In most countries the legal minimum tread depth requirement for passenger cars is 1.6 mm. As an indication to the consumer, there are tread wear indicator bars in the main grooves of the tire that become level with the tread surface at approximately 1.6 mm of remaining tread.
In addition to acknowledging the above, we recommend that all passenger and light truck tires in highway motor vehicle application be removed from service at the following tread depths:
• summer / high performance tires, all season tires = 3 mm
• winter tires = 4 mm
These recommendations are based upon our testing as well as real world experience which shows that drivers can maintain the performance potential (e.g. wet grip) of their tires by replacing them before they reach the regulatory minimum tread depth of 1.6 mm. This applies especially to winter tires for which winter driving properties such as snow traction are significantly reduced at tread depths below 4 mm.
Once tires are applied to a vehicle and put into service, they are considered “used”. There are risks associated with the purchase of used tires for which the service history is uncertain or unknown. Used tires may have been exposed to improper service and may have damage that could eventually lead to a tire disablement.
Not all tire damage or conditions that can lead to a tire disablement are easily detectable. For instance, improper repairs or damage to a tire's inner liner can only be observed through an inspection of the inside of the tire, demounted from the wheel. A qualified tire service professional should inspect the internal and external condition of a used tire prior to application. If a used vehicle is purchased and the history of the tires is unknown, it is recommended that the tires be inspected by a tire service professional, including demounting for internal inspection as appropriate for the characteristics as recommended below.
DO NOT purchase, sell, or install used tires that exhibit any of the following characteristics:
• Any punctures, or other penetrations, whether repaired or not.
• Indication of internal separation, such as tread or belt separation (e.g.,bulges, bumps, lumps, localised tread wear, vibrations, unusual tire noise, etc.)
• Indication of run-flat, under inflated, and/or overloaded damage (e.g. inner liner abrasion, delamination, or discolouration; excessive tread shoulder wear, etc.)
• ANY inner liner or bead damage.
• ANY history of continuous inflation pressure loss requiring frequent re-inflation.
• Defaced or removed DOT tire identification number (TIN), which is located on the tire sidewall.
• Tires that have a date code that is older than 10 years. The date code – the last three or four digits of the DOT TIN – indicates the week and year the tire was manufactured. Vehicle manufacturers may recommend a different chronological age at which a tire should be replaced based on their understanding of the specific vehicle application; Continental Tire recommends that any such instruction be followed.
• Involved in a recall or a replacement programme.
• Inadequate tread depth for continued service (i.e. nearly worn out). Tires with a tread depth of 2/32” or less at any point on the tire are worn out.
• Chemical, fire, excessive heat damage, or other environmental damage.
• Designated as a “scrap tire” or otherwise not intended for continued highway service.
• Prior use of tire sealant or balance/filler material.
• Tires that have been altered to look like new tires (e.g., a re-grooved tread).
• Labelled on the sidewall as “Not For Highway Use”, “NHS”, “For Racing Purposes Only”, “Agricultural Use Only”, “SL” (service limited agricultural tire), or any other indication that the tire is barred from use on public roads.