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Old 02-10-2003, 08:40 AM
mithra mithra is offline
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Join Date: Apr 2002
Location: a space in time
Posts: 132
tire pressures

greetings to the 401 GP crowd. A few thoughts on tire pressure; although there are experts in the tire field who have forgotton more than i have learned, i'll give this a crack. For safe high speed motoring, an individual should follow the automobile manufacturer' s specs for tire pressure as outlined in the manual or elsewhere on the car. The auto manufacturer, not the tire company determines what tire pressures are appropriate for a given auto. The tire pressure on the sidewall of the tire is the maximum allowable air pressure for that tire as determined by the tire maker and does not reflect a pressure to be used on any vehicle. Air pressure is critical to the life and safe handling of the tire(s) on any vehicle. The cold inflation pressure as indicated by the auto manufacturer takes into account the weight of the car, the normal intended purpose of the car (luxury, sporting), and the natural rise in pressure in the tire as it is operated at normal highway speeds. The tire itself merely holds the air, it is the air pressure that actually supports the vehicle. As the tire turns, the sidewalls flex causing heat buildup within the tire structure itself. The "normal" pressure is selected after extensive testing by the auto manufacturer at normal highway speeds and takes into account weight, ride, handling, and heat buildup in the tire. The manufacturer's recommendation to raise the air pressure for higher sustained speeds is as a result of the recoqnition that at higher speeds there is more sidewall flex generating more internal heat in the tire. The raised pressure helps minimize the heat buildup by essentially stiffening the sidewall of the tire and preventing more flexing. The heat buildup in a tire can become so high in a tire that is underflated relative to the tire's true need for a certain air pressure, that the tire's components will start to break down, sometimes catastrophically. I have attended numerous accident scenes, where upon investigation, at least one of the tires on one of the involved vehicles indicates that the tire was operated severely underinflated; the sidewall of the tire looked like it had been scorched with a blowtorch. I would suggest that the handling of that vehicle at speed would have been seriously compromised, and quite possibly have contributed to the accident. With the amount of highway travel that the forum's membership travels, i am sure that you have at some point seen the remains of large truck tires on the road. Inevitably, investigation of the vehicle and the tire casing will show that that tire as well as the other tires on the vehicle are underinflated from minimum specs. One of the tire manufacturer's websites has a chart for a specialty tire (ultra performance) showing the adjustments needed for air pressure based on anticipated sustained speeds; it also outlines the decreased weight (load) carrying capacity of the tire as the rate of sustained speeds are raised. The tire pressure ratings in your manual or on the vehicle are minimums for safe operation of the vehicle at minimum load; bear in mind that these ratings may be heavily weighted in favour of ride quality, and not life expectancy or handling.(can you say explorer?)

93 sl600
93 600sel

A mercedes is an inanimate object and therefore must respond to logic and reason.
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