LT vs Radial

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Originally Posted by Pedro_The_Swift

The front tyres we raced on at Donald were "tractor" tyres,, 16x5",, REALLY high profile,,
no more than 6" of tyre on the road,,


and at 210kph they raised up, in the centre, quite a bit!!


<snip>

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interesting that you mention this Pedro as I was thinking of this characteristic when I wrote my little reply above.

This is a typical characteristic of a Bias/Cross ply tyre.

Watch a Top Fuel Dragster as it launches and watch the Goodyears grow. They use this as an adjunct to the cars normal gears when launching down the strip, and it's for this reason Drag tyres will always be bias construction. Drag car tyres grow enormously at speed. A radila tyre, due to its construction can't do this.

Back in the early eighties at the height of the Ground Effects era in Formula One a tyre war was raging between Goodyear and Michelin, with Goodyear using bias construction, and Michelin radials.
Goodyear had the upper hand drawing on its previous decade of racing dominance until the sliding skirts that were used on the outside of the ground effects tunnels were banned, and a mandatory minimum ride height introduced. These skirts literally ran on the ground and sealed off the underbody venturi, maximising the pressure differential between the upper and lower body surfaces and hence maximising down force.
The FIA, in its endeavour to reduce cornering speeds banned sliding skirts, forcing the teams to run their cars with virtually no suspension to minimise ride height changes and keep downforce and hence grip at a maximum.

Instantly the rules had turned in favour of Michelin as a radial tyre grows very little at speed, whereas a bias tyre grows substantially, in this instance increasing the distance between the skirts and ground and letting air bleed, drastically reducing down force.

Goodyear were forced to try and develop radial race tyres to compete with the French manufacturer, and Michelin dominated F1 for the next couple of years.

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Originally Posted by Lotz-A-Landies

That may have been, but when you were racing they probably didn't have a speed rating on the tyre. I also don't know enough about bias "belted" tyres to be able to argue that issue.

<snip>
Diana

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I was only being a smart ar$#, but that particular tyre is still used in that category, although it is a race specific tyre and marked 'Not for Highway Use' :D

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Originally Posted by rick130

I was only being a smart ar$#, ...:D

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I would never say that about you! :)

Not to your face anyway :angel:

Diana :D:D

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Originally Posted by Lotz-A-Landies

Whether Mr Plod would even look at the rating on the tyres, or in-fact know what the respective speed rating applied by a tyre manufacturer means is anyone's guess. However, these days it seems that tyre manufacturers won't rate bias ply tyres above 90KPH irrespective of whether they are capable of the speeds we used to do on them. I bet it all comes down to the insurance companies and what they will cover. :mad:

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As already said, my Simex are rated to 160km/h.

As already said, racing tyres are also bias in construction and are safe for use at speeds well above 90km/h. Road legality is irrelevant for them.

The last couple of times I bought radial 265R75 16" muddies, in the same size, make, style there were different load/ply rating to choose from.

The ones with the highest load/ply rating were designated LT (light truck) they were 10 ply equivalent vs (from memory) 8 ply equivalent.

Don't assume that LT means bias ply - many truck tyres are radial ply.

Heavier sidewalls will normally mean lower speed rating as they heat up more at the higher speeds, but a decent LT tyre is plenty good enough for our use and the legal speed limits (even in the NT). The benefits of the stonger side walls is a deciding factor for me.

I killed two LT BFG's last summer and replaced them with some P carcass michelins the tyre shop had going cheap.

The difference in ride is amazing, even with the same 40psi in them the P casing is a much softer ride. But the michelins rounded shoulders are death on gravel roads, they follow ruts that the square shouldered BFG AT's climb out of.

The sidewalls on the BFG's are at least twice as thick, I'd expect airing down in soft sand and the like you could heat up and wear out a BFG sidewall faster than a thinner P casing. But the michelin feels thin enough to push a ballpoint pen through.