Johan Bornman

Hmmm. I can just see you in your red Audi approaching a non-helmet wearing cyclist: "Look at that stupid idiot there, I hate him." And subconsciously: "Let me ride a bit closer and show him why he should be wearing a helmet." You've just admitted that your blood pressure goes up, heart starts to race and you have pre-judged the situation. OK maybe you are exempt from those emotions when you drive but I'm driving home a point.

Sanding it doesn't work. The alu bits are about 1mm in length and penetrate deeper than you can sand. The best way to get it out is with a sharp pick. I used to show this technique to the students in my class in the Sunday-afternoon-yawn session on maintaining caliper brakes. The secret to avoiding this irritation is to use Koolstop pads - Salmon colour. These have a patented rubber compound that no-one else uses and it works. I think the patent has another 4 or so years to go before it expires, then you'll see everyone's brakpads turning dark orange from the FeO2 on there.

Well, give the man some credit then, he didn't say it was a waste of time. There is a difference between mandated and timewasting. On the face of it, mandating it sounds like a good idea. But think it through. Should toddlers with their first little bike wear a helmet? Should a father be prosecuted if he teaches little Johnny how to ride a bike on the lawn? Should a bike mechanic taking a bike for a ride in the carpark be fined for not putting a lid on? Should Farmer John be hauled before the magistrate for not wearing a helmet when riding to the cowshed? And ultimately, how many people will not get to learn cycling because of these laws and then ultimately, ultimately, how much more dangerous will commuting be because there are less cyclists on the roads and thus less people with empathy for cyclists out there? Blanket mandating is easy to say and seems obvious when you're sewing up a facial cut, but I don't think a all-or-nothing law is sensible.

Statistically it has been shown that attitude should be considered. Whether we adjust for it by not wearing helmets, or somehow brainwash drivers into better behavior...I am out of my depth on those issues. But it doesn't negate the issue. I simply wanted to show that helmets do have an influence on motorist attitudes. Of course we should laud that helmets do their job but we should also aim to reduce injuries even further. Clearly visors (and those plastic rivets that hold them to the helmet) are dangerous, yet the anvil nest done by ANSI and Snell doesn't take that into account when they give a helmet a rating. Further, I'd like to see sunglass manufacturers create safer sunglasses. Having the skin sliced off your cheekbone isn't fun.

I don't think Gary is saying that? Is he? As for evidence that helmet wearing exacerbates head injuries, you need to look at cycling injuries in general and change your view from a head injury being a brain injury to a head injury being an injury to the entire head area, including the face and all soft tissue. Helmet strikes cause dangerous cuts. I've had my face cut open on two occasions by a helmet that moves forward to force the lens of my sunglasses to cut my face. These were standard, late-model helmets and sunglasses of the standard polycarbonate type that is typically non-rimmed. Another anecdote - a customer of mine had her face so badly cut by her helmet visor that she lost an eye and is badly disfigured on her face. These are head injuries that would not have happened without helmets. Clearly brain injury could have resulted were helmets not involved. Point is, the helmet argument isn't as clearcut as it appears. DJR makes a good point above and his guidelines seem sensible. I can also see different attitudes from motorists towards two cyclists at either side of the spectrum. Imagine thirty-something Joe Audi R6S coming up behind a fit, energetic cyclist in full lycra, fancy bike and of course, helmet. Now imagine Joe Audi R6S coming up behind aunt Mabel on her step-through ladies bike with a basket with a handbag inside. Aunt Mabel represents nothing that he hates, envies or has to compete against. He passes with a three inch bigger margin. A real-life example of the above thought-experiment: My friend Steven has two motorbikes, a Hayabusha (SP?) and a Harley. When on his Harley, the Hayabushas "buzz him" because (I imagine) he's a wannabe ponytail executive that doesn't ride a real bike and deserves a wake-up call. Riding the same speed on his Hayabusha he doesn't get buzzed. Humans unconsciously change their behavior according to their perceptions of the environment and its participants and I can see helmeted cyclist being seen in a different light from aunt Mabel.

You won't notice impaired braking performance with carbon wheels except like you observed, in the rain. However, down a long steep hill, poor performance is very noticeable. They just don't stop as quick as alu rims. It's like cars with drum brakes versus disc brakes. The difference is only noticeable if you really push it. Aunt Mabel in her 1100 Yaris doesn't know the difference. The average ZA race just doesn't test the rims to their limits.

That is pretty scary. I've had it happen to me only in one place, in the Suikerbosrand nature reserve, down the mineshaft. My experience was slightly different from yours. I didn't smell anything (only in my shorts afterwards) but felt a sensation on my thighs like going through a swarm of muggies. Afterwards when I could look and think, it turned out to be rubber sawdust. It seems to me that the rubber melts, gets thrown out by the revolving rim, solidifies in the air and then settles on your (hairy) thighs. It took me a while to figure out what the sawdust was. The sensation was unpleasant. One second you have brakes and the next, nothing. Common sense overcame my instinct and I released the brakes for a second or two. This helped the rim cool down enough to be below the rubber melting point again and I suddenly had brakes again. More recently, I rode down Huisrevierspas near Ladysmit (?) in the Karoo with a fully loaded rim brake bike and fully expected the same to happen. This time however I alternated between front and back brake and used it differently. I would brake hard for a short section, release, swap sides and brake hard again. This seemed to have done the trick. However, the only way to test that theory is to go back to Suikerbosrand to Knyp-'n-Washer hill and do it with the modified technique. I'lll leave it to someone else to do and report back.

West coast of Scotland. Beautiful day here. Think I'll go and find meself a nice moore somewhere and go for a wee walk.

No. Tubbes and clinchers can be made from the same fibres and rubber. The exact materials are chosen for characteristics other than whether the tyre will be a clincher or a tubular. Tubbies are not made thicker, that would defeat the object of attempting to lower the rolling resistance. If anything, they will be thinner. Therefore, the only way to make them stronger from a cut and puncture perspective is to make them thicker and thicker is bad, in the context of this discussion - performance. Further, "rubber compound" refers to the type of rubber. The compound has nothing to do with the thickness. They make it as thick/thin as they want, irrespective of the compound. Lets not forget that silly gormless ass, Ale Erwin, with his "bolt substance" that was supposedly chucked into Koeberg's turbine by saboteurs.

These are just numbers they throw out to fill space on the website and to give a scientific flair to their high-tech mumble-jumble. Firstly, they don't say how often the rider applied brakes. He may only have braked once and a peak temperature of X appeared on the apparatus. The number is useless. What is important is how a wheel handles the heat generated at the brake/rim interface. Heat is generated in the softest of the two friction materials, in this case, the rubber brake block. Heat is generated in the block at the actual surface touching the rim, through stretching and breaking the bonds between the rubber molecules. Since rubber is a reasonably good insulator, the heat cannot move backwards through the rubber into the metal brake shoe. It gets transferred to the rim via conduction. If it is an aluminium rim, the rim readily accepts the heat and disperses of it via radiation and contact with air. It is a large heat sink with ample cooling and only heavy overload of the system will cause the input heat to exceed the wheel's capacity to get rid of it. With the same scenario in carbon: the pad generates heat but it cannot go anywhere - not backwards, not forwards, since carbon is a poor conductor and doesn't accept the heat as readily as aluminium does. The result is melting pads and sticky rubber smear on the rims. The solution to this problem is pads that don't melt but sublimate - like wood or cork. It doesn't turn liquid but smokes. This solves the problem of melting pads that cause sudden loss of braking force. But, it doesn't solve the problem of poor braking performance in the first place, and all the subsequent issues of accelerated brake track wear, delamination etc etc. Some wheel manufacturers play around with alu tracks and alu cores, but the informed buyer will be able to distinguish between real heat dissipation and compromised heat dissipation based on the facts above. A simple temperature reading tells us nothing.

You don't need help, the gullible needs help.

Thanks.

The mechanics of tribology is sometimes not obvious. Stuff that goes black is good and stuff that doesn't go black is bad. I'll explain. The black in the oil is metal particles worn off the chain, cassette and chainrings. It gets suspended in the oil and effectively removed (albeit just diluted) in the oil. Oil is liquid and gets pumped in and out of the various cavities of the chain via capillary action. If it turns black, you know what a) not all grit is still trapped inside the chain and b) that the oil is still lubricious. If it doesn't turn black, you have a) no idea whether there is still lubrication inside the chain where it matters and b) you are assured that all wear grit is still trapped inside where it can do maximum damage via abrasion. I suggest you look for a PDF on this side called Everything You Need to Know about chains. It is explained in detail in there.

Your friend's chain hygiene is bad, hence the accelerated wear. However, those chain checker tools are rubbish. They have two errors: 1) a large reading error due to its short length and 2) a clean and dirty chain will give a different measurement since they read against the mobile rollers that will move lots on a chain and little on a dirty chain. Use the method shown above where an imperial measuring device longer than 12 inches is used.

Nope. Acceptable wear is up to the 1/16th point. Once it has worn to double that, i.e. 1/18th elongation of 12 (24) links, you've ruined the cassette. 1/16th of an inch approximates 0.5% wear and 1/8th of an inch approximates 1% wear. Chain engineers have chosen 0.5% elongation as the upper limit.

Regarding the new fighting-suspension bike you're building and the shock bushing. Lets distinguish between some parts in the shock mounting system, 1) Shock eye - the round eye at the end of each shock. These are not wear parts and wear parts need to be pressed into them. You shock eye is missing a wear part. 2) DU Bushing. This is the wear part that fits directly into the shock eye. As you've measured, the shock eye is 15mm and therefore the DU bushing should have an OD of 15mm (in reality a titsy bit bigger). 3) Reducer bush. Such a bush is a two-part affair as pictured in your first photo. 4) Through the reducer bush goes a mounting bolt. These are available in two sizes and the sizes are frame-dependent; 6mm and 8mm. They are usually special bolts and should ideally be made from stainless steel. In your case it is a smooth-shaft male-female bolt in SS. Make sure that the leading edges are nicely chamfered lest they eat up the Teflon inner coating of the DU bush, What's missing from your picture is the DU bush. Go to Bearing man and order a 15mm x 1/2 inch x 1/2 inch DU bush. Press it in using a soft-jaw vice. Inside the DU bush will be your reducer bushes. The ones you have don't look to buggered but measure them at two places on the narrowest section - against the flange and at the end. If the measurements differ, get new ones. If you're having a machinist make you new reducers, make them from 6000-series aluminium. The measurements are as you confirmed, except for the area where I said you should measure. There you should be 1/10th of a mm oversize. It should be a tight press fit inside the DU bush. The hole drilled through the centre is nominally a 6mm or 8mm but in reality, a 6mm or 8mm drill will make a 6.1mm and 8.1mm hole, which causes some irritating play between reducer and mounting bolt. I drill those to 5.9mm and 7.8mm for a better fit. Supply of reducers is erratic. In theory Omnico (Fox agents) should have these bushes in stock by the dozens, but they don't. Reducers come in various widths and I believe every bike shop should have a little compartmentalized container with a few of each size in stock at all times. The Omnico rep should come around once every two weeks and replenish it. This happens in Nirvana only, hence our frequent problems and self-manufacture.

I had a quick look in my hub measurement database to see how various manufacturers handle 150mm hub spacing and what they do with the "extra spacing" Some use it to balance the spoke bracing angle on the left and right of the wheel, others squander it by maintaining unequal spoke tension. Examples cited as hub flange distance from centre of hub: Novatek: Left 42mm/Right 28mm Ringle: 34/29 Hope: 26.5/26.5 DT: 25.8/25.8 The bracing angle for a given hub laced to a 29 and 26 inch wheel differs by less than 1 degree. This means that we have to widen the hubs (110mm in front and approx. 150mm in the rear) and use the extra width to improve the bracing angle, in order to catch up with 26 inch wheel stiffness. In addition, we require four extra spokes in a 29er. I think the 29er format has a long way to go before strength is optimum.

I agree that these are all threshold level valves but the difference lies in where the spike comes from. The Brain's valve is located on the rear chainstay and picks up spikes from the ground up, i.e. bumps. The others have the valve located on the shock and this pick up spikes from the rider down or ground up., it cannot distinguish. I'll give you a bizarre example. Put a Brain bike stationary on the ground and have a rider jump onto the bike like Clint Eastwood does to his horse from the first floor of the saloon. Nothing will happen with the rear suspension and the bike will not soften his fall. Do the same with a SPV bike and Clint lives to procreate. I'm not assigning value to any of the methods. Also the Brain's valve is an inertia valve and the SPV one not. In my limited experience of test-riding SPV and Brain shocks, I think the SPV blow-off is less sudden than the pop-release feel of a Brain. But, all this is just a side-show to the interesting RE: Active discussion.

I have no doubt that you can answer that question for yourself.

That changes the picture for this specific case, obviously.

You won't find any rules and in a civilized society we can't always expect rules. In multi-use environments such as yours, where pedestrians, equestrians, cyclists and animals share the facility, you can't speed. No matter how you look at it, it doesn't make sense. Cyclists are increasingly under fire here and rightfully so. I'm a cyclist, a dog walker and pedestrian on The Spruit. Jo'burg's recreational highway. Here we have the entire mix and in my view, cyclists are at the bottom of the courtesy hierarchy. A bicycle can scare a horse, a dog and a pedestrian and, cause considerable injury to all of the above. I would argue that none of those pose a threat to cyclist. I suggest more cyclists should try out walking amongst these trails just to experience what it is like being buzzed by cyclists. The etiquette on this particular trial is atrocious. My advice is to ride as fast as you can see. In other words, don't charge around corners,

Pleasure, but if you are still stuck, I can mail you a fresh spring and some pawls.

A rim has nothing to do with the hub's axle configuration.

It isn't normal. Something is amiss.

I bet it isn't worn, but rusted. Those hubs have really crappy seals and water that enters easily eats away at that very rustable carbon-steel spring. If you look with a magnifier, you'll see it is rusted. I just make them. Go to an airplane hobby shop and buy yourself a length of 0.5mm piano wire and bend one.