littlebrownbike Posted September 7, 2009 Report Share Posted September 7, 2009 This I have wondered for years, its easy to say "XL tyres have reinforced sidewalls", but there must be more to it than that. What I want to know is, why, and whats the benefit? For example, lets say we have have two tyres, same make & model,....one is 92Y and the other is 92Y XL. Off the top of my head each tyre can hold 680kg, but what can the XL tyre do that the non-XL can't? Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted September 7, 2009 Author Report Share Posted September 7, 2009 Found this; "Extra Load tyres are designed to be used at higher pressures than normal tyres. They have the same maximum load capacity as a normal tyre with the same Load Index but achieve this at a higher pressure. Normal tyres are inflated to pressures between 2 bar and 2.5 bar. They reach the maximum load capacity as specified by the Load Index when inflated to 2.5 bar (35psi) Eg for a Load Index of 94 this is 670kg. Extra Load tyres can be inflated to pressures up to 2.9 bar (41psi) and actually have a lower load capacity at the same pressure as a normal tyre with the same Load Index. To get the 670kg load capacity for a Load Index of 94, an Extra Load tyre must be inflated to 2.9 bar. At 2.5bar it will only have a load capacity of 595kg. Use the tyre specified by the vehicle manufacturer and inflated to the pressures they specify. Differing from this could be dangerous or at least uncomfortable with a harsher ride." Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted September 7, 2009 Author Report Share Posted September 7, 2009 Air Pressure (psi) 20 23 26 29 32 35 38 41 P235/75R15 SL 1543 1635 1753 1852 1940 2028 P235/75R15 XL 1543 1635 1753 1852 1940 2028 2105 2183 Note: 35 psi is the assigned "maximum load" pressure for standard load tires and 41 psi is the assigned "maximum load" pressure for extra load tires. The above chart correctly shows that an extra load tire is not rated to carry any more load than a standard load tire when both are inflated to the same pressure (up to the standard load tire's "maximum load" pressure of 35 psi). This is because a tire's load capacity is a function of its size (which determines the size of the "air chamber"), its construction (which determines how much pressure can be held) and the actual air pressure used (which determines how many air molecules are forced inside the chamber). All tires with equivalent physical dimensions carry equivalent loads (until they reach their maximum load pressure). Quote Link to comment Share on other sites More sharing options...
Tony Posted September 7, 2009 Report Share Posted September 7, 2009 They also make for a harder ride and tram-line quite badly. Quote Link to comment Share on other sites More sharing options...
littlebrownbike Posted September 7, 2009 Author Report Share Posted September 7, 2009 it would appear they do not affect a cars handling though? I have just read that E46 M3 has 87 indexed tyres as standard, one would assume if they had handling benefits then BMW would have reeped them. Quote Link to comment Share on other sites More sharing options...
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