29ers

[Cyclist33]

Depending on how you model the wheel,

If you model it as a hollow disc then that would be correct, but the hub and spokes account for probably half of the weight. So more accurate to model it is a solid disc rather than a hollow one.

So it would be I=1/2M*R^2 So the change of inertia by a bigger wheel will be even less.

Looked on wiggle and picked 2 pricier wheels, that seemed identical other than size.

http://www.wiggle.co.uk/sram-rise-60-29er-rear-mtb-wheel/
http://www.wiggle.co.uk/sram-rise-60-mtb-rear-wheel/

It only gives the weight as a wheel set, so lets assume that front and rear are equal and half the weights.

29er rear is 710g
26 is 665

Without tyres, 29 radius is 0.3683m
26 is 0.3302

Inertia for the 29 is 0.048 kg m^2
and for the 26 0.036 kg m^2

So while the numbers may seem small, it's actually just over a 30% increase of inertia PER WHEEL, and not a difference I would call negligible.

BUT,



Inertia of the wheels is relevant to acceleration, deceleration, and turning. That all acts independently of momentum.

Though the momentum p = mv
Lets assume a 10kg bike without wheels, and a 70kg rider. And, a speed of just over 12mph to give an easy 5.5m/s

For the 26 you have a total weight of 81.33kg with momentum of 447.32 kg m/s
For the 29 a total weight of 81.42kg and momentum of 447.81 kg m/s

So about 0.1% difference in momentum by changing. So, in some situations it will like to have an effect. Changing direction is unlikely to be any different between the 2 wheel sizes.

Climbing hills? Climbing a steep hill at just under 8mph or 3.5 m/s?
26 is 284.66 kg m/s
29 is 284.97 kg m/s

A difference of less than 0.05% so sticking 29s on going up a hill isn't going to slow you down much.

A quick descent at 20mph ish or 8.5m/s?
26 is 691.31 kg m/s vs
29 at 692.07 kg m/s

A difference of 0.1% again.

So it seems what you gain downhill is similar or equal to what you would lose going uphill. The difference in acceleration between them would be negligible. The idea that the wheels spin up easier is flawed in that the wheel is independent of the bicycle. Stick it on a spindle and sure it will spin up and slow down quicker, but having to transmit that motion into the whole bicycle the 29" wheel isn't likely to have a massive effect.

They shown some considerable differences, but with such a small study, as he said it's statistically negligible. There are too many factors that could have accounted for the difference, course familiarity for one, more familiar with the course later on in the day when the 29" wheel was used? They didn't say in what order each run was done in? Course changes, becoming cleaner and faster throughout the day? It happens in all forms of gravel racing too.

Did they change the gearing between the different wheels? As the larger wheels will roll faster for the same gearing and cadence. A true test should have made sure that the gearing of the bike was adjusted for each wheel size.

The angle of attack works out around 2degrees ish less for the 29" wheel (I really can't be bothered typing out the differentiation, much easier on paper )

So there is an advantage for 29" wheels there, though it only works out to be an advantage of around 15mm or so. Hitting something 115mm on a 29" wheel is roughly the same as hitting something 100mm on a 26" wheel. Again, I don't think that is enough to cause a massive difference in speed, especially with suspension systems too.

It honestly doesn't seem to have any significant advantage, other than a psychological one, as with anything involving human performance. If you think you're quicker with it, you most likely will be.

Careful now - you demonstrated a point logically from scientific principles - now you will be villified as if a crackpot who thinks the world is (roughly) spherical.

 

[Cyclist33]

My sentence structure is a little weird there. It is of course entirely negligible, I was expecting there to be a larger difference, so was preparing to prove you wrong But instead, I proved you correct, and missed that paragraph out while proof reading.

Sometimes, our own in depth analysis proves our own logical thoughts incorrect. As a mechanical design engineer, I can do nothing but believe in the numbers, maths doesn't lie.

Now you're *really* skating on thin ice. The emperor will not be happy that you don't wuvv his new clothes.

 

[marzjennings]

I hope you are reading Phil Dawson's analysis above. I've now come to realize that you only know how to attack a problem with bluster and then modify your statements as the story unfolds. For the second time in this thread you've put words in my mouth and built an argument around it. This time you pretend I say wheel size is immaterial. Go shoot your straw man somewhere else. Tangible differences you say? Have a good look and figure out a new way to define tangible your way.

So what exactly is your opinion on 29ers wheels, as your initial post seemed to imply you think there's no difference and no advantage.

I haven't changed or modified my position or story. 29er's have their benefits and it's up to the rider to determine if these benefits fit their style of riding.

And I see your reading comprehension is on a par with your maths and physics, I think my use of tangible is appropriate to describe how a rider may feel by touch the differences in wheel size.

I read Phil's post, some good detail, and my constant position still stands that these calculable differences can be felt by the rider. Is your position is that they can't?

 

[jowwy]

I like my 29er.........who cares what everyone else thinks, just ride it

 

[Cyclist33]

So what exactly is your opinion on 29ers wheels, as your initial post seemed to imply you think there's no difference and no advantage.

I haven't changed or modified my position or story. 29er's have their benefits and it's up to the rider to determine if these benefits fit their style of riding.

And I see your reading comprehension is on a par with your maths and physics, I think my use of tangible is appropriate to describe how a rider may feel by touch the differences in wheel size.

I read Phil's post, some good detail, and my constant position still stands that these calculable differences can be felt by the rider. Is your position is that they can't?

I imagine it is, although I don't want to put words into anyone's mouth. I am just wondering though, if you took a bath, and then put enough extra hot water in to raise it by the same kind of %ages, would any sane human being notice the difference?

 

[Crackle]

Wheel size is not the whole story though is it. COG, wheelbase, stay length, fork offset, head height, BB height, tyre volume all make a difference to the handling of the bike and all need to be slightly different to accommodate different wheel sizes. Differences in frame design alter stiffness, feedback, response and none of it lends itself to an easy analysis. It isn't enough to say a 29er is like this and a 26er is like this, except perhaps at extreme ends, like xc racing or downhill, everywhere else is a bit greyer.

 

[marzjennings]

Wheel size is not the whole story though is it. COG, wheelbase, stay length, fork offset, head height, BB height, tyre volume all make a difference to the handling of the bike and all need to be slightly different to accommodate different wheel sizes. Differences in frame design alter stiffness, feedback, response and none of it lends itself to an easy analysis. It isn't enough to say a 29er is like this and a 26er is like this, except perhaps at extreme ends, like xc racing or downhill, everywhere else is a bit greyer.

Oh yes, absolutely. All the variables that go into bike design and build will impact how a bike feels and rides. That's why, as others have mentioned, test riding a bike is key to knowing if all those differences fit with an individuals riding style.

 

[Yellow Saddle]

So what exactly is your opinion on 29ers wheels, as your initial post seemed to imply you think there's no difference and no advantage.

I haven't changed or modified my position or story. 29er's have their benefits and it's up to the rider to determine if these benefits fit their style of riding.

And I see your reading comprehension is on a par with your maths and physics, I think my use of tangible is appropriate to describe how a rider may feel by touch the differences in wheel size. The best you can do is to claim that I seem to imply. It is superfluous to point out that you stand firm by your incorrect claims, but I'll nevertheless do so. Bluster makes you feel better about your errors. So be it.



I read Phil's post, some good detail, and my constant position still stands that these calculable differences can be felt by the rider. Is your position is that they can't?

You only now ask what my position is. How strange. You've attacked and insulted me before you even knew how I feel on the topic. Having a bad day or just an online bully?

Then, you say Phil's post has some good detail. You make it sound like he only stated half-truths and that you know something that no-one else knows. You don't have the courage to keep quiet or admit that you've been shown a rational way to examine your spurious beliefs.

 

[marzjennings]

You only now ask what my position is. How strange. You've attacked and insulted me before you even knew how I feel on the topic. Having a bad day or just an online bully?

Then, you say Phil's post has some good detail. You make it sound like he only stated half-truths and that you know something that no-one else knows. You don't have the courage to keep quiet or admit that you've been shown a rational way to examine our spurious beliefs.

Well, to be honest I was really asking you to expand on your initial statement, "I cannot come up with a single advantage of that format." to see if you really think differences in wheel size are imperceivable to a rider.

My spurious beliefs are shared with almost every single MTB XC racer I know, from Cat 3 to Open Pro and the few they don't ride 29er ride 26er because it's what works for them. After they've tested both, noted the differences and made an informed choice.

In the clinics we give we guide people in how to handle different wheel sizes, wider bars for 29ers, different gears choices for climbs, etc. The bikes ride differently because they are different.

Have you actually ridden a 29er?

 

[Eagone]

Well now now!

Got fed up reading all of Page 2 and 3,

I've just got a Trek X-calibre 29er its heavier than my Trek 26er but it looks good, rides great and the key thing is its fun.
I'll never got back to a 26er!!

We have a local trail center with only blue trails, a few berms, some small jumps and various twists and turns and it handles them all well, it takes bridleways in its stride and hills are as easy as riding the lighter 26er.

The bike gives me the confidence to get out the house and take it anywhere I want to.... and thats all that matters.

 

[si_c]

I'm convinced my 26" er is better than my 29" er, but that's partly because I don't have a 29" er

 

[Spoked Wheels]

I've never ridden a 29er and I don't think I'd want to. I find this is just companies marketing an idea without any substantial benefits to the riders.

I said in another thread that 29er would not make as strong wheels as 26", hoping somebody would bite and educate me as to why 29er were a good idea but nobody did basically, I just cannot see these wheels as other than a commercial "upgrade" , heavy, more expensive, etc I helped one of our club lady riders to load her new 29er bike on her VW polo and I can tell you, she could not do it by herself..... she kept cursing the man who stole her 26"

 

[Slioch]

Putting the discussion around which size is more efficient to one side for a moment, which wheel is stronger?

I appreciate there are a whole load of variables but, assuming component quality and wheelbuilder skills are equal, which wheel size will give you more confidence of not getting trashed when you are out on the trails miles from anywhere?

My gut feel would be that the 26er would be less likely to get bent than the 29er due to the smaller size, shorter spokes, less "torque" (if that's the right term) etc, but I have no science to back this up.

I would appreciate anyone's thoughts as I am considering a new Hardtail mountain bike but not sure whether to go for 26, 29, or even 27.5. My current MTB is 26, so that may be causing me to be biased.

To be honest, when I am out on the trails I would put reliability ahead of marginal performance gains.

 

[Crackle]

Is wheel strength an issue for most of us? I ride factory built wheels on all my bikes and as for weight, depends on the bike and components. Based on anecdote, 26ers are really heavy cause I needed a crane to get a full suss Apollo on my roofrack!

 

[Yellow Saddle]

Putting the discussion around which size is more efficient to one side for a moment, which wheel is stronger?

I appreciate there are a whole load of variables but, assuming component quality and wheelbuilder skills are equal, which wheel size will give you more confidence of not getting trashed when you are out on the trails miles from anywhere?

My gut feel would be that the 26er would be less likely to get bent than the 29er due to the smaller size, shorter spokes, less "torque" (if that's the right term) etc, but I have no science to back this up.

I would appreciate anyone's thoughts as I am considering a new Hardtail mountain bike but not sure whether to go for 26, 29, or even 27.5. My current MTB is 26, so that may be causing me to be biased.

To be honest, when I am out on the trails I would put reliability ahead of marginal performance gains.

It is an interesting question. Before I go ahead, I'd first like to define strong in this context. First thing is to differentiate between durability and strength. A wheel that can support a fat man without breaking is strong and one that will break when porky sits down is weak - in that context. However, most wheels are strong enough. Think of a plastic ballpoint pen. The shaft is made of plastic and is relatively weak - you can break it. However, there is no need to make it from titanium, because it is strong enough. A durable wheel is one that can carry its designated payload over many, many miles without failure.

Pertaining to the above, a lightweight racing wheel with 20 spokes is strong enough but it is not as durable as a heavier wheel with 36 spokes and a heavier (hence thicker and more material used) rim.

Strength in wheels:

Wheel strength is a function of:
1) The spoke bracing angle. This is the angle the spoke follows when it departs from the rim on its way to the hub. The bigger this angle, the better the rim is braced and the stronger the rim is in resisting side (lateral) forces. However, that angle does not make it better at carrying more weight. So, a steep angle resists sideways force but does nothing for its carrying capacity. the difference in bracing angle for two similar wheels I calculated using the same hub (Hope PRO II if you need to know) but two rims identical in materials and construction but the one is a 26" and the other one a 29". The left/right spoke angles for the 26" are 6.6º and 4.8º. For the 29" wheel they are 5.9º and 4.3º degrees respectively. The difference is minuscule however, take point two in consideration.
2) The distance between spokes on the rim. The bigger the distance between spokes, called unsupported span, the weaker the rim. Picture a wooden bridge with a large span and one with a short span. Which one will you steer your truck over? The distance between spokes (for a 36 spoke wheel) on a 26" rim is 57mm.
The difference between spokes on a 29" wheel is 64mm. Percentage-wise it is 12%
3) Quantity of material in rim and spokes. We're talking thickness here. More is stronger, less is weaker. Because 29" wheels are heavier but weight is a primary driver for bike equipment sales, manufacturers skimp on weight to bring the 29" wheels more in line with 26" wheels. This weakens the wheel considerably.
4) Overall strength is a combination of bracing angle, plus spoke span plus materials. Crudely expressed, our strength formula would then look like this: small angle x 12% x weight skimping. I thumbsuck a figure of 20% for the above example.

This figure of 20% is not unrealistic. Wheelbuilders perform a procedure called stress relieving at the end of the build. You put the wheel flat on the floor, grab it like a steering wheel in the quarter to three position and push down hard. The difference in flex between the two is remarkable. First-timers with a 29" wheel usually freak out.

Durability: This is a function of beefiness of the components, spoke count (translating as spoke span). All of these are compromised in a 29" wheel. How much? Too complicated without doing a materials assessment and FEA.

How does this translate in trail experience? Statistically more 29" front wheels collapse upon impact than 26" wheels. This was our experience in a large workshop over a period of about five years before I sold it.