Tyre Construction Methods

AIUI crossply tyres are manufactured as a series of steel plys which cross alternately from inside wall, across the tread, to the outside wall at an (arbitrary but plausible) 90deg to the next one which goes from outside wall to inside wall (think of crossing the finger's of your hand and you'll see what I mean).

However - radial tyres. Are they constructed as a linear series of steel wires stretching from wall to wall across the tread (one behind the other), or as a linear series of steel wires, each one going completely around the circumference of the tyre, laid across the width of the tyre, with decreasing diameter ones for the sidewalls as the diameter to the bead decreases?

I ask because I recently had a tyre from a major manufacturer (marked radial) destroyed by a blowout and noticed lots of wire "loops".

Reply to
Paul King
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Cross-ply tyres run diagonally, the overlapping plies of fabric run in opposite directions make the tyre very stiff.

Radial tyres run fabric plies from bead to bead straight over which makes them more flexible and softer ride.

BOTH SORTS have steel belt wires which run round the circumference.

What you've seen is perfectly normal and nothing to worry about.

Reply to
Guy King

Thanks for clearing that up :-)

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Reply to
Paul King

Hi Paul, I worked for Michelin - on the engineering side for many years and moved to the Dundee plant in '86 where they make car tyres. Both radial and crossply tyres used cross braced rayon strands and later steel and rayon plies under the tread area. The plies are laid so that they sit diagonally across the tread area. There may be two or more such layers of diagonally cut fabric each at approx 70 deg to the previous layer. This construction is used to stabilise and reinforce the tyres footprint on the road so preventing unnecessary tread block deformation, heat build up and accelerated wear / tyre self destruction. The carcase cords on a radial tyre are laid so that they run from bead to bead (The bead is the bit that locates and seals to the wheel rim) and are terminated where they wrap themselves around the wire 'tringle' that maintains rigidity within the bead where it comes into contact with the wheel rim. With most new tyres if you look closely at and or feel around the sidewall of the inflated tyre you will see a small localised depression running from the bead area to the tread. This is not caused by curb damage but the overlap joint on the rayon carcase cords that run radially from bead to bead. The overlap if slightly at top tolerance locally strengthens the sidewall and hence it does not deform as much as the rest of the tyre. If you see a slight localised bulge in a new tyre that is often associated with a spacing out of the radial plies. Often this happens during inflation as detailed below or during the curing press moulding process when the carcase is further inflated into a mould and heated.

There is an advert running on the TV for the TA at the moment. It briefly shows an actual tyre making machine with the radial carcase cords still in a 'toilet tube' shape with the cross braced tread plies laid in the centre. The tread if I recall correctly, has been cut and jointed into a ring and is waiting for the 'radial' carcase to be inflated onto it and then rolled into place. You have to imagine a flexible toilet tube shape with a layer of paper still on it, then push the ends of the tube towards each other and blow compressed air into the tube at the same time. The flexible tube would deform into a ring shape. -the rudiments of a tyre carcase.

If that description has not confused and put you to sleep, nothing will ;-)

Gio

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Reply to
Gio

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