Johan Bornman

I'm pretty sure the BB height from the floor will be the same for most MTBs, whether they have large or small wheels. You can't go and nilly-willy fiddle with the heights since it will affect the bike's usability. By that I mean your ability to put a foot out to stop at a stop street - whatever version of that action you'd like to picture. BB height is actually expressed as BB drop - the distance the BB is below the hub height. However, this changes for road bikes, 26ers and 29ers even if technically, they are all equally high. So it is more useful to look at the actual BB height. I would look for the problem elsewhere than the cranks. Crank lengths typically change in 2.5mm or 5mm incremenents and the max difference you'll find between the longest and shortest is 15mm (165mm to 180mm). Your problem is elsewhere, be it talent, luck or suspension.

It's weird that truck owners should even think of mineral oil in their brake reservoirs. At least with cyclists there is some confusion, with two systems and all that. But gooing oil into your truck brake reservoir is just super daft.

A customer came in with sticky brake levers this week and couldn't understand why the levers would not budge, especially after he went and bought a litre of Shimano Mineral Oil from CRC and bled his Hope brakes with it. It was quite interesting fixing that little mistake - Hope brakes work with brake fluid (DOT fluid if you like) and Shimano with oil. He injected oil into his brakes and within hours the levers were seized. The one lever still kinda worked, but was stiff. The next day when I had to disassemble it, I could not get the master cyclinder piston out. I had to punch it out with a pin punch. I then noticed how much the rubbers have swollen from exposure to incompatible oil. So much so that the two piston seals were locking the piston solidly in place. When I say solid, that's what I mean, hammer blows were required to free it. It was a real pain stripping and cleaning everyrhing. Even the hoses had to be flushed out, washed and dried. Please don't do this at home. Here's a photo of the reservoir cap seal. The one on the left is the new one, the one on the right the swollen one.

OK, so it seems your spokes did break from metal fatigue and you were just very unlucky. Usually it is a non-event. Weight has very little do do with it and age absolutely zero to do with it. A million year old wheel that hasn't ridden will still be "unfatigued." Metal fatigue in spokes come from poor wheelbuilding the wheelbuilder doesn't understant the concept and purpose of stress relieving. A stresss-relieved wheel has a near infinite spoke life. The repair mechanic's first clue should have been the mode of spoke failure. He then should have advised you that if one spoke broke from fatigue, the others are on their way out too. Tension here was not the issue, but stress relieving. Either do like Chippo here says or have them rebuild with double-butted spokes by someone who understands stress relieving. Only the very cheapest bikes nowadays have galvanised steel spokes, they're just about all stainless, so I doubt that rust played a role. Besides, spokes that can rust are of such poor quality that they break quicker from fatigue than from rust, even at the coast.

Are you sure you have the order of events right? A broken spoke very seldom takes a derailer with it. However, a broken derailer or jammed derailer always breaks spokes. Spokes that break for no obvious reason failed due to metal fatigue and the break is very characteristic - straight, square and clean. A spoke that broke because of derailer and chain issues is a dog's breakfast. Which is which?

Thanks for all the enquiries guys. Workshop is full. Next one, next year sometime.

Stop pooftering around. Led Lenser!

I'm pulling your leg. Switcing isn't an easy option once you own something. Latex does dry out with time and heat exacerbates the drying out. Once a tubbie is full of rubber latex balls, it's screwed. So look after it, keep it out of hot cars and out of the sun when not in use, and never bomb it. You could also try one of the non-latex sealants, like No-Flats. It was vigorously discussed here about a year ago.

Latex doesn't do damage to tubes, whether they're in a tubbie or not. However, latex dries out over time leaving lumpy deposits inside. Using CO2 to inflate when there's latex inside renders the latex useless. Your problem is not the sealant, but the tubbie. Tubbies are an anachronism from the 50's. Switch to clinchers and get on with life.

There is no room for tubbies in contemporary cycling, no matter what the discipline. Tubulars were borne out of necessity - technology for clinchers weren't available 100 years ago and the tubular was designed. Today's users base their decision entirely on myth, lore, sentiment and nostalgia. Clinchers are cheaper, easier to maintain and match tubulars on all the important factors including puncture resistance, pressure and rolling resistance. Althoug a tubby can sustain higher pressures, the rule of diminishing returns kicks in at about 6 bar. Thereafter tubbies and clinchers have equal rolling resistance. The only condition under which a tubbie has lower rolling resistance is when it is glued with shellac (hard glue) not today's contact glues. Contact glues cause hysteris between the tyre and rim that robs power (adds resistance). I don't know of anyone who even knows what shellac is, nevermind use the stuff. Tubbies supposedly have higher resistance to pressure punctures. Well, at today's pressures you have to hit a clincher extremely hard to snakebite. Most tubbies at the high-end are carbon and those rims cannot sustain a snake-bite type impact in anyway. The tubby may survive, but the rim not. Tubbies that are not glued on properly, are a risk and are outright dangerous. They can bunch up under braking (they even bunch up under hard braking in alpine conditions due to the glue melting. Someone mentioned a R450-00 tubbie. That is almost certainly an inferior product compared to a R450-00 clincher. It costs a lot to manufacture a good tubbie. Lots of manual work involved. That said, not all clinchers are the same. Gatorskins and their ilk are sluggish tyres designed for robust riding in adverse conditions. The're not the best in terms of rolling resistance, no matter what the brochure says. The optimal tyre in terms of performance, cost, convenience and safety on a long competitive ride would be a lightweight clincher with a 120TPI carcass and silica (as opposed to carbon) rubber.

Sorry, forgot to mention that little detail. Yes.

I'm presenting a wheelbuilding course sometime during the second week of December. I have two candidates who are flexible regarding the timing and are thus prepared to fall in with other candidates. This is a two-day course covering the theoretical and practical side of wheelbuilding. Each student will have to build two wheels of their own. Day one covers mostly theory and lacing, day two, tensioning and truing. The course will suit someone who wants to build wheels professionally, a mechanic who wants to up his skills or someone who simply wants to build a set of wheels here and there for own use and friends. Due to the nature of the supervision and assistance, your first two wheels will be perfect, albeit slow in building.Practice will increase your speed. The cost of this course is R2500-00 and excludes hubs, spokes, rims and nipples. Each student will calcualte his/her own spoke lenghs using techniques learnt on the course and cut and thread spokes to the exact required lenghts. Lunches and refreshments are provided on both days. I have a course overview document I can send should you be interested. johanatyellowsaddledotceeodotzeda

I'mpresenting a Fork Service Workshop this coming Saturday morning from 9:30 to 13:00 in our Jhb training studio. The purpose of this workshop is to show you how to service your suspension fork and your Fox/Rox shock. It is easy to DIY and you need a minimum of tools and consumables. Servicing your own fork will save you a couple of hundred rands per year and give you peace-of-mind that your equipment is in tip-top condition at all times. The workshop is not as sophisticated as the Pro Mechanic Suspension Elements course. Therefore we won't deal with the intricacies of multiple brands, the mixing of suspension fluids and damper modifications. However, you'll learn how to do your own fork and shock, whatever brand or model it is. On the fork side we'll do a full service and on the shock side, only an air sleeve service, not damper service. However, I'll show you how to test your damper (Rebound and RP23 settings) The workshop starts at 9:30 and we should be finished by lunchtime. Cost is R650 pp and includes consumables, oil, O-rings and lubricants for one fork. It excludes fork seal kits which can be purchased on the day. Approximate cost (brand dependant) is R240-00. I have space for 6 people, two places are already taken. Contact me on johanatyellowsaddledotceeodotzeda if you're interested.

They have a limited life if not serviced regularly. Fox forks are particularly prone to stanchion damage, especially the 29" models. They're so bad I think the company should do a recall. If not serviced regularly, dirt gets in behind the wiper and forms a grinding paste with the oil that eats away at the stanchions just below the wipers. It is usually invisible to the casual observer. Once the stanchions are rough, the bushes quickly go the same way. The user manual will recommend a service interval of between 40 and 60 hours, depending on the conditions. Shocks have a slightly longer service life if the shock is protected from back wheel spray. I'm doing a fork/shock service workshop on Saturday morning. Come learn how to do this yourself. I'll post details in Tech Q&A later today.

Pretend you didn't see it and never mention it again.

Revolution (DT) or Laser (SAPIM) spokes are 1.5mm in the shaft whereas the SAPIM Race spokes in question are 1.8mm in the shaft. This makes a significant difference in wheel stiffness. On a 29er with a heavy rider (70kgs and over), Revo/Laser spokes are a stupid idea. The wheels will just flex too much. However, wheel flex is a function of both spoke diameter and rim weight and counter-intuitively, not of spoke tension. A Crest rim is a soft, lighweight poofter rim suitable only for the lightest of riders. On a 26" wheel is performs much better. As for the Evans question. Yes, it is a good price and Evans is a reputable outfit. However, you have no idea to what standard those wheels will be built and whether they are stress-relieved or not. I may be biased, but I say have them built locally. You will pay more, but remember to add at least 20% to the price you see on the Evans website for VAT, shipping and the Post Office handlilng fee. Like someone said, it is good to have access to the wheelbuilder. As an aside, the stupitest (stupidest??) wheels I saw in a long time was a set of Shimano 29" factory wheels with 24 spokes. The wheel was so flexible that it routinely rubbed against the frame and fork. 32 spokes should be the minimum on a 29" wheel.

I'm not sure what you are observing on your bike. I'll have to look before I can voice an opinion. Howerver, chainsuck happens under load or under slack and equally so. Since it is a phenomena in the slack cycle of the chain circle, it doesnt know when the chain is under load. Your 1/4 roation observation is more accurate. Chainrings wear only on one half of the chainring. The wear happens where the chain is engaged during the more powerful arc of your pedal circle on the left and right leg. In other words, if you look at your right crank face-on with the crank in the horizontal position, the most worn section will be at the top of the circle from say 12:00 O'clock to 3:00 O'clock (for the right leg( and at the exact oposite side for the other leg. Therefore chainsuck will be most prevalent when those wear spots are at the "25 to" position on the crank. Like you observed, if feels like chainsuck happens in quarters. It is easily observed if you have a clean chain and you have a helper ride the bike in a circle around you. You keep your eye on the rear derailer and you will see it jump as the chain just-just attempts to suck.

If it is one of the older PowerTap hubs, the magnet on the axle may have come loose. The earlier ones were glued on and later they were glued and taped. Have someone remove the axle and look for the magnet. It is a round, button magnet attached to the aluminium axle or axle sleeve - can't remember exactly where. Also, if someone recently opened it, the magnet may be in the wrong position, i.e. the sleeve was turned round.

Hmmmmm. Load bearing on a ball bearing is a function of the ball size and quantity of balls. A large ball, lotsa ball, bearing will carry more load than a small-ball, few-ball bearing. Obviously the former is a larger bearing by definition. Since the wheel doesn't give you a choice of bearing sizes, you take what you get, the ball size being a function of the ID and OD and width of the bearing. Load capacity also has nothing to do with maximum speed. This is a function of the type of grease, seal and smoothness of a bearing. Someone else mentioned ABEC as if that means something. It means nothing. ABEC stands for Annular Bearing Engineering Committee, an American bearing standards organisation. The fact that a bearing is ABEC is meaningless other than to suggest it was made or certified in the US. The rest of the world uses a "Class" system. ABEC (the consortium) grades bearings according to ball and race smoothness. An ABEC 2 bearing is approximately twice as smooth as an ABEC 1 bearing and ABEC 9 aproximately twice as smooth as a ABEC 8 bearing. Bearing smoothness is measured by the size of the largest imperfection on the race/ball surface, usually measured in microns. Europe and AFRIK Japan, uses the Class system which is easier to grasp than ABEC. A class 100 bearing has its largest imperfection (called ashperity in bearingnese) at 100 micros. A class 50 bearing is twice as smooth with an aspherity of only 50 microns, etc etc etc. Class 5 is about the best we can make at any reasonable cost. Class 20 is absolutely good enough for bicycle use but older Campag hubs were as smooth as Class 5 - really classy. If you buy a bearing ball from Bearing Man, you'll get Class 100 by defaut. If you buy a Shimano bearing ball, you'll get Class 20 by default. Enduro bearings are ABEC 3 which are about 200 micron or Class 200 - quite rough. They do have some better ones but at a huge cost and in a limited range. The message is that ABEC 3 is good enough for our game. Bearing numbers are standardised and a code like 6802 LLB2 tells us that it is a deep-groove ball bearing of the cartridge type with the dimensions 24 OD, 15 ID and 5 Width. You cannot deduct the dimensions from the code, you have to look it up. The LLB part tells us that the above bearing has a low-temperature seal made of one or other synthetic rubber, usually nitrile or buna. The 2 tells us that it has two of those seals, one on each size. This code is stamped on the coloured seal or laser etched on the outer race. A "Z" seal is a steel dust cap (not really a seal) and a RS stands for rubber seal, another way of saying LLB. "Z" seals should never be used on bicycles. Bearing quality and longevity is determined by the quality and quantityof the grease and the way the engineer made the bearing fit in the rolling element. Enduro sells overpriced bearings with a bit of extra grease in for suspension pivot use. They've denoted these as "Max". As someone very observant above noted, never buy a Chinese or Indian bearing. Although I cannot say that all Chinese bearings are rubbish, I can say I've never come across a good one. China will get there, it is not a stupid nation. Just that for now, the best bearings come from European factories.

What Tim says about forced hydration can be clearly seen in the movie Jarhead. That deals with Iraq War 1, early 1990s. In training the troops are forced to drink and it is nicely (if subtly) documented there. Camelback is also on the bandwagon. It's slogan is Hydrate or Die! The message is clear - drink more than what you can fit into two frame-mounted water bottles.

If the bike is made from yoghurt, you may have a problem, otherwise not. However, there is one disclaimer. Latex-based sealant doesn't like heat and dries out very quickly at temperatures above 30 degrees or so. That tin roof is a frying pan. Continue to hang your bike there but next time you open your tyres, switch to glycol type sealant.

You don't say which adapters you need. I have some, but not all the combos.

Shocks and forks and rims don't mind this type of treatment at all. There is no danger, damage or doubt about that. However, A gadget that disables a door like that is stupid. Someone's gonna get hurt or burnt with that contraption. Rather find something similar, but that mounts to a wall.

That is the most contrived contraption I've ever seen. Daar is 'n makliker manier!

The only wheel that will give you satisfactory stiffness on a 29er is one with 32 spokes of the standard double-butted type and a rim that weighs more than whatever a Crest weighs. Crest rims are just too flexy for most people...yes I know there are thousands of you out there who are happy with Crests, but I see the other side of the coin - bent wheels in the workshop. Right now we have a 29" bike here that came in 'cause there is "play in the wheels". There is no play in the wheels, but plenty of flex. Lots. It only has 24 spokes. spokes are not expensive, buy lots of them and yoru wheels will be solid.