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Tyre tales | Tyre – tales |
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Pumps - There are pumps for mtbiking, and pumps for road biking. It all has to do with the difference in tyres: Co2 bombs - Carbon dioxide tyre-inflators inflate a tyre in a flash, but caution is called for as they often cause a blowout. A relatively expensive tool that does add a bit of weight, but worthwhile to shave 8 minutes of pumping-time when out on the road. The CO2 molecule is smaller than nitrogen (the main component of air) and leaks faster from the tube (which could be of some significance during a long distance endurance event). These ‘bombs’ basically come in 12gram (roadwheels), 16gram (offroad& tandem) and 40gram (3 use) canisters, requiring an additional valve-coupling mechanism. Overall they are well received, but some problems such as the coupling mechanism not puncturing the canister when inserted, and an incompatibility of the CO2 with specific tyres and/or sludge systems, have been reported. It' s good practise to check the bomb’s compatibility with the coupler mechanism prior to your ride, and -having used a bomb ‘out on the road’ - to check and inflate the tyre with a floor pump when back home. Beware the cold when releasing the bomb… Presta or Schräder? - Presta valves (skinny) fit all rims, while Schrader valves (fat) only fit Schrader-drilled rims. Schrader valves are supported at most garages’ compressors, and work better with the insertion of a slime system. Schrader valves are more robust, but tend to leak marginally more. Valves should always be kept clean, and Presta (skinny) valves’ bead occasionally tightened! Correct tyre pressure – As a starting point try the tyre manufacturer's recommended pressure - which you'll find printed on the sidewall - but experiment to find which pressure works and feels best for your individual setup. (The maximum figure stamped on the tyre’s sidewall is simply half the rated pressure the tyre could possibly take, before exploding off the rim.) The tyre’s ‘perfect pressure’ is wholly dependant on the weight it has to carry (that be you!) and cannot really be ‘standardised’. Higher tyre pressures often help reduce the chances of puncture, especially snake-bite, but a ‘softer’ tyre’s potential lower rolling resistance and better traction must be off-set against it. Find your preference. Harder, thicker tyres - particularly in the side-walls - are less prone to punctures, but weigh more. Lighter tyres puncture more. Ultra light tyres & tubbies should only be used on a track, or when you have a team car following with ‘wheels on demand.’
Road tubes: light v heavy? - High-end tubes can come in at about 50g, a number of midrange tubes range between 75-150g, but various brands weigh in at about 200g per tube. In evaluating the pro’s and cons of the more expensive purchase one will have to accept that once the tyre has been pierced, such intrusion will probably pierce the tube (thick or thin). However, a thinner & softer high-end tyre will increase the occurrence of the dreaded pothole induced ‘snake bite’ puncture, as a result of its relative lack of strength. In addition high-end tubes are constructed from latex, while the heavier and intermediate tubes are made of butyl. Latex breathes even more than butyl, and high-end tubes will necessitate pumping more often. Rotational inertia. = Anything that rotates needs to be spun up to speed being accelerated along a straight line, and the lighter the better. The rotating weight of wheels are very important with bicycles, as the ‘weight’ near the perimeter of a wheel has about twice the stored energy of non-rotating weight when moving. The rotation of cranks, wheel hubs and other parts are of little significance because the radius and speed of rotation are small. Rotating weight resists acceleration (and deceleration), therefore lighter rims, spoke nipples, and tyres allow quicker acceleration. There is no significant difference between rotating and non-rotating weight when at steady speeds or when climbing. You need to go really fast for it to make a difference, but for professional cyclists cycling "on the edge" it constitutes technology they can't do without. Tyre liners – Tyre liners (strips of plastic that lay between your tube and tyre) help deflect piercing objects and significantly help reduce punctures coming through the tread. They require some patience in set up, refitting and may add to rolling resistance, but give a little bit of tyre bulk to ward off snake-bites. Sludge - There are a number of aftermarket tyre sealant applications that work well. They do not always require a tubeless tyre, but compatible rims and some care and patience in fitment is essential. In roadie application it would seem that there could be too much pressure loss before the tyre is effectively sealed (the practical problem is that there is just not a lot of air in a road wheel) but if the puncture can be quickly sealed before pressure has dropped too much, results are good (despite the weight gained). Top cyclists suggest that training wheels can be sludged and even coupled with a tyre liner, but in serious racing the weight gained reduces speed, and is not advisable. In any event, the sludge does not have an indefinite lifespan, is best replaced every 6 months - throw tube away – and has a very messy effect when punctured with ‘old stuff’, or when the tyre is cut. In a nutshell, sludge limits your ability to swap tyres, but is effective in plugging punctures. See the comments about rotational inertia. (NOTE: Tubes with Presta valves require ‘puncturing’ the tube in order to insert the slime, whereas Shrader valves merely require the valve to be removed. Tubbys. - These tyres consist out of an outer casing made of a rubber running surface and a material part that is glued onto the tubular compatible rim. The inner inflatable casing is made of thin latex. Some “tubbys” can be inflated to 200PSI and only weigh 135g each. These days’ high-pressure tyres and tubes are widely used on track bikes as tubbied wheels are lighter than clinchers, but whether the weight saving is worth the hassle of gluing is a fair question. Popular opinion loves the weight saving - coupled with a ceramic bearing set it can free up to 6 watts of power! – and the ride quality seems to be marginally better, but all of that that comes at a cost of purchase and the repair difficulty inherent to a glued tyre. Tubbys are perhaps useful for pro riders having the benefit of pre- glued wheels at hand in a support vehicle. Talcum powder between the rim and the tube can reduce the wear on the tube, and the chances of spoke puncture. Tubeless tyres (expensive) do not snakebite, as there is no tube to pinch. However, their softer compound mean they are more prone to sidewall cuts, wear and lose pressure faster (up to 10psi/day from 60psi), and they are more difficult to repair when punctured. They do provide better traction as they can be run at a relatively lower pressure. A more expensive option, and punctures are harder to fix out on the road/track/bush.
Punctures Piercing punctures involve an object (thorns, branches, or glass, for example) penetrating your tyre rupturing the tube. There is typically a single hole on the outer circumference of the tube, usually small and round, but it can be rather large and irregular Snake-bites occur when the tube is pinched between a rock / pothole / sidewalk on the one side, and your rim on the other. They are typically two parallel slits along the length of your tube. Spoke punctures are like piercing punctures, except the offending object is an over-stretched spoke that pokes through the rim tape. The hole is usually a little larger than a piercing puncture, and may be irregular; however, the give-away is that it is on the inner circumference. Replace the offending spoke, or file down the end. Blow-outs occur when the tyre jumps off the rim and is no longer able to contain the tube. These are instantaneous (although a “bubble” may exist for some time before the tube ruptures) and are easy to identify – your tyre is partially or completely off the rim, and there are tatters of tube hanging out. Blow-outs are often the result of running tyres outside recommended pressures, having worn beads (the bit of wire or Kevlar that holds your tyre onto your rim), a major cut or wear in the side-walls, hitting a stone too hard, or poor technique when replacing a tube. If you hit stones too hard on a regular basis, try running a slightly higher pressure with wider tyres (tyres up to 2.3” for strong riders). If you generally blow out soon after changing a tyre or tube, take more care to properly seat your tyre onto your rim, as the tube might be trapped between the two.
No tube or patchkit?
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