All About Tyre

Source: http://www.car-tyres.org.uk/faq.asp#faq7
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Source: http://www.fulda.com/fulda_home_en/test_and_tips/tyre_technology/how_to_read_a_tyre/index.jsp
Typical markings as found on a tyre are illustrated:
1. Tyre section width in mm.
2. Section height to section width relation in %.
3. Tyre construction (R= Radial).
4. Rim diameter in inches.
5. Maximum load capacity (load index)
6. Speed symbol
7. TUBELESS tyre.
8. ECE Type approval mark and number.
9. Location of treadwear Indicator.
10. M&S (Mud & Snow) Winter capabilities.
11. Tested and qualified for Severe Snow Usage.
12. Production date (week, year : decade 1990-1999 ).
13. Department of Transportation compliance symbol.
14. D.O.T. manufacturer code.
15. Country of manufacture.
16. Trade name.
17. Tyre construction details (D.O.T.).
18. Load and pressure marking (D.O.T.).
19. Tyre type (radial).
20. Mark required by U.S.A. Consumer information regulations (Quality Grade).
21. Location of winter tread wear indicator

Tyre Width
The tyre width is shown in millimetres and is the width from one side of the tyre to the other. Wider tyres give the car more contact with the road and therefore more traction.

Tyre Profile
The tyre profile is actually a ratio, not a metric measurement. The profile is the ratio of tyre width to profile height shown as a percentage.

For example: If the tyre has the dimensions shown – 205/50. Then the profile is 50% of the width, so 50% of 205mm is 102.5mm. The tyre height from the rim to the tread is 102.5mm

Tyre Speed Rating
All tyres have a speed rating letter. The letter denotes a maximum speed that the tyre can sustain for a 10 minute period without falling to pieces.

Note: the letter R is nothing to do with the speed rating. This letter denotes the tyre construction, so if your tyre is a 255/35 ZR19, it just means that it’s a Z rated tyre of Radial construction. This letter is redundant really, because nearly all tyres are radial these days.

Symbol

Max Speed

Symbol

Max Speed

Km/h

MPH

Km/h

MPH

L

120

75

180

113

M

130

81

T

190

118

140

87

U

200

125

150

95

H

210

130

Q

160

100

V

240

150

R

170

105

W

270

168

Z

240+

150+

Wheel Size
This is the diameter of the wheel rim in inches that the tyre is designed to fit. It’s strange that they mix metric and imperial measurements, but they just do.

Load Rating
On some tyres you will see an extra number after the R eg. 205/50/R/16/91/V. In this format the figure 91 denotes the tyre’s load rating. The load rating is the weight in Kilos (multiplied by 10) that the tyre can support at speeds of up to 130MPH. It’s worth noting that above speeds of 130MPH the load rating decreases.

If you’re car weighs 2 metric tons (2,000Kg) then if we do a simple calculation we can assume that there will be roughly 500Kg supported by each tyre. This gives us a tyre load index rating of 84. If you then add a further 20% for passengers and a nice safety margin that takes the up to 600Kg per tyre, giving us a load rating of about 91.

How can I measure my tyre tread depth?

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You can use a tyre depth gauge. However most tyres have a tread wear indicator to help you to visually identify when you are close to the tread depth limit. If you’re looking at your front tyres, lock your steering wheel to either the left or the right and look around the tread carefully, you should see a small rubber bar running across the tread grooves. The wear indicator is usually placed in the tyre at a depth of 2mm. If the tyre tread is flush with this rubber bar then it’s time to replace your tyres.

DOT Codes and the 6-year shelf life
Source:http://www.carbibles.com/tyre_bible.html
The code is pretty simple. The three-digit code was used for tyres manufactured before 2000. So for example 1 7 6 means it was manufactured in the 17th week of 6th year of the decade. In this case it means 1986. For tyres manufactured in the 90’s, the same code holds true but there is a little triangle after the DOT code. So for this example, a tyre manufactured in the 17th week of 1996 would have the code 176
After 2000, the code was switched to a 4-digit code. Same rules apply, so for example 3 0 0 3 means the tyre was manufactured in the 30th week of 2003.

The E-Mark
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All tyres sold in Europe after July 1997 must carry an E-mark. The mark itself is either an upper or lower case "E" followed by a number in a circle or rectangle, followed by a further number.
An "E" (upper case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of ECE regulation 30.
An "e" (lower case) indicates that the tyre is certified to comply with the dimensional, performance and marking requirements of Directive 92/33/EEC.
The number in the circle or rectangle denotes the country code of the government that granted the type approval. 11 is the UK. The last number outside the circle or rectangle is the number of the type approval certificate issued for that particular tyre size and type.

What are RFT tyres and why are they so expensive?
RFT stand for Run Flat Tyre. These tyres can survive a puncture and still be driven on, albeit at a reduced speed and limited distance. The RFT tyre is more expensive partly because of the thicker tyre wall that prevents the tyre from collapsing due to a loss of pressure.

Typically you should be able to drive approximately 100 miles at 50MPH on a punctured run flat tyre. There are several benefits to the RFT system; RFT tyres are safer, if you lose pressure with a conventional tyre you could career off the road. The RFT keeps you on the road as the tyre does not collapse. If you sustain a puncture in a dangerous area or on a busy wet motorway, you don’t have to change the tyre there and then, just drive on and find a tyre repair centre. With RFT there’s no need for a spare wheel, which saves you money and boot space.

Upgrading to RFT on a non RFT vehicle is not really practical or cheap to do. RFT tyres only work with specially designed RFT rims, so you’ll need to buy 4 new rims from BMW / Audi etc. Then you’ll need to source and install an Electronic Tyre Pressure Monitor System (ETPMS or TPMS). Because a RFT puncture may not always be obvious to a driver, an electronic tyre pressure monitor is required to alert the driver to the loss of pressure.

Follow this link for information on Run Flat Tyre repairs

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