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

INDEX No KGS INDEX No KGS INDEX No KGS
40 140 71 345 102 850
41 145 72 355 103 875
42 150 73 365 104 900
43 155 74 375 105 925
44 160 75 387 106 950
45 165 76 400 107 975
46 170 77 412 108 1000
47 175 78 425 109 1030
48 180 79 437 110 1060
49 185 80 450 111 1090
50 190 81 462 112 1120
51 195 82 475 113 1150
52 200 83 487 114 1180
53 206 84 500 115 1215
54 212 85 515 116 1250
55 218 86 530 117 1285
56 224 87 545 118 1320
57 230 88 560 119 1360
58 236 89 580 120 1400
59 243 90 600 121 1450
60 250 91 615 122 1500
61 257 92 630 123 1550
62 265 93 650 124 1600
63 272 94 670 125 1650
64 280 95 690 126 1700
65 290 96 710 127 1750
66 300 97 730 128 1800
67 307 98 750 129 1850
68 315 99 775 130 1900
69 325 100 800 131 2000
70 335 101 825 132 2060

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

Speed Symbol MPH (UP TO) Speed Symbol MPH (UP TO)
L 75    
M 81 H 130
P 93  V 149
Q 100 VR (1) 131 +
R 106 W 168
S 112  Y 186
T 118 ZR (2) 149+

(1) Tyres marked "VR" within the size designation ( 235/60VR15) are designed for speeds in excess of 131 MPH

(2) Tyres marked "ZR" within the size designation ( 235/60ZR15) are designed for speeds in excess of 149 MPH

Tyres marked with a speed index ( 235/60ZR15 98Y )  use the above chart Y would be up to 186 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.

Pre-1964 65 to 72 80 Series metric Alpha Numeric 78 series

Alpha Numeric 70
series

P-Metric 75 Series Radial P-Metric 70 Series Radial
520 - 12 - 125R12 - - 125/75R12 -
520 - 13 560 - 13 155R13 - - 155/75R13 155/70R13
590 - 13 600 - 13 165R13 A78-13 - 165/75R13 175/70R13
640 - 13 650 - 13 175R13 B78-13 - 175/75R13 185/70R13
725 - 13 700 - 13 185R13 D78-13 - 185/75R13 205/70R13
590 - 14 645 - 14 155R14 B78-14 - 175/75R14 185/70R14
650 - 14 695 - 14 175R14 C78-14 - 185/75R14 195/70R14
700 - 14 735 - 14 185R14 E78-14 E70-14 195/75R14 205/70R14
750 - 14 775 - 14 195R14 F78-14 F70-14 205/75R14 215/70R14
800 - 14 825 - 14 205R14 G78-14 G70-14 215/75R14 225/70R14
850 - 14 855 - 14 215R14 H78-14 - 225/75R14 235/70R14
590 - 15 600 - 15 165R15 A78-15 - 165/75R15 175/70R15
640 - 15 685 - 15 175R15 C78-15 - 175/75R15 185/70R15
650 - 15 735 - 15 185R15 E78-15 E70-15 195/75R15 -
670 - 15 775 - 15 195R15 F78-15 F70-15 205/75R15 215/70R15
710 - 15 825 - 15 205R15 G78-15 G70-15 215/75R15 225/70R15
760 - 15 855 - 15 215R15 H78-15 H70-15 225/75R15 235/70R15
800 - 15 855 - 15 230R15 J78-15 K70-15 235/75R15 235/70R15
820 - 15 900 - 15 235R15 L78R15 L70-15 235/75R15 255/70R15

This Chart  doesn't imply complete interchangeable

 

Whitewall and RWL Maintenance.

If you have just purchased either whitewall tyre or a raised white letter tyre it has been delivered to you in wrapping (premium brands) with a blue protector film over the whitewall or RWL. This is there to protect the natural white rubber whilst in transit; if you are going to use the vehicle straight away it is a water soluble protector and comes off easily with warm water and a nail brush. If you are still building your vehicle or are not ready for the road we suggest that you leave it on the tyre until you are ready to use the car, it will protect the whitewall/RWL from impurities/UV and grease/oil etc.

Maintenance.

Just like your car bodywork the whitewall/RWL will need continual maintenance; they are not a fit and forget item, they need love too! You will need to keep the tyres clean with soapy water and an all-purpose cleaner, if you have just black tyres then you can use a Tyre shine that is available in shiny, matt or new tyre finishes, there are lots of companies selling this product on the market. DO NOT use them on Whitewall or RWL letters many of these products have enhancers for black tyres that will discolour the white rubber permanently, or you will have a very difficult job to remove the silicone.

Why are my ancient tyres still white and my new tyres are turning brown?

Unfortunately we are getting asked this question more and more frequently and the common name for this is called "Blooming" Tyre manufactures are continually pushing the envelope with chemistry and design to create tyres that can keep up with the demand of today's cars and drivers. Higher mileage, more miles per gallon, better all-weather traction, or high speed and cornering as cars get better, faster, more intense the tyres they roll on must change to keep up. We expect increased performance from our vehicles and tyres are an integral part of that, but rarely do we take the time to understand what exactly has changed about tyres other than going from Bias to Radial in the late 60's. Not only has this but Governments and policy makers liked to put regulations in place. Over the years we have had E marks and ECE legislation, then tyre labeling to see how noisy and fuel economy and wet weather braking, they are also demanding that we do not damage the environment and are banning ingredients that Tyre manufacturers used to use because of their carcinogenic reactions to the world.

A few years ago there was a change in the law and it was illegal to sell tyres that were not PAH compliant, the PAH meant that manufacturers had to remove some oils that were carcinogenic and since that time we have experienced this problem, the stupid thing is that more carcinogens are produced burning a sausage on a BBQ than produced by a tyre in its whole life. For detailed information just put my tyres are going brown in Google you will see black tyres go brown as well, they say to use a tyre shine but if you use them on your
whitewall tyres they will turn it browner even quicker. Any tyre shine product is bad news for a whitewall tyre.

Unfortunately all brands of tyres now need a higher degree of cleaning and even a stored vehicle will be affected by tyre blooming.

Those who have had whitewall tyres for many years all have a secret to keeping them clean. We do sell a Bletchley Whitewall cleaner but this is a strong chemical, the best that we have seen is Brake fluid and a very fine wet and dry, lightly clean and the whitewall will be restored. Be careful not to rub too hard as all the narrow band whitewalls and RWL tyres including BFG use a whitewall veneer. Only the wide whitewalls have a white rubber sidewall.

Anti-Ozonant.

An anti-ozonant is probably something you've never heard of. It's an organic compound added to rubber materials that prevents, or at the very least, slows the deterioration caused by exposure to the elements. Anti-ozonants are used as an additive in most all of the exterior rubber and plastic parts to one degree or another, but they are most prevalent in tyre manufacturing. The anti-ozonant additive keeps plastics and rubbers from becoming dry, brittle, oxidized or cracking. It does this by preventing the surface of the material from oxidizing and keeps the material pliable.

Thanks to anti-ozonants in rubber compounds we have high mileage tyres, performance tyres, and everything in between. Without it sports cars would shred tires incredibly fast after just a few high speed turns or long track runs where the tires were heated up. Even your daily driven commuter car would need tyres far more often as the sun and heat slowly rotted away the rubber compounds.

Tyre Blooming.

Tyre rubber compounds are designed in a way that allows the anti-ozonant to continually work its way to the outside of the tire and as such, continually keeps the outer surface and sidewall pliable and resistant to oxidation.

Once anti-ozonant reaches the outside of the tire and is exposed to air and moisture it oxidizes, the result being a brownish residue. The term for this ugly brownish tyre look is 'tyre blooming'. Just like metals left exposed to the outside world will slowly begin to rust (oxidize) as it is exposed to water and air, so does the anti-ozonant component of the tire rubber.

Making matters worse is the use of mould releases in the manufacturing processes. These lubricant type chemicals provide a non-stick surface for the inside of a tyre mould. The mold release chemical bonds with the tire and hold anti-ozonants onto the surface of the tyre. While some people will point to mould release as the primary and/or only source of tyre blooming, it is in fact often times only a part of the problem. Even after the removal of mould release a tyre will continue to push anti-ozonant to the surface allowing the brown residue to return.

Henry John House. 2 Ivy Road, Aldershot, Hampshire GU12 4TX Telephone:01252 318666
sales@northhantstyres.com