Cycling UK Forum

Mark R wrote:+1

Very few of the best mechanics will have paper qualifications to show. Seem like an odd approach to ask for them.

Why not just design a practical aptitude test? You would soon find out who has the skills (it wouldn't necessarily correlate with paper qualifications)

My grandfather took his HGV driving test (or whatever the equivalent was in those days) in the army. It was standard practice that when you tried to start the lorry, it wouldn't start, and to pass the test you first had to demonstrate sufficient mechanical knowledge to fix whatever deliberate fault the examiner had introduced into the engine.

I may have recounted before:

Twenty years ago, I was just starting to climb Hardknott, E-W, having just come over Wrynose, on a tradional tourer with panniers, twiddling a sub-20" bottom gear. Some fit person on a lightweight bike and a much, much higher gear overtook me at two or three times my speed, honked out of the saddle round the first bend, and disappeared from my sight round the corner ... to the unmistakeable pinging sound of at least two spokes breaking.

CJ wrote:I think that in the rural situation, we should campaign to convert these usurped general-purpose roads into honest motorways whilst providing parallel service roads for non-motorway traffic....

It's also a win-win for both motorist and cyclist, which makes it politically possible - apart from the colateral environmental damage, that would cause an outcry from the green and nature lobby, which includes most cycling campaigners

That's the problem, isn't it. I am persuaded by your logic - but Chris, as a man who clearly appreciates scenery as well as bicycles, who tours to see places as well as to get in the cycling miles, do you think extra road building in our countryside really is a price worth paying?

CJ wrote:The stem length has negligible effect upon the steering characteristics of a bicycle, which is entirely a function of steering geometry, front tyre properties and the weight carried by it. And that's the one way in which stem length does have a small effect, by letting the rider sit a bit further back, there will be a bit less weight on the front tyre, which makes the bike insignificantly less stable and easier to steer. But if you need to sit futher back, you need to sit further back and needs must locate the handgrips accordingly.

I entirely agree that getting the posture right is the top priority (I have remarked before that the first thing I did on receiving a mega-expensive, supposedly custom-built tandem from Chas Roberts was to change the stems because he hadn't believed us when we said we wanted a more upright posture).

I also agree that in practice, the biggest effect on steering handling comes from any shift in weight from front to back, and this is likely to dominate all other effects of moving the bars while keeping the rest of the steering constant.

But surely, in principle even if not important in practice, bars in front of the steering axis is a stable equilibrium, bars through the steering axis is a neutral equilibrium, and bars behind the steering axis is an unstable equilibrium? That is, when there is a deflection from straight ahead for whatever reason, the tiller effect corrects it for bars in front but exacerbates it for bars behind.

You would not notice this in actual riding because the other effects of a slight deflection, set by the steering geometry, would probably dominate, e.g. whether a small deflection of the steering raises the bike's CoG or not, and how the castor effect works. We all know that bike steering is very complicated to describe mathematically. But you would notice it if you experiment with a bike on a bike stand. I wonder if this could be the origin of the assertion by some bike shops that bars in front of steering axis is more stable - they say it because it is actually true for a bike not touching the ground?!

Just speculation on my part. The real reason could just as easily be that bars in front is traditional for racers. My advice to anyone would be the same as other people have said: by far the most important thing is to be comfortable, never mind what it looks like.

http://onlinelibrary.wiley.com/doi/10.1111/j.1539-6924.2012.01770.x/abstract

I can't be bothered paying for the full paper to see what conclusion he actually reaches. But the first page, viewable for free, is not promising: he appears to treat lambda, the accident rate per km cycled, as a constant, dependent on neither helmet wearing nor total miles cycled by cyclists. Maybe he explores the effect of lambda in fact depending on both these later in the paper...

rhoadsy wrote:I use these over my normal gloves when it's really cold/ wet.
http://www.britishmilitarysurplus.co.uk/shopscr221.html

Quick bit of feedback. I bought a pair of these last week based on your post. Cycled 10 miles this morning in -7.5 degrees. Wore fairly standard fleece gloves with these army surplus mittens over the top and it kept my hands adequately warm, the first time I've managed that in this really cold weather. I reckon if I'd worn thin inner gloves as well I'd have been really warm. I guess the principle of completely wind proof over-mittens would work with any comparable mittens, but these ones seem ideal and cheap so thanks for the suggestion.

GeoffL wrote:

karlt wrote:I daresay it is. I'd be willing to suggest an alternative explanation, which is that the reduced limits are introduced when there's heavy congestion, and that's one of the circumstances where people tend to leave inadequate space.

That seems reasonable at first sight. However, the Government say that variable speed limits increase the traffic flow in terms of vehicles per hour. If the number of vehicles per hour increases then the average vehicle separation must decrease. That is, the degree of tailgating has increased.

Arguments based on different understanding or interpretation of words are usually futile; and that is what is happening here. In this case the problem is the word "tailgating". You use it to mean closer separation (in distance) between cars, regardless of speed; most of the rest of us are using it to mean closer separation than is appropriate for the speed in question. We all agree that when variable speed limits are in operation, the distance separation between cars reduces. You insist that cars ought to maintain a constant time interval, and say, correctly on that assumption, that this reduced distance separation is tailgating. The rest of us think you are wrong in your starting point (the constant time interval) but correct that if you start with that assumption, the consequences you state would indeed follow. For those of us who think the safe distance between cars reduces with reduced speed, the closer distance between cars that you report is evidence that the system does indeed work correctly and delivers a greater throughput of cars with greater safety.

Just to repeat, for clarity: thinking time is (roughly) a constant, so thinking/reaction distance is a linear function of speed. Stopping distance is proportional to the square of distance, where the proportionality varies a bit between car and car depending principally on the coefficient of friction between tyres and road, the efficiency of the respective ABS systems (or the driver's skill if they don't have ABS), and how much down force the aerodynamics generates. So, to follow the principle "always be able to stop in the distance you can see to be clear", the distance you need to leave to the car in front is a quadratic function of speed. That is the only truly safe principle to follow, because the car in front could stop abruptly for any of several reasons, the most likely being that it hits a solid barrier.

In practice, most of us assume that the car in front will not stop instantaneously, and so we don't "stop in the distance you can see to be clear", we "stop in the distance you can reasonably anticipate remaining clear". If you only leave your thinking/reaction time, you are assuming that the car in front will only ever deccelerate at the same rate as you. That is extremely rash; the instances where the car in front stops instantaneously may be rare, but the instances where the car in from stops more quickly than you can are legion, including them hitting the car in front of them, and them simply having better braking than you. So even if you don't leave the full stopping distance between you and the car in front, you would be wise to leave some significant fraction of it, and therefore a sensible separation between cars is still a quadratic function of speed.

By all means carry on your argument about the merits or otherwise of speed (or whatever your argument is actually about, I've rather lost track). But there's no need whatever to have an argument about physics, because the physics is very clear and straightforward, all that differs isthe choices different people make about what they regard as safe behaviour.

GeoffL wrote:

hubgearfreak wrote:

GeoffL wrote:Thus the maximum safe capacity is 25.29, 26.32, 26.98, 27.44, and 27.78 vehicles per minute at 30, 40, 50, 60, and 70 mph respectively. That is, as the travelling speed increases, the maximum safe capacity also increases; as the travelling speed reduces, so does the maximum safe capacity.

either you're being deliberately obtuse or are genuinely struggling to understand. the 2s is a much, much safer margin at 50mph than it is at 70.
let's try 150mph, shall we? is 2s still adequate?

Either you're being deliberately obtuse or are genuinely struggling to understand. The 2s is not the time it takes to stop. It is made up of reaction time plus the time it takes to stop after the vehicle in front has come to rest.

Actually, when you do the maths it does work from any speed. So at 150 mph, two seconds is still adequate. Provided that the deceleration of both vehicles is constant and the same, the following vehicle will come to rest at a time equal to twice the reaction time after the leading vehicle no matter what the initial speed. According to RoSPA, reaction times for alert drivers is typically between 0.67 and 1 second, so 2 seconds is a reasonable absolute minimum. However, it can be a lot more for drivers who have 'switched off'. I'll leave it as an exercise for you to create an appropriate spreadsheet or similar to check this for yourself.

What you say is (partly) valid if you assume that both vehicles come to a controlled stop under the influence solely of the friction between tyre and road. In real life you have to allow for the vehicle in front hitting something and stopping more rapidly, perhaps almost instantaneously. Which is why the Highway Code quoted above starts by saying "stop well within the distance you can see to be clear". Which is why the safe separation is a quadratic function of speed. Which is why the capacity of roads goes up as the speed goes down.

GeoffL wrote:The recommended minimum interval between vehicles is two seconds under ideal conditions, double that or more under adverse conditions.

If you express the safe separation of cars as a fixed time eg 2 seconds, the capacity of a road increases as the speed increases.
If you express the safe separation of cars as the stopping distance eg as in the above graph, the capacity of a road increases as speed decreases (in both cases assuming that cars actually do separate by the minimum safe distance).
I prefer to view the safe separation as the stopping distance as that corresponds to physics. I think the 2 s is a way of presenting it to motorists that is intended to be more readily assessed but which can only be true for one speed.
So reducing the speed eg by variable speed limits does increase the capacity.
In fact, though, there's another benefit of reducing the speed, which is that it promotes more uniform driving and reduces bunching caused by sudden accelerating and braking, and this is more efficient at getting cars through a road. That was presented as a benefit, possibly the main benefit, of variable speed limits when they were first introduced on the M25.

Edit: cross-post hubgrarfreak above

meic wrote:

Vorpal wrote:I don't think we need to worry too much. I mean, £15 million is lip-service kind of money when we talking about governmental budgets.

Sustrans can feel good about all the new barriers they can put up, the rail folks can feel good about the number of cycle stands they can install, and only a few of us will feel any pain.

Is that misrepresentation deliberate?

It is a very tiny minority of Sustrans people who like barriers, the vast majority of us hate them.
They are normally a penalty imposed by external bodies.

It wasn't me that said it, but I have some sympathy with the serious underlying point.

I don't for one moment believe that many people in Sustrans see erecting barriers as a desirable end in themselves. But the fact is that the strategy that Sustrans have gone down does indeed appear* to result in many paths with barriers or other features that make them less useful for functional cycling across the whole range of cyclists. I think the rest of us are entitled to think there's an element of "by their fruits shall ye know them". If I do something that has a consequence, saying "oh but I never intended the consequence to happen" strikes me as only a rather limited defence, especially if I keep doing it and it keeps having the same consequence. I accept that the defence may actually be "we have no choice and it's a price worth paying in return for the benefits", but the rest of us are, I think entitled at least to ask the question whether the degree of effort Sustrans put into avoiding barriers etc reflects their own cultural beliefs about how serious a problem they are.

(*Disclaimer: I don't use Sustrans paths that much myself so have only limited experience of the barriers and other problems, I tend to rely on other people's accounts to confirm that my own limited experience is not untypical.)

meic wrote:Does anybody really think that Murdoch himself is in anyway connected with this initiative?

I dont think so, I imagine this is purely the doing of the staff and he is totally disinterested in the whole issue.

Yes.

I would guess - and I freely admit it's just a guess- that Murdoch told his remaining editors to find stories/ campaigns that would rehabilitate the brand. I would guess this campaign originated from journalistic colleagues of the injured journalist who genuinely wanted to do something about cycling safety; but when the idea got put to management and editors, they seized on it in part because it serves that function: it cynically helps sanitise a seriously malign corporate entity. Of course, as I hinted in my earlier post and others have pointed out, it is also quite likely to be a Good Thing for cyclists, and that's the dilemma: is perpetuating in a small way the Murdoch influence on British life a price worth paying?

pete75 wrote:Exactly!! I don't know why some here are moaning about it.

I have a reluctance to support this campaign simply because it originates from a Murdoch newspaper. We have had exposed to us over the last year something of the true extent of the calculatedly pernicious influence this media group have had on UK public life. I think we have come to understand how the Times is part of the strategy of influence as much as the News of the World was. I respect anyone who says:
(a) this campaign is too good an opportunity to improve things for cyclists to reject on grounds that it emanates from Murdoch
(b) bad people should be encouraged when they do something good
(c) absolute good and evil are a myth, it's all shades of grey, and deciding to boycott Murdoch is an inconsistent moral standard compared with all sorts of other corporate entities (and other outworkings of Murdoch for that matter) that we tolerate

But personally, I rather suspect that part of the purpose of this campaign is to rehabilitate the Murdoch empire by espousing worthy causes (note that I say "part", I am not doubting that there are very genuine motives as well), and I resent being put in a position where I am expected to lend support and moral credence to a commercial organisation that has such a malign effect on national life, including the life of cyclists.

CJ wrote:If one bike was less efficient than the other, but being more comfortable made the rider happy to work a bit harder and thus complete the ride in the same time, what's not to like about that? The journey takes no longer, the rider is just as happy, and as a bonus in fact, his body has had a slightly better workout!

I agree that is valid consideration. But what if, in this test, he worked harder on the less efficient bike, not because it was more comfortable, but because he knew from riding the more efficient bike what speed he was capable of, and felt subconscious pressure to match that speed on the less efficient bike? In this scenario, if the only bike you ride is the less efficient one so that you have no comparison, you don't put in the extra effort and your speed is slower.

I think there are three separate issues: how efficient a bike is in absolute terms - mph per hundred watts; how much a bike, by its comfort, its feel, its image, whatever, encourages the rider to put in extra effort; and how much the rider is motivated to work harder by factors external to the bike, such as being able to compare two bikes over the same route. For real life situations, it is the combined effect of the first two that is relevant; but I don't think this test allows us to separate those two from the last, and we need to be able to separate the two to transfer the results to situations where there isn't a direct comparison between two different bikes.

I make this observation for the sake of academic rigour only. Given that I cycle a bike with hub gears, 38 mm Marathon Plus tyres, and straight handlebars, you can deduce what priority I personally set on the absolute efficiency of my bike!

My understanding (perhaps someone who knows better can comment whether this is correct):

electronic gear shifts are programmed so that when you press for a gear change, nothing happens until the chainrings/sprockets have rotated such that the teeth that have been specifically profiled to suit the change you want are correctly aligned. Thus every change is made only on the optimum teeth, and conversely, the teeth can be profiled more efficiently - knowing that some teeth will never be required to participate in a change, those teeth can presumably be left normal size.

I am not a fan of profiling teeth to facilitate slicker gear changes, as it seems to me inevitable that it will lead to greater wear. But if you are going to have profiled teeth, it seems reasonable to me that a system that allows changes to be limited to specific teeth and therefore require fewer dodgy teeth could have advantages. I suspect those advantages are principally in racing (I understand electronic gear changes allow efficient changing even when maintaining continuous full pressure on the pedals, and, once they start, are accomplished quicker than even a pro can achieve with manual levers) where the disadvantages of fiddly set up and compatibility with worn components matter less. But I can see advantages in other cycling as well: being able to change sprockets more easily (specifically, having to ease off less) while slowly grinding laden up a steep hill must be a Good Thing. (Of course, the alternative way of solving that problem is to fit a Rohloff...)

I had my work laptop die after a couple of years with a mechanical (ie as opposed to software) problem. I have absolutely no evidence that it was caused by being stuck in a pannier for my commute, and it was within the normally expected range of life for a laptop, but it made me a bit paranoid. I now put it in an Ortlieb padded laptop bag. That padded bag stays permanantly in one pannier, padded out all round and at the bottom with enough bubblewrap to fill out the pannier. The other pannier then carries tools, waterproof, lock, lunch etc, partially redressing any weight imbalance (not that I've ever found it a problem).