MUST WATCH: E-Thirteen Finally Answers the Age-Old Question

[Captain Fastbastard Mayhem]

that experiment shows nothing between 26" and 29". what it shows is that weight further away from the center accelerates slower that's all.

 

if they wanted to show the difference between the two, the weights need to be in the same place, give or take a millimeter for the difference in weight, and the cones need to be of different sizes eg: 2.6" and 2.9". only then can you say that the smaller or larger cone is faster.

 

Read your first paragraph, then think about what you said in the 2nd.

 

26er - weight closer to centre. 29er - weight further from centre.

 

In other words - it mimics the 29er vs 26er acceleration scenario. In an exaggerated way, sure. but the concept is applicable.

[Erroli8a8]

No I disagree. yes the weight is further away from the center with a 29er. the difference is that the rotating surface is also bigger on a 29er. the point is that the 26er would have to accelerate and turn faster to cover the same ground in the same time as a 29er. therefore if the cones were of different sizes the experiment might be different. the point is that the larger the wheel the slower it can turn to reach the same distance in the same time that it would take a smaller wheel turning faster. the 26 would have to be faster and have higher acceleration to maintain the same pace as a 29.

 

I do not know which one would be better just that it would be an interesting experiment to see.

Edited August 28, 2014 by Erroli8a8

[Rocket-Boy]

Read your first paragraph, then think about what you said in the 2nd.

 

26er - weight closer to centre. 29er - weight further from centre.

 

In other words - it mimics the 29er vs 26er acceleration scenario. In an exaggerated way, sure. but the concept is applicable.

Spot on, for this exact test. There are other tests they could to to compare wheel sizes but I dont think that is what the test was about.

Its not hard to tell the difference in acceleration between a 26 and a 29, 26 is always quicker. the difference comes in with maintaining speed on even terrain being easier on a 29.

 

To me its pretty simple in terms of wheel size, lots of quick acceleration and close to stop start riding 26 wins.

Longer easier riding with few stop starts 29 wins.

Horses for courses and such.

[Captain Fastbastard Mayhem]

No I disagree. yes the weight is further away from the center with a 29er. the difference is that the rotating surface is also bigger on a 29er. the point is that the 26er would have to accelerate and turn faster to cover the same ground in the same time as a 29er. therefore if the cones were of different sizes the experiment might be different. the point is that the larger the wheel the slower it can turn to reach the same distance in the same time that it would take a smaller wheel turning faster. the 26 would have to be faster and have higher acceleration to maintain the same pace as a 29.

 

I do not know which one would be better just that it would be an interesting experiment to see.

 

That wasn't the point of the experiment though, was it? It was to determine which wheel accelerates quicker, with all other variables remaining constant. That is all.

[Eldron]

That wasn't the point of the experiment though, was it? It was to determine which wheel accelerates quicker, with all other variables remaining constant. That is all.

 

This is always the issue with 26650B29 tests - you cannot replicate ALL conditions in a lab - only isolate 1 or 2. People then emotionally extrapolate the data so suit their wheel size/choice.

 

If we want to get REALLY nerdy - the test only tells us that if both wheels are the same size then the wheel with the weight closest to the hub accelerates faster (both the wheels in the test are the same diameter).

 

The other issue with wheel size debates is that people use "wiki knowledge/peer absorbed knowledge" rather than science to determine which is better.

[Captain Fastbastard Mayhem]

This is always the issue with 26650B29 tests - you cannot replicate ALL conditions in a lab - only isolate 1 or 2. People then emotionally extrapolate the data so suit their wheel size/choice.

 

If we want to get REALLY nerdy - the test only tells us that if both wheels are the same size then the wheel with the weight closest to the hub accelerates faster (both the wheels in the test are the same diameter).

 

The other issue with wheel size debates is that people use "wiki knowledge/peer absorbed knowledge" rather than science to determine which is better.

 

pweeee cisely.

[Headshot]

My dik sixer wheels with dik dh type tyres on them weigh a bomb. I am just glad that I am not on a 29er looking for the same kind of tyre/rim strength because those suckers would really be like proverbial wagon wheels...

[tikki]

I am going to post this interesting but very LONG piece i found a while back , im only posting this for others to read and i am not interesting in getting in a debate nor will i comment on this article .

 

 

One piece of marketing that is so constantly referred to, that is has become unquestioned - and is again repeated early in this thread - ‘a larger diameter wheel has a larger contact patch'.

If 10 bikes with different diameters rims and different widths of tyres all pressured at 30psi, all the same elasticity (ie the same brand /tyre type) were placed with an 80kg rider onboard... Which would have the greatest area of contact patch? The answer is that the area of contact would be the same. Only the shape of that contact area would be different. The reason is 30psi is a measurement of the pressure of the tyre not the volume of air in it.

Volume is very different. The higher the volume of the tyre allows a lower pressure to be run due to less chance of rim hits etc. This lower pressure allows a larger area of contact patch to form. More volume also means less sidewall flex (better efficiency) and more capacity for deformation (more comfort is one upside of the latter). There are many positives for large volume tyres.

Volume of a tyre is the same calc as a volume of a cylinder: v=r²πh , with r being ½ the tyre width and h being 2πr of the tyre dia taken from the longitudinal axis.

It is therefore easy to determine that a smaller dia wheel can have a larger volume of tyre simply by having more width in the tyre. For example. A 29x2.25 Racing Ralph which has a approx dia of 57mm has around 5214cm³ whereas a 26x2.4 Racing Ralph has a approx dia of 62mm has around 5595cm³.

The smaller wheel has the larger volume tyre. This would allow the smaller dia wheel to run less air pressure creating more contact patch area. The smaller dia wheel would also have less sidewall flex and less deformation than the larger wheel - not the other way around.

A popular race tyre is 26x2.25 Racing Ralph (57mm dia) with 4709 cm³ and in volume terms the corresponding 29 sized tyre would be the 54mm 29x2.1 Ralph with 4669 cm³ . Tubulars are popular in race teams with large dia wheels – a 29x50mm tubular - 4000 cm³ has a little less to a Racing Ralph 26x2.1(54mm) at 4216 cm³.

That a large dia wheel is the main determinant for a larger contact patch is incorrect. It is pressure of the tyre that determines these parameters and volume is the large determinant of pressure used and, in this context, the width of the tyre is the main determinant in volume not the dia of the wheel.

One downside to a larger volume tyre is the greater mass which leads to the next myth and where this equation is important.

The simple formulae for translational energy for a wheel: (1/2)mv².

Rotational energy for a wheel: (1/2)Iω²

Total energy of a wheel is therefore: 1/2(mv² + Iω² )

For a wheel with all mass at the outer edge: I=mr²

For a rolling wheel: ω=v/r

Putting it all together you would get: 1/2(mv² + Iω² ) = 1/2((mv² + (mr² )(v/2) ² ) = 1/2(mv² + mv2).

The outcome is 2x.

This means any extra weight that is on the outside of Wheel A compared to Wheel B is pretty close to double by the time it hits the riders legs to apply power to accelerate it.

A real world illustration of this is demonstrated in the power data collected by WC XCO race teams.

Early in 2012 I was sent power data sets for different analysis (nothing to do with bikes per se rather robustness of an aspect of the data collected). The sets contained different tyres and setups, some different frame setups, some different wheel dia setups used in short course XC. The majority of data is for tyres - from heavy sidewall, differing pressure, tubs, high pressure 29 skinny to low pressure 26 baggies. The riders were elite girls and guys riding test courses and WC courses in the 2010 and most of 2011 comp. There were nearly a hundred data sets each containing the results of many hours of testing. Every major XCO team on the World Cup circuit would have similar with the three larger corporate teams probably many times more.

For example. The stronger sidewall tyres predominantly used and tested in this team weighed an approx 50g heavier than the standard tyres. The additional 100 grams on the edge of the wheels returned between 1.2%ave and 2.9%ave less efficiency ie more power over time, from the different courses of the 18mths of tests. The spread is caused by the varying amount of climbing etc between courses. When the climbs are considered separately the figure got up to a high of 7.5%ave difference. This might be considered a small weight on the outside edge but this amount of weight can be significant on a course with significant elevation, pinches or accelerations. When the rider/bike weight is low, as elite XC racers usually are, it becomes more significant.

In all of the data sets any time significant weight was added to a wheel there was an assessable decrease in efficiency of that wheel. So although the laws of physics prevailed, how much loss was dependent on different factors – this data did not show a linear correlation for weight increase. There are many factors that influence power which must be considered in the context of the test circuit.

Larger dia wheels are at an inherent weight disadvantage compared to smaller dia wheelsets created by mass difference of the rim and stronger build needed to offset additional flex (about 10% to 14% of the rims and build) and WC teams use different methods to gain parity.

For example. Analysis included a 1160g 29 tubular wheelset that when a similar volume tub tyre was added was of comparable weight of the standard team 26 clincher wheelset with a tyre of similar volume. The data returned was within or about the same for both wheelsets. (This team – and most others – judge that due to accuracy tolerances of equipment and other variances that if sets of data return less 1% difference it is too close to call).

Another Example. An investigation of a heavier (than the previous 1160g) tubular 29 wheelset with the standard 26 clincher race wheelset with a higher volume tyre to create similar weight. Again the results fell on or under 1%.

Also. The larger WC teams use ‘line’ rims and ‘line’ tyres (pulled from manufacturing lines, they are lighter than normal due to manufacturing tolerances) Using these components it is possible with ½ nipples and cleaning up the rims to construct 29 wheels as light or lighter than many 26 wheels used. If that team then used similar volume clincher tyres then the expectation (amongst this team that is without these resources) is the larger dia wheelset can be as power efficient as a team with the smaller dia clincher wheelsets without the disadvantages that tubulars pose.

The team determined, as suggested by this data (ie with the short course XC setups, tyres and riders tested), if rotating weight is similar there is no assessable loss of efficiency between dia of wheelsets used. There is some practical restriction in choice of stronger sidewalls/volume etc for larger wheels due to the corresponding increase in weight when it is already compromising to get the larger wheelset down to acceptable weight.

Tyres are most easily adjusted to get a wheel to an acceptable weight. For example. When 29 wheels first appeared a 24hr racer (Ed Harris) ran a test in a race – and uploaded it - between the two available wheel dia at the time using powertap hubs. His first impressions were the smoothness and perceived speed of the 29 bike. He discovered after reviewing the power data the smaller dia bike had a 7% power efficiency advantage over the larger wheel dia bike. The large figure had come about because he had used the same width of tyre on both bikes as opposed to the same volume. So as well as the already 10% - 14% weight penalty on the rim/ spokes/nipples of the stock 29 wheels he had added more weight with a larger volume tyre. He may well have had an extra 100 to 200 extra grams on each wheel.

Similarly the AMB 26v29 test published in Sept 2011 edition. They used a more accurate crank power meter with more riders and more loops so more data. The article talked a lot about the smoothness of the larger dia wheel through the rock sections and rougher sections of the loops they rode. This may have been taken by the testers to assume that therefore the larger wheelsets were going to return quicker figures over the entirety of the loops. They didn’t seem to take into account that as well as the 10% - 14% weight penalty of the rim/ spokes/nipples of the stock large dia wheels, the testers used the same stock width tyre adding more weight and more volume, to the 29 wheelset which had to be ridden over the entire course not just the rougher/rockier areas. Again there was probably in the vicinity of 100 to 200grams extra on each wheel. The difference was enough to give the small dia wheel a 7.7% advantage over the whole circuit and up to 19% on some climbs with one 1’30” pinch climb giving a 30% advantage to the smaller wheel.

These figures are large and were not reproduced in any of the race teams tests for the reason WC XCO racing is not done with stock wheels. However with that much extra weight the numbers would probably be consistent with expectations.

Incident angle (the angle the tyre hits an object) and lever point advantage (a longer patch makes contact earlier in front of the axis). These give a larger dia wheel smoothness over rocks or rough ground. (and this would be a factor for more consideration in many cases eg in longer events - this data has context for short course XC only). Tyre manufacturers provide lab analysis from wheels and tyres tested on tyre roller machines to the teams that use their products. There are measurable differences in these lab analyses of lower incident angle and the lever point advantage of a longer contact patch of a larger dia tyre in these studies. However this team’s test results have been unable to clearly demonstrate any incident angle efficiency advantage when those wheels are used in a race setup over the entirety of the test loop. In some courses there was above 1%ave which signify advantage on most others the data fell between + /-1%. This is not unusual and doesn’t mean it is not an important parameter - it is just that any efficiency of the incidence angle, in singularity (ie other parameters are the same on both wheelsets so as to attempt to test a single parameter), was not assessable enough to clearly demonstrate an advantage in this testing within the set boundaries. There are many parts of the bike that, while they have advantage in a section of a course, are difficult to quantify when the results are taken from racing the entire circuit.

Setting up the test between similar weight 26 and 29 wheelsets was problematic in itself. The first 29 wheelset was not considered sufficiently robust for racing after a failure of one in testing. This team used 29 tubular wheels to create light wheelsets and while tubulars have some positives they have their own set of drawbacks.

This leaves weight in the context of short course XC racing as the overarching consideration for performance in wheels - though tougher sidewalls, tread, high volume, psi are some of the many other tyre parameters to consider when race tactics and courses dictate.

This is at odds with the prevailing marketing message of the corporations pushing a wheel size which seems to suggest that larger volume, lower incident angle and lever point but more mass of the larger wheel can somehow defy the laws of physics. And despite the library of power data that the large corporate teams have at their disposal from their race teams, their marketing departments have not been able to find data to back their claims that could be released or leaked, relevant to racing, that is contrary to the data repeated here.

At the end of it – in the real world of age group racing that most of us now live in - if someone is putting in double the hours of the next guy, it doesn’t matter about the bike - he should beat him up a hill on a clunker. Equally, if two riders are matched in fitness, and the bikes are of similar weight - then the person who is riding rims/tyres that are 10 to 14 percent heavier is going to have a hard time catching the other guy.

Corporations exist to make profit. Profit is made by creating a demand and selling product. It seems hobbies/interests are driven by marketing departments and appear to escape any regulatory scrutiny of their wilder claims. Cycling is no exception.

[Captain Fastbastard Mayhem]

I am going to post this interesting but very LONG piece i found a while back , im only posting this for others to read and i am not interesting in getting in a debate nor will i comment on this article .

 

 

One piece of marketing that is so constantly referred to, that is has become unquestioned - and is again repeated early in this thread - ‘a larger diameter wheel has a larger contact patch'.

If 10 bikes with different diameters rims and different widths of tyres all pressured at 30psi, all the same elasticity (ie the same brand /tyre type) were placed with an 80kg rider onboard... Which would have the greatest area of contact patch? The answer is that the area of contact would be the same. Only the shape of that contact area would be different. The reason is 30psi is a measurement of the pressure of the tyre not the volume of air in it.

Volume is very different. The higher the volume of the tyre allows a lower pressure to be run due to less chance of rim hits etc. This lower pressure allows a larger area of contact patch to form. More volume also means less sidewall flex (better efficiency) and more capacity for deformation (more comfort is one upside of the latter). There are many positives for large volume tyres.

Volume of a tyre is the same calc as a volume of a cylinder: v=r²πh , with r being ½ the tyre width and h being 2πr of the tyre dia taken from the longitudinal axis.

It is therefore easy to determine that a smaller dia wheel can have a larger volume of tyre simply by having more width in the tyre. For example. A 29x2.25 Racing Ralph which has a approx dia of 57mm has around 5214cm³ whereas a 26x2.4 Racing Ralph has a approx dia of 62mm has around 5595cm³.

The smaller wheel has the larger volume tyre. This would allow the smaller dia wheel to run less air pressure creating more contact patch area. The smaller dia wheel would also have less sidewall flex and less deformation than the larger wheel - not the other way around.

A popular race tyre is 26x2.25 Racing Ralph (57mm dia) with 4709 cm³ and in volume terms the corresponding 29 sized tyre would be the 54mm 29x2.1 Ralph with 4669 cm³ . Tubulars are popular in race teams with large dia wheels – a 29x50mm tubular - 4000 cm³ has a little less to a Racing Ralph 26x2.1(54mm) at 4216 cm³.

That a large dia wheel is the main determinant for a larger contact patch is incorrect. It is pressure of the tyre that determines these parameters and volume is the large determinant of pressure used and, in this context, the width of the tyre is the main determinant in volume not the dia of the wheel.

One downside to a larger volume tyre is the greater mass which leads to the next myth and where this equation is important.

The simple formulae for translational energy for a wheel: (1/2)mv².

Rotational energy for a wheel: (1/2)Iω²

Total energy of a wheel is therefore: 1/2(mv² + Iω² )

For a wheel with all mass at the outer edge: I=mr²

For a rolling wheel: ω=v/r

Putting it all together you would get: 1/2(mv² + Iω² ) = 1/2((mv² + (mr² )(v/2) ² ) = 1/2(mv² + mv2).

The outcome is 2x.

This means any extra weight that is on the outside of Wheel A compared to Wheel B is pretty close to double by the time it hits the riders legs to apply power to accelerate it.

A real world illustration of this is demonstrated in the power data collected by WC XCO race teams.

Early in 2012 I was sent power data sets for different analysis (nothing to do with bikes per se rather robustness of an aspect of the data collected). The sets contained different tyres and setups, some different frame setups, some different wheel dia setups used in short course XC. The majority of data is for tyres - from heavy sidewall, differing pressure, tubs, high pressure 29 skinny to low pressure 26 baggies. The riders were elite girls and guys riding test courses and WC courses in the 2010 and most of 2011 comp. There were nearly a hundred data sets each containing the results of many hours of testing. Every major XCO team on the World Cup circuit would have similar with the three larger corporate teams probably many times more.

For example. The stronger sidewall tyres predominantly used and tested in this team weighed an approx 50g heavier than the standard tyres. The additional 100 grams on the edge of the wheels returned between 1.2%ave and 2.9%ave less efficiency ie more power over time, from the different courses of the 18mths of tests. The spread is caused by the varying amount of climbing etc between courses. When the climbs are considered separately the figure got up to a high of 7.5%ave difference. This might be considered a small weight on the outside edge but this amount of weight can be significant on a course with significant elevation, pinches or accelerations. When the rider/bike weight is low, as elite XC racers usually are, it becomes more significant.

In all of the data sets any time significant weight was added to a wheel there was an assessable decrease in efficiency of that wheel. So although the laws of physics prevailed, how much loss was dependent on different factors – this data did not show a linear correlation for weight increase. There are many factors that influence power which must be considered in the context of the test circuit.

Larger dia wheels are at an inherent weight disadvantage compared to smaller dia wheelsets created by mass difference of the rim and stronger build needed to offset additional flex (about 10% to 14% of the rims and build) and WC teams use different methods to gain parity.

For example. Analysis included a 1160g 29 tubular wheelset that when a similar volume tub tyre was added was of comparable weight of the standard team 26 clincher wheelset with a tyre of similar volume. The data returned was within or about the same for both wheelsets. (This team – and most others – judge that due to accuracy tolerances of equipment and other variances that if sets of data return less 1% difference it is too close to call).

Another Example. An investigation of a heavier (than the previous 1160g) tubular 29 wheelset with the standard 26 clincher race wheelset with a higher volume tyre to create similar weight. Again the results fell on or under 1%.

Also. The larger WC teams use ‘line’ rims and ‘line’ tyres (pulled from manufacturing lines, they are lighter than normal due to manufacturing tolerances) Using these components it is possible with ½ nipples and cleaning up the rims to construct 29 wheels as light or lighter than many 26 wheels used. If that team then used similar volume clincher tyres then the expectation (amongst this team that is without these resources) is the larger dia wheelset can be as power efficient as a team with the smaller dia clincher wheelsets without the disadvantages that tubulars pose.

The team determined, as suggested by this data (ie with the short course XC setups, tyres and riders tested), if rotating weight is similar there is no assessable loss of efficiency between dia of wheelsets used. There is some practical restriction in choice of stronger sidewalls/volume etc for larger wheels due to the corresponding increase in weight when it is already compromising to get the larger wheelset down to acceptable weight.

Tyres are most easily adjusted to get a wheel to an acceptable weight. For example. When 29 wheels first appeared a 24hr racer (Ed Harris) ran a test in a race – and uploaded it - between the two available wheel dia at the time using powertap hubs. His first impressions were the smoothness and perceived speed of the 29 bike. He discovered after reviewing the power data the smaller dia bike had a 7% power efficiency advantage over the larger wheel dia bike. The large figure had come about because he had used the same width of tyre on both bikes as opposed to the same volume. So as well as the already 10% - 14% weight penalty on the rim/ spokes/nipples of the stock 29 wheels he had added more weight with a larger volume tyre. He may well have had an extra 100 to 200 extra grams on each wheel.

Similarly the AMB 26v29 test published in Sept 2011 edition. They used a more accurate crank power meter with more riders and more loops so more data. The article talked a lot about the smoothness of the larger dia wheel through the rock sections and rougher sections of the loops they rode. This may have been taken by the testers to assume that therefore the larger wheelsets were going to return quicker figures over the entirety of the loops. They didn’t seem to take into account that as well as the 10% - 14% weight penalty of the rim/ spokes/nipples of the stock large dia wheels, the testers used the same stock width tyre adding more weight and more volume, to the 29 wheelset which had to be ridden over the entire course not just the rougher/rockier areas. Again there was probably in the vicinity of 100 to 200grams extra on each wheel. The difference was enough to give the small dia wheel a 7.7% advantage over the whole circuit and up to 19% on some climbs with one 1’30” pinch climb giving a 30% advantage to the smaller wheel.

These figures are large and were not reproduced in any of the race teams tests for the reason WC XCO racing is not done with stock wheels. However with that much extra weight the numbers would probably be consistent with expectations.

Incident angle (the angle the tyre hits an object) and lever point advantage (a longer patch makes contact earlier in front of the axis). These give a larger dia wheel smoothness over rocks or rough ground. (and this would be a factor for more consideration in many cases eg in longer events - this data has context for short course XC only). Tyre manufacturers provide lab analysis from wheels and tyres tested on tyre roller machines to the teams that use their products. There are measurable differences in these lab analyses of lower incident angle and the lever point advantage of a longer contact patch of a larger dia tyre in these studies. However this team’s test results have been unable to clearly demonstrate any incident angle efficiency advantage when those wheels are used in a race setup over the entirety of the test loop. In some courses there was above 1%ave which signify advantage on most others the data fell between + /-1%. This is not unusual and doesn’t mean it is not an important parameter - it is just that any efficiency of the incidence angle, in singularity (ie other parameters are the same on both wheelsets so as to attempt to test a single parameter), was not assessable enough to clearly demonstrate an advantage in this testing within the set boundaries. There are many parts of the bike that, while they have advantage in a section of a course, are difficult to quantify when the results are taken from racing the entire circuit.

Setting up the test between similar weight 26 and 29 wheelsets was problematic in itself. The first 29 wheelset was not considered sufficiently robust for racing after a failure of one in testing. This team used 29 tubular wheels to create light wheelsets and while tubulars have some positives they have their own set of drawbacks.

This leaves weight in the context of short course XC racing as the overarching consideration for performance in wheels - though tougher sidewalls, tread, high volume, psi are some of the many other tyre parameters to consider when race tactics and courses dictate.

This is at odds with the prevailing marketing message of the corporations pushing a wheel size which seems to suggest that larger volume, lower incident angle and lever point but more mass of the larger wheel can somehow defy the laws of physics. And despite the library of power data that the large corporate teams have at their disposal from their race teams, their marketing departments have not been able to find data to back their claims that could be released or leaked, relevant to racing, that is contrary to the data repeated here.

At the end of it – in the real world of age group racing that most of us now live in - if someone is putting in double the hours of the next guy, it doesn’t matter about the bike - he should beat him up a hill on a clunker. Equally, if two riders are matched in fitness, and the bikes are of similar weight - then the person who is riding rims/tyres that are 10 to 14 percent heavier is going to have a hard time catching the other guy.

Corporations exist to make profit. Profit is made by creating a demand and selling product. It seems hobbies/interests are driven by marketing departments and appear to escape any regulatory scrutiny of their wilder claims. Cycling is no exception.

 

Brilliant.

[Erroli8a8]

this is like Tim Noakes on wheel sizes. hehehehe, as long as I have my bike I am happy.

[MarcBurger]

Best comparison of the 2 I've ever read.

 

Less "It's just better" and more straight logical results, that humans can understand.

<gives my 10-year old 26er a hug>

Edited August 28, 2014 by MarcBurger

[droo]

If we want to get REALLY nerdy - the test only tells us that if both wheels are the same size then the wheel with the weight closest to the hub accelerates faster (both the wheels in the test are the same diameter).

 

Oh look, a rational person

 

Pretty much what I said on page 1, which was conveniently ignored by most because then we wouldn't be able to have 2665029 debate number 4 327.

 

Yawn.

 

(Protip: It's 99.3% marketing BS anyway, and 78.2% of statistics supporting one viewpoint or another are made up on the spot.)

[droo]

Corporations exist to make profit. Profit is made by creating a demand and selling product. It seems hobbies/interests are driven by marketing departments and appear to escape any regulatory scrutiny of their wilder claims. Cycling is no exception.

 

Also, this.

[Headshot]

Also, this.

 

I have a friend who does marathon races and smugly claims that one day I will see the light and get a 29er. He spends thousand on carbon rims to make his big wheeler lighter and faster so he can enjoy the same advantage a smaller cheaper wheel used to give him. I don't have that kind of money and a 29er suited to my kind of riding will cost more than double what I paid for my bike. I am clearly not the bike industries ideal customer.

[GoLefty!!]

So 26ers are faster than 29ers? And I should attach weights to my hubs to accelerate faster

 

The wheel with the Moment of Inertia closer to the axis of rotation will accelerate faster. Since a bicycles wheel under constant acceleration the wheel with the lower moment of inertia is faster. That would be the 26 er yes. Science has known this for centuries. But Marketers are not scientists and 29er riders are clearly not scientists either...

Since SA has the lowest maths and science literacy rate in the world. its hardly surprising that the 29er is most popular here

[GoLefty!!]

I am going to post this interesting but very LONG piece i found a while back , im only posting this for others to read and i am not interesting in getting in a debate nor will i comment on this article .

 

 

One piece of marketing that is so constantly referred to, that is has become unquestioned - and is again repeated early in this thread - ‘a larger diameter wheel has a larger contact patch'.

If 10 bikes with different diameters rims and different widths of tyres all pressured at 30psi, all the same elasticity (ie the same brand /tyre type) were placed with an 80kg rider onboard... Which would have the greatest area of contact patch? The answer is that the area of contact would be the same. Only the shape of that contact area would be different. The reason is 30psi is a measurement of the pressure of the tyre not the volume of air in it.

Volume is very different. The higher the volume of the tyre allows a lower pressure to be run due to less chance of rim hits etc. This lower pressure allows a larger area of contact patch to form. More volume also means less sidewall flex (better efficiency) and more capacity for deformation (more comfort is one upside of the latter). There are many positives for large volume tyres.

Volume of a tyre is the same calc as a volume of a cylinder: v=r²πh , with r being ½ the tyre width and h being 2πr of the tyre dia taken from the longitudinal axis.

It is therefore easy to determine that a smaller dia wheel can have a larger volume of tyre simply by having more width in the tyre. For example. A 29x2.25 Racing Ralph which has a approx dia of 57mm has around 5214cm³ whereas a 26x2.4 Racing Ralph has a approx dia of 62mm has around 5595cm³.

The smaller wheel has the larger volume tyre. This would allow the smaller dia wheel to run less air pressure creating more contact patch area. The smaller dia wheel would also have less sidewall flex and less deformation than the larger wheel - not the other way around.

A popular race tyre is 26x2.25 Racing Ralph (57mm dia) with 4709 cm³ and in volume terms the corresponding 29 sized tyre would be the 54mm 29x2.1 Ralph with 4669 cm³ . Tubulars are popular in race teams with large dia wheels – a 29x50mm tubular - 4000 cm³ has a little less to a Racing Ralph 26x2.1(54mm) at 4216 cm³.

That a large dia wheel is the main determinant for a larger contact patch is incorrect. It is pressure of the tyre that determines these parameters and volume is the large determinant of pressure used and, in this context, the width of the tyre is the main determinant in volume not the dia of the wheel.

One downside to a larger volume tyre is the greater mass which leads to the next myth and where this equation is important.

The simple formulae for translational energy for a wheel: (1/2)mv².

Rotational energy for a wheel: (1/2)Iω²

Total energy of a wheel is therefore: 1/2(mv² + Iω² )

For a wheel with all mass at the outer edge: I=mr²

For a rolling wheel: ω=v/r

Putting it all together you would get: 1/2(mv² + Iω² ) = 1/2((mv² + (mr² )(v/2) ² ) = 1/2(mv² + mv2).

The outcome is 2x.

This means any extra weight that is on the outside of Wheel A compared to Wheel B is pretty close to double by the time it hits the riders legs to apply power to accelerate it.

A real world illustration of this is demonstrated in the power data collected by WC XCO race teams.

Early in 2012 I was sent power data sets for different analysis (nothing to do with bikes per se rather robustness of an aspect of the data collected). The sets contained different tyres and setups, some different frame setups, some different wheel dia setups used in short course XC. The majority of data is for tyres - from heavy sidewall, differing pressure, tubs, high pressure 29 skinny to low pressure 26 baggies. The riders were elite girls and guys riding test courses and WC courses in the 2010 and most of 2011 comp. There were nearly a hundred data sets each containing the results of many hours of testing. Every major XCO team on the World Cup circuit would have similar with the three larger corporate teams probably many times more.

For example. The stronger sidewall tyres predominantly used and tested in this team weighed an approx 50g heavier than the standard tyres. The additional 100 grams on the edge of the wheels returned between 1.2%ave and 2.9%ave less efficiency ie more power over time, from the different courses of the 18mths of tests. The spread is caused by the varying amount of climbing etc between courses. When the climbs are considered separately the figure got up to a high of 7.5%ave difference. This might be considered a small weight on the outside edge but this amount of weight can be significant on a course with significant elevation, pinches or accelerations. When the rider/bike weight is low, as elite XC racers usually are, it becomes more significant.

In all of the data sets any time significant weight was added to a wheel there was an assessable decrease in efficiency of that wheel. So although the laws of physics prevailed, how much loss was dependent on different factors – this data did not show a linear correlation for weight increase. There are many factors that influence power which must be considered in the context of the test circuit.

Larger dia wheels are at an inherent weight disadvantage compared to smaller dia wheelsets created by mass difference of the rim and stronger build needed to offset additional flex (about 10% to 14% of the rims and build) and WC teams use different methods to gain parity.

For example. Analysis included a 1160g 29 tubular wheelset that when a similar volume tub tyre was added was of comparable weight of the standard team 26 clincher wheelset with a tyre of similar volume. The data returned was within or about the same for both wheelsets. (This team – and most others – judge that due to accuracy tolerances of equipment and other variances that if sets of data return less 1% difference it is too close to call).

Another Example. An investigation of a heavier (than the previous 1160g) tubular 29 wheelset with the standard 26 clincher race wheelset with a higher volume tyre to create similar weight. Again the results fell on or under 1%.

Also. The larger WC teams use ‘line’ rims and ‘line’ tyres (pulled from manufacturing lines, they are lighter than normal due to manufacturing tolerances) Using these components it is possible with ½ nipples and cleaning up the rims to construct 29 wheels as light or lighter than many 26 wheels used. If that team then used similar volume clincher tyres then the expectation (amongst this team that is without these resources) is the larger dia wheelset can be as power efficient as a team with the smaller dia clincher wheelsets without the disadvantages that tubulars pose.

The team determined, as suggested by this data (ie with the short course XC setups, tyres and riders tested), if rotating weight is similar there is no assessable loss of efficiency between dia of wheelsets used. There is some practical restriction in choice of stronger sidewalls/volume etc for larger wheels due to the corresponding increase in weight when it is already compromising to get the larger wheelset down to acceptable weight.

Tyres are most easily adjusted to get a wheel to an acceptable weight. For example. When 29 wheels first appeared a 24hr racer (Ed Harris) ran a test in a race – and uploaded it - between the two available wheel dia at the time using powertap hubs. His first impressions were the smoothness and perceived speed of the 29 bike. He discovered after reviewing the power data the smaller dia bike had a 7% power efficiency advantage over the larger wheel dia bike. The large figure had come about because he had used the same width of tyre on both bikes as opposed to the same volume. So as well as the already 10% - 14% weight penalty on the rim/ spokes/nipples of the stock 29 wheels he had added more weight with a larger volume tyre. He may well have had an extra 100 to 200 extra grams on each wheel.

Similarly the AMB 26v29 test published in Sept 2011 edition. They used a more accurate crank power meter with more riders and more loops so more data. The article talked a lot about the smoothness of the larger dia wheel through the rock sections and rougher sections of the loops they rode. This may have been taken by the testers to assume that therefore the larger wheelsets were going to return quicker figures over the entirety of the loops. They didn’t seem to take into account that as well as the 10% - 14% weight penalty of the rim/ spokes/nipples of the stock large dia wheels, the testers used the same stock width tyre adding more weight and more volume, to the 29 wheelset which had to be ridden over the entire course not just the rougher/rockier areas. Again there was probably in the vicinity of 100 to 200grams extra on each wheel. The difference was enough to give the small dia wheel a 7.7% advantage over the whole circuit and up to 19% on some climbs with one 1’30” pinch climb giving a 30% advantage to the smaller wheel.

These figures are large and were not reproduced in any of the race teams tests for the reason WC XCO racing is not done with stock wheels. However with that much extra weight the numbers would probably be consistent with expectations.

Incident angle (the angle the tyre hits an object) and lever point advantage (a longer patch makes contact earlier in front of the axis). These give a larger dia wheel smoothness over rocks or rough ground. (and this would be a factor for more consideration in many cases eg in longer events - this data has context for short course XC only). Tyre manufacturers provide lab analysis from wheels and tyres tested on tyre roller machines to the teams that use their products. There are measurable differences in these lab analyses of lower incident angle and the lever point advantage of a longer contact patch of a larger dia tyre in these studies. However this team’s test results have been unable to clearly demonstrate any incident angle efficiency advantage when those wheels are used in a race setup over the entirety of the test loop. In some courses there was above 1%ave which signify advantage on most others the data fell between + /-1%. This is not unusual and doesn’t mean it is not an important parameter - it is just that any efficiency of the incidence angle, in singularity (ie other parameters are the same on both wheelsets so as to attempt to test a single parameter), was not assessable enough to clearly demonstrate an advantage in this testing within the set boundaries. There are many parts of the bike that, while they have advantage in a section of a course, are difficult to quantify when the results are taken from racing the entire circuit.

Setting up the test between similar weight 26 and 29 wheelsets was problematic in itself. The first 29 wheelset was not considered sufficiently robust for racing after a failure of one in testing. This team used 29 tubular wheels to create light wheelsets and while tubulars have some positives they have their own set of drawbacks.

This leaves weight in the context of short course XC racing as the overarching consideration for performance in wheels - though tougher sidewalls, tread, high volume, psi are some of the many other tyre parameters to consider when race tactics and courses dictate.

This is at odds with the prevailing marketing message of the corporations pushing a wheel size which seems to suggest that larger volume, lower incident angle and lever point but more mass of the larger wheel can somehow defy the laws of physics. And despite the library of power data that the large corporate teams have at their disposal from their race teams, their marketing departments have not been able to find data to back their claims that could be released or leaked, relevant to racing, that is contrary to the data repeated here.

At the end of it – in the real world of age group racing that most of us now live in - if someone is putting in double the hours of the next guy, it doesn’t matter about the bike - he should beat him up a hill on a clunker. Equally, if two riders are matched in fitness, and the bikes are of similar weight - then the person who is riding rims/tyres that are 10 to 14 percent heavier is going to have a hard time catching the other guy.

Corporations exist to make profit. Profit is made by creating a demand and selling product. It seems hobbies/interests are driven by marketing departments and appear to escape any regulatory scrutiny of their wilder claims. Cycling is no exception.

 

 

 

I recently tested my 26 against 5 very good 29 ers bikes over a course from home up to level 4 in Tokai and back home again.

 

My 26er was faster everytime.

 

My conclusion is that 29ers are tanks with weak flexible wheels.

 

 

hey hold on I've been sayin that for years

 

oh well nothing to see, moving swiftly along