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Wheel Size
NB: Originally posted elsewhere on the Global Riders Network and appears via syndication.
So recently I have been riding my mates dual 29er around to get a feel for it to see if its for me and I have noticed a few differences to my hardtail 26er. I find that up hills it a lot slower and takes a lot more energy to get up a hill on the 29er than my 26er. Is this due to suspension or wheelsize or am I just imagining things?
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gearing if the same size sprockets on the 26 and 29er will be higher on the 29er de to larger wheel size.
The difference between FS and hardtail is likely to be more significant than the wheel size alone for difference in pedalling efficiency, and feeling of pedalling energy.
Hardtails climb faster than duallies due to lower energy absorption, and 29ers are slower to spin up, but they don't drop into the rough stuff as much so they don't lose momentum as much when up to speed. And hardtails are more tiring to ride longer distances because you're out of the saddle a lot more, so the longer the ride the more you'll like a dually.
So the answer is .... it depends.
Theres such little change that makes quite a big bit of difference, would you say for a hill ride (so up a long way and down) it would be better going witha 26er rear suspension as 26ers go up hills better and you can always turn off the rear suspension?
Watch this video
http://youtu.be/i0fJzRQVZPU
Bit of both.
A bigger wheel means more rotational mass further out from the center. This means more resistance to acceleration. Climbing a hill is accelerating against gravity
So given same rim and tyre type a 29er will be harder to ride up hill than a 26.
However suspension, frame design, bike setup and a bunch of other factors come into play would would have just as much if not more effect on your result.
As for the vid macr a sample size of one is a poor test
Any DHer will tell you the first run is the slowest. I'd like to see them test it over several runs on consecutive days
(Day 1 3 runs on the 26er first followed by 3 on the 29er. then swap for day 2) and take the average. If there was much difference between the two results I'd be surprised
Climbing at hill at constant speed isn't accelerating against gravity so a larger wheel with a higher moment of intertia (5 yrs of uni went into that term) won't make any difference in how hard it is to get up the hill. It will however be hard to get spinning from rest and will not respond as well to surges of power as the slope changes or you increase your speed
and Specialized's marketing department would have a video on their website which said their latest technology (29er) was inferior to their older bikes (26) and they were idiots for wasting so much time and money developing it?
Any climbing involves providing a force greater than gravity to be able to overcome it. Remember that gravity is a force that is constantly accelerating - If you fall from a plane your speed will increase at a constant rate (9.8m/s/s minus wind resistance) until wind resistance = gravity & then you're at terminal velocity. If you remember from Newton's Law that Force = Mass x Acceleration, then Flynny is correct in saying that in climbing a hill is accelerating against gravity, because any force has acceleration as an essential component. This equation also shows that for a lighter mass, the acceleration you provide will be lower to achieve the same net force. ie lighter bikes climb easier.
And yet, the Discodan is also correct in that a 29er wheel has a larger moment of inertia - which means that once it is up to speed it will maintain momentum better than a 26er, as it will resist decelleration in the same way that is resists acceleration. It acts more like a flywheel due to the increased mass around the circumference. But the steeper the hill, the more gravity you need to overcome & the increased 29er's momentum becomes less significant.
This is all getting quite complicated and scientific! All I know is that I have previously ridden a 26er and am now the proud owner of a much loved (Specialized) 29er and...it goes like a rocket. Up hill, down hill, on the flat, everywhere. It goes like a rocket. Yes, it probably does take a miniscule more effort (and I really mean miniscule) to get it up to speed but once up to speed, wow, it really flies. I don't notice it being any more effort up hill than the 26er - in the Fling it was a dream to ride and I even enjoyed the hills!
Will my 26er still get a work-out? Definitely. Will I buy another 26er? Probably not. Then again, where 26ers have it well over 29ers (downhill, freeride, etc.) is not what I do these days.
I don't want to turn this into an engineering pissing match but..
climbing isn't 'accelerating' against gravity if you're at a constant speed, it's only acceleration if your speed is changing. If going up a slope at constant speed you need to apply a force equal to the bike/rider mass times the gravitational constant g (9.8 m/s/s) which means a lighter bike requires less force in your legs to get up the hill.
The slower feel of the 29er may be due to being in the same gear which is not the same due to the effect of wheel size?
My 2c worth.
Well I own an Epic 26er (2008 alloy large) and an Epic 29er (2012 carbon medium). Both bikes are about the same weight and length. I feel the 29er is about a half gear harder to pedal up hill (only way I can think to describe it), so it requires a bit more effort to get going, however, down hill and on the flat it is significantly faster and handles better. Now I know there is an additional four years of tech in the 2012 model, however, that aside, I do think the 29er is the better bike in terms of overall performance and the additional push required to get going up hill is only a minor thing and something that is easily trained into.
So in answer to your question,(IMO)I don't think it takes a lot more energy to get up a hill on a 29er.
I think someone else has already made the point that if you're running the same gearing on the two bikes, the 29'er will feel slower uphill than a 26'er because you are effectively pushing a slightly higher gearing ratio courtesy of the bigger wheel. I went to a 36t rear at the top of the cluster to get me roughly the same ratio as the 34t on my previous 26'er, so I could be just as slow up the steeper hills......
Have a look at the units of 'g'.
Or to put it another way if you stopped pedalling uphill would you decelerate?
Riding a bike always involves acceleration wether it be against friction and/or gravity or preferably with gravities assistance. Since you are 'rolling' on a bike (rather than sliding which is bad!) the larger your rotational inertia the more torque you will have to apply at the pedals to accelerate.
29ers generally have a greater rotational inertia than 26ers (otherwise you should look at a wheel upgrade for your 26er). 29ers generally experience less friction due to bumpy terrain (but this is really difficult to quantify).
To sum it all up I wish I was riding any bike 26", 29" or even 700cc rather than stuck in the office on a Sat!!
If you are at a constant speed, regardless of whether you are on the flat or going up a hill, you are not accelerating. Acceleration is the rate of change of speed, if speed doesn't change then you're not accelerating which we all know as common sense but are getting confused since we've bought gravity into it.
When riding up a hill at constant speed you are inputting a force (which is equal to mass x g plus a bit for friction) to increase the potential energy of the bike (i.e. get it higher) but you are not accelerating. If you stop pedalling you decellerate and stop but that doesn't mean you were accelerating in the first place, actually you we're roughly in equilibrium between the force of gravity and the force of your pedalling (remembering a body will travel at constant speed unless acted on by a net force).
Bring it back to rotational intertia; bigger wheels take more force to get up to speed but have more momentum once they're turning. They take the same amount of force to keep pedalling at a constant speed which is just the force to overcome friction and any bumps you're hitting
When riding uphill you have to overcome the force of gravity. This force is essentially constant regardless of your wheel size and indeed your mass (as the Earth's mass is so much greater) this is why we can simplify it as a constant acceleration.
You apply this force to the ground at your rear wheel contact patch, therefore your rear wheel is transmitting a torque = rotational inertia x angular acceleration. So assuming a 29er has a greater rotational inertia than a 26er, and you have not gained any weight since since going back to the 26er, more of your energy (not force so we don't have to account for gearing ratios) will be required to acheive the same constant speed uphill on the 29er.
The advantages of the 29er on flat are that the opposing force due to friction (fewer rotations of the wheel at the same speed) and losses from bumps and uneven terrain should be less. Also the flywheel effect (a discussion in it own right having to do with energy storage).
Have a look at 700cc time trial wheels vs mountain stage wheels, why are lighter rims (less rotational inertia) so important in mtn stages?
If your staying at a constant speed and direction its not accelerating. If your changing direction its accelerating even if you stay at the same speed.
Therefore if you have corners or changes in gradient then your accelerating (or decelerating if it gets steeper) however if the gradient stays the same then its constant.
i like big wheels
by that logic (that the torque/force to get up a hill is the product of rotational intertia and the angular acceleration of the wheel) if you could half the rotational internia it would only take half the effort to get up a hill. Extend it further and if you could create wheels of zero angular intertia then you wouldn't have to pedal at all to get up hills, now we know that's not the case because there is the rest of the bike and rider to get up the hill. The flaw in your logic is that old chessnut of acceleration vs constant speed, your equation is right for the EXTRA force to increase your speed if you're accelerating (which we're not in this example) but forgets about the base force to get you up a hill at constant speed.
Anyway I'm going to punch out of this thread for now. Without waving my willy around too much I went through all of this stuff when I got my mechanical engineering degree (with honours)(do you like what I did there, subtle don't you think?) so I'm pretty confident about this crap
I don't usually make ad hominen replies but all this talk of degrees and waving willies... Honors eng degrees are a dime a dozen around my industry and unfortunately amongst all that education there is still a lack of critical thinking and problem solving capability (subtle yes?).
The following equation expresses the kinteic energy of a rolling wheel:
KE = 0.5mv^2 + 0.5Iw^2
where m is the mass of the wheel,
v is the translational velocity of the centre of mass of the wheel (you can think of this as the speed of the bike),
I is the mass moment of inertia of the wheel about the axle and,
w is the angular velocity of the wheel (rpm of the wheel)
Conservation of energy tells us that we must input kinetic energy to get up the hill (equivalent to the rate of gain of potential energy).
As you can see for a constant speed (v) up the hill if I and m increase (for instance a 29" wheel instead of a 26" wheel) KE increases. It is true to say that w will decrease for the larger diameter wheel (one revolution covers more distance) but w decreases linearly with increase in diameter (C = Pi * d) while I increases exponentially (I = mr^2 for a hoop).
It takes more energy to push a heavier mass up a hill and it also takes more enery to roll a larger moment of inertia up a hill.
So what your saying is I should make my pancakes bigger to get the most benefit.
Mechanical engineering degree? Even a dumby like me can get one of those.
Last week I couldn't spell ungineer, now I are one.
Or we're all gonna end up getting paid a whole lot less
just go ride
Maybe this will all be more interesting once A Current Affair decides to do an expose of the 29" myth.
I think what largethomas is saying is, to roll well uphill, we should all ride bromptons?
His post could do with re-reading as there may be some obfuscation in the interpretation of the equations, but in all honesty, theres a lot more to the difference between a 29er and a 26er than just the equtions of power. As engineers we all know that theories are written to be adapted by real life trial. If not, then we'd never need do another destructive test again, and accountants could rule the world.
Engineering is the science of asking questions, and seeking knowledge, about the physical environment and applying it in a controlled and considered manner. Not the science of willy waving about what you learned from a book during a 4 year break between school and life.
"theres a lot more to the difference between a 29er and a 26er than just the equtions of power"
This.
There seem to be a lot more 29" MTBs at UCI events than bromptons!?!
Could be a new niche, just need to convince Absalon to ride one. I hear that the frame flex has been specially engineered to combine the ride benefits of a dually and the power transfer of a hardtail.
Just shut up and Ride!
Don't nice any difference riding my Paradox to my Spitfire, must be the ribbed short chainstays that let you get the power down, you know about that single speeding?
Here's a quick and easy practical demonstration of rotational inertia and angular momentum.
Take your bike and shift it into top gear, then flip it over so it’s resting on the seat and handle bars.
Spin the pedals to get up to a maximum speed (eg 100 cadence), the work you have done is the work required to overcome the rotational inertia and increase the angular momentum of the wheel, plus a little energy lost to noise and friction.
Now maintain that speed, the work you doing is the work required to maintain equilibrium. This is the energy lost to noise and friction.
Now stop spinning the pedals and time how long the wheel comes to a stop (could be a while). You are now measuring how long it takes the work you put into building the angular momentum of the wheel to be dissipated by the energy loss due to noise and friction.
RESULT: You've demonstrated how much work you do to speed up your wheel to maximum speed and shown what inherent losses are in your system (bicycle) due to noise and friction. You'll likely to have noted that the work done to get up to speed is not that great (you've done it quite quickly with your arms alone). All being well with your bicycle you've probably also noted that it’s not too much work to maintain the top speed.
WHAT HAVE WE LEARNED? : Quite quickly we've learned how much work it takes to speed up and maintain a wheel on our bicycle and observed that it’s not that much. Since our bicycle has two wheels we know that actual riding is roughly double that work. Still not that much. We already knew from experience that the most work we do on the bike is increasing our potential energy (riding up hills) and that the faster we go the more other factors like wind and rolling resistance become significant.
WHAT ELSE CAN WE LEARN? : We can use the demonstration to make a rough comparison between bikes. With the assumption that the top gear of one bike results in the same top speed as another (the more anal can find gears are closely matched in speed) we can compare the work needed to bring a wheel up to maximum speed, then hold it there, then compare the time it takes for the losses in the system to deplete the energy stored in the wheel. We will generally observe that it takes less work to speed up a small wheel and that a big wheel takes longer to spin down. But we also might observe that other factors such as quality of components, wear and tear, and mass of the wheel and tyre can make a big difference.
OTHER THINGS TO TRY: Put the bike on a trainer with no load, feel the work you are (not) doing with your legs.
So what's the big deal with 29ers? I've found that switching to a 29er has made a big improvement to riding trails uphill and on the flat compared to my old 26er. Sure some of this has got to do with the mechanical improvements of a newer bike, but much is also due to the properties of the bigger wheel. The 29er simply rolls over irregularities and carries it's momentum better than a 26er. Not being contentious here, simply take the comparison to extremes and compare how a 12" wheel rolls over something compared to say a monster truck.
There are compromises with everything and for me I don't know if I'm any faster, perhaps I'm even slower downhill on the 29er. That’s largely because of my lack of skill and building confidence in the 29er. A better, braver downhill rider is undoubtedly quicker downhill on a 29er than I could be on 26er or a BMX.
I don't yet feel I dominate the 29er like I can with the 26er, it feels bigger, less manoeuvrable and more unwieldy, but I'm still happy with the compromise and am building confidence every ride.
I hope this helps with the wheel size question. Suspension is a whole different and probably more complicated question again, but there are undoubtedly losses and compromises assocated to suspension systems. If the dual has a lockout then try that on the uphills to see what difference it makes. I decided to stick with the hardtail as I'm happy to compromise downhill speed and comfort to less weight and complexity. If it means I crash at a lower speed when going downhill, then that’s a good thing.
http://www.reynoldscycling.com/uploads/RZR_no6_L...
Interesting reading.
That said the larger wheels on the new XTC 2 29er I picked up are rolling over rocks nicely, but not sure I'm ready to give up the full suss 26er just yet.
We know that a lighter wheel accelerates quicker and is easier to pedal uphills (generally) Ive found this out myself as too im sure many have.
So here's a thought for all the mathematicians, mech engineers, nasa astronaughts etc
For the sake of the excercise im using general numbers.
Lets say the average 26" wheelset weighs in at a total weight of 3000 grams (tyres, rims, everything) It will have a rotational inertia of X (forgive me if i get my tech terms wrong, its been a while)
A lighter 26" wheelset weighing in at 2500 grams will have less inertia (therefore easier to pedal up hill etc)
So we know that if a 26" and a 29" wheelset weigh the same, the 26" is still easier to pedal.
So how much lighter than a 26" wheelset (weighing 3000g) does the 29" wheelset need to be to start gaining an advantage?
IMO im thinking that a 29er wheelset weighing 2600g (very light) MAY be easier to pedal uphill/accelerate than a standard 26" wheelset at 3000g.
Would i be close to correct, or should i just stick to breaking things on my bike....
OH BTW - this thread has been quite enlightening... i like it.
Certainly, at some point a lighter 29er wheel will be easier to pedal uphill & accelerate than a heavier 26er wheel. The reason that the 29er wheel needs to be lighter to achieve this is due to its moment of inertia being greater than a 26er wheel - there is more mass further away from the centre of rotation.
So as you gradually decrease the weight of the 29er wheel, it's moment of inertia will also decrease until you reach a break-even point that is equivalent to that of the heavier 26er wheel.
Of course, if you continue lowering the weight of the 29er wheel it will pedal uphill & accelerate better than the heavier 26er wheel.
However, this is not a general advantage of 29er wheels because if you can make a 29er wheel light enough to out pedal & accelerate a 26er, then there is no reason that you can't make a similar 26er wheel with the same technology & materials - back to square one!!
Doesn't this all imply that "other things being equal", a smaller wheel should be easier to pedal uphill than a larger wheel?
Surely there must come a point where this stops being true - possibly related to area of contact and degree of slope?
I don't know where that idea goes to, but I sure don't want to contemplate trying to ride a bike with 2" wheels.....
The 26 V 29 uphill discussion seems to avoid the issue of terrain. On smooth uphills then the 26r MAY be easier to climb with. But if the terrain is anything but smooth and hard then wouldn't the 29r possibly be a better bet. Over any obstacle, rock, branch, washout, etc. doesn't the 29r wheel takes less of a hit to forward momentum and power absorbtion than a 26r? So on roughish/boggy uphill terrain wouldn't the 29r be the easier?
Secondly, until recently 29rs carried the same gearing to the 26r, resulting in the 29r being about 11% higher geared. Change the gearing so revs and speed are the same for each bike and the difference on smooth terrain reduces. (eg on a 29r a f20/r36 has approximately the same rev/speed as a 26r with f22/r36) To really test the subjective feeling the gearing would need to be changed so they are equivalent.
Guess the real test is the 'suck it and see' which suits you and which you prefer.
I'm willing to bet that in 10 years time 29inch MTBs will no longer be with us. All consumer items tend towards smaller rather than larger, it's all about economics and space. It's easier and cheaper to make and transport a smaller wheel rather than a large one. When most of the worlds population is living in a one room apartment like they do in Hong Kong, and most of China, smallness counts. And with the worlds population set to double in the next forty years the availablity of resources will be pushing the limits. The 29er market will fade then die.
Anyone willing to bet a weeks pay that 29ers won't be pretty much gone in 10 years?
We'll all be on 20" bikes and 26ers will be dead as well
and a smart car will win Bathurst.....
I don't think so.... Long live 29ers.
... well the smart car does have smaller wheels & Bathurst is a hilly course
Yep smaller will win! that means smaller wheels and smaller riders
http://members.westnet.com.au/bancrofh/determina...
The future of 4 wheel racing is, however, in the hands of us Baby Boomers!
http://members.westnet.com.au/bancrofh/Geriatric...
To see links right click and open in new window - haven't worked out how to link pics in here yet
.
You had it HostileMonk... mostly.
If trails were perfectly smooth, then the advantage of a bigger wheel would be negated to a large extent. To get a picture of what's happening, think of the example of the wheel of a shopping cart vs. the wheel of a truck. Because of the small diameter of the shopping cart wheel, it tends to get stuck in small ruts or jammed by small obstacles that the truck just keeps on trucking right over. Technically this is largely because of the vectors of the force acting on the wheel by the obstacle and the moments of force reacting against those vectors, engineers will understand this, but the rest of us just know that smaller wheels get stuck on smaller stuff.
There are other factors too, like the size of the contact patch, which is smaller on smaller wheels which causes more contact pressure on the surface which then results in energy wasted deforming that surface, plus you are making your own deeper rut to climb out of and you have a smaller wheel to climb out of it with. This is just one reason why we are not running roller skate wheels. There are more, mostly to do with friction and speed, but I won’t delve into those.
Another factor is the depth of the sidewall, since this is pretty much the same for 26" vs. 29" we can rule out its effect in soaking up small irregularities, but its one big reason why running a 700C would be a very bad idea indeed.
It’s important to remember that the inertial difference between wheels is only a factor when the *speed is changing*. If your speed is constant then you only have to work against friction and the other factors I've just mentioned. It doesn't matter if you are going uphill, on the flat or downhill, its acceleration (or deceleration) that requires the *extra* work. But we are only talking about a 3" difference here on wheels that are already pretty light, go back to my practical example in the previous post and put the bikes on a trainer without load. If you can feel the difference in work to accelerate the wheels then you are doing better than me. Yes, there is a difference, can you feel it? Probably not. It isn't that significant. So if you are maintaining a pretty constant speed when you are climbing / riding on the trail then the work you do on the 29er is going to be less than the 26er.
Remember too, that the energy you put into spinning the wheel up is not wasted, its stored in the momentum of the wheel, so when to do go to roll up and over something the energy stored in the momentum of you, the bike and the wheels will help you keep going. The energy is only wasted when you use the brakes, so get rid of those.
So why not have really, really big wheels on a mountain bike? There are compromises like reduced maneuverability and enlarged turning circle that you can't design around as wheels get bigger. Also you are dealing with a raised centre of gravity and further height to fall from that us riders don't like. You could put the rider in a reclined position in the middle of the frame to combat this, but that’s not going to be popular with anyone. Yes, the rotational inertia is greater as the wheel size increases, accelerating and decelerating does require more work. Also the gyro effect requires more force to overcome for a bigger wheel, this same effect that helps keep us upright also opposes us as we turn making the bike feel less responsive.
If you haven't seen it, check out the gyro effect on YouTube.
http://youtu.be/8H98BgRzpOM
The gearing on 26" vs. 29" might not make as much difference as you think. You don't really go into a climb thinking 'I'll use the first chain ring on the front, and 3rd on the rear for this slope'. You just learn to pick a gear you can push. Unless you are a single speeder, which IMO you are a) Mad b) Superman c) Waiting for your knees to explode or d) All of the above.
The key to efficiency is being smooth, not bouncing on the pedals causing lots of little waves of acceleration/deceleration which can spin a wheel and waste lots of energy. It’s only when you run out of gears and you wish you had one granny gear lower that ratios become a factor and as you mentioned, that's now fixed on 29er's anyhow.
The 26er has been with us a long time now, from those dark ages when wheels were made of steel (shock, horror!
) and brakes worked by gripping the rim which gave us some pretty heavy wheels indeed. Advances in the areas of materials and design have made a bigger, stronger, lighter wheel a practical option which has some appreciable advantages (and a few compromises) that most of us can benefit from. Wheels have grown up and the 29er is here to stay. 
A long time ago (1978), I attended an open day at the UWA. They had a lot of exhibitions set up to show the public, one of them being a small computer, the size of a bathroom, that could play chess by programming in the moves made by a human. (Incidentaly, I met this same computer some years later when it was installed at Muja Power Station as a data logger. Last time I saw it was in a rubbish skip after an upgrade, a sad end for a PDP11.) Getting back to my story, another exhibition was they sat you on a swivel chair and you held a bicycle wheel which had the rim filled with lead. You held onto the long axle and someone span up the wheel. If you tilted it from vertical to the right about 45 degrees you rotated clockwise on the chair. If you tilted it to the left you rotated anti-clockwise. I thought it was pretty interesting. They must have a lot of fun at Uni thinking up these things.
One of the many properties of a gyroscope. We'd be lost without them.
There's an absolute s**tload (the technical term) of factors that make up the difference in ride between a 26er and 29er. It may even come to pro's keeping one of each in their stable and selecting their ride based on the race-course.
BUT even if you keep an impossibly constant speed uphill you are accelerating your wheels against gravity and a larger inertia becomes a factor.
At the risk of further confusion you are applying a torque to your wheels therefore you are applying an angular acceleration to your wheels.
That is all
I had a few 29ers last year, but sold them off after about 6 months.
When compared to a 26 I found:
1. Better bump absorbtion for any given suspension
2. More traction uphill and cornering
3. Smoother and more confidence inspiring through corners
4. Much harder to get airtime and much less responsive in the air
5. Great conservation of speed when you got them wound up (feels like you have a little motor)
The major disadvantage though was suspension, any more than 3" of travel makes the centre of gravity too high. I prefer a bike with 5-6" travel and that just doesn't work with a 29er.
So my conclusion is that they are best as a budget hardtail cross country bike as the 29" wheels are way cheaper than shocks. But if you want to ride more rugged tracks and get air then a 26" with good suspension is the way to go.
I am a beginner with a 29er and cranked sums it up but I think that 29er's are still new and need tweeking...the more you ride the better you handle the differences.
I love my 29er and when I get on a 26 It feels like a toy.
absolutaly Floydo. paradox is a weapon of a climber, i've built it heavy but it rockets out of corners and up climbs,
Isn't that the point?
Isn't that the point?
yes! I agree 100% Flynny mtb's are grown up's toy's
(but I was exagerating the size difference)
I now know why planners are put in charge of engineers. Check ou this article on pinkbike re 29'er v 26 free ride / DH type sleds. http://www.pinkbike.com/news/Burning-Question-Wi...
The yeti superbike comes in 2 9 now as well which I didn't ever think I'd see (a Yeti dual sus 29 - what next a roadie....actually I hope so)point being the 29'er is turning out to be way more versatile than first thought. The guy from norco is where I'm at and you could say that I have the fence right in my bum but in the end the logic of this bad boy is undeniable
garage + 26 + 29 = one happy mofo
mechanical that biotches.