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Misconceptions and fairy tales about technical matters, and notes on what reviews should be about

Here I present some of the views and 'facts' that I came across which are wrong or negligible, usually made by people who don't do calculations and thus base all of what they assume, by what they think they feel (not what they really feel! See below on light weight tyres), but most of all by what they 'imagine to be true', or on trusting someone who supposedly knows the facts. Dynamo design and buying tradeoffs are a good example on seeing how a review should be done. All the points I mention illustrate the issues which I mentioned on my other pages with criticism, namely that people are influenced a lot by advertising, and that they believe what they want to believe, not the truth.

1. Weight of a bike makes a lot of difference to speed?

Related to this I recently (well, ca. Dec. 2012 IIRC) read on a German forum a claim by someone who rode ca. 20 km/h using Big Apple tyres, then with skinnier tyres he suddenly rode ca. 24 km/h. This is impossible! Rolling resistance should be lower with the wider tyres with the same tyre pressure (only if the wide tyres have been pumped up far too low, then rolling resistance can be huge and thus an issue in slowing you down) and wind resistance is not much higher with those wider tyres. Such a speed difference is possible, but not because of the tyres, but because of psychological effects: The bike feels slower (in steering, see further on), therefore the rider is slower (does less effort to ride fast!). Note that I can feel such things too, but I know they are not true from calculations, and even before I did the calculations, such a feeling of a bike steering or riding heavier did not influence my speed in most cases, i.e. the speed with which I ride on my touring bike is a few km/h less than on a road bike, but this is exactly what was to be expected, at the speeds given (37 km/h average on road bike, 34 km/h average on touring bike with bags, using the same exertion). The roadbike is about 9kg (with Conti 23mm Grandprix tyres or equivalent), the touring bike with bags about 19 kg (with Schwalbe Marathon 37mm) but that's not what makes it slower, the main difference is the more aerodynamic drag from all the stuff on it, such as fenders but esp. the bags. So if I only see a 3 km/h difference in speed at higher speed, then no way in hell can anyone get a speed difference of 4 km/h at speeds in the low 20s, from changing to lighter tyres (which saves at most 1kg), even when riding in an area with hills. You can verify this for hills by calculating the power and difference the weight makes in speed (bike + rider say 84 vs 85 kg, can this mean a speed difference of 20 to 24 km/h? No... If you just take the power as needed to go uphill and keep power constant then the speed will simply reduce inverse proportionally to the weight increase or decrease. So 20 km/h * 1 / (85 kg (with old tyres) / 84 kg (with new lighter tyres)) = 20.24 km/h. Note that in this example calculation I take all the power to be used to fight gravity/rolling resistance which are both linearly dependent on the mass. In reality wind resistance is the largest part of the resistance and thus power required depends mostly on that, even at speeds of 20-25 km/h.

2016-11-18: Didn't get round to finish completing this section until now: From aerodynamical drag the speed can also not increase to (anywhere near) 24 km/h, again using the example of the road bike and touring bike which has a lot of stuff on it that causes drag (bags, fenders, wider tyres, lights), the difference for just wider tyres cannot be anywhere near 4 km/h. The speed would be far less than 37/34 * 20 = 21.76 km/h. More accurately, from a high estimate of the front surface of the wider tyres (counting front and rear wheel, taking 30 mm instead of 50 mm wide tyres), the speed difference would only be about 0.20 km/h.

Summary: In reality a 0.20 km/h speed increase is likely, and 4km/h is complete and utter BS!

2. Smaller wheels make a bike much faster to accelerate than 622mm wheels?

Would 559mm wheels make a bike much faster than a bike with 622mm wheels? Would even smaller wheels accelerate faster? This is what for example Alex Moulton claimed long ago and which the company moultonbicycles stated on their website several years ago (and still does as of 2014).

Theoretically, yes, you accelerate faster with smaller or lighter wheels, but the effect is so little that in practice you will not notice this! Thus actually, there is no advantage for small wheels.

So I did the calculations for small wheels vs. 622mm wheels that show the difference is so small, in the order of centimetres difference in distance when both bikes have accelerated from 0 to 30 km/h, that it is negligible in practice. However, you can certainly feel the difference of smaller or lighter wheels. But not in accelaration! As I will explain:

Long ago on a cross/hybrid bike I had road tyres on it, and the light weight craze had just started. Wolber introduced ultra light inner tyres, about 60g instead of normally about 120g I think. So that means 120g less. As it's rotating mass rotating at the same time as going forward at the same speed, you feel it double in power you must provide to accelerate to a given speed. So that means about 240g. That's not much on a total of say 11 kg bike, 75 kg rider. (75+11)/(75+11-0.24)=1.0028

But why did I notice a big change? Well, it was not a big change in accelerating, it can't be, but it certainly is a big change in steering, which feels to be much lighter! I think that is what makes people feel smaller wheels are 'quicker' and they then assume you accelerate a lot faster because of that.

Try putting in a roadbike wheel in your touring bike and suddenly it feels like a racer! I've done this, I know the effects... (But it doesn't make me go faster) It's also why I can feel the difference between a bike with cannondale headshok (suspension is in the centre) and other suspension (suspension stuff is ca. 10 cm away from the centre, and when turning, I can feel that it is slower with the same force I normally use...). So a heavier front wheel just feels slower steering. It's no different from after a long tour with bike bags full of stuff on the front low riders: Removing them when I come home, the bike suddenly feels unbelievably twitchy, unsteerable almost :)

The same type of effect I felt with an aero-bar. The bike was ungainly, the steering slow... In the end I only mounted one of the 2 bars (I mounted it near the centre, wrong way around so the bend went towards the centre of the handlebar and thus I was not off-centre with both hands holding on to that section of that single bar) and used some foam wrapped around the handlebar to put my arms onto. This was much better! But only better for more agile steering.

3. How important is efficiency in a dynamo hub? And what are the important factors in a review

Some people say they can feel they are being slowed down by a dynamo:

Let's look at the difference of SP or Schmidt dynamo hubs, versus the best Shimano dynamo hubs: The Shimano hubs are not much less efficient, but they have an advantage: user serviceable bearings... (cup-and-cone, if you know how to open the hubs, which is not a problem with the pdf I have on my site from a now defunct website).

So why this design of non user-serviceable bearings? Surely it must be possible with SP hubs, and Schmidt hubs, if they altered the design a little to make the hubs user-serviceable. Perhaps with less tight tolerances the hubs would become a little less efficient, but who cares?

Well, then we get into what buyers want: Why are the PD-7s far less popular than the PD-8/PV-8? Because of price and because people believe that 250 g. in mass makes a huge difference in speed. Which it doesn't (even uphill). It's all about advertising, about what they desire (which is based on what they believe or what they think looks nice or sometimes other factors), about what they believe, and about what they want to believe (what they believe is based on what they want to believe, which is influenced by advertising, peer pressure. It makes many people believe something which is not true). I don't mean to say that weight doesn't matter, but, it matters a lot less than one might think. Only if everything is low weight, does it make sense to insist on low weight for 1 specific part. And then, what about your own weight? You can surely shave off much more there, well, most people can! ;-)

Surprisingly, immoral behaviour of companies (such as Supernova) is not a big influence, people buy from them despite their behaviour... In other fields it's the same, only some people dislike companies such as Sony (remember the rootkit on CDs? Or here in NL the fake demonstration of minidisc players being vibration resistant, so resistant even that when the audio cable from the minidisc player fell out while shaking, the music went on...!) or Microsoft (a company started by psychopath Gates, and they got big with criminal behaviour). I use no Microsoft products (I use FreeBSD and various other software, some of my own making), and Sony, well, just twice I bought a product from them because there was no other choice (in 2013 I bought the RX100 camera, no other camera maker made anything like it).

Efficiency is nice, but there are far more important issues... You don't in practice notice the difference between a low and high efficiency dynamo hub, at least in power. It can make a difference in vibrations because the more kinetic power is needed to generate the required electrical power for the lighting, the stronger the jolts from the hub will be. You will notice the vibrations (though it depends on the road and front fork of the bicycle), and it would be nice to be able to service bearings without sending your dynamo/wheel away! So from this for a review it is clear that the design preferences should be: 1. vibrations (this is possibly coupled with efficiency, as I mentioned), 2. durability/serviceability (this is possibly coupled with price), 3. efficiency (also possibly coupled with price as to get a higher efficiency needs more design work), 4. price.

A complainer about some of my pages who didn't even do what he himself said others should do (look at the dates of my website to see how up to date it is, this guy claimed it was all old, when if he had followed his own advice he would know that it's all up to date) wrote in his complain-email to me that he could feel the difference in power required between the Shimano DH-3N80 and the SP PV-8. This is BS! You can't feel this unless you always ride in no-wind conditions. And even then it would be almost impossible, after all, do you know when you ride say 20 km/h or 21 km/h without looking at the bike computer? And with wind it's even worse: With a little difference in wind the difference in efficiency is completely snowed under. Can you feel when riding "oh, the wind is now 1.4m/s at a direction of 10 degrees, yesterday it was 1.1m/s at 40 degrees"? I can't, and he certainly can't!

It's the same with people claiming that with smaller wheels you accelate faster (e.g. Alex Moulton did that, and it's still mentioned on the moultonbicycles website, as I mentioned in an earlier point) which is true but the difference is negligible.

This is quite different from vibrations, which you can notice because they stand out (helped by resonance of the front fork depending on bicycle) above the normal background vibrations of riding on a good road. If you only ride on bad roads, you will never notice it. If you only ever ride with light on, even on perfect roads, you will assume this vibration is normal for a bike and thus not 'notice' it. If you have ridden on a bike without dynamo hub on good roads, or with a headlamp that uses auto on/off, then if you have a bike/fork susceptible to low frequency resonance, you know/feel the difference between when the hub is producing power and when it is not, from vibrations in the handlebar. But with power loss you can't feel such a difference because the difference is snowed under in other factors that are much larger.

4. Rolling resistance of tyres, is it important? What does it really feel like?

2016-11-18: I've been working on the preparation for this section for quite a while, which deals with what I mentioned a few times in a few places, namely about dynamos and speed loss and ditto with the Nuvinci hub: Why do people in cities usually ride bicycle at a specific, low speed, of about 14-15 km/h? (sometimes less!) Do such cyclists lose speed as per the power calculations, or not? The approach I'm taking here (perhaps I will place it on a different page) is in some way similar to what I mentioned in dynamos: If you feel the dynamo vibrations strongly, then it's a bad product, and with tyres I want to see if you can feel the difference, but this is esp. important it seems for very weak cyclists. If you don't ride bicycle according to how it feels, but just ride hard, then the speed difference with dynamo on vs. off is very small, that you will not notice while riding. If you ride according to how it feels then still tyres make little difference to speed for cyclists who are in reasonable shape, but for very weak cyclists this could be different.

I will explain this better later, but I will tell already that I have done various experiments with how it feels, with a bicycle as normal, and then with an added load on the rear rack (the main effect of this is to increase mass and thus what it shows is what more force needed to accelerate feels like) and the results are quite interesting. This was after I hadn't ridden a bicycle much for nearly 5 months. After more riding (and my speed getting higher as I was getting used to it again), and different circumstances, I got a different feeling...

More on this to come with some example calculations on power/speed achieved, using diffferent tyres at various speeds.

Related to all this: Why hasn't manufacturer xyz hired me?

2014-8-6, with addition 2017-2-13: Over the years I have received various questions and comments, such as that a bicycle manufacturer should have hired me in relation to kickstands, or 'why hasn't Philips hired you?', etc. Well, these comments are good (the naysayers need not comment) but the reason is obvious: First of all note that I am interested in doing things right, according to proper test criteria. This means giving criticism... In products my ideas would also change from product-only to product family.

I will give an example, if Philips had hired me: The ball-head debacle with the Saferide 80 would have been avoided as I instantly knew this would be a bad idea. What else I would have done is to steer developments towards a non-StVZO killer dynamo headlamp based on the Saferide 80 which would undoubtedly have wiped out all other top dynamo headlamps, but also, I would have put a lot of emphasis on a very cheap headlamp (much cheaper than the Saferide 40) so as to cover the most important segments: High priced/high performance for advertising and status symbols that will give the entire brand's image a boost, then very low priced lamps for OEMs, as I think this is where most money is made. There is not much to convince manufacturers to use such cheap lamps: Price, and simple criteria for advertising are everything. Lowering prices beyond already available budget models means almost no money made, so the effort should go into convincing manufacturers these lamps are the ones to get, despite possibly lower test values (while still being a better lamp). For this you need a change in reviews, and/or influence from the 'status symbol' of the brand.

However, the people who make the decisions in the bicycle business are generally not interested in doing it right, but in making the most money as quickly as possible, which is of course true in all businesses, not just those in bicycling. This means that to make designs better than they are now, or even 'optimal', is in their view not a priority unless they can get ahead of the competition in some predetermined benchmark (such as StVZO's lux rating), and to get ahead in lower production costs and thus OEM prices which means more sales direct to bike manufacturers which means lots of sales, and to get ahead in reviews which means as long as reviews are poorly done, emphasis on the wrong matters... Longer term strategies such as above with the high class+very cheap range, is something they are not interested in, obviously, as most people and businesses do not plan ahead in such a way.

For those companies that are interested in doing it 'the right way' there is a huge obstacle to overcome, manipulation and misleading reviews, and the wishes from buyers resulting from that. This is why I suggested the 2 way strategy above, but it may not be enough.

Also note that those benchmarks such as lux-rating, are only important because most reviews are not well done. I found in forums that various people don't even see (or should I say 'notice'?) the unevenness in the beam of say the Edelux-II, just to give an example, and having uncritical people as reviewers means that lamps are rated only with criteria which are important to them and as various people don't see the unevennes, they will look for other critera. The same effect happens of course for any other type of bicycle components... When more competent reviewers are chosen to do reviews that have influence with the general buyer (i.e. when the testing criteria I use to evaluate components are used by such reviewers), then the naysayers and manipulators (manipulating others to follow them in their criteria/ratings etc.) will not have an influence any more, and things will finally change, but not sooner...

Then we have the problem that many people and businesses cannot deal with criticism. Imagine hiring someone who criticises your product! And yet, only from criticism will there be improvements. Praise means nothing. For my own website I am, by the way, not interested in praise, but only in (1) criticism which will make me think and analyse more on a topic, and (2) stimulation, ideas and suggestions to do something else or to do it differently.

Doing something myself: Well, this could come, but lots of issues have delayed some designs I have played with... This year (2017), the manufacturers that I contacted so far with a summary of improvement suggestions have not expressed an interest, most have not even responded...

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