Keith Scott of Banshee bikes has done a blog post applying science to the wheel size debate.

http://bansheebikes.blogspot.co.uk/2013/10/wheel-size-facts-part-1-dimensions.html

Keith has a MEng degree, in which his thesis was mountain bike design before he went to Banshee, so he is qualified to make these assessments. Personally it appeals to the scientist in me.

I am not going to come down on one side or the other as a large part of the conclusion is personal preference – but thought it was worth a share!

NOOO,

JUST STOP IT.

NOBODY CARES ANYMORE WHAT THE **** YOUR ********* WHELL SIZE IS

We’re A ll SICK TO THE BACK TEETH WITH IT.

Stop it before I goughe your EYES OUT with a rusty spoon!,,!,,,!

Maybe I should just post this here instead;
[video]http://www.youtube.com/watch?v=S2oymHHyV1M[/video]

Lol – to be honest my choice is solely based on cost!

The speed difference is not worth bothering about unless your after a podium place.

The speed difference is not worth bothering about unless you’re after a podium place on a STRAAAAAAAAAAAAAAAAAAAAVAAAAAAAAAAAAAAAAA run

Different wheel sizes contribute to the feel of a bike. Pick the bike you like the feel of, that makes you smile the most. It may or may not have unconventional sized wheels.

Keith has a MEng degree, in which his thesis was mountain bike design before he went to Banshee, so he is qualified to make these assessments. Personally it appeals to the scientist in me.

Unless I’ve missed something there’s no useful assessment of anything there. Knowing bigger wheels have a great moment of inertia helps the decision process how?

Unless I’ve missed something there’s no useful assessment of anything there. Knowing bigger wheels have a great moment of inertia helps the decision process how?

He does say its the first in a series

ahsat
applying science to the wheel size debate.

a large part of the conclusion is personal preference

hmmm, i’m not sure you have got the hang of this science thing…… 😉

hmmm, i’m not sure you have got the hang of this science thing……

Hypothesis testing fail! D’oh! 😛

Why can’t I post replies from abroad?

A bigger wheel may have a larger moment of inertia, but it’s cancelled out by slower rotation, so it’s only any gain in weight that matters.

I proved bigger wheels were faster when I built this.

Anytime I rode it anywhere, the big wheel got there fractionally ahead of the small wheel .

The exception was when I rode it backwards when the whole theory just fell over in a heap.

with no mention of bringing the trails alive then I’m out. (That and any absence of a conclusion – why string it out just write an article and publish it rather than just advertise that Banshee make bikes)

at the moment I care more about the merits of X Factor vs Strictly than wheel size debates

It’s all rubbish. Red bikes are always fastest. Red 29ers though….

More important than the wheel size debate; why do people put an apostrophe in “doh”?

jameso – Member
A bigger wheel may have a larger moment of inertia, but it’s cancelled out by slower rotation, so it’s only any gain in weight that matters.

that doesn’t make sense, the rotation can be the same speed in both, and on the flat with two people pedalling at the same speed the larger wheel (due to it’s larger diameter) will roll faster.

Anyway, the blogger doesn’t offer conclusions because he’s not saying one is better than the other, he’s just pointing out the reasons the wheels feel different and it makes sense, except he forgot the third law of Newtonian rotational mass theory; if your wheel is obsolete then you will die… although in long term tests this has been proven for all wheel sizes, because we all die eventually.

X Factor vs Strictly

As if that’s a competition – the level of musicianship, comedy and entertainment in Strictly surpasses absolutely everything about the Xfactor.

Strictly makes the sofa come alive under my arse.

A bigger wheel may have a larger moment of inertia, but it’s cancelled out by slower rotation, so it’s only any gain in weight that matters.

For a given bike speed, the rate of wheel rotation changes linearly with radius but the inertia changes with the square of radius. And for a given price/stiffness/strength the larger wheel gets heavier too.

I still think 29ers make a lot of sense, particularly on beginner bikes and very large frame sizes. But smaller wheels definitely change velocity more efficiently and feel more responsive.

shifter – Member

More important than the wheel size debate; why do people put an apostrophe in “doh”? because it’s correct, innit

36er FTW
[video]http://www.youtube.com/watch?v=fYt6IqaHk_Q[/video]

Sorry but…how the **** is that a scientific approach to wheel size?

A scientific approach would include randomized blind tests carried out to answer a predefined question.

Was thinking about blind testing, but I can see a major issue to overcome with it….

Big fenders up front to hide the wheel?

Strictly makes the sofa come alive under my arse.

Best line on STW for a while.

A scientific approach would include randomized blind tests carried out to answer a predefined question

Of course first there’s got to be an argument over what the predefined question is.

Strava should collect a bit more user data and produce a graph of wheel size related to KOMs 😀

I hope 29ers don’t become the sole choice in future: at 5ft 4 I’d look like a kid on an adult’s bike!

Tom_W1987 – Member
Sorry but…how the **** is that a scientific approach to wheel size?

A scientific approach would include randomized blind tests carried out to answer a predefined question

Sorry but…how the **** is that a scientific approach to wheel size?

HTF do you do a blind test on riding bikes with different wheel sizes? How do you take subjectivity out of it?

The article show promise IMO – needs to go a lot further than moment of inertia though, the effect that (and mass, within the limits of what is available) has on overall speed is **** all

HTF do you do a blind test on riding bikes with different wheel sizes? How do you take subjectivity out of it?

Well, if you coloured in the logo’s on the tyres, I reckon that 95% couldn’t tell 650 from 26″ unless they were side by side (and obviously until they rode it and felt the trail literally come alive beneath them)

realistically, I don’t think you could totally blind them, but you’d need decent data to overcome the subjectivity

something like 10 riders, at least 3 courses, 3 runs on each course on each bike, randomise the order of the courses that they ride and randomise the order of wheel sizes they do it on – so you’ve got 270 sets of data to play with?

but you’d need decent data to overcome the subjectivity

But as said above you need to decide what question you’re trying to answer. To me at the end of the day what matters is how much the riders enjoyed the ride. Now for some that might come down to outright speed but to others it won’t be, so you’re back to subjectivity.

Why are some having a go at the blogger or his approach to quantifying the differences between the various wheels?

Maybe I’m missing the point of the blog, but to me he isn’t saying one is better than the other, he’s just pointing out the physics involved in different wheel sizes and how that affects their use / performance.

I found it interesting and I’m looking forward to his next blog.

Well I read the article, all set to slag off the pseudo-science. But, to be fair, all he’s done so far is define his terms. We don’t even have a hypothesis to test yet.

I’d take issue with his argument that he must be unbiased because Banshee make bikes with all three wheel sizes though. He may be unbiased (although he’d be the first observer in history who was), but making bikes with all three wheel sizes doesn’t mean that you don’t have a preference for one. Maybe there is more profit in one. Maybe this is laying the groundwork so that they can drop one. I don’t know, but Banshees current catalogue isn’t really relevant.

I suspect that this article will just fall into the same trap as every other supposedly scientific study of wheel sizes. In an attempt to make it more scientific you try to just isolate the effect of the wheel and in the process make the whole thing irrelevant. In practice the wheel only matters within the context of the bike. For example, you may be able to show that wheel A rolls over a bump x% easier than wheel B, but without putting that into context it’s useless. Wheel B may also roll over the bump x% easier if you reduce type pressure by a few psi, or change the head angle a fraction, or increase the travel my a few mm, or change any number of other parameters.

What matters is the whole package. A 120mm 29er with a 69 degree head angle and a 140mm 26″ or 650B bike with a 67 degree head angle (for example) may both end up doing a very similar job as well as each other, just in a slightly different way.

Some good numbers though.

27.5 is only 1″ bigger diameter than 26 (or 13mm bigger radius) but the wheels are 150g heavier (pair).

I suspect you could probably test 26 against 27.5 single blind, as there isn’t much between them visually.

I suspect you could probably test 26 against 27.5 single blind, as there isn’t much between them visually

You could; I wouldn’t hold your breath though. People seem to find it really hard to accept that they are biased. I suspect that we’ll just see lots of tests where the testers knew what wheel size they were on but will try to convince us that they weren’t biased. The joke is that they probably really do believe that.

ameso – Member
A bigger wheel may have a larger moment of inertia, but it’s cancelled out by slower rotation, so it’s only any gain in weight that matters.

that doesn’t make sense, the rotation can be the same speed in both, and on the flat with two people pedaling at the same speed the larger wheel (due to it’s larger diameter) will roll faster.

Nah you’ve got it the wrong way round the larger the diameter the slower the wheel rotates at any given ground speed, I done a fag packet calcamulation it’s really pretty simple:

Fewer rotations per meter traveled means a larger wheel is rotating slower for the same ground speed, hence Jameso is sort of right if looking at the force required to to decelerate a wheel you need to factor for both the increased mass and the relatively lower rotational speed of a larger wheel, it helps to be specific about what ground speed you are basing the calculation on, then you can work back to each wheel’s rotational speed or angular velocity and then apply the moment of inertia as you try to affect a change in speed…

Or to put it another way, you might have to pull the brake lever slightly harder, or not…

For a given bike speed, the rate of wheel rotation changes linearly with radius but the inertia changes with the square of radius. And for a given price/stiffness/strength the larger wheel gets heavier too.

Yep, but wheel rotation is linearly proportional with size too. So a 29er rim is rotating 10% slower, weighs 10% more.

e=0.5mv^2

‘rim counts double’ as the rotational velocity of the rim is equal to the overall foreward velocity.

e=mv^2

v is constant between the two bikes riding side by side

e is therefore proportional only to m. An 1800g 29er wheels accelerates just easily as an 1800g 26″ wheel. The difference is the 26″ wheel is probably only 1600g.

Differentiate it you get q=2ma, which shows the same thing, acceleration of the rim is proportional to power/weight, radius is irelavent.

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Please god/budda make it stop please just think of the children

spot the deliberate mistake in my maths :p

on the flat with two people pedalling at the same speed the larger wheel (due to it’s larger diameter) will roll faster.

yay – free energy!
all world problems solved by 29er wheels!

snigger

Well, if you coloured in the logo’s on the tyres, I reckon that 95% couldn’t tell 650 from 26″ unless they were side by side (and obviously until they rode it and felt the trail literally come alive beneath them)

Exaaaaaaaaaaaaaaaaaaaactly.

Sure…the veracity of assuming most people can’t spot the size difference is not going to get it published any time soon….but it would at least be kind of interesting….instead of the continual theorizing found here.