TECHNICAL ADVICES FROM
LE GAULOIS !
Le Gaulois may not have invented the wheel, but when it comes to tires, he knows a thing or two!
Follow his advice to avoid buying the wrong tires for your vintage bike.
I - The different types of tires
1- Tubular tires
A tubular tire consists of an inner tube surrounded by cotton (or more recently nylon) fabric, covered with a rubber band on the part in contact with the ground.
It's glued to the rim (wooden at the time, now made of aluminum or composite materials). This makes it long and difficult to repair in the event of a puncture.
A tubular tire can be half-covered, in which case the rubber tread only covers the part in contact with the ground. This is the most flexible and lightest type of tire, with the best performance. As the cotton fabric remains exposed on the sides, it is very fragile and sensitive to moisture. It is reserved for track use only.
When the canvas is completely covered by the rubber tread, it's perfect for road racing.
2- Beaded-edge tires
In this type of tire, air pressure holds the expandable beads in the rim hooks. A specific rim is therefore required for this type of tire.
This type of casing is very robust and flexible. This makes them very easy to mount and dismount. Another advantage of beaded-edge tires is that they have one or two inner lugs that act as rim bands. The inner tube is ideally housed here, limiting the stress zones that could weaken it.
3- Wire bead tires
This is the most common type. It is held to the rim by metal bead wires. It offers greater freedom in rim design than a beaded-edge tire, it allows the use of stiffer, lighter rim shapes.
It requires the use of a rim band protector to provide the ideal housing for the inner tube. With a Westwood-style rim, band protector should be a thick cotton cord rather than a thin tape as modern rim band protector.
Bead wires were originally made of a single thick steel wire. This made the tire rigid and therefore difficult to mount. Moreover, this could lead to breakage or deformation of the bead wire. As a result, bead wires evolved to consist of several steel wires with smaller cross-sections. Today, there are tires with “folding bead”, where the steel bead wires are replaced by very high-strength synthetic fibers. Lighter, these tires can even be rolled on themselves, making them very practical for storage. However, these folding bead tires are not recommended for use on older rim profiles.
II - The different tire sizes
Since the invention and spread of tires in the 1890s, tire sizes (diameters and cross-sections) have constantly evolved over the years, in line with changing practices.
When renovating an old bike, it's important to understand which tire size is right for your machine.
As is often the case, two different nomenclatures are used to define tire size. There's the French system (metric) and the Anglo-Saxon system (imperial, dimensions in inches).
1- French notation
French size consists of two numbers separated by an “x” followed by a capital letter (e.g. 700 x 28C).
Originally, the first number indicated the tire's exact outside diameter, and the second its cross-section. The aim was to standardize outside diameters (e.g. 750mm or 700mm), and depending on the tire's cross-section, rims had different diameters. This led to the definition of three rim sizes: A, B and C.
Size A corresponds to the narrowest tires, with the smallest cross-sections, and therefore mounted on the largest-diameter rims.
And then, gradually, a whole range of cross-sections was developed for each rim size (A, B or C), and the first dimension of the notation became very imprecise. That's why a tire rated 700 x 28 C is not 700mm in diameter, but around 680mm!
2- Anglo-Saxon notation
Basically the same principle than the French notation, but it is more complex as it can include a third number. Dimensions are of course given in the imperial system, in inches.
In the following example: 28 x 1-1/2 x 1 3/8, the first number always designates the approximate outside diameter of the tire. The last number designates the width of the tire when inflated, and the middle number plays much the same role as the letter used in French notation: it specifies, in combination with the first number, the rim dimension. It's often referred to as “tire height”, which can make sense when the tire is narrow: it's taller than it is wide.
To further complicate matters, two tires marked in the same way could differ in size, depending on whether they were made in the U.S. or in England. Even more complicated, German manufacturers also used the inch system, but could invert the second and third numbers.
3- The ETRTO standard (ISO 5775)
In today's globalized world, historical notations have become complex, and the ETRTO standard simplifies denominations without any possible ambiguity.
It consists of two numbers in mm, separated only by a “-”. The first indicates the width of the inflated tire, and the second the tire inside diameter.
Ø: Tire inside diameter (mm)
III - Which tire size for my old bike?
When the tire is no longer present on its rim, or when the tire size is no longer readable, it's necessary to start by measuring the rim diameter in order to define its size. Then, depending on the model and construction of the bike, you need to determine the maximum permissible cross-section.
1- Define your rim size
Use a tape measure to measure the rim diameter edge to edge (outer edges), passing as close as possible to the hub. Even if the length is slightly distorted because of the hub, the measurement is sufficient to determine the correct tire size.
Measure twice on two perpendicular diameters, and take the average of the two measurements if the wheel is not perfectly round.
2- Define the admissible cross-section
Depending on the type of bike, the cross-section of the tire will be different.
A racing bike, with a narrow fork head and rear end, will generally not allow tire sections larger than 32mm
Whereas a touring bike designed for “balloon” tires will need 50mm cross-section tires.
It's everyone's responsibility to find the perfect tire for their machine.