Home
Things that 'everyone knows' aren't necessarily so

There are things every cyclist seems to believe, pieces of cycling lore passed down from rider to rider through the ages like holy writ. Problem is, an awful lot of them are either completely wrong, or based on a grain of truth that’s been mangled beyond recognition. Let’s pick a few of them apart.

Aluminium frames only last five years

Frame crack (CC BY 2.0 garycycles7|Flickr).jpg

Yes, aluminium frames can  fail; this crack was almost certainly caused by hanging a rack and bags from teh seatpost (CC BY 2.0 garycycles7|Flickr)

Or two years, or whatever. There’s a grain of fact in this one and it’s all about metal fatigue. If a piece of metal is repeatedly flexed it will eventually break, as anyone who has idly bent and unbent a paperclip knows. This happens even if you don’t flex the metal enough to permanently bend it.

This is metal fatigue, and it’s an odd phenomenon because not all metals behave the same way. If you repeatedly flex a piece of steel by a large amount, it will eventually break. But if you only flex it slightly, it won’t. The load below which a piece of steel doesn’t break from metal fatigue is called the fatigue limit.

This kind of cyclical loading and unloading is exactly what happens to bike frames, so you can design a steel frame that will essentially last forever, as long as it’s not crashed and it’s protected from corrosion. (Bike designer Brant Richards has pointed out it's not quite that simple. "To actually hit true fatigue limit stress levels frame would be very heavy indeed," he says. Nevertheless, the relationship between stress and lifespan for steel is such that you can build frames that last literally decades.)

Aluminium is different. If you repeatedly load and unload a piece of aluminium it will eventually break, however small the load. However, the smaller the load, the longer this takes.

Having more material spreads the load around, increasing lifespan, and the shape of the piece makes a difference too. That’s why aluminium frames have fat tubes, because a larger and therefore stiffer tube has a longer fatigue life.

Using these design techniques it’s possible to make an aluminium frame that will last many years, which is why there are still plenty around from the 1990s.

Steel frames go ‘dead’

The Light Blue Kings 853 - lug detail

You don’t hear this one as much as you did when steel was the dominant frame material. It was rubbish then and it’s rubbish now. As discussed above, a properly-designed steel frame can last forever, and that’s been obvious for decades.

How did this one get started then? A cynic might say that it’s good for bike shops to have people believe that you need to replace something you don’t, but I think there’s more to it than that.

On a new bike, everything works perfectly, and there’s a certain excitement about getting used to the differences in feel between your new and old rides. Your old bike, whatever it’s made from, feels familiar. Familiarity can easily become boredom. It’s not that an old bike feels ‘dead’ (whatever that even means) but that the unfamiliarity of a new one is exciting.

There’s one saddle height rule that works for everyone

sadle height.jpg

Read half a dozen general books on cycling and you will find as many recommendations for ways to set the distance between your saddle and pedals. Saddle height nostrums will be based on your inside leg multiplied by a certain number (1.09 from pedal to saddle is common; 0.883 from bottom bracket to saddle is a suspiciously precise other); the angle of your knee; or placing your heel on the pedal with your leg straight, among others.

These methods produce a wide variety of saddle heights for any particular rider, which should ring alarm bells. Not only that, but they variously fail to take into account flexibility, shoe size and the sole-axle distance of your shoes and pedals.

At the very best these methods give you a starting point for where your saddle should be, though they can be off by quite a bit, especially the “inside leg times 1.09” rule, which tends to produce high saddle positions.

A bike fit expert will be able to help you fine tune things, though you can do this by feel as well, making small adjustments to saddle height. It’s hard to know what’s perfect, but aches and pains in hips. knees and ankles will soon tell you if something’s wrong. Carry an Allen key and make adjustments on the road, especially if you’re doing a long ride. 100Km of hills on a wrongly-adjusted bike can do damage that takes weeks to heal.

Tyres must have a tread pattern

ritchey tom slick tread

This one’s simple. Car and motorcycle tyres have grooves in the tread to disperse water, otherwise they can aquaplane. Bicycle tyres, being much narrower, can’t aquaplane at typical bike speeds. In fact, you’d have to be doing over 200mph aquaplane a bike tyre, in which case Dave Brailsford probably wants to hear from you.

But tyre company marketing departments remain wedded to grooves, even though they can actually degrade tyre performance. That’s because the sections of rubber between the grooves can flex and squirm into them, and that increases the tyre’s rolling resistance.

It’s telling that when a tyre manufacturer wants to make a tyre for those situations where every second counts, such as a time trial, they make slicks. Look at the Continental Grand Prix Supersonic, for example, or, for a slightly less extreme example, Michelin’s new Power Competition tyres.

Carbon frames go ‘soft’

Colnago V1-r - seat clamp.jpg

Sound familiar? It’s the modern version of ‘steel frames go dead’ and ‘aluminium frames only last five years’. And it’s almost as daft.

As long as it’s not crashed, a carbon fibre frame won’t become weaker in use. In fact, many carbon fibre frames hugely exceed standard tests for fatigue life, to the point where manufacturers get bored and turn off the testing machines.

It doesn’t seem like they get more flexible either, at least not in ways riders can tell. The first widely-available carbon frames appeared in the early 1990s, and some have been in continual use ever since. They’d be seriously floppy by now if this was a real issue.

However, while the fibres themselves are almost infinitely durable, you can imagine that the resin might degrade over time with repeated flexing. It turns out this is what happens.

Tour magazine flex-tested carbon fibre forks and found that after 100,000 cycles they became less stiff. Chuck Texiera, a senior engineer at Specialized told CyclingTips.com what happens: “The epoxy matrix will at some point start to form little cracks, and then over time it will just have the connectivity of the fibre.”

As with so many of these beliefs, there’s a disconnect between what the engineering says is happening and what a rider can actually feel. A frame might be less stiff, but Texiera doesn’t think a rider could tell.

He said: “Over really extended periods of time, you can expect the stiffness of the frame to change ever so slightly but it’s such a small number. We can measure it but I really wouldn’t think it would be perceivable.”

Rotating weight is crucial

Lightweight Meilenstein wheelset Detail

“An ounce off the wheels is worth a pound off the frame,” goes the old saying, implying that rotating weight, especially on the wheels, is supremely important. The claim is sometimes laid out in less hyperbolic terms that weight on the wheels counts twice because when you accelerate you have to get it both spinning and moving forward.

Problem is, it’s not true. In 2001 bike engineer Kraig Willett analysed the forces on wheels and concluded:

“When evaluating wheel performance, wheel aerodynamics are the most important, distantly followed by wheel mass. Wheel inertia effects in all cases are so small that they are arguably insignificant.”

The idea that rotating mass is important comes from the belief that wheel inertia matters, because it’s inertia that has to be overcome to accelerate a wheel. But Willett clearly demonstrates that wheel inertia doesn’t matter, so rotating weight is also relatively unimportant.

Why not? Well, you don't do much accelerating when you ride a bike, and even when you do the acceleration is relatively low, so the power expended accelerating a bike with ‘heavy’ wheels is only fractionally higher than that needed for light wheels. Overall weight matters when you’re climbing, but even that’s not as big a factor as people imagine and it’s a lot cheaper to save weight off your middle than the bike.

In fact you spend most of your time, and therefore effort, shoving the air out of the way, and that’s a far better basis for choosing wheels. The roughly tenfold difference in the effect of aerodynamics versus total mass means you’re far better off with a pair of good aero wheels than a pair of light ones.

Narrow tyres are faster

Tyre close up for pressure.jpg

You can see where this one comes from. In cycling, smaller things are lighter and lighter things make you go faster, right? Well, no, not for tyres. Countless measurements have demonstrated beyond doubt that rolling resistance of tyres is lower if the tyres are wider, as long as the construction — carcass thickness and materials, tread rubber and depth etc — is identical.

But is that the whole story? What about weight and aerodynamics?

As discussed above, weight, even rotating weight, has a much lower effect on performance than people think, so the few grams difference between 23mm and 25mm tyres is immaterial.

We’re not aware of any detailed modelling of the aerodynamic effects of fatter tyres, but let’s have a bit of a stab at it. Aerodynamic drag arises from an object’s frontal area and its drag coefficient.

Drag coefficient depends on an object’s shape and how air flows over its surface. A very aerodynamic shape such as a smooth wing might have a drag coefficient of 0.005, while a brick’s is more like 2.0.

Multiplying the drag coefficient by the frontal area gives you the aerodynamic drag, so drag force increases as, say, a tyre gets wider.

According to CyclingPowerLab, the frontal area of a cyclist in the drops is about 0.36m². The change from 23mm to 25mm tyres adds 0.001436m², an increase of 0.4%. That’s the increase in power you’ll need to maintain any given speed. It takes 102 watts to maintain 18 miles per hour in this scenario, which increases to 102.5 watts with the fatter tyres.

According to BicycleRollingResistance.com, there’s a 0.3 watt difference in rolling resistance per tyre at this speed between 23mm and 25mm versions of Continental GP4000s II tyres at 120psi. The half-watt increase in aerodynamic drag is therefore almost exactly countered by the decrease in rolling resistance.

The problem here is that you’re not going to get the other benefit of fat tyres – a softer ride – if you keep the pressure the same. If you do reduce the pressure, then the rolling resistance goes up too, and you end up with slightly more total resistance.

With 28mm tyres it turns out you have a bit more leeway and can drop the pressure a little. At 100psi our 28mm GP4000s IIs have 0.5 watts per tyre less resistance than 23mm tyres at 120psi, and one watt more aerodynamic drag.

Narrow tyres, then, faster or slower? The answer, it turns out, is “it depends.” The total aerodynamic and rolling resistance depends on tyre size and pressure, and which is faster changes with how you fine-tune those variables.

An extra complication we haven’t mentioned yet is speed. As you go faster aerodynamic drag increases more than rolling resistance. At finishing sprint and time trial speeds, you’re almost certainly better off with narrow tyres.

If you don’t race, though, you might have noticed that we’re talking about small differences in resistance. A 28mm GP4000s II at 80psi has the same rolling resistance as a 23mm at 120psi. Does the extra watt of air resistance matter? It’s definitely not a difference you can feel (the threshold for that is 5-10 watts depending on the individual) and it’s going to make a tiny difference to your ride time even on a long ride. You might well decide the comfort is more than worth it.

Kirkpatrick Macmillan or Leonardo Davinci invented the bike

The bicycle sketch allegedly drawn by a student of Leonardo Da Vinci (Wikimedia Commons).jpg

The bicycle sketch allegedly drawn by a student of Leonardo Da Vinci (Portolanero / Wikimedia Commons (link is external) (link is external))

It’d be nice to believe the bike was invented by a Scottish blacksmith, but the evidence is very thin indeed.

The claim that Kirkpatrick Macmillan built a treadle-powered two-wheeler in 1839 didn’t emerge until after his death in 1878. A relative of Macmillan, James Johnston, made the claim in the 1890s, but was unable to produce any documentary evidence that what Macmillan had built was a two-wheeler.

The story goes that Macmillan built the first bike, but over the following years others copied the design. Cooper Gavin Dalzell was supposed to have built one in 1845, but again there is no contemporary evidence.

Treadle-drive tricycles and quadricycles were not unusual in the middle of the 19th century and it seems likely that the late-19th century recollections of velocipedes that formed the basis for Johnston’s claims were actually of three-or four-wheeled vehicles. Cycling historian David Herlihy covers the Macmillan claims extensively in his book Bicycle: The History and points out that none of the claimed accounts of Macmillan’s bike or others derived from it actually say it was a two-wheeler.

This, Herlihy points out, is remarkable, given what a novelty a two-wheeler would have been. When the French front-drive bicycles emerged in the late 1860s they were a sensation, because riders were able to travel on them without touching the ground. That Scottish newspapers of the time made no mention of this is remarkable.

“After all,” Herlihy writes, “a single French-style bicycle in the United States in 1866 led to both a clear-cut description of the article in a local newspaper and a patent application. It seems highly improbable that an arbitrary number of equally eye-catching machines could have operated in and around Scotland's largest cities—or anywhere else for that matter—for nearly thirty years without leaving the slightest paper trail.”

Herlihy doesn’t even bother to mention Leonardo da Vinci’s alleged invention of the bike. A sketch of a bicycle-like device emerged in 1974, claimed to be part of Leonardo da Vinci’s Codex Atlanticus. The sketch was attributed to Gian Giacomo Caprotti, a pupil of da Vinci, and was claimed to be a reproduction of a lost drawing of a bicycle by da Vinci himself. It was later established to be a forgery, though da Vinci’s reputation and that of literary historian Augusto Marinoni were powerful enough that it took until 1997 for the forgery to be unveiled.

According to a 1997 paper by Prof. Dr. Hans-Erhard Lessing, the Codex Atlanticus was examined by another da Vinci scholar in 1961 and the bicycle sketch was not present, though there were some geometrical doodles that the forger incorporated into the bicycle.

Lessing writes: “the bicycle sketch is definitely a recent forgery that can be dated between 1967 and 1974”.

But why would anyone forge a drawing of a bike? The short answer seems to be ‘national pride’. The bicycle was a seminal device that laid the basis for many vital technologies of the 20th century. Karl Benz’ Patent Motorwagen — the first internal combustion engined vehicle — was essentially a tricycle with an engine, with roller chains for power transmission, tension-spoked wire wheels and a tubular steel frame. The Wright brothers, who flew the first heavier-than-air plane in 1903, were bike mechanics and like Benz used bike technologies to save weight on their Flyer.

There’s a certain kudos, then, to being the country that invented the bicycle, which is why the strongest proponents of the Da Vinci drawing were Italian, Macmillan advocates were Scottish and so on. Marinoni never conceded the Da Vinci sketch was a forgery and as recently as 2009 his followers were still defending it, albeit rather incoherently.

Our official grumpy Northerner, John has been riding bikes for over 30 years since discovering as an uncoordinated teen that a sport could be fun if it didn't require you to catch a ball or get in the way of a hulking prop forward.

Road touring was followed by mountain biking and a career racing in the mud that was as brief as it was unsuccessful.

Somewhere along the line came the discovery that he could string a few words together, followed by the even more remarkable discovery that people were mug enough to pay for this rather than expecting him to do an honest day's work. He's pretty certain he's worked for even more bike publications than Mat Brett.

The inevitable 30-something MAMIL transition saw him shift to skinny tyres and these days he lives in Cambridge where the lack of hills is more than made up for by the headwinds.

74 comments

Avatar
Morgoth985 [163 posts] 1 year ago
0 likes
wellsprop wrote:
Morgoth985 wrote:
Welsh boy wrote:
Morgoth985 wrote:

Are you not effectively accelerating all the time even at constant speed, because you are overcoming air resistance / road friction etc?

 

Do you know what acceleration means?  Put simply, it is the rate of change of speed with time.  If you are riding at constant speed you have no acceleration as there is no change (constant) of speed.  So, in answer to your question, no, you are not accelerating all the time.

Listen mate, chill.  I appreciate that acceleration is the second derivative of displacement with respect to time.  I'm on an iPhone so didn't fancy writing a journal article.  My point was that by moving forward you are experiencing a force in the direction opposite your direction of motion (being air resistance) and a force opposite the direction of the rotational motion of your wheels (being rolling resistance).  Therefore, since force is proportionate to acceleration, you have a negative linear acceleration and a negative angular acceleration.  These will operate to reduce your velocity, being your forward vector speed.  You therefore need to apply a positive vector force and hence a positive vector acceleration just to maintain constant velocity, or in the absence of any directional analysis, constant speed.  Hopefully this helps.

To be fair, that's all pretty much bang on. When cycling you do exert a force and thereby an acceleration, even if the actual object is in equilibrium.

Being in equilibrium, i.e. cycling along at a constant velocity, just means the sum of all the accelerations acting on an object is zero.

 

Correct.  And expressed a lot more eloquently than I managed.

Avatar
Anthony.C [273 posts] 1 year ago
0 likes
hawkinspeter wrote:
Anthony.C wrote:

It is science fact that extra weight at a wheel rim takes more effort to accelerate up to speed than extra weight at the hub and it is certainly noticeable in real life.  One study I read added about 100g to  hubs and and the  same to  rims and found that the wheels with the extra rim weight  took about 25% more effort to accelerate up to  a given speed on a hill.

However, the amount of time that cyclists spend accelerating is dwarfed by the amount of time travelling at a constant speed - this is why aero matters more than weight. Also, I imagine that the 25% relates just to getting the wheel moving and not 25% related to getting the human rider up to speed too (share the link to the study if I'm wrong).

No, you imagine wrong, It relates to an actual person  riding a whole bicycle.

Avatar
BeatPoet [83 posts] 1 year ago
0 likes
festina wrote:

I'm gonna call bogus on the wheel weights too.  I'very ridden the same bike with a 50% change in wheel weight and the difference was night and day.  No one is paying me to say that and I built them wheels me self.  I agree it's only an issue when you are accelerating but I think there is a tendency to forget that the wheel acceleration is different to rider acceleration.  Yes aerodynamics play a part too but it's very dependant on what you are doing.  A nice flat TT at a constant pace then it's best to go aero.  A crit race where you spend an amount of time in a bunch (and therefore in 'dirty' air where aerodynamics have lesser effect) or a hill climb then wheel weight is important.  If you don't believe me add some weights inside your rim and test it.  There is a reason pros use light weight aero wheels and it isn't just to get the rest of us to part with cash, otherwise they'do use alloy ones as they brake better.

If the math doesn't match empirical data then the math is wrong not the empirical data.

But you don't have empirical data do you? You have subjective experience. 

Avatar
HawkinsPeter [3079 posts] 1 year ago
0 likes
Anthony.C wrote:
hawkinspeter wrote:
Anthony.C wrote:

It is science fact that extra weight at a wheel rim takes more effort to accelerate up to speed than extra weight at the hub and it is certainly noticeable in real life.  One study I read added about 100g to  hubs and and the  same to  rims and found that the wheels with the extra rim weight  took about 25% more effort to accelerate up to  a given speed on a hill.

However, the amount of time that cyclists spend accelerating is dwarfed by the amount of time travelling at a constant speed - this is why aero matters more than weight. Also, I imagine that the 25% relates just to getting the wheel moving and not 25% related to getting the human rider up to speed too (share the link to the study if I'm wrong).

No, you imagine wrong, It relates to an actual person  riding a whole bicycle.

That's surprising- got a link to that study?

Avatar
SpinZero [1 post] 1 year ago
0 likes
Morgoth985 wrote:
vonhelmet wrote:

GCSE physics, do you speak it?

f=ma

If your speed is constant then a=0. If a=0 then f=0 as well. If f=0 it's because the force you're exerting through your massive thighs is the same as the forces of friction on the road surface, air resistance, gravity if you're going uphill, whatever else that I've missed.

You don't met off forward and backward accelerations, that's crazy talk. You net off forces. I mean, you could calculate all the individual accelerations, but why would you?

yep, I do speak it.  And actually a bit more than GCSE as it happens.  And sorry to disappoint you, but you do net off forward and backward accelerations.  They're vectors, so direction matters.  You net off forces as well, and the constant of proportionality is the mass.

it's really just semantics here, as one can mathematically think of an object having accelerations in different directions that net to the actual acceleration vector and get the right answer. however, strictly speaking an object only has one linear acceleration in a given frame of reference. you won't find physicists talking about an object having accelerations in different directions. that doesn't line up with the definition of acceleration. whereas physicist do think of multiple forces acting on an object that net out. the f=ma equation is technincally f_net = ma. you can't just substitute in any force you want into the f=ma equation, e.g. gravity or air resistence. the f in that equation always represents the net force on the given object. i think that's what vonhelmet was getting at. physics ph.d. here by the way, not that i deserved it.

Avatar
kevvjj [457 posts] 1 year ago
0 likes
SpinZero wrote:
Morgoth985 wrote:
vonhelmet wrote:

GCSE physics, do you speak it?

f=ma

If your speed is constant then a=0. If a=0 then f=0 as well. If f=0 it's because the force you're exerting through your massive thighs is the same as the forces of friction on the road surface, air resistance, gravity if you're going uphill, whatever else that I've missed.

You don't met off forward and backward accelerations, that's crazy talk. You net off forces. I mean, you could calculate all the individual accelerations, but why would you?

yep, I do speak it.  And actually a bit more than GCSE as it happens.  And sorry to disappoint you, but you do net off forward and backward accelerations.  They're vectors, so direction matters.  You net off forces as well, and the constant of proportionality is the mass.

it's really just semantics here, as one can mathematically think of an object having accelerations in different directions that net to the actual acceleration vector and get the right answer. however, strictly speaking an object only has one linear acceleration in a given frame of reference. you won't find physicists talking about an object having accelerations in different directions. that doesn't line up with the definition of acceleration. whereas physicist do think of multiple forces acting on an object that net out. the f=ma equation is technincally f_net = ma. you can't just substitute in any force you want into the f=ma equation, e.g. gravity or air resistence. the f in that equation always represents the net force on the given object. i think that's what vonhelmet was getting at. physics ph.d. here by the way, not that i deserved it.

agreed, if the net force on the object (in this case bike and rider) is zero there ain't no acceleration -the physics doesn't need a phd...

Avatar
rix [258 posts] 1 year ago
1 like

I was about to write ,that it seams to me, that road.cc does not know what they are talking about, but then I realized that more likely explanation is reader content generation. The more controversial statements are expressed in article the more comments you'll have.

P.S. And it looks like they have succeeded! And we have fallen for it! laugh

Avatar
fukawitribe [2714 posts] 1 year ago
2 likes

I'd be willing to wager a small amount that what people think of as constant speed on a bike is actually nothing of the sort - particularly as the road points upwards. The magnitude of the accelerations vs aero- (and other) considerations is another matter.

Avatar
Cugel [72 posts] 1 year ago
1 like

A revived posting but here's a comment on one of the "busteds" that wasn't covered (as far as I can see) in the comments from a year ago....

The road CC article allges that bicycle road tyres gain nothing from a tread and that slicks with sticky rubber are all that are needed for good grip.

Jan Heine's article concerning tread patterns on road tyres suggests how tread patterns on road tyres do, in fact, increase grip in various circumtances:

https://janheine.wordpress.com/2018/02/22/myth-6-tread-patterns-dont-mat...

A quote capturing the essence of the article:

"There is another way to increase the interlocking between tire and road: provide edges on the tire that ‘hook up’ with the road surface irregularities. Each edge provides a point where a road irregularity can hook up. The more edges you have, the better the tire hooks up".

Jan Heine's website has another set of myth-busting articles, some of which co-incide with the roadCC article; but there are a couple of others not covered here.

******

Here's another article from another website that's semi-myth-busting concerning helmets.   1

http://www.cyclist.co.uk/in-depth/1365/is-it-safer-to-wear-a-helmet-when...

What other hoary old cycling myths would you like to have a go at busting?

Cugel

 

Avatar
DavidC [164 posts] 1 year ago
0 likes

"We’re not aware of any detailed modelling of the aerodynamic effects of fatter tyres,"

The original Zipp 404s recommended tyre size was 20 or 21 mm (IIRC). The narrower tyre was said to improve aerodynamics by flattening out the sidewalls, so there was smoother airflow between the sidewall and the braking surface. When the wider 404s were introduced, 23 mm was recommended, for the same reason but with improved handling and comfort — but everyone slapped on 25 mm, forsaking the claimed aero advantage for even greater comfort, and a trend was born. 

The idea of having smoother airflow between the sidewall and braking surface was also pursued by Mavic, albeit in a different way: their short-lived rings which attached to rims and covered up the joint of tyre and rim.

Avatar
UberEclectic [3 posts] 1 year ago
1 like

Overall a good read.  =D  W.r.t. weight vs. tire width, rolling resistance, etc. you neglected to mention the importance of rim vs. tire width and specifically the “rule of 105” — check it here:

https://silca.cc/blogs/journal/part-5-tire-pressure-and-aerodynamics

Avatar
tsarouxaz [134 posts] 1 year ago
0 likes

f.y.i fatigue is the MAIN reason that materials undel load fail and the top subject on engineering materials. far far away from mumbo jumbo...

Avatar
Bryin [41 posts] 2 months ago
0 likes

  It is IMPOSSIBLE for a tire with less pressure to have less rolling resistance.  I want to see a power meter verified test that proves a 28mm tire with 100psi has less rolling resistance than a 25mm tire with 120psi.  No one has done this becasue it is not possible.  

Avatar
HawkinsPeter [3079 posts] 2 months ago
0 likes
Bryin wrote:

  It is IMPOSSIBLE for a tire with less pressure to have less rolling resistance.  I want to see a power meter verified test that proves a 28mm tire with 100psi has less rolling resistance than a 25mm tire with 120psi.  No one has done this becasue it is not possible.  

What about over rough surfaces? I can imagine a situation where a lower pressure allows the tyre to conform to a rough surface and thus roll relatively easily whereas a higher pressure would cause energy loss through the up/down motion of bike and rider.

Pages