TYRE CONSTRUCTION

 BEADED EDGE TYRES have  flexible grooved beads that are held in place by the clinches of the rim. They were used on early bicycles, most cars up to 1924 and most motorcycles up to 1927. Some European cars used them up until 1928. European sizes were mainly in millimetres, whilst American sizes were in inches.

 

 

 

 

 

 

STRAIGHT SIDED TYRES  were  the forerunner of wired on tyres and contrary to popular belief were invented as early as the beaded edge tyre. They have inextensible wire beads and employed either rims with detachable flange or rims that could be reduced in diameter for fitting and removal. Principally developed in the USA, where they preferred to beaded edge.

 

 

WIRED ON TYRES were the logical development of the straight sided tyre. Similar in construction, they were usually mounted on one piece rims with a central well to facilitate fitting. From their inception to the present, they have proved the most successful method of attachment. More recent developments include the radial, as opposed to cross-ply casing, and lower, squatter profile. Often referred to as "well base"

 

 

 

 

BIBENDUM TYRES are another type of wired on construction, developed in France. The wheel rim only has a well around half its circumference, so the tyre can only be fitted from one position. Sizes are always in centimetres and are NOT INTERCHANGEABLE with ordinary wired on tyres phased out in the 30s.

 

 

 

TUBULAR or single Tube Tyres were another early American development. The tyre and tube is all in one piece; is completely flexible and is either glued or bolted to a wooden or steel semi-circular rim. Mostly used on bicycles and still popular on modern racing bicycles.

 

 

 

 

READING A TYRE

 

P215/65R15 95S

P = Tyre Type (Passenger)
215 = Section width in millimeters
65 = Aspect Ratio
R = Radial Construction
15 = Rim diameter in inches
95 = Load index (see chart)
S =Speed rating ( see Chart)

 

TYRE TYPE

P= Passenger car , LT= Light Truck

Section Width

ASPECT RATIO/SERIES NUMBER 

The height and width relationship of the tyre. This number is determined by dividing a tyres section height by its section width. For example: the section height of 205/70R14 is 70% of the section width which is 205.

RIM DIAMETER 

The diameter of the rim at the bead seat. The most accurate method to determine the diameter is to measure the circumference of the rim at the bead seat and divide by 3.14

LOAD INDEX

The load index is an assigned number ranging from 0 to 279 that corresponds with the load carrying capacity of the tyre. Most car passenger car

LOAD CAPACITY

The maximum weight a tyre can support at its maximum inflation pressure (i.e.....1360lbs @ 32 PSI)

SPEED RATING

For MOT requirements in this country, it is not necessary to fit a tyre with a speed rating to match the original vehicle fitment or the maximum speed of the vehicle. Tyres must be suitable for the purpose for which the vehicle will be used.

Insurance companies might say that a vehicle should be fitted with the tyres having the speed rating recommended by the car manufacturer: but even if you fit Z-rated tyres for speeds over 150 mph they will not insure you if you drive in excess of 70 mph in this country!

The vehicle manufacturer has to recommend a tyre with a rating to match the maximum speed of the car because when it leaves the factory he does not know exactly where the car is going or for what purpose it might be used. You might want to use the car in a country where higher speed limits apply than the UK or take it to a race track at the weekend

The tyre speed rating (i.e. S) is the maximum speed for which the tyre is rated. For example, the S rating identifies speeds up to 112 mph

OTHER TYRES TERMINOLOGY

 

SECTION HEIGHT

The tyres section measured from the rim seat to the outer tread surface of an inflated tyre.

CROSS SECTION 

The linear distance between the exteriors of the sidewalls of an inflated tyre.

BEAD 

The specialized area of the tyre designed to mate with the rim flange. Reinforced with steel cable on straight side tyres; reinforced with fabric on clincher tyres.

BEAD SEAT 

The horizontal surface of the rim where the bottom of the tyre bead contact the rim.

TREAD WIDTH 

The portion of the tread design that comes in contact with the surface

OVERALL DIAMETER 

The linear distance between the exterior tread surface from the ground to the top of the tyre.

 

Uniform Tyre Quality Grading

Treadwear

The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would last twice as long on the government test course under specified test conditions as one graded 100. It is an oversimplification to assume treadwear grades will be proportional directly to your actual tire mileage. The relative performance of tires depends upon the actual conditions of their use and may vary due to driving habits, service practices, differences in road characteristics and climate.

Traction

Traction grades, from highest to lowest, are AA, A, B and C. They represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The testing does not take into account cornering, hydroplaning or acceleration.

Temperature

The temperature grades, from highest to lowest, are A, B and C. These represent the tire's resistance to the generation of heat.

 

 

Cross Reference Chart.

This Chart  doesn't imply complete interchangeable