When tyre fitment technique is critical - Road Cycling UK

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Richard

When tyre fitment technique is critical



It is not unusual to find an RCUK forum user expressing distress at some perceived difficulty in either removing or replacing a bicycle tyre. Both aspects of the job seem equally able to defeat many cyclists, despite the fact that both are very easy – at least in comparison to doing the same job on a motorcycle tyre.

As I found out recently, when, on returning to my moto, I found the rear tyre flat.  A 4″ decking screw driven in at a tangent was the culprit.

The tyre, like that on the front wheel, is tubed; like most cycle tyres it encloses an inner tube and there’s a rim tape to protect the tube from the spoke ends. Most modern motorcycles run on tubeless tyres, which have one major advantage; they usually don’t deflate when pierced by a screw or nail and even when they do, it happens slowly. They can also be temporarily repaired on the spot by inserting from the outside a plug coated in adhesive and then slicing off the protruding remnant. The disadvantage is that a permanent repair requires tyre removal so a mushroom-shaped patch can be applied from the inside, the stalk being pulled through the puncture hole.

A tubed tyre offers several repair options. There’s sealant sludge of the sort used in tubeless cycle tyres, which generally makes a mess and is not entirely reliable. The tube can be patched, but the shearing forces within a moto tyre usually peel a patch off fairly quickly. So, it is best fitted with a new inner tube, which constitutes a permanent repair.

Being the kind of person who dislikes having to wait around, unless I have to, for rescue by whatever motoring organisation gets my breakdown insurance spons, I carry the means to repair a moto puncture when riding one. Gas cartridges in either case and a tubeless kit for tubeless tyres or an inner tube plus tyre levers for a tubed tyre. The last time I had to fit a new tube was a couple of years ago on the M4 in steady rain as darkness fell…

This time, the sun was shining as I removed the wheel, which is not difficult. Anticipating a quick result, I turned to the first part of inner tube removal, which is breaking the tyre bead away from the rim. The same has to be done with a cycle tyre, but the bead grips the rim with so little force that it usually falls away and is in any case easy to press free.

Not the moto tyre. The bead is invariably difficult to break free and there is a bead-breaker tool available. It’s too big to carry on the bike… Next best, assuming another bike is around, is to press its side stand foot against the side if the miscreant tyre and use the weight of the bike to do the job. Often the only option is to use the heel of the boot, which is one reason to wear a stout pair.

This is, in fact, often the hardest part of the entire task, as it was this time. After kicking the tyre for about 40 minutes, it finally broke free and allowed me to lever one side of the tyre over the rim.

Which is where the technique common to moto and cycle tyres comes in. Given correct technique, even moto tyre removal requires little force using levers short enough to carry on the bike. Indeed, using long levers incorrectly will usually damage something.

The trick is to start removal at the valve, having depressed the bead into the rim trough at the point opposite. This allows the bead enough slack to pass over the rim at the point diametrically opposite the point where it is depressed into the trough, and removal starts at the valve because otherwise the valve stem prevents the bead from falling into the trough.

Failure to follow this principle when removing a cycle tyre will usuually only result in minor difficulty and irritation; failure to follow it when removing a moto tyre will result in failure to remove the tyre.

Once the tube’s valve has been pushed through the rim, its nut can be fitted to prevent it falling back into the tyre. Once the tyre is inflated, the nut should be tightened against the cap, not the rim; otherwise, the firmly-held valve can be ripped out of the tube if the tyre slips around the rim under power. The nut is not needed on a cycle.

And, of course, fitment follows the process in reverse. Standing on the tyre to keep the bead located in the trough eases fitment, which unlike a cycle tyre can only be done with levers. Light prior inflation of the tube obviates the risk of pinching it.

All that remains is to inflate the tyre hard enough to pop the bead back onto the rim shoulder, wipe it clean and refit the wheel to the moto. Which is a lot harder than removing it… and a whole lot harder than refitting a rear cycle wheel.

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