Quote:

What about the coloured stripes in the tread?
Often when you buy tyres, there will be a coloured band or stripe running around the tyre inside the tread. These can be any colour and can be placed laterally almost anyhwere across the tread. For ages I thought they were either a uniformity check - a painted mark used to check the "roundness" of the tyre - or and indication of the tyre runout. Turns out the answer is far simpler and much more disappointing. The lines are sprayed on to the rubber tread stock after it has been extruded during the manufacturing process. The problem is that the tread stock can be manufactured hours or days before it's actually used to make the tyres. So the lines serve one main purpose - they're an in-factory identification for the tyre builders to make sure they're using the correct tread stock for the carcass of the tyre they're assembling. Think of them like a barcode. They can sometimes indicate the rubber compound or the intended tyre size and often you'll find other information printed on to the tread as well as the stripes (see the example below of a number code).
When a tyre is being assembled, all the components are put together (carcass, beads, belts etc) inside a tyre mould and the stripes help the technician to align the tread stock properly. The inside of the mould has the inverse pattern of the tyre tread in it so that when heat and pressure are applied, the rubber in the tread stock is forced into the mould. Excess rubber is allowed to escape through little holes (called spew holes) which is why you'll often find what look like rubber hairs on a new tyre - they're excess rubber from the spew holes that was never trimmed. If you look closely at where one of the sprayed-on lines crosses a tread block, you'll be able to see where it's been stretched during the moulding process. The picture above is a good example.
All this is well and good if the manufacturing plant uses an 8-segment petal-type tyre machine (where the mould is on the inside of a bunch of metal 'petals' that close to form the finished shape), but on older 2-part moulds, the tread stock can be pushed off-centre as the mould closes so the lines also serve one other function - a visual inspection post-assembly to make sure the tyre tread remained in the correct place. As the tyre is being spun during inspection, the lines will wander across the tread if something became misaligned during the manufacturing process.

bobbycrispbox wrote:

Didn't need to check - I noticed when they mounted mine. Three red stripes on the outside, one on the inside.