Vintage Tyres

Vintage and classic tyres are of either crossply or radial construction Never mix Crossply and Radial

Crossply Vintage Tyres

The cross-ply vintage tyre is made up of superimposed layers of textile cord running at alternate angles from bead to bead. With this design the sidewalls and tread are not differentiated and this gives the tyre structure great rigidity. With a cross-ply the maximum width and the height of the tyre above the rim are approximately equal. This relationship is known as the aspect ratio and with cross-ply tyres is approximately 100%, giving the cross-ply tyre its unique "tall" appearance.

Radial Classic Tyres

The beauty of the radial design is that it separates the functions of the sidewall and crown of the tyre, allowing greater vertical flexibility whilst ensuring that there is still as much surface in contact with the road as possible. In radial classic tyres the sidewall has a one or two layers of textile cord giving good flexibility, and the tread is made rigid by combining the casing layer with two (or more) layers of steel cord bracing plies. Both these factors give the radial classic tyre excellent road holding capabilities and a longer life span when compared to vintage cross-ply tyres.

It is well worth noting that although radial tyre technology has developed over the years, fitting a proper period radial tyre such as a Pirelli Cinturato or a Michelin XAS will make a classic car handle better than it would fitting modern tyres that are developed to be fitted to a very different chassis design, and work in a different environment.

Classic Tyre and Wheel Measurements

There are a number of relevant dimensions of a tyre or a wheel:

• Diameter of the tyre
• Width of the tyre
• Height of the tyre section
• Aspect ratio (the relation of the width of the tyre to the height of the tyre section)
• Diameter of the wheel (rim size)

All measurement systems refer to two or more of these dimensions, but there are several different traditions of expressing tyre and wheel size.

Diameter of the Wheel (Rim Size) Measurements

The pre-war tradition of expressing tyre size gives the diameter of the tyre, followed by the height of the tyre section. For example, 33x5 describes a vintage tyre with a diameter of 33 inches and a section height of 5 inches. To calculate the rim size, double the section height and take it away from the overall diameter of the tyre. A 33x5 tyre fits a rim diameter of 23 inches.

In the majority of post-1924 vintage tyre descriptions, the last number is the rim size. For example, 600x16 and 185R16 both describe tyres for a rim diameter of 16 inches.

Michelin also produced some tyres and rims with a metric measurement, for example vintage cross-ply 14x45 (measured in centimetres) & classic radial 155R400 (measured in millimetres). In both cases the last figure is the rim size.

Beaded Edge Vintage Tyre Measurements

The measurements for beaded edge tyres are given as the diameter of the tyre X the height of the tyre section predominantly in millimetres. For example, 760X90 describes a tyre with a diameter of 760mm and a section height of 90mm (to fit a 580mm rim). Some manufacturers gave the measurements in inches. For example, 31X4 describes a tyre with a diameter of 31 inches and a section height of 4 inches (to fit a 23 inch rim).

Straight-Sided and Split Rim Vintage Tyre Measurements

The measurements for tyres used on straight-sided and split rim wheels are given as the diameter of the tyre X the height of the tyre section in inches. For example, 33X5 describes a tyre with a diameter of 33 inches and a section height of 5 inches (to fit a 23 inch rim).

Crossply Vintage Tyre Measurements

The measurements for crossply tyres are given as the height of the tyre section and the width of the tyre (one measurement refers to both dimensions) x the diameter of the tyre in inches. For example, 5.00x21 describes a tyre with a diameter of 31 inches and a section height and width of 5 inches (to fit a 21 inch rim). Occasionally measurements for crossply tyres were given as the diameter of the tyre X the height of the tyre section in inches (as for beaded edge, straight-sided and split rim tyre measurements).

Commonly today, tyre manufacturers do not have the demand to warrant making all tyre sizes. Crossply tyre measurements such as 5.00/5.25x16 indicate that one tyre has been produced to fulfil original fitments of tyres with 5 and 5 1/4 inch section heights (to fit a 16 inch rim).

Bibendum or Millimetric Crossply Vintage Tyre Measurements

The measurements for crossply tyres may be given in centimetres. For example, 14x45 describes a tyre with a diameter of 73cm and a section height and width of 14cm (to fit a 45cm rim). Crossply tyre measurements such as 12/13/14x45 indicate that one tyre has been produced to fulfil original fitments of tyres with 12, 13 and 14cm section heights (to fit a 45cm rim).

Radial Classic Tyre Measurements

The correct technical notation for radial tyre measurements is: the width of the tyre in millimetres / aspect ratio as a percentage, a letter for speed rating, R (standing for radial), and the rim size in inches. For example, 205/70HR15 describes a tyre with a diameter of 668mm, a width of 205mm, a section height of 143.5mm (to fit a 15 inch rim). The measurements are calculated:

• Section height = (aspect ratio / 100) * width of tyre
• Rim size in mm = rim size * 25.4
• Diameter of tyre = rim size in mm + (2 * section height)

Aspect ratios began to be reduced at the end of the 1960s to improve cornering. Previously no aspect ratio was given on radial tyres; and in these cases an aspect ratio of 80% should be assumed. For example, 185VR16 describes a tyre with a diameter of 602.4mm, a section height of 148mm and a width of 185mm (to fit a 16 inch rim and with a speed rating of V).

Where the rim size is a three figure number, the measurement has been given in millimetres. For example, 280/45VR415 describes a tyre to fit a 415mm rim.

The following table indicates rough correspondence between alternative notations for radial tyre sizes.

Classic Tyres

Tyres Speed Ratings

Speed ratings for radial tyres are given below. New speed ratings are currently being developed to subdivide the Z rating.

Classic Tyres Load Index

Radial classic tyres often bear a load index, indicating the maximum safe load for the tyre.

Alternative Notations for Radial Classic Tyre Sizes

Several notations for radial tyre sizes are in common usage. For example, although the technically correct notation for a radial tyre may be 135SR15, the size may be referred to as 135x15, or 135 15, or 135R15. The table below shows alternative notations for all available radial tyre sizes.