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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) (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.

77 comments

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700c [1267 posts] 3 years ago
0 likes
pdw wrote:

It's often said that lighter wheels are important for climbing.  Even if you start your climb from a standing start, you've only got to spin it up to your climbing speed once.  

That's maybe a bit of a generalisation - it depends how you climb. Plus the hills  I climb tend not to be a single ramp at a constant gradient - ie climbing speed goes up and down during the ascent.

If you like to attack a hill, race (officially, or against your mates), keep up with a group which is also accelerating and slowing, then there would be multiple accelerations.

I agree that aero trumps weight, however.

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BikeJon [211 posts] 3 years ago
0 likes
rjfrussell wrote:
bigblue wrote:

How fast do you have to be going for aero wheels to make a perceivable / significant difference, compared to non-aero wheels ? 20 mph ? 30 mph ?

 

I was going to say "sick"- but does that now mean good or bad-  it is so hard to keep up.

And here's me thinking it meant 'unwell'.

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pdw [68 posts] 3 years ago
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700c wrote:
pdw wrote:

It's often said that lighter wheels are important for climbing.  Even if you start your climb from a standing start, you've only got to spin it up to your climbing speed once.  

That's maybe a bit of a generalisation - it depends how you climb. Plus the hills  I climb tend not to be a single ramp at a constant gradient - ie climbing speed goes up and down during the ascent.

Those changes will cancel out.  When the gradient ramps up, the heavier wheels are actually an advantage as you've got more kinetic energy.  If you hit the same hill at the same speed on two bikes with the same overall weight and don't pedal, the one with the heavier wheels will roll further up it.  

But all this is pretty mariginal: you're talking about a few mph of speed change, no more than 0.5kg between a set of heavy wheels and a set of light wheels, and much of that weight difference at the hub where it makes the least difference.

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Yorkshire wallet [2428 posts] 3 years ago
1 like
Boss Hogg wrote:

It makes a hell of a difference climbing steep sections (8%, 9%, 10% or more) on lightweight wheels. You can also corner with much more precision - and thus safety - when decending fast on lighter wheels. So I ride the lightest hoops (and tires) I can afford.

Have you caught those Duke boys yet?

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DaveE128 [1010 posts] 3 years ago
1 like
hawkinspeter wrote:

I didn't think about deformation of the rim. I'm surprised that there's any noticeable deformation that would affect the forces on the spokes by a measurable amount.

My point about momentum is that if there's more forces acting on the bottom half vs the top half of the wheel, then wouldn't that produce a net force either upwards? I would think that in a tensioned structure, the forces should balance out, but then I'm no engineer.

The forces don't cancel out because the net force on the hub is supporting the weight of the bike. Both the reduction in tension of the lower spokes and any increase in tension in the upper spokes contribute to this, but they act together not against each other - hence no need for equilibrium between them.

In other words, A+B=C

where:

A is reduction in tension in lower spokes,

B is increase in tension in upper spokes,

C is the portion of the bike's weight pushing down on the hub.

This doesn't mean that A=B.

Yes, deflection is always present in structures. This is actually how the structures provide the forces to provide equilibrium against the applied load. Think of a spring - it can't push back on your hand unless your hand has deformed it. Everything works like a spring, just most things are like a very stiff one.

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700c [1267 posts] 3 years ago
3 likes
pdw wrote:

When the gradient ramps up, the heavier wheels are actually an advantage as you've got more kinetic energy.

Ok now I'm lost!

Dammit I need to sell my wheels for heavier ones and put on some weight to get up those hills faster!  3

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BBB [502 posts] 3 years ago
0 likes
Boss Hogg wrote:

"...It makes a hell of a difference climbing steep sections (8%, 9%, 10% or more) on lightweight wheels..."

1. Try pushing your bike up a +10% hill...

2. Try pushing your mate on your bike up a 10% hill...

Report your findings back to us...

Avatar
Boss Hogg [143 posts] 3 years ago
1 like
Yorkshire wallet wrote:
Boss Hogg wrote:

It makes a hell of a difference climbing steep sections (8%, 9%, 10% or more) on lightweight wheels. You can also corner with much more precision - and thus safety - when decending fast on lighter wheels. So I ride the lightest hoops (and tires) I can afford.

Have you caught those Duke boys yet?

That's Rosco's job.

Avatar
Boss Hogg [143 posts] 3 years ago
1 like
BBB wrote:
Boss Hogg wrote:

"...It makes a hell of a difference climbing steep sections (8%, 9%, 10% or more) on lightweight wheels..."

1. Try pushing your bike up a +10% hill...

2. Try pushing your mate on your bike up a 10% hill...

Report your findings back to us...

?

Avatar
brooksby [4736 posts] 3 years ago
0 likes
Boss Hogg wrote:
Yorkshire wallet wrote:

Have you caught those Duke boys yet?

That's Rosco's job.

Now I always did wonder, whether Boss Hogg was any relation to Sheriff Buford T Justice? Hey, enquiring minds want to know...

Avatar
BBB [502 posts] 3 years ago
0 likes
Boss Hogg wrote:
BBB wrote:
Boss Hogg wrote:

"...It makes a hell of a difference climbing steep sections (8%, 9%, 10% or more) on lightweight wheels..."

1. Try pushing your bike up a +10% hill...

2. Try pushing your mate on your bike up a 10% hill...

Report your findings back to us...

?

a

The experiment will demonstrate how insignificant the weight of the wheels is.

Avatar
fukawitribe [2837 posts] 3 years ago
3 likes
BBB wrote:
Boss Hogg wrote:
BBB wrote:
Boss Hogg wrote:

"...It makes a hell of a difference climbing steep sections (8%, 9%, 10% or more) on lightweight wheels..."

1. Try pushing your bike up a +10% hill...

2. Try pushing your mate on your bike up a 10% hill...

Report your findings back to us...

?

a

The experiment will demonstrate how insignificant the weight of the wheels is.

I think it just demonstrates you don't know how significantly weighty my mate is.

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Freddy56 [415 posts] 3 years ago
0 likes

Super article .. I have no long winded problem with the content

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biga [31 posts] 3 years ago
0 likes

Sorry to disagree but skinny tyres and tread patterns DO make a difference. It's not in terms of added grip for the tread, as correctly stated, but both guarantee the aero performance of the wheels. Almost all wheel aero data are for 23. Only a few show for 25, and based on these few there's a clear tendency to lose aero performance. Larger than 25 and you're not aero anymore (maybe only 28 with newer super large Zipps but there's no data on that...). Treads will serve as flow trippers and are fundamental to wheel aero performance. A good collection of all this can be found in the swissside web site (and they are one of the few that guarantee aero even for 25).

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philtregear [135 posts] 3 years ago
1 like

i have no doubt that all this science is relevant  and, unlike michael gove, i value the fact we have experts in industry who understand it`s relevance aand applications. However, as a mere cyclist I have found the following to be subjectively true:

 

riding a heavier bike is harder work than ridinga light bike

fatter tyres are more comfortable than skinny ones

I feel reassured that their are grooves in my tyres on very wet days 

spiked  ice tyres prevent me from falling off when ice is on the road ( this one would stand up to proper testing i think)

 

i have 3 bikes:

a heavy steel one with fat tyres (35mm, treads) ( my winter warrior)

an ali one with workaday parts ( 35mm  treadat the front, 25mm slick at the back) ( my ok weather commuter)

a carbon one with 23mm slicks  and quite nice bits and pieces.( this bike i love but  it gives me piles)

 

i usually ride commutes of 20 miles each way but used to do longer rides, one day i hope to do so again.

I cant really follow all the science, so end up reflecting on trends and deciding whether they add up or  are just hype.

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jollygoodvelo [1849 posts] 3 years ago
1 like

So, having read all that, what you're saying is I need to buy a set of Zipp 808s and a lighter bike to fit them to, yes?

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gbayf2308 [3 posts] 3 years ago
4 likes

How can "normal" spokes ever be in compression when the nipple is not fixed? If you cut a spoke at the hub you could push it into the innertube and tyre. 

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fukawitribe [2837 posts] 3 years ago
0 likes
gbayf2308 wrote:

How can "normal" spokes ever be in compression when the nipple is not fixed? If you cut a spoke at the hub you could push it into the innertube and tyre. 

A traditional spoked bicycle wheel is a pretensioned structure under a compressive load.

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Liaman [68 posts] 2 years ago
0 likes
festina wrote:

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

The plural word for anecdote is not data

 

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Liaman [68 posts] 2 years ago
1 like
bigblue wrote:

How fast do you have to be going for aero wheels to make a perceivable / significant difference, compared to non-aero wheels ? 20 mph ? 30 mph ?

OK, depends on what perceivable / significant means, but you get the idea. Maybe compare it to the actual numbers quoted for varying tyre width ? Or more intuitively, if I'm doing 20 or 30 mph on aero wheels, how fast would I go for the same effort on non-aero wheels ? I would imagine the difference is really small at 20mph, but I don't actually know for sure.

Rider speed isn't the key factor here, it's actually relative air speed.
If you're riding at 20mph into a 10mph headwind then you're experiencing identical aerodynamic drag levels as a rider travelling at 30mph on a still day. The wind doesn't have to be head-on either. Even if the wind is travelling east-west and you're riding north-south, you'll still mostly experience it as mostly a head on force depending on the speeds.

Add to this that it has been proven that on a course of the same distance, a slower rider will save *more* time by becoming more aero than a faster rider will.
It sounds counter-intuitive, but it's correct - the math backs it up. Check materials published by Cervelo and FLO Cycling.

In terms of practicality out on the road, check the GCN video where Simon Richardson does a test where he rides as hard as her can for 20mins on non-aero wheels and records the speed. He then rides at that same speed for as long as he can on some Zipp 808s and manages it for over 50 minutes

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pockstone [297 posts] 2 years ago
1 like

' Dammit I need to sell my wheels for heavier ones and put on some weight to get up those hills faster! ;)[/quote]

I'm way ahead of you.

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Anthony.C [278 posts] 2 years ago
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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.

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hawkinspeter [3848 posts] 2 years ago
1 like
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).

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Morgoth985 [180 posts] 2 years ago
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Are you not effectively accelerating all the time even at constant speed, because you are overcoming air resistance / road friction etc?

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Welsh boy [673 posts] 2 years ago
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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.

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hawkinspeter [3848 posts] 2 years ago
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Morgoth985 wrote:

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

No.

You are applying a force which usually would result in acceleration, but that's balanced by the resistive forces. If you're at a constant speed, then the wheels are spinning at a constant speed and thus the weight is irrelevant. Even when accelerating, the extra force required to spin the heavier rim up to speed is tiny compared to accelerating the heavy human up to speed and similarly the total wheel weight is unlikely to make much difference to you unless you're doing lots of hill climbs (and if you've got more than 10% body fat, then eating less makes far more difference than expensive wheels).

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Morgoth985 [180 posts] 2 years ago
1 like
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.

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Canyon48 [1147 posts] 2 years ago
0 likes
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.

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vonhelmet [1356 posts] 2 years ago
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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?

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Morgoth985 [180 posts] 2 years ago
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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.

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