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given the debate, I'm surprised there dooesn't seem to be more quantifiable evidence of the differences (that I have been able to find anyway)
I know Dirt sort of did something a couple of months back, but this was predominantly downhill
I'd have thought it would be prety easy to take 2 similar bikes (eg Transition Bandit 26 and 29 seem very close to me other than wheel size) and time a number of riders around different parts of a course
Would have thought the manufacturers would have done this?
I'd have thought it would be prety easy to take 2 similar bikes (eg Transition Bandit 26 and 29 seem very close to me other than wheel size) and time a number of riders around different parts of a course
There have been a quite a few back to back comparisons posted on the web.
a lot of the racers have.
MattPage did a lot of experiments with 26/650/29 wheels recently.
Not sure he wants the results in the public domain though 🙂
From the department that brings you the science bit in shampoo commercials
Easy in theory. Nightmare in practice.....
For example do you give them the same tyres. Yes you say thats fair...
But is it. If the 29er has more grip then it could run a shallower tread for the same traction. Or if the 29 er is more comfortable over roots it could trade this comfort away for a thinner tyre. Which is presuambly is what a racer would do. If we are not talking about racing who cares which is faster....
mikewsmith - yeah like Michael McIntyre - "my wife bought some anti-wrinkle cream. I'm going to take it back in 20 years and ask for my money back"
Blind tests are pretty hard to arrange on a bike and as soon as the rider knows what they are riding it's pretty much impossible to control for their preconceptions. Basically, bikes tend to feel like we expect them to and whatever bike it was that you wanted to buy in the first place will probably feel the best.
Cheers,
Andy
If you're going to compare 26 and 29 you probably want to do so with tyres with equal contact patch size, so wider on the 26, and run the same pressures. Tyre theory would then suggest that the 26 roll quicker when it's smoother and harder whilst the 29 roll quicker when it's bumpier or boggier. So on the face of it 29 should be better offroad much of the time.
29-26=3.
HTH
Math-S- Are you an American?
imo, there is no maths of value aside from physical comparisons of the wheels. And that tells you only a part of it. ie roll-over angles don't also consider tyre deformation differences at impact point. Volume variances. Contact patch etc etc. Too complex to model with any validity.
Would you try to balance variables between wheels, or keep tyres and pressures optimised for each wheel as a rider would? How do you test when off-road riding and riders themselves vary so much? I guess a rider, 2 or 3 otherwise near-equal bikes, a track and a HRM can help them decide what works best for them (many mags have done this - a feature rather than a test imo, but still, some result trends seem to appear in them), but I wouldn't call that 'doing the maths' as it can't be applied to riders or terrain equally.
I've done back-to-back runs on 3 wheel sizes and the only thing of value was how I felt the bikes rode differently and of that, what I would attribute to the wheels as one of those 'princess and the pea' kind of riders. I've also done roll down / along types of 'tests' on different tyres and pressures.
After all that, I only had more questions about accepted component designs and what we feel is important on a bike. Rim diameter isn't as important as we may think / in the way the generalisations suggest imo. ie, why all the focus on just that aspect of the wheel? We're happy to challenge one accepted norm yet not others, or we get distracted by one aspect and lose focus. Perhaps because (like suspension) it's too complex to sell easily without being distilled down to easily digested ideas.
Mountain Flyer did a test recently - last issue but 1 IIRC. They took 2 similar bikes a 29er and a 26er and did back to back loops over a range of loops. The net result was about even with the smaller wheel performing better in some areas and the bigger in others.
As others have said there's too many variables to be able to make a truly scientific test valid
I've rode my Cotic Soul and Solaris back to back
If bigger = Better then
29 > 26
therefore 29 is better than 26
QED
It'd be easy to time a downslope roll over roughish ground (not DH, just mimicking xc riding without pedalling). Done over a few different types of terrain in terms of bumpiness, that should sort out "rolling".
Grippiness, much harder
Handling, essentially impossible I'd think, as it's too subjective
So we're left with making up our own minds (as long as manufacturers allow us to, i.e. continue to supply both/either/650/wotevva)
@ failed engineer - no I'm not, just using an American expression.
In the Queen's own we tend not to use the expression "where's the maths", whereas the American's do tend to use "where's the math" or "show me the math" so I thought that would be obvious to one so clearly intellectual as yourself!
Why do people think 29rs have a bigger tyre contact patch size?
The size of the contact patch is related to the pressure in the tyre and the weight of the bike+rider, not the size of the wheel. Do 29r tyres tend to be run at lower pressures than 26r tyres?
Why do people think 29rs have a bigger tyre contact patch size?The size of the contact patch is related to the pressure in the tyre and the weight of the bike+rider, not the size of the wheel. Do 29r tyres tend to be run at lower pressures than 26r tyres?
Agreed, but if all things are equal then the 29er will have a very slightly larger contact area. One could then argue that this larger contact area would have a higher drag/rolling resistance.
[i]if all things are equal then the 29er will have a very slightly larger contact area.[/i]
Why (assuming that by 'all things' you mean the weight of the bike, the weight of the rider and the pressures in the tyres)?
IHN - totally agree.
You often see comments about better cornering grip and how that's related to a larger contact patch (shakes head in disbelief)....
Different shaped contact patch maybe but definitely not a different size.
[One of our standard training/interview questions used to be "how do you estimate the contact area of a tyre with the ground?" - some of the answers were hilarious bearing in mind they'd just spent 4 years studying engineering 🙂 .... my other favourite was "if you've got 1 newton in each pocket would your trousers fall down?"]
Wow, the seconds must have absolutely flown by!
[i]"how do you estimate the contact area of a tyre with the ground?"[/i]
Er, my answer would be divide the weight of the thing by the pressure in the tyres (using same 'weight' units for each, obviously) and then by the number of tyres on the ground. Is there an easier way... 😐
Give a Pro a 26, 650b and 29er - tell them they can ride any of the three and they're paid on results, easy. Although they may choose different bikes for different days/course/weather etc...
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Ah well spotted IHN 🙂
Oh no, not again...
Totally agree with jameso though. The tests are pretty pointless. Even if you had the same rider on two bikes, the one he rides first might be given an advantage or disadvantage, depending on how tired he gets and whether he's had his Weetabix. And anyone can post quite different times on every run down the same trail on the same day. That fact that the first three riders in the Olympics, from a field dominated by 29ers, were all on different wheel sizes shows that it's the rider, not the wheel, and that all these wheel sizes are perfectly valid sizes to have as a bike wheel. But it also shows, I think, that most of the claims are just pure marketing bull. If wheel size doesn't make a difference, how else do you sell it? So it's really just personal preference - and the power of suggestion.
Was I right? 🙂
Now to question 2; how many pockets and what kind of newtons are they?
The size of the contact patch is related to the pressure in the tyre and the weight of the bike+rider, not the size of the wheel
Correct. 29ers and 650B don't have a bigger contact patch than 26", it just tends to be a different shape, elongated as wheel diameter increases. So it can feel grippier sometimes and is percieved as bigger. If the tyre contact patch actually is bigger for a given pressure it will feel firmer to ride ie you can use less pressure for the same 'feel' over bumps (pressure, force and area), I think that's the only relationship. Sidewall thickness, rim width etc is a distraction though.
I don't get why it is so complicated.......
Okay - there is always a variable when a human is involved, but if there was a really significant difference between 2 bikes, same tread patterns, same tyre pressures, same shock pressures etc., the only real difference being wheel size, I think this would show. A few percent here or there could be put down to human variables, but a big difference would show through - imho....
Static contact patch is proportional to the system weight divided by tyre pressure. Dynamic contact patch increases with wider and/or larger diameter tyres. There's a reason supercars have bigger tyres than superminis.
Why do people think 29rs have a bigger tyre contact patch size?The size of the contact patch is related to the pressure in the tyre and the weight of the bike+rider, not the size of the wheel. Do 29r tyres tend to be run at lower pressures than 26r tyres?
Contact patch is related to the size of the wheel. The bigger the wheel, the bigger the contact patch.
Static contact patch is proportional to the system weight divided by tyre pressure. Dynamic contact patch increases with wider and/or larger diameter tyres. There's a reason supercars have bigger tyres than superminis.
Yep.
By reducing tyre width but increasing wheel size, contact patch is maintained but drag is reduced.
Give a Pro a 26, 650b and 29er - tell them they can ride any of the three and they're paid on results, easy. Although they may choose different bikes for different days/course/weather etc...
Scott did just that.
Nino Schurter chose 650b
Florian Vogel chose 29er
Both did perfectly well on 26" wheels, so it's not hugely helpful!
I don't get why it is so complicated.......
Humna variables aside, imagine trying to set up a computer model that included all the terrain variations and riding dynamics over a 2 hr or 12 hr ride. It's too complicated. I think the results of the fictional test would be very easy to tip either way just by changing a small variable ie there's not a lot in it unless you know what you want the wheel for. There is no 'better', just 'more fun for me'.
If in doubt, pick the middle size )
I had a look at this recently. One quanitfiable difference is that 29" wheels and tyres weigh around 15% more than their 26" equivalents. The tyres and rims are also further away from the hub so I am guessing that makes them around 20% harder to accelerate but that they have 20% more "momentum".
This would suggest that a rider doing a lot of techy climbs and descents with constant variations in speed would be better off on 26", but someone favouring smoother XC type trails would be better off on 29"
^ True, but then consider roll-over and momentum benefit etc on those techy sections, and the ease of moving around a smaller wheel ..
We get to the point of Rorschach's gif very quickly )
Where does a 69er fit in this equation?
and does a 69er = 650b F+R once it's all equated?
I'm out..
49er fat bike anyone?
CaptainMainwaring - MemberI had a look at this recently. One quanitfiable difference is that 29" wheels and tyres weigh around 15% more than their 26" equivalents. The tyres and rims are also further away from the hub so I am guessing that makes them around 20% harder to accelerate but that they have 20% more "momentum".
This would suggest that a rider doing a lot of techy climbs and descents with constant variations in speed would be better off on 26", but someone favouring smoother XC type trails would be better off on 29"
Posted 13 minutes ago # Edit
jameso - Member
^ True, but then consider roll-over and momentum benefit etc on those techy sections, and the ease of moving around a smaller wheel ..
We get to the point of Rorschach's gif very quickly )
I agree that that there are lots of other factors, but they are difficult to quantify and in some cases could be +ve or -ve depending on circumstances.
Yet another factor is that apart from weighing more, 29" wheels are more prone to lateral distortion under load so again MAY be an issue for techy sections or cornering hard
I've rode 24", 26", 650b, 29" and 29" front with 26" rear - all good fun in their own way as they all ride and handle different over similar terrain, none were necessarily quantifiably better or worse than the other for the entirety of a given trail, they're just bikes and if you're a crap rider on one wheel size you'll be an equally crap rider on any other wheel size so stop believing there is a holy grail of wheel size that'll turn you into a riding god.
If you're tall n' lanky like a big streak of piss then a 29" wheeled bike may be the better bike for you, if your short n' squat like a turd dropped from a height then a 26" wheeled bike may be better for you, if you're one of those "normal" folk in the middle then perhaps a 650b wheeled bike may be better for you.
Personally i resemble a short n' squat turd so i ride a 26".
Better at rolling over big rocks and more momentum. Sounds like they should be good for downhill to me... More so than XC even.
If you're comparing, would you use the same travel forks, or the same length/height?
It's not about the science.
Big wheels are more fun.
(I find).
No maths required. The rolling resistance thing is a bit of a red herring as it is more related to tyre pressure. Simply put it is all about conservation of momentum. A larger wheel effectively flattens a bump, meaning less kinetic energy is wasted when the wheel rolls over a bump (i.e. less speed is lost), which in turn requires less energy the rider has to put in to maintain speed or in riding over bumps on a downhill. This is obviouly only of importance to those where speed over the ground is important - if you are into jumps, then suspension is far more important so you're not going to be keen to compromise suspension travel for speed over the ground - so 26ers will still rule here. The reality is can you tell the difference? I have, but it is not that great - its not transformed me from an average rider into a superstar overnight. I wonder if they have these debates over on the tractor forum?