Help with Tire and Rim Types & Sizes

Prior to 1924, in the veteran and vintage period, the majority of European manufacturers fitted wheels for use with beaded edge tires, and some continued to do so after this date. Beaded edge veteran and vintage tires have large circumferential ridges of hard rubber(beads). These beads fit into the hook (clincher) of the wheel rim. A minimum tire pressure of 60psi is needed to push the beads into the clincher of the rim and keep the tire in place. The most common cause of a beaded edge vintage tire failure is lack of pressure allowing the tire to detach itself. Beaded edge tires can only be used with a beaded edge wheel rim. We currently have a small number of Michelin Double Rivet beaded edge tires in stock.

Beaded edge vintage car tires were succeeded by safer wired-on tires in and around 1924 in Europe and slightly earlier in America. Within the bead a solid wire ensures that the tire’s bead circumference cannot stretch and will always be smaller than the external circumference of the wheel rim.

Wired-on tires can be used with the wheel types discussed below.

The split-rim was very popular with American manufacturers such as Packard, Dodge and Buick and was also used on Rolls Royce Silver Ghosts built in the U.S.A. From prior to World War One until the late 20’s this style of rim enabled manufacturers to utilise and gain experience of wired-on tires before the general acceptance of the well-base rim. The split-rim incorporates a rim which is detachable from a wooden wheel. The rim is cut through, and when removed from the wheel, can be drawn inside itself reducing its circumference and allowing the tire to be removed and refitted. These rims have various locking mechanisms which prevent the rim collapsing during normal use.

Another style of rim that was very popular with the American market ,and in the mid twenties some European manufacturers. The straight-sided rim has a detachable flange on one side, when this is removed the tire can be slipped on to the rim and the flange replaced. This style of rim can still be found on some heavy goods vehicles today. We currently have the Michelin Double Rivet tire available in a number of straight sided sizes.

The well-base wheel has, as the name suggests, a depression in the centre of the rim and is used only with wired-on tires. To facilitate fitment part of the bead of the tire must be pushed into this well before the rest of the tire can be worked over the flange. The technique for fitment is similar to that of a standard bicycle tire. Initially there were worries that tires may detach themselves from well-base rims when deflated, however a test involving an Alvis being driven in tight circles with flat rear tires proved that such worries were unfounded. This type of rim became commonplace on cars in the mid 1920’s but was originally conceived for bicycle tires in 1890.

Michelin, aware of the concerns over tires detaching themselves, pursued the design of a rim with a well for only half its circumference. However as the well-base wheel proved its integrity and its design was refined the bibendum rim was discontinued. Tire dimensions for these bibendum rims are predominantly given in metric terms rather than the more commonplace imperial measurements used for well-base wheels.

The invention of the TRX by Michelin in 1973 was the first instance of tire and rim being designed to work together as a single unit. The new Michelin TRX rim was designed with a lower, flatter flange than that of conventional rims . The bead of the Michelin TRX tire was also altered to suit this new rim design and the result is a more gradual curvature of the tire sidewall giving exceptional directional stability and ‘on the limit’ handling, whilst also allowing for a comfortable ride. Michelin also designed the TDX rim which again can only be fitted with a purpose built TDX tire. The TDX rim has two grooves running circumferentially around the bead seats and the tires have specially extended bead toes which are held in place by the grooves. The purpose of this is to prevent the tire leaving the rim thus giving the tire a limited ‘run-on’ capability allowing control of the car to be maintained in the event of a deflation, and a safe place to be reached for it to be changed. These Michelin TRX tires and rims were standard fitment on many performance cars of the seventies, eighties and early nineties, such as Ferrari, BMW, Renault Alpine, Alfa Romeo, Peugeot and Renault 5 Turbo.

Vintage tires and classic tires are of either crossply or radial construction.

The cross-ply tire 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 tire structure great rigidity. With a cross-ply tire the maximum width and the height of the tire above the rim are approximately equal. This relationship is known as the aspect ratio and with cross-ply tires is approximately 100%, giving the cross-ply tire its unique "tall" appearance.

The beauty of the radial design is that it separates the functions of the sidewall and crown of the tire, allowing greater vertical flexibility whilst ensuring that there is still as much surface in contact with the road as possible. In classic radial tires 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 classic radial tire excellent road holding capabilities and a longer life span when compared to vintage cross-ply tires.

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

• Diameter of the tire
• Width of the tire
• Height of the tire section
• Aspect ratio (the relation of the width of the tire to the height of the tire 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 tire and wheel size.

The oldest tradition of expressing tire size gives the diameter of the tire, followed by the height of the tire section. For example, 33x5 describes a tire 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 tire. A 33x5 tire fits a rim diameter of 23 inches.

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

Michelin also produced some tires 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.

The measurements for beaded edge tires are given as the diameter of the tire X the height of the tire section in millimetres. For example, 760X90 describes a tire 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 tire with a diameter of 31 inches and a section height of 4 inches (to fit a 23 inch rim).

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

The measurements for crossply tires are given as the height of the tire section and the width of the tire (one measurement refers to both dimensions) x the diameter of the tire in inches. For example, 5.00x21 describes a tire 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 tires were given as the diameter of the tire X the height of the tire section in inches (as for beaded edge, straight-sided and split rim tire measurements).

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

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

The correct technical notation for radial tire measurements is: the width of the tire 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 tire 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 tire
• Rim size in mm = rim size * 25.4
• Diameter of tire = 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 tires; and in these cases an aspect ratio of 80% should be assumed. For example, 185VR16 describes a tire 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 tire to fit a 415mm rim.

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

Older European Size Aspect Ration of 80	Older American Size Aspect Ratio of 78	Newer Size Aspect Ratio of 75	Newer Size Aspect Ratio of 70
165x13	A78x13	P165/75R13	P175/70R13
175x13	B78x13	P175/75R13	P185/70R13
185x13	D78x13	P185/75R13	P205/70R13
155x14	B78x14	P175/75R14	P185/70R14
175x14	C78x14	P185/75R14	P195/70R14
185x14	E78x14	P195/75R14	P205/70R14
195x14	F78x14	P205/75R14	P215/70R14
205x14	G78x14	P215/75R14	P225/70R14
215x14	H78x14	P225/75R14	P235/70R14
165x15	A78x15	P165/75R15	P175/70R15
175x15	C78x15	P175/75R15	P185/70R15
185x15	E78x15	P195/75R15	P205/70R15
195x15	F78x15	P205/75R15	P215/70R15
205x15	G78x15	P215/75R15	P225/70R15
215x15	H78x15	P225/75R15	P235/70R15
230x15	J78x15	P225/75R15	P235/70R15
235x15	L78x15	P235/75R15	P255/70R15

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

Speed Rating	mph	Km/h
J		100
K		110
L		120
M		130
N		140
P	93	150
Q		160
R		170
S	112	180
T	118	190
H	130	210
V	149	240
W		270
Y		300
VR		210
ZR	149	240

Radial tires often bear a load index, indicating the maximum safe load for the tire.

Several notations for radial tire sizes are in common usage. For example, although the technically correct notation for a radial tire 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 tire sizes.

Size	Alternatives
145SR10	145x10	145 10	145R10
165/70SR10	165/70x10	165/70 10	165/70R10
125SR12	125x12	125 12	125R12
145SR12	145x12	145 12	145R12
145/70TR12	145/70x12	145/70 12	145/70R12
155/70SR12	155/70x12	155/70 12	155/70R12
145SR13	145x13	145 13	145R13
155TR13	155x13	155 13	155R13
155SR13	155x13	155 13	155R13
155HR13	155x13	155 13	155R13
155SR13	155x13	155 13	155R13
165TR13	165x13	165 13	165R13
165SR13	165x13	165 13	165R13
165HR13	165x13	165 13	165R13
165SR13	165x13	165 13	165R13
640SR13	640x13	640 13	640R13
175SR13	175x13	175 13	175R13
175/70SR13	175/70x13	175/70 13	175/70R13
185HR13	185x13	185 13	185R13
185/70VR13	185/70x13	185/70 13	185/70R13
185/70HR13	185/70x13	185/70 13	185/70R13
205/70VR13	205/70x13	205/70 13	205/70R13
205/60HR13	205/60x13	205/60 13	205/60R13
145SR14	145x14	145 14	145R14
155SR14	155x14	155 14	155R14
165HR14	165x14	165 14	165R14
165SR14	165x14	165 14	165R14
175TR14	175x14	175 14	175R14
185HR14	185x14	185 14	185R14
185/75SR14	185/75x14	185/75 14	185/75R14
185/70SR14	185/70x14	185/70 14	185/70R14
195/75SR14	195/75x14	195/75 14	195/75R14
195/70VR14	195/70x14	195/70 14	195/70R14
205VR14	205x14	205 14	205R14
205/70VR14	205/70x14	205/70 14	205/70R14
205/70HR14	205/70x14	205/70 14	205/70R14
215/70VR14	215/70x14	215/70 14	215/70R14
215/70SR14	215/70x14	215/70 14	215/70R14
225/75SR14	225/75x14	225/75 14	225/75R14
225/70SR14	225/70x14	225/70 14	225/70R14
125SR15	125x15	125 15	125R15
135SR15	135x15	135 15	135R15
145SR15	145x15	145 15	145R15
155HR15	155x15	155 15	155R15
155SR15	155x15	155 15	155R15
165SR15	165x15	165 15	165R15
165HR15	165x15	165 15	165R15
165SR15	165x15	165 15	165R15
175QR15	175x15	175 15	175R15
175R15	175x15	175 15	175R15
175/70HR15	175/70x15	175/70 15	175/70R15
180HR15	180x15	180 15	180R15
185HR15	185x15	185 15	185R15
185SR15	185x15	185 15	185R15
185HR15	185x15	185 15	185R15
185R15	185x15	185 15	185R15
185/70HR15	185/70x15	185/70 15	185/70R15
185/70VR15	185/70x15	185/70 15	185/70R15
185/70HR15	185/70x15	185/70 15	185/70R15
185/70SR15	185/70x15	185/70 15	185/70R15
195/70VR15	195/70x15	195/70 15	195/70R15
205HR15	205x15	205 15	205R15
205/75SR15	205/75x15	205/75 15	205/75R15
ER70HR15	ER70x15	ER70 15	ER70R15
205/70VR15	205/70x15	205/70 15	205/70R15
205/70SR15	205/70x15	205/70 15	205/70R15
215/75SR15	215/75x15	215/75 15	215/75R15
215/70VR15	215/70x15	215/70 15	215/70R15
225/75SR15	225/75x15	225/75 15	225/75R15
225/70VR15	225/70x15	225/70 15	225/70R15
235/75SR15	235/75x15	235/75 15	235/75R15
235/70VR15	235/70x15	235/70 15	235/70R15
235/70HR15	235/70x15	235/70 15	235/70R15
235/70SR15	235/70x15	235/70 15	235/70R15
275/55VR15	275/55x15	275/55 15	275/55R15
175SR16	175x16	175 16	175R16
185HR16	185x16	185 16	185R16
185VR16	185x16	185 16	185R16
185SR16	185x16	185S 16	185R16
125R400	125x400	125 400	125R400
135R400	135x400	135 400	135R400
145R400	145x400	145 400	145R400
155R400	155x400	155 400	155R400
165R400	165x400	165 400	165R400
185R400	185x400	185 400	185R400
160/65R340	160/65x340	160/65 340	160/65R340
190/55HR340	190/55x340	190/55 340	190/55R340
190/55VR340	190/55x340	190/55 340	190/55R340
200/65R340	200/65x340	200/65 340	200/65R340
170/65R365	170/65x365	170/65 365	170/65R365
190/55HR365	190/55x365	190/55 365	190/55R365
200/60HR365	200/60x365	200/60 365	200/60R365
210/65R365	210/65x365	210/65 365	210/65R365
220/55VR365	220/55x365	220/55 365	220/55R365
180/65HR390	180/65x390	180/65 390	180/65R390
190/65HR390	190/65x390	190/65 390	190/65R390
220/45VR390	220/45x390	220/45 390	220/45R390
230/45VR390	230/45x390	230/45 390	230/45R390
220/55VR390	220/55x390	220/55 390	220/55R390
230/55ZR390	230/55x390	230/55 390	230/55R390
240/55VR390	240/55x390	240/55 390	240/55R390
220/65VR390	220/65x390	220/65 390	220/65R390
220/45VR415	220/45x415	220/45 415	220/45R415
240/55VR415	240/55x415	240/55 415	240/55R415
280/45VR415	280/45x415	280/45 415	280/45R415