Converting old tyre size with table: This must be observed

Classic tyre sizes are no longer produced mainly for technical reasons. If you are looking for a suitable equivalent for your classic, you are therefore not only faced with a visual challenge. You also need to know that and to what extent the specifications for the dimensions of tyres of that time have changed. Good thing you're here, because we've provided a table here to help you convert old tyre sizes.

The dimensions of cross-ply tyres are given in inches and the overall height is always 80% of the tyre width. For radial tyres, the tyre width is given in millimetres. The tyre cross-section is given as a percentage directly behind the width of the tread.

Author: Adrian Starr
Position: Sales
Updated on: 21.11.2023

Vintage tyre table: Conversion at a glance

Inch measurement	Metric measurement
1965-1977	Height 60	Height 70	Height 80
5.50-12	165/60 R12	165/70 R12	155/80 R12
5.60-12	165/60 R12	165/70 R12	155/80 R12
6.00-12
5.20-13	165/60 R13	145/70 R13	135/80 R13
5.60-13	175/60 R13	155/70 R13	145/80 R13
6.15-13	185/60 R13	165/70 R13	155/80 R13
6.40-13	195/60 R13	175/70 R13	165/80 R13
6.70-13	205/60 R13	185/70 R13	175/80 R13
6.90-13
7.00-13	215/60 R13	195/70 R13	185/80 R13
7.25-13
7.75-13			195/80 R13
5.20-14	165/60 R14	145/70 R14	135/80 R14
5.60-14	175/60 R14	155/70 R14	145/80 R14
5.90-14
6.15-14	185/60 R14	165/70 R14	155/80 R14
6.45-14	195/60 R14	175/70 R14	165/80 R14
6.95-14	205/60 R14	185/70 R14	175/80 R14

Inch measurement	Metric measurement
1965-1977	Height 60	Height 70	Height 80
7.35-14	215/60 R13	195/70 R14	185/80 R14
7.75-14	225/60 R14	200/70 R14	195/80 R14
8.25-14	235/60 R14	205/70 R14	205/80 R14
8.55-14	245/60 R14	215/70 R14	215/80 R14
8.85-14	255/60 R14	225/70 R14	225/80 R14
9.15-14	265/60 R14	235/70 R14
5.60-15	185/60 R15	165/70 R15	155/80 R15
6.35-15	195/60 R15	175/70 R15	165/80 R15
6.85-15	205/60 R15	185/70 R15	175/80 R15

7.35-15	215/60 R15	195/70 R15	185/80 R15
7.75-15	225/60 R15	205/70 R15	195/80 R15
8.15-15	235/60 R15	215/70 R15	205/80 R15
8.25-15	235/60 R15	215/70 R15	205/80 R15
8.45-15	245/60 R15	225/70 R15	215/80 R15
8.55-15	245/60 R15	225/70 R15	215/80 R15
8.85-15	255/60 R15	235/70 R15	225/80 R15
8.90-15	255/60 R15	235/70 R15	225/80 R15
9.00-15	265/60 R15	245/70 R15	230/80 R15
9.15-15			235/80 R15
			255/80 R15

1949-1964	1965-1970	1970-1980	Since 1960	Since 1980
Height 80-90		Height 50-78	Height 82	Height 75-80	Height 70	Height 65	Height 60	Height 50
5.20-10			145R10		165/70 R10
5.20-12			145R12	145/80 R12	165/70 R12
5.60-12	6.00-12		155R12	155/80 R12
						165/65 R13
			145R13
			155R13	155/80 R13	175/70 R13		195/60 R13	215/50 R13
5.60-13	6.00-13	A	165R13	165/80 R13	185/70 R13		205/60 R13
	6.50-13	B	165R14	175/80 R13
		C	175R13	185/80 R13
	7.00-12	D
			185R13
5.60-14	6.00-14		195R13			175/65 R14
6.00-14	6.45-14		145R14		175/70 R14	185/65 R14
		B	155R14	175/75 R14	185/70 R14	195/65 R14	205/60 R14
6.50-14	6.95-14	C	175R14	185/75 R14	195/70 R14		215/60 R14
		D
7.00-14	7.35-14	E	185R14	195/75 R14	205/70 R14		225/60 R14	245/50 R14
7.50-14	7.75-14	F	195R14	205/75 R14	215/70 R14		235/60 R14
8.00-14	8.25-14	G	205R14	215/75 R14	225/70 R14		245/60 R14	265/50 R14
8.50-14	8.55-14	H	215R14	225/75 R14
9.00-14		J	225R14
9.50-14		L
	5.60-15	A	155R15	155/80 R15			195/60 R15
6.00-15		B	165R15	165/80 R15	185/70 R15	185/65 R15	205/60 R15	225/50 R15
6.50-15	6.85-15	C	175R15		195/70 R15	195/65 R15	215/60 R15
		D				205/65 R15
	7.35-15	E	185R15	195/75 R15	205/70 R15		225/60 R15
6.70-15	7.75-15	F	195R15	205/75 R15	215/70 R15	215/65 R15	235/60 R15
	8.15-15
7.10-15		G	205R15	215/75 R15	225/70 R15	235/65 R15	245/60 R15	265/50 R15
	5.25-15
	8.45-15
7.60-15		H	215R15	225/75 R15	235/70 R15		255/60 R15	275/50 R15
	8.55-15
8.00-15	8.85-15	J	225R15	225/75 R15	235/70 R15		265/60 R15
8.20-15	9.00-15	K
	9.15-15	L	235R15	235/75 R15	225/70 R15		275/60 R15	295/50 R15
		N

Convert old tyre size: Basic questions

Various key figures and abbreviations provide information about the different properties of tyres, such as ...

... the tyre width (in inches or mm),
... the height ratio (height to width ratio),
... the rim diameter & the load index (maximum permissible load per wheel)
... or the speed index (maximum permissible speed).

Over the years, the way these dimensions are indicated has evolved. Where classic tyres made do with 2 indices to tell their owners everything they needed to know, modern tyres have up to 5 relevant indices that can be found on the tyre. We will break down what these mean in the next section.

What do the key figures on modern tyres actually mean?

Let's look at the 185 65 H R 13 tyre data and break down the records using the example:

185: Indicates the width of the tread in mm measured from side wall to side wall.
65 : Indicates the height of the tyre wall relative to the tread - here, for example, 65 % of 185 mm, i.e. 120.5 mm.
H: Stands for the speed index. H corresponds to a top speed of 210 km/h.
R: Indicates that the tyre is a radial tyre.
13: Indicates in inches the diameter of the rim on which the tyre is to be mounted.

However, if you drive a classic, you will notice that some tyre size measurements are given in inches. So our example tyre would show 6.15 x 13 (bias-ply) instead of 185 65 H R 1 (radial). How to arrive at this is shown in the table above.

But before that, a very important question needs to be clarified: When do the tyres of a classic car need to be changed at all?

When does a vintage tyre need to be replaced?

Unlike tyres on everyday vehicles, classic car tyres are rarely changed due to wear. This is because classic vehicles are rarely moved so frequently that the tread wears out even after years. The main reason for replacement is age-related hardening. It brings with it cracks and brittleness, and so a significant safety risk arises with tyres that are too old.

Some sources recommend a change every 10 years, others after 8 years. Depending on the mileage, however, it can make sense to change the tyres of a classic car after 5 to 6 years. A change is also beneficial in the case of longer standing times and flat tyres, and minimises the risk of accidents.

Info: The age of the tyres can be read off the tyre sidewall: The first two digits of the four-digit DOT number stand for the calendar week, the other two for the year in which the tyre was produced.

Which tyres are better: Radial or bias-ply tyres?

This question is quickly answered. In any case, radial tyres offer greater driving safety than cross-ply tyres. They have been established since the 1980s and have virtually replaced diagonal tyres. You can therefore confidently convert your classic to this type of tyre and thus eliminate a safety risk.

Should the tubes also be replaced when changing the tyres?

Yes, because an inner tube also wears out, even in high-quality designs, and can cause massive pressure marks on the tyre over the years. This has a negative effect on the life expectancy of the tyres. It is therefore advisable to replace the inner tubes when changing the tyres.

Learn more about wheel, tyres and rims

How is a wheel constructed, what is important to consider? For all terms around wheel, tyre and rim, please visit our Youtube channel!

Convert old tyre size and buy the right tyre online

Now you hopefully know which tyre fits your classic and can convert your old tyre size thanks to our table. Replacing old tyres these days unfortunately involves conversion and some compromises. But it doesn't have to be! At SC Parts, you are guaranteed to find the tyre that visually matches your enthusiast vehicle. From manufacturers like Michelin to Blockley to Dunlop, we offer high-quality tyres, inner tubes and rim tapes.