developing mechanic

Fixing a Puncture - A Few Procedures, Hints and Tips

Removing and Fitting the Wheel

 

Brakes

Most rim brakes have a quick release mechanism to increase the space between the brake pads enough to allow an inflated tyre to pass between them. Use this to allow easy wheel removal and installation, but don’t forget to close it again before riding! V-Brakes have a slotted stop for the elbow or “noodle”; pull the elbow back and slip the cable through the slot to release the brake. Many Sidepull Brakes have a quick release lever on the caliper, but not all. You might need to deflate the tyre to fit it through the brake. Don’t remove a brake pad or undo the cable. If you have Disc Brakes you don’t need to do anything. Though there’s not a lot of room, the brakes will not obstruct the disc rotor. If you have hydraulic disc brakes, be sure not to squeeze the brake lever while the wheel is out as hydraulic brakes are self-adjusting and the pads will close in too far to fit the rotor between them. If this happens, you’ll need to reseat the pistons by gently prising the pads apart with a clean screwdriver or similar.

 

Gears

A note for beginners: There is no need to remove the rear derailleur or chain from the bike. Simply put the chain in top gear at the back (the small sprocket) and pull the derailleur back and out of the way while you remove the wheel. Do the same when refitting the wheel and your gear adjustments will not change.

 

Dropouts

On a bike with vertical dropouts (all front and most rear wheels), sit the bike vertically on the wheel before doing up the skewer. The wheel should fit all the way up in the tips (and the brake should be adjusted to the wheel in this position).

If you are fitting a wheel in a single speed or hub-gear bike, you’ll probably be dealing with horizontal dropouts and an adjustable wheel position. My tip here is that wheel position adjustment and chain tension adjustment is easy if you “walk” the wheel to position. Get it somewhere about right and half-tighten the wheel nuts. From now, loosen only one side at a time and move it forward or back by forcing the front of the wheel to the right or left, using the bike frame to brace against. You might have to make a fair number of “steps” this way but you’ll have good control.

 

Removing and Fitting the Tyre and Tube

 

Squeeze all the air out of the tyre that you can. Put the wheel on the ground with the valve near the bottom, and hold the valve open while leaning your chest on the top of the tyre and wrapping your arms firmly around the rest of the tyre. That is, squeeze every part that you can to get as much air out of the tube as possible. If you have a Presta valve, do the valve nut up to prevent air getting back in before you let it go.

Unstick the tyre. Work around the tyre, pulling the tyre away from the sides of the rim (toward the centre) to unstick it if it’s stuck.

If you can, remove the tyre and tube together from the rim without using tyre levers. This is the fastest way and the least likely to damage the tube.

 

Removing the tyre without using tyre levers

Starting at the valve and working both ways at once around the tyre, pinch the tyre beads into the deep part in the centre of the rim with your fingers, while pulling the tyre up and around the wheel so that it ends up good and loose at the top. If successful, you can then simply pull the tyre off one side of the wheel without using levers.

There are two ways to do the above step. I usually start by holding the wheel in the air in front of me, using only the weight of the wheel to hold the beads in the centre of the rim. When this isn’t enough (usually something other than a mountain bike wheel) I’ll stand the wheel on the ground and use my feet to hold the rim down while I work up from the bottom around the tyre, centring the beads and pulling the tyre up.

 

Using tyre levers

If you can’t get the tyre off using the method above you’ll need to use levers, taking the associated risk of pinching the tube and puncturing it again.

Lay the wheel down on a bench or the floor, insert a lever opposite the valve and lever the tyre over the rim. Insert your second lever about 2 spokes away and do the same. If you have three levers (recommended) then insert your third lever a couple of spokes further on again. Remove the middle lever and continue the process until the tyre is loose enough for you to slide a lever around the rim to remove the rest of the tyre.

Starting opposite the valve and using your hands only, pull the tyre, complete with tube, from the rim. If you can’t, then you’ll need to remove the tube first (start opposite the valve) and then you can use levers if necessary to get the other side of the tyre from the rim.

 

Fitting the tyre and tube onto the wheel

Fit one side of the tyre onto the rim, aligning the tyre logo with the valve, on the right side. Pay attention to the direction indicator on the side of the tyre if it’s there.

Inflate the tube enough to give it shape, but not to stretch it at all.

Pull the tyre back at the valve hole to allow you to insert the valve through the rim. If you have a rubber rim tape, pull the tape up from the rim (use a screwdriver or similar) and push the valve through the rim tape first, then through the valve hole in the rim. This prevents the common jamming and resultant tearing of the rim tape. (It took me three years as a professional bicycle mechanic to work that one out.)

Push the tube into the tyre. Don’t worry if the tube looks too big for the rim. The tube sits in the outside of the tyre and inflates in to the rim. The tyre should fit comfortably in the tyre and must not have any folds. If it doesn’t fit into the tyre (if you’ve fitted a narrower tyre) then you’ll need to use a narrower (or newer) tube.

Shove the tube, inside the tyre, onto the rim. This precedes fitting the second side of the tyre onto the rim and is just a matter of locating the tyre and tube about where they want to end up.

Fit the second side of the tyre. My method is opposite to all the instructions I’ve read in all the good books, but I’ll bravely recommend it to you: Start at the valve! Using your hands only, push the tyre onto the rim, starting at the valve, and work out in both directions until it starts to get difficult. Then, seat the valve inside the tyre. The valve has a double layer of rubber around it, which is probably sitting between the tyre bead and the rim. This keeps the tyre out from the rim (making it tighter) so what you want to do is get the base of the valve into the tyre and away from the rim. So, push the valve into the tyre until it almost disappears through the rim, then pat the tyre firmly from the outside to get the bead in toward the rim, then pull the valve back out into its normal position. Keep pushing the tyre onto the rim until it’s difficult again, and then squeeze the air out of the tube. All that you can, as described in the tyre removal process. It’s amazing what a big difference a very small amount of air can make. Centre the tyre beads in the rim in the part already fitted so the remaining section is as loose as possible.

Keep pushing the tyre onto the rim. Hold the wheel so the side with the section of tyre needing fitting onto the rim faces away from you, hold your hands around the rim and tyre and roll them back toward you, popping the tyre into the rim as you go. Your ability to continue doing this with a tight tyre will be limited not only by your strength but also by the toughness of the skin on your fingers – it’s easy to lose skin doing this!

Can’t finish? OK, you can use your levers again now. The previous steps of inflating the tube to give it shape, and later of locating the tyre and tube over the rim before fitting the second side of the tyre become important now as they minimise the likelihood of the tube hiding between the tyre and rim, waiting for your levers to inflict a snakebite (“pinch flat”).

 

Inflate the tyre

 

Seat the valve inside the tyre, as described above. Yes this is a repeated step; there’s no harm in doing it twice, but if you don’t do it then a double layer of rubber will get itself between the tyre and rim and will prevent the tyre from fitting evenly (round) on the rim, and will make it likely that the tyre will therefore blow off the rim when the tyre is inflated, sounding like rifle shot (road tyre) or shotgun (mountain bike tyre) and leaving a big tear in the tube up to 15cm either side of the valve.

Inflate the tyre one third of the way to full inflation (to about 30psi in a road tyre or 20psi in a mountain bike tyre). Give the wheel a spin to check that the tyre is sitting evenly on the rim. If not, shove and push and pull to try to even it up before inflating further.

Inflate to two thirds of the recommended final pressure. Again check the roundness of the tyre. Pushing and pulling might be harder now and might require deflation to a lower pressure then reinflation to get it about right.

Inflate fully. If the last step got the tyre reasonably close to round then this step will usually do the rest, via an unsettling popping as the tyre seats correctly on the rim.

If the tyre is not even and does not show any high spots but only shows a low spot or area, then over inflating the tyre slightly might pop the tyre into place. I’ve seen this step taken to an extreme, successfully, but I don’t recommend going more than about 10% over the recommended maximum inflation pressure in this step (call it cowardice, but I really don’t like the sound of bursting tyres).

If it’s still not round:

Deflate the tyre and spray or brush a fairly concentrated mix of washing up detergent and water between the tyre and rim to act as a lubricant.

Check your rim tape. If the rim tape sits up over the bead seat on the rim it can make the effective bead seat diameter too large, preventing the tyre bead from sitting on the bead seat all the way around (requiring it to sit in the wheel well for a small section). If this is the case you’ll need a narrower rim tape.

A combination of the above steps should get the tyre sitting evenly on the rim. If not, see a professional bike mechanic!

 

Finding, Diagnosing and Repairing a Puncture

 

 

Check the tyre

Run your fingers around the inside of the tyre feeling for possible causes of the puncture. Do this carefully because you’re looking for the pointy end of thorns or small shards of glass. If you find it/them, remove it/them. This can be easiest to do by pushing the object further through the tyre from the outside.

Pump it up
Don’t be afraid! Inflate the tube until it is stretched well beyond its normal size to make finding a small puncture much easier.
Find the Puncture

Easiest if you’re at home with a tub of water handy. This is why it’s good practice to carry a spare tube on your bike – fit the new tube and fix the old when you get home.

But if you’re finding the puncture without water, start at the valve and slowly turn the tube and locate the hole using one of the following three methods

Listen You’ll hear a hiss if it’s a decent sized hole. Once located approximately this way, you’ll probably be able to find the hole visually (might need glasses if you’re over 40).

Look This is my method for finding small holes – it’s not really looking, but it looks like it! Pass the tube slowly past your wide-open eyes, only a few centimetres away, feeling for the small current of air from the puncture. It appears a bit daft to onlookers but it works.

Lick A variation on the look idea that I saw an old (born a long time ago) friend use once. Jack licked his lips with gusto and passed the tube slowly close by his lips to locate the puncture. Drawback: it appears even more daft to onlookers than the look method.

Of course none of the above methods will be needed if you’ve blown a tyre and shredded your tube. Like I said, carrying a spare is good practice.

 

Keep the spot

If you’re at home, use a ballpoint pen or similar to mark two pointers to the hole, at right angles to each other. Keep each a few centimetres from the hole, beyond the reach of the glue and patch. If you’re out on the trail, keep a finger or thumb on the hole until you’re ready to sand and patch.

 

Repair the Puncture

Prepare the tube. Whether you’re using glued or glueless patches, you need to sand the tube before gluing. If you have a puncture kit with a steel scraper, you’ll hopefully have thrown it out by now and replaced it with a small piece of sandpaper. Those mini cheese-graters inflict a few token scratches but don’t do a good surface prep like sandpaper does. Sand beyond where the patch will be.

Deflate the tube to an unstretched size or you’ll blow bubbles in your glue.

Apply the glue, generously but not flagrantly, and spread the glue beyond where you expect the edges of the patch to be. Spread it with the nozzle of the glue tube and keep your fingers out! Yes, there will be thicker and thinner parts but don’t worry about that.

Wait! Wait at least five minutes. Look at your watch or a clock and work out a time that’s easy to remember and that’s five minutes or more away. Go inside and listen to a couple of favourite tracks on the stereo (maybe only one if you’re into classical). If you forget, and don’t come back for half an hour, no problem. 2 hours? Dunno – I’ve not tried that one yet.

Remove the foil from the patch, take note of the pointers and put the patch over the hole. Press it firmly in the centre then press firmly over the rest of the patch working out from the centre.

You’re done! Ready to fit the tube and tyre back onto the wheel.

 

 

 

Diagnose the problem

What sort of hole is it and where is it?

2 holes close together on the side of the tube: Pinch flat. You’ve pinched the tube (and tyre, but it probably survived) between the rim and the ground. You may also have damaged your rim. If you’ve just fitted the tube and not ridden yet, and you used levers to get the tyre on, then you’ve pinched the tube during fitting.

A single hole under the tread area of the tyre: An everyday puncture. If you’ve not found the culprit in the tyre yet, take a closer look at the relevant section of tyre.

A hole on the inner section of the tube (where it sits in the rim). Hey, it’s not your fifth today is it? This can occasionally be from a spoke end or nipple in a single wall rim, but by far the most common problem is the rim tape on a double wall rim. It takes the pressure of the tube, preventing the tube from blowing out into each valve hole around the rim. Misaligned or weak, the rim tape won’t do its job and the tube will burst into the rim cavity endlessly until the rim tape is aligned, or more likely, replaced.

 

A note on tyre and tube positioning

Always position the logo of the tyre at the valve (the right side by default unless this conflicts with the tyre’s tread direction).

Mark the right side of the tube when you fit it, and always fit it this way.

When removing the tyre and tube, confirm this positioning of the tyre and mark the right side of the tube with a ballpoint pen near the valve if it’s not already been done.

This way, it’ll look like your bike has been worked on by a pro! Oh, and also, you’ll more easily be able to trace the cause of a puncture if it remains in the tyre.