I’m quite shocked by those Giant diagrams – they’re basically BS as the 27.5 wheel will actually be closer to the 26 than the 29 – it is basic geometry we’re talking here after all. That sort of lying (there I’ve said it) really boils my piss.

Just to make sure it wasn’t counter intuitive I ran the numbers for the attack angle, and I have to admit I was surprised by the result. Not that 27.5 is closer to 29 than 26 (that does indeed work as you’d expect with the change being roughly in proportion to the change in wheelsize), but that the difference even for 29 is smaller than I expected, and far smaller than Giant’s claims. Even a 100mm step which results in an attack angle of ~45 degrees there’s only an advantage of just over 2 degrees with a 29er wheel (and under 1 degree with 27). In fact the largest difference I can get is when the step is the same height as the axle on the 26er wheel, so the attack angle for that is 90 degrees – the 29er attack angle is then just over 85 degrees (-5) and the 27er just under 88 degrees (-2).

In case anybody is interested and wants to check my numbers, I’m using 336mm 349mm and 368mm for the wheel/tyre radius for 26/27/29, based on a 2.25 tyre. The formula I’m using is:
attack angle = acos ((radius-step) / radius)

Not that 27.5 is closer to 29 than 26 (that does indeed work as you’d expect with the change being roughly in proportion to the change in wheelsize), but that the difference even for 29 is smaller than I expected, and far smaller than Giant’s claims. Even a 100mm step which results in an attack angle of ~45 degrees there’s only an advantage of just over 2 degrees with a 29er wheel (and under 1 degree with 27). In fact the largest difference I can get is when the step is the same height as the axle on the 26er wheel, so the attack angle for that is 90 degrees – the 29er attack angle is then just over 85 degrees (-5) and the 27er just under 88 degrees (-2).

In case anybody is interested and wants to check my numbers, I’m using 336mm 349mm and 368mm for the wheel/tyre radius for 26/27/29, based on a 2.25 tyre. The formula I’m using is:
attack angle = acos ((radius-step) / radius)
depends what happens when the rear of the bike is loaded/under sag

don’t really get mikewsmiths post, but the differences are really small. And since when did we all lose the ability to lift or unweight our wheels when riding?

you’re right those diagrams from Giant are complete crap

No it doesn’t – we’re talking about how a wheel rolls over stuff, and that’s totally unaffected by bike geometry.

probably true just the difference is so small that things like how the back end of the bike moves makes as much difference

sweet FA
when you can become a world champ without 29″ wheels or not win WC Dh with 650b’s who cares. It’s all a lot of numbers designed to prove that something is worth buying. People buy into numbers as it’s easier to pay for better than train harder and develop skills or worse have talent.

Well for my two penneth. I am no fan of the industry bull. Most bike manufacturers reps are trying to sell you whatever crap they have designed for the market where they are based. So that means usa or European. As uk riding is imo different and we ride in the woods a lot more than both usa and Europe I never understood 29ers except for tall people. 27 is marketing. But I am now riding the kona explosif and the process 153. And have to admit I am loving them both. I didn’t plan a wholehearted leap in to the new wheel size it just happened. But I am a fan now of these bikes with their big wheels. That is probably more to do with the frames than can inch on the rim.

From Giants 2014 catalogue – ‘Arguably the most important benefit of 27.5 over 29 is quicker acceleration. This is the “snap” that a rider feels when they push hard on the pedals. It is affected not just by overall static weight but also where the weight is distributed throughout the wheel. The farther the weight is from the center of the hub, the slower the acceleration. So a similarly constructed 1000-gram 29-inch wheel is slower to accelerate than a 1000-gram 26-inch wheel—because the larger diameter rim and longer spokes place weight farther from the hub.

Now that is also complete BS. A 1000g wheel will accelerate just as fast no matter how big it is (if we make the not unreasonable assumption that all the weight is effectively either in the middle or at the edge). Of course a heavier wheel will accelerate slower and given a 29er wheel of similar construction to a 26er is heavier it will accelerate slower, but that’s not what they’re saying.

What’s worse is that they completely ignore the elephant in the room that if you are bothered about wheel acceleration then 26 is better than 27.5

Having owned and ridden 29ers,this is one of the reasons why I got rid of them. I keep posting over the years gone by on why I can’t see the point in me riding this wheelsize when,like I continue to point out,yet get told by these companies that the bigger wheel climbs better and faster,only to be told that they’ve done their testing to agree with me all along.. the riding I do up here,lets say over a 4 hour mountain ride,consists of approx 3.5 hours of climbing, the remainder descending. I have noticed on all the 29ers how slow and awful they are on climbs compared to the equivalent bike sporting the 26 inch wheel. I was really feeling like I was imagining things over the years as nobody seemed to agree. Most still don’t. Yet Giant have done the math to keep me a little more sane.

Unfortunately Giant’s maths doesn’t agree with you (which is arguably a good thing – do you really want to confirm any of their marketing guff?) I can believe that a bigger wheel feels slower, but all the testing results I’ve seen show that it’s just a perception thing – they’re actually faster on almost all terrain. The thing is you’re not actually accelerating when you’re climbing (or at least the accelerations are small, and arguably decreasing the amount of acceleration with a heavier wheel is actually an advantage) so that makes no difference. The improved rolling of the bigger wheel does.

As mentioned above, in the very direct configuration I have the improvement with 29 is actually really obvious – you could put that down to perception, but climbs where I was on the limit for clearing on a 26 I do just as well if not better on a 29. That’s using the same gear ratio – ie effectively a higher gear on the 29.

what this forum needs is more wheel size threads

But one thing that doesn’t change is people thinking their wheel choice is better than the others.
I still find it amusing

Where’s that pic from, mikewsmith? Thanks for that as it confirms my figures nicely (except that as far as I can work out they’ve put 26 and 29 into their calcs, rather than the real 26.5/29 or 26/28.5 depending on tyre size).

But one thing that doesn’t change is people thinking their wheel choice is better than the others.
I still find it amusing

Would it interest you to know that I only own 26″ MTBs?

But one thing that doesn’t change is people thinking their wheel choice is better than the others.
I still find it amusing

Have you seen the nsmb.com “how to be a mountain biker” video thats doing the rounds its number 19 i think

How to be a mountainbiker vid got this completely correct.

Personally i shall continue to use the wheels I have, rather than the wheels I don’t, because I find imaginary wheels don’t work as well as real ones.

I might take 27 inch seriously if the difference in logo size wasn’t so much bigger than the difference in tyre size- if the bike companies have to devote so much space to telling you that there’s a difference, then it’s not as big as they’d like you to think.

(I think the fact that they settled on the misleading 27.5 not 650b in order to exaggerate the difference is telling personally)

what this forum needs is more wheel size threads

I think its funny that a group of blokes who think its perfectly normal to spend £2k plus on a “push bike” are jumping up and down over an inch or so on wheels.

Personally i shall continue to use the wheels I have, rather than the wheels I don’t, because I find imaginary wheels don’t work as well as real ones.

+1

and when it comes to buying a new bike, I’ll still just buy the best one I can afford regardless of what size wheels it has.

Ha ha not really.
But I bet you enjoy your bike
And I defend your right to choose your wheel size in a diverse multi radial society without fear threat persecution or piss take

In case anybody is interested and wants to check my numbers,

Numbers look right. But it assumes a rigid wheel, not one that deforms under impact. So my point about tyre volume making as much or more difference may be valid. And, a degree or 2 in roll-over angle may sound like not much, but a degree or 2 on a head angle is noted.

edit to add, the angle of attack isn’t all either, it’s the relationship between contact patch and axle that changes too. Axle is a little further over the bump when a 26″ hits it, hence the feeling of a 29er being smoother. Back-seat-of-bus effect (no not that one)

“And since when did we all lose the ability to lift or unweight our wheels when riding?”

“People buy into numbers as it’s easier to pay for better than train harder and develop skills or worse have talent.”

That’s is just it, People where getting 29″ because it “felt more stable” “rolled over stuff better” instead of learning/improving there rider skills. It’s another “skill compensator” 😈

I believe that the Swiss have banned juniors and below racing 29″ and BC strongly recommend that the same for the riders on there programs.

google images, bit of Trek shite I think, still if everyone wants to parade around on their big wheeled skill compensators let them, still fun to overtake them 🙂

People where getting 29″ because it “felt more stable” “rolled over stuff better” instead of learning/improving there rider skills. It’s another “skill compensator”

Unicycles for all then eh ) and those suspension-things, ban them.

We suggest consumers try all three and decide what works best for them. We’re phasing out two of them though.

Should we all run long crank arms too? Fairly obvious that a longer lever will be more efficient/produce better marketing generated force diagrams etc Cant see any downsides……

So how do i go about lengthening my legs so that i can fit onto one of these more efficient 27.5/29 speed machines with 227.5mm cranks?

You guys are lucky I’ve had to put up with all the guff being spouted about electric bikes being the future. Parts of the industry are disappearing up their own @rse

Should we all run long crank arms too? Fairly obvious that a longer lever will be more efficient/produce better marketing generated force diagrams etc Cant see any downsides……

There are, if the crank’s too long the leg is extended longer at the bottom of the stroke, and the knee too closed at the top of the stroke, that’s bad because these are the parts of the stroke producing the least power.

ha!

You guys are lucky I’ve had to put up with all the guff being spouted about electric bikes being the future.

What size wheels will the electric bikes need? 😉

Numbers look right. But it assumes a rigid wheel, not one that deforms under impact. So my point about tyre volume making as much or more difference may be valid. And, a degree or 2 in roll-over angle may sound like not much, but a degree or 2 on a head angle is noted.

If the tyre squishes to only 1″ high (from 2.25″) then the difference changes to 1 degree 27, 2.4 degrees 29 for my 100mm block – in reality there’s probably slightly more advantage to the bigger wheels as the smaller wheel will hit harder so the tyre deflects more. I’m assuming the same tyre size for all wheels, which seems the only reasonable way to do it (I do after all own a 26″ tyre with a larger diameter than most 29″ tyres which would completely change the game).

Differences in head angle is a completely different subject to differences in wheel attack angles, and one where I’d expect you to notice the difference more. Though to be honest I only did the numbers as a critique of those Giant diagrams, and I think I’ve proved them to be completely made up.

Could somebody explain why I should care about angle of attack please? OK, I can understand that it would make the trail feel smoother if I were on a rigid bike, but my bike has suspension. Furthermore I can tune the suspension to react in different ways to slower and faster hits. If I’ve got to get over this 100mm bump then I’ve got to absorb the same sized bump regardless of the wheel size haven’t I? Making the transition slower just changes the way the suspension needs to be setup doesn’t it?

@mattjg Can’t i counter that with a phased deployment of a dropper post?

that’s quite a good idea!

especially if it could be automated with a servo and synched with electronic shifting and that digital suspension platform bike (Lapierre?) that adjusts itself to the trail 100 times a second

genius!

but if the cranks are too long they will hit the ground however much the dropper goes up and down – I can see it now… 😆

maybe the answer is bigger wheels – no wait isnt that circular?

One would think, given how much Giant are marketing 650b as the second coming of Jesus in bicycle form, that one of their representatives would have popped onto the thread to state their case?

…unless they have, and I missed it?

catch up! at the bottom of the stroke the suspension extends to prevent pedal strike, and the dropper sinks a bit

Could somebody explain why I should care about angle of attack please?

Because it’s a measure of how well a wheel rolls over bumps – you’ll still get the same instantaneous stopping effect due to the bump no matter how good your suspension is. Makes far more difference to how you roll over the ground than suspension. Not something which only matters to racers.

Note that as mentioned above I was mainly proving the Giant diagrams to be lies rather than trying to make any point about the importance of angle of attack.

If you care about the angle of attack of your wheels then I can only imagine that you are over analysing and probably riding too slow. I guess if you don’t give a toss you will be concentrating more on the trail and thus faster.
Hence you shouldn’t worry about it

Surely this should all be bollocks now anyway.

I distinctly remember being promised hoverbikes by now thus rendering wheels of any size completely redundant.

Disappointed.

I am kind of interested to see how things go in the Enduro World Series next year and to see if it’s still riders with 26″ wheeled bikes at the top.

On a side note, due to how aggressively Giant are with pricing, their new Trance will most likely sell well regardless of attitudes towards the company.

I distinctly remember being promised hoverbikes by now

Skill compensators.

and a <whoosh> for Sancho

Sancho – Member

If you care about the angle of attack of your wheels then I can only imagine that you are over analysing and probably riding too slow. I guess if you don’t give a toss you will be concentrating more on the trail and thus faster.

The wheels do it for you, you don’t have to concentrate to make it happen.

Because it’s a measure of how well a wheel rolls over bumps – you’ll still get the same instantaneous stopping effect due to the bump no matter how good your suspension is

Sorry, I guess I’m being dim here, but I still don’t get it. If I ride over a small bump then, in the absence of any suspension, the whole weight of the system has to be lifted up over the bump. With perfect suspension it is just the wheel and fork lowers that move up and down. Isn’t this what makes a suspended system more efficient than one without suspension?

depends on what you mean by efficient? Dont you just store up the energy from hitting the bump (and not lifting the suspended parts of the bike) in the springs? Isnt this energy then released again after the bump pushing backwards on the bike?

That’s where damping comes in. At least some of the energy should be dissipated as heat in the damping fluid.

yay 10 pages!