Volvo 2005 S40 Manual page 72

Tread wear indicator
The tires have wear indicator strips running across or parallel to the tread. The letters TWI are printed on the side of
the tire. When approximately 1/16" (1.6 mm) is left on the tread, these strips become visible and indicate that the tire
should be replaced. Tires with less than 1/16" (1.6 mm) tread offer very poor traction.
When replacing worn tires, it is recommended that the tire be identical in type (radial) and size as the one being
replaced. Using a tire of the same make (manufacturer) will prevent alteration of the driving characteristics of the
vehicle.
New tires
Remember that tires are perishable goods. As of 2000, the manufacturing week and year will be indicated with 4 digits
(e.g. 1502 means that the tire illustrated was manufactured during week 15 of 2002).
Improving tire economy:
Maintain correct tire pressure. See the tire pressure table on
Drive smoothly: avoid fast starts, hard braking and tire screeching.
Tire wear increases with speed.
Correct front wheel alignment is very important.
Unbalanced wheels impair tire economy and driving comfort.
Tires must maintain the same direction of rotation throughout their lifetime.
When replacing tires, the tires with the most tread should be mounted on the rear wheels to reduce the chance of
oversteer during hard braking.
Hitting curbs or potholes can damage the tires and/or wheels permanently.
pg. 125 Tire inflation
Tread wear indicator
page 127.