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  Last updated: 12/06/2009

Tires and Tubes

Tire Size

There is a lot of mystique in choosing tires.

23 mm tires produced better results than narrower 18 mm versions in a recent comparison of rolling resistance. The wider tire formed a curved D shape compared to the flat based U shape of the narrower one. This resulted in a smoother ride, less rolling resistance, and a greater resistance to impact, pinch-type, punctures. The size of the contact area with the road depends on the inflation pressure. If you run the same pressure in a fat and a skinny tire, the contact areas remain the same. That being the case, it is the shape of the contact area that will change, and a D shape (above) has the performance advantage.

Cornering differences are related more to the rubber compound than the width of the tire. But rubber compound being equal, a wider tires has a much better grip for cornering as the contact are remains curved over a greater surface during banking around tight alpine bends.

Here's another explanation I've run across in a chat room for a similar question: Q. Why does it feel harder on the turbo trainer with a narrow tire than a wide one?

A. Might I suggest it is simple mechanics. The air pressure in a narrow tyre must be greater to resist deformation at the area in contact. A wider tyre requires less pressure. Narrow tyres must wrap themselves around the roller of the drive wheel until equilibrium has been achieved, using F=PxA, where F is Force, P is pressure and A is area.. A wider bag will give more area therefore less deformation. Go for a 23 mm bag and it will give a better ride both on the road and on the roller than a 18 mm or 20 mm bag. Of course if you can get a narrow tyre at 200+psi the equation balances OK as well, but that requires a big effort to do that. Settle for 120-130psi.

Bottom line - It would seem that a 23 mm tire, kept at maximum inflation pressure is the logical choice. And I think most experts would agree that today’s clinchers are as good if not better than sew ups.

Tire Pressure

Most bike tires can withstand significantly more pressure than is inscribed on the sidewall. But using higher pressures will not benefit your riding. In fact, inflating road tires to even the maximum recommended pressure will make them wear faster and corner worse while giving you a more uncomfortable ride. For the most commonly used size, 700x23C, an inflation of 95 psi front and 100 rear will give you excellent performance no matter what pressure the sidewall says can be used. Heavy riders can go a bit higher (up 5 psi or so) in each tire, especially if they're having pinch flats.

And here is another idea - for those who get uncomfortable on long rides or on very rough roads. And it will decrease your level of fatigue when the ride is over as well. Frame stiffness isn't the most important factor in how a bike feels on an irregular surface. More of an issue is tire size and inflation pressure. So the easiest way to make a "stiff bike" more comfortable is to mount a pair of 25 or 28mm tires and inflate them no higher than 95 psi.

Changing a Flat

As you put the tire around the rim, squeeze it so the beads (the open edges) go into the rim's center, which is the deepest part. With the beads in this depression, the effective diameter of the rim is reduced. Then when you get to the last several inches of unmounted tire, you can pull it up and slip it into place.

It helps to have a thin rim strip and a skinny tube that takes up minimal space inside the tire. And make sure that no part of the tube gets trapped between the beads and the rim. (This would increase the effective rim diameter and makes it even more difficult to mount the tire by hand.) Inflating the tube just enough to remove wrinkles prevents it from getting floppy and finding its way beneath the beads. But remember to deflate it before rolling the last tough section of tire onto the rim. Dusting the tube and inside of the tire with talcum powder may make a difference. The theory is that it helps the last bit of bead slide easily over the rim. (an added benefit - talc may reduce flats by preventing abrasion between the tube and tire.)

Here's a step by step:

Patching a tube

Glueless patches? They work well. The hard part is peeling the backing away, especially with cold hands. Either use sandpaper provided or wipe the punctured area with a clean rag to remove any tire talc. Remember to clean an area bigger than the patch.

Traditional patches are a bit messier because of the glue. For these, use the sandpaper to gently rough up an area slightly bigger than the patch. Put on glue sparingly in an area slightly bigger than the patch. Wait for the glue to dry. Peel off the foil and apply the patch. Removing the cellophane is optional although the directions say you should.

How many patches? That is a personal choice, more patches mean more chance there will be a slow leak. Is the next flat a leaky patch, a new hole, or all of the above? The best approach is to avoid patching a flat during a ride. To do this, carry a couple of new tubes in your seat bag and if you puncture, find the culprit in the tire, remove it and put in a fresh tube. Then you can patch the bad one when you get home (don't forget) and put it in your bag as a spare.

Here is some additional information excerpted from the Newsletter Issue No. 269 - 11/09/06

The original article was in Vol. 5 No. 1 issue of The Bicycle Quarterly (

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