The “repairable area” of a tyre is designated as that where a repair can be carried out to British Standards (currently BS AU 159f). Because a tyre curves away from the middle of where the tyre rolls on the road, only the centre area is repairable.
Sidewalls are not repairable.
The repairable area is defined as a percentage of the tyre’s “nominal” section width and thus varies by the size of the tyre. The repairable area is based on the centre line, eg. 82mm means 41mm on either side of the centre line of the tyre. Using a metric rule, you can quickly find out if a puncture in your tyre is likely to be repairable.
If the puncture falls between the markings for that size tyre, it is probably repairable.
135 82 mm
145 88 mm
155 93 mm
165 108 mm
175 114 mm
185 120 mm
195 128 mm
205 145 mm
215 153 mm
225 159 mm
235 167 mm
245 174 mm
255 180 mm
265 187 mm
275 194 mm
285 201 mm
295 208 mm
335 236 mm
345 243 mm
(Note that the tyre may not be repairable if the hole is larger than 3mm or there is other internal damage to the tyre.)
If the tyre has been run on even for a very short distance when it is flat, the tyre cannot be repaired.
You thought tread was the shape of the rubber blocks around the outside of your tyre didn’t you? Well it is, but it’s also so much more. The proper choice of tread design for a specific application can mean the difference between a comfortable, quiet ride, and a piss poor excuse for a tyre that leaves you feeling exhausted whenever you get out of your car.
A proper tread design improves traction, improves handling and increases Durability. It also has a direct effect on ride comfort, noise level and fuel efficiency. Believe it or not, each part of the tread of your tyre has a different name, and a different function and effect on the overall tyre. Your tyres might not have all these features, but here’s a rundown of what they look like, what they’re called and why the tyre manufacturers spend millions each year fiddling with all this stuff.
Sipes are the small, slit-like grooves in the tread blocks that allow the blocks to flex. This added flexibility increases traction by creating an additional biting edge. Sipes are especially helpful on ice, light snow and loose dirt.
Grooves create voids for better water channelling on wet road surfaces. Grooves are the most efficient way of channelling water from in front of the tyres to behind it. By designing grooves circumferentially, water has less distance to be channelled.
Blocks are the segments that make up the majority of a tyre’s tread. Their primary function is to provide traction.
Ribs are the straight-lined row of blocks that create a circumferential contact “band.”
Dimples are the indentations in the tread, normally towards the outer edge of the tyre. They improve cooling.
Shoulders provide continuous contact with the road while manoeuvring. The shoulders wrap slightly over the inner and outer sidewall of a tyre.
The Void Ratio is the amount of open space in the tread. A low void ratio means a tyre has more rubber is in contact with the road. A high void ratio increases the ability to drain water. Sports, dry-weather and high performance tyres have a low void ratio for grip and traction. Wet-weather and snow tyres have high void ratios.
Hope this helps someone!