Here's an interesting read about tyre blackening from the Aussie Offroaders Forum I'm a member of on Yahoo:
Our 4WD club recently had a tour of the Bridgestone Tyre Factory here in
Salisbury. Now I don't mind paying the $200 plus for a tyre after seeing the
engineering that goes on behind the scenes.
One thing that came out of the tour was that using tyre blackening materials
on the side walls of your tyre is probably the worst thing you can do! The
sidewall is the most flexible part of the tyre and most tyre blackening
compounds, while making the tyre nice and black actually strips the
silicones out of the rubber compounds.
The best thing we can do is now and then spray the side walls with products
like Armourall which have a silicone base.This keeps the sidewalls nice and
flexible. This for 4WD'ers is most important as we air down when driving in
sand etc and the side walls bow out even more with low air pressure.
Don't forget the spare and the inner side of the tyres (the side that is the
most difficult to get to unless it is removed)
Other items of interest
1. Once the tyre is cured in the mould at the factory, keeping them home in
the shed to harden is pointless as the tyre is as hard as it is going to
get. What does happen in the shed is that the silicones and other chemicals
actually evaporate out. So what appears as a hard tyre is actually a hard
oxidised surface which will wear unevenly when put on the road.
2.Car tyres are cured between 20 and 30 mins. Light truck (4WD) 30 to 40
mins and Large truck tyres mainly due to the shear volume of material to
cure, up to an Hour.
3. The tyre is made up by combining different materials at different times.
The bead has many strands of steel wire embedded into the rubber to provide
strength to stay on the rim.
4. The inside of all Tubeless tyres actually have the same rubber used in
Tubes laid into the tyre so that it seals the inside of the tyre. As the
normal rubber would allow the air to slowly escape through the rubber.
5. The 2 steel belts are actually laid diagonally in two directions
providing the greatest strength.
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