain. Note I said *my* bikes, and for *me*. I have no time, funding, or even inclination to do such studies for the masses. I want to know what is faster for me, and where.
He's really pretty much hostile to critism. That ain't science, that's a guy with a couple powertaps going out and looking at what data they give him, writing it up to look like science, then some idiot sports journalist reporting on it as science.

Now, are his findings complete bunk? I dunno. I think that on certain terrain, a good consistent pebbly surface for example, the little-wheel bike might very well more efficient. And I think maybe that on a really tough technical course, the bigwheel might be.

Not meaning to be insulting. I don't think this fellow is dumb, and I think he did a fine job of testing his own curiosity in a situation that was important to him. But it's wrong to pass it off as science. And it's always wrong for a journalist to elevate junk science and help pass it off as real science.
 

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Energy Storage

Mr. Harris does not give a full bike build list, but we can rather safely presume that his complete 29er wheelset (with tires) is heavier at the rim. If that is so, then at any given ground speed there is more energy stored in his 29er wheels- and that is energy the rider must supply every time he accelerates the bicycle. It would explain the discrepancy in required power he measured. It is NOT the same as simple rolling resistance, where the bigger wheel still rules. Once up to speed, your 29er requires less energy to keep it there than its 26" equivalent. So which of those two factors predominates depends on the course, in some places they will just cancel each other out entirely. Really though, Harris' experiment is not so surprising, he appears to be simply confirming long-known velo-physics that a heavier bicycle wheel accelerates slower (i.e. requires more energy) than a heavier one. He is also fair enough to comment on where the bigger wheels should have an advantage though he didn't test there.

What I'm taking home from this is weight at the rim is still very important to overall performance- same as it ever was! That, and remember to use the 29er's added cornering grip and better balance to carry a little more speed through turns. Slow down less, accelerate less.
 

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I think it's more important how you handle wheel weight. Can't handle it, light is what you need.
I bet really heavy wheels can be built (of just weight added) and two equally strong riders all at once start lapping very differently.
Really, the 29 vs 26 weight increase IMO is hardly worth discussion about, a factor so small it's effect cannot be measured in the wild. In an XC race situation, if you apply yor usual out-of-corner sprinting power to just the 300-350g of added weight in dragless wheel form, after a couple seconds you have it past safe tafe-off/landing speeds for airliners. 10s to Mach 1?
See what happens of you apply the same sprinting power to a yourself+bike a couple seconds, you barely hit jogging speeds :) That's how minute the wheelweight difference is. If you go from 26" folding to wire tires, you're often there already.
 

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C'mon Now

I totally agree there are guys who can push heavier wheels- stronger riders, of course. Now give that stronger rider a lighter wheelset- he will accelerate faster, every time. The same thing happens with a motorcycle, a car, whatever. Same power + lighter wheels = faster acceleration. Physical laws apply that go beyond "I think", "I bet", "IMHO".

Harris himself acknowledged that there are places where the 29er wheels would be advantageous, so maybe we can admit that a lighter wheel is quicker to accelerate. It is after all the truth. Let's not hurt our own credibility.
 
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