Just built a 29'er. Will I ever ride on 26" wheels again?
- Thread starter NeilM
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I go for 40psi, see how it feels. Regardless of tyre size. Seems to work ok for me.
Just to throw a spanner in the works though, I recently did a race on my '93 Scott Pro Racing, and after some discussion amongst fellow Retrobike members, was running 20-25 psi in my tyres. Bloody flew around the course, and no pinch punctures either. Sure, they dragged a bit on thefire roads but more than made up the time I the woods.
Cheers Max
Just to throw a spanner in the works though, I recently did a race on my '93 Scott Pro Racing, and after some discussion amongst fellow Retrobike members, was running 20-25 psi in my tyres. Bloody flew around the course, and no pinch punctures either. Sure, they dragged a bit on thefire roads but more than made up the time I the woods.
Cheers Max
PurpleFrog
Kona Fan
stevet1":1uqklvc0 said:
I think most people believe that the wheels store a significant amount of energy as flywheels, but this isn't true. If your and your bike weigh 100kg and the wheels and tyres are 2kg of this, then at most they'll store about 4% of total energy. And 29er wheels only store perhaps 25% more energy that 26s - and 25% of 4% will have no noticeable impact on bike performance.
Longer wheelbase might be very important though - it will change the leverage exerted at the rear wheel by bumps under the front tyre.
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Thanks for the info.
The minimum recommended pressure on my Schwalbe Racing Ralph 26"x2.25 is 30psi and 26psi for my Racing Ralph 29"x2.25. That's a 15.4% difference. But whether that makes the 29er versions 15.4% more "smoother rolling" is another question.
The received wisdom amongst 29er enthusiasts was that 29ers have a larger ground contact patch compared to 26" bikes, hence they had more traction.
But that is now widely thought to be incorrect as the area of the contact patch is a product of the pounds per square inch (PSI) of the air in the tyre and the weight bearing down on the wheel. So a 20" tyre run at 20PSI will have the same contact area as a 29" tyre run at the same pressure. (20PSI x the area of the contact patch) However the 20" tyre may almost be bottoming against the rim whilst the 29" will look well inflated.
Therefore if people inflate their tyres by observing how much the tyres sag when they sit on the bike, then 29er riders will unwittingly be using lower pressures in their tyres compared to when they follow the same procedure for 26" wheels. And given the same tyre width, loading and distance from ground to rim, it should be possible to calculate the pressure differential between different wheel diameters.
Also, the shape of the contact patch between wheel sizes differs considerably as bigger wheels generally produce narrower and longer ground contact shapes. Though differences in rolling resistance due to this are probably small.
http://www.bikeradar.com/gear/article/b ... ths-29245/
Thanks for the info.
The minimum recommended pressure on my Schwalbe Racing Ralph 26"x2.25 is 30psi and 26psi for my Racing Ralph 29"x2.25. That's a 15.4% difference. But whether that makes the 29er versions 15.4% more "smoother rolling" is another question.
The received wisdom amongst 29er enthusiasts was that 29ers have a larger ground contact patch compared to 26" bikes, hence they had more traction.
But that is now widely thought to be incorrect as the area of the contact patch is a product of the pounds per square inch (PSI) of the air in the tyre and the weight bearing down on the wheel. So a 20" tyre run at 20PSI will have the same contact area as a 29" tyre run at the same pressure. (20PSI x the area of the contact patch) However the 20" tyre may almost be bottoming against the rim whilst the 29" will look well inflated.
Therefore if people inflate their tyres by observing how much the tyres sag when they sit on the bike, then 29er riders will unwittingly be using lower pressures in their tyres compared to when they follow the same procedure for 26" wheels. And given the same tyre width, loading and distance from ground to rim, it should be possible to calculate the pressure differential between different wheel diameters.
Also, the shape of the contact patch between wheel sizes differs considerably as bigger wheels generally produce narrower and longer ground contact shapes. Though differences in rolling resistance due to this are probably small.
http://www.bikeradar.com/gear/article/b ... ths-29245/
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If you have a 29er, one simple way to test the effect of tyre pressures on the 'free rolling' phenomenon is to experiment with tyre pressures.
If you pump both tyres up hard does the 'free rolling' effect decrease or disappear?
And if you reduce the pressures does the sensation of 'free rolling' increase?
If you have a 29er, one simple way to test the effect of tyre pressures on the 'free rolling' phenomenon is to experiment with tyre pressures.
If you pump both tyres up hard does the 'free rolling' effect decrease or disappear?
And if you reduce the pressures does the sensation of 'free rolling' increase?
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As mentioned before, I went from a 26" Orange 5 to a 29" Orange 5 29. Very similar bikes when the wheels size change is taken in to consideration. I put the same pressure in the 29" as I did in the 26".
The simple fact is that the often stated differences are true as in 29" rolls easier, gobbles up roots that would have the 26" stalling, is slower to get up to speed but once there holds it better but isn't as playful as 26" and prefers to stick to the ground rather then get air.
I was not a fan of 29" early on but the more I rode my friends 29ers the more I got it. I'm still not sure 29" will be my long term choice for an allrounder as I like aspects of the smaller wheels as much as I do the bigger but as a XC weapon it should be your only choice.
I'm willing to let anyone with a 26" Orange 5 have a go back to back with my 29er to see what I mean. The 29er is not necessarily better but it is different.
As mentioned before, I went from a 26" Orange 5 to a 29" Orange 5 29. Very similar bikes when the wheels size change is taken in to consideration. I put the same pressure in the 29" as I did in the 26".
The simple fact is that the often stated differences are true as in 29" rolls easier, gobbles up roots that would have the 26" stalling, is slower to get up to speed but once there holds it better but isn't as playful as 26" and prefers to stick to the ground rather then get air.
I was not a fan of 29" early on but the more I rode my friends 29ers the more I got it. I'm still not sure 29" will be my long term choice for an allrounder as I like aspects of the smaller wheels as much as I do the bigger but as a XC weapon it should be your only choice.
I'm willing to let anyone with a 26" Orange 5 have a go back to back with my 29er to see what I mean. The 29er is not necessarily better but it is different.
PurpleFrog
Kona Fan
Re: Re:
If you over pump the tyres on both bike sizes than the 29er may well feel better because of the longer wheel base - it will be the only thing left smoothing out bumps.
The interesting question is how a 26 would feel if it was built with the same wheelbase as a 29. People build bikes to look sexy, because that's what it sells. And a long empty section in the rear triangle does not look sexy... but a couple of extra inches of chainstay would give more roll-over. Then increase the volume of the 26er tyre so it is equal to the 29. I'm moderately sure that you'd have a bike with more roll-over at the cost of reduced agility, and which should stick to the ground more but be harder to manual - simple leverage alone should guarantee this.
GrahamJohnWallace":2abwcl1w said:
If you over pump the tyres on both bike sizes than the 29er may well feel better because of the longer wheel base - it will be the only thing left smoothing out bumps.
The interesting question is how a 26 would feel if it was built with the same wheelbase as a 29. People build bikes to look sexy, because that's what it sells. And a long empty section in the rear triangle does not look sexy... but a couple of extra inches of chainstay would give more roll-over. Then increase the volume of the 26er tyre so it is equal to the 29. I'm moderately sure that you'd have a bike with more roll-over at the cost of reduced agility, and which should stick to the ground more but be harder to manual - simple leverage alone should guarantee this.
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The theory I have for this is that the contact patch is roughly elliptical with the minor axis determined by the tyre width. Recently published research has confirmed that the contact patch area of a 29er tyre is the same as that of a 26" at the same pressure. Therefore if the tyre widths and resultant minor axis are the same then, the major axis must also be the same if we are to have contact patches of the same area.
In other words. If the contact patch area of different tyre diameters are the same, and the contact area width is the same, then the length must also be the same.
So narrower tyres have longer contact patches than wider tyres run at the same pressure. Roughly speaking, if you halve the with of the tyre you will double the length of the patch, thus making bottoming out against the rim more likely. So 29er style low pressures, would not be a good idea on cyclocross bikes.
And whilst a 29er tyre has roughly 10% more air volume than a 26er of the same width, running a slightly wider 26" tyre would even things out.
I have been playing about with tyre pressures on a variety of wheel sizes and my above statement appears to be wrong. Tyre contact patch shape differ with tyre width but not tyre diameter.GrahamJohnWallace":2owa1de8 said:
The theory I have for this is that the contact patch is roughly elliptical with the minor axis determined by the tyre width. Recently published research has confirmed that the contact patch area of a 29er tyre is the same as that of a 26" at the same pressure. Therefore if the tyre widths and resultant minor axis are the same then, the major axis must also be the same if we are to have contact patches of the same area.
In other words. If the contact patch area of different tyre diameters are the same, and the contact area width is the same, then the length must also be the same.
So narrower tyres have longer contact patches than wider tyres run at the same pressure. Roughly speaking, if you halve the with of the tyre you will double the length of the patch, thus making bottoming out against the rim more likely. So 29er style low pressures, would not be a good idea on cyclocross bikes.
And whilst a 29er tyre has roughly 10% more air volume than a 26er of the same width, running a slightly wider 26" tyre would even things out.
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