robert1@ihuxx.UUCP (Robert Duncan) (05/15/84)
In response to article i.d.: sdccs6.1466 ----- > I have read in several sources that tire pressure measurements > should be made when the tire is cold. Does this mean that the > tires should be a certain temperature or simply that the car on > which the tires have been mounted had not been driven for a given > period of time. ----- Setting "Cold" Tire Pressures ----------------------------- Yes, the "manufacturer's recommended" inflation values are for tires which have been idle for at least 4 hours or which have not been driven over 1 mile (so sez my manual). As Bob Fishell points out, this is confusing since the tire pressures of interest are active/loaded tire pressures. However, I suppose that setting the pressures at controlled starting point is a decent idea, sidestepping the distinction between hot/cold temperatures. This "owner's manual" prose seems to respect the fact that most driver's do not even check their tire pressures (or anything else), so that undue attention or detail is left out. But since you're interested: in addition to regularly checking your tire pressures (and weighing them against the ride firmness that you are trying to obtain) you should modify your tire pressures if you change your use of the car (e.g., long highway trip, etc.). Tire dealers have always recommended that you slightly overinflate your tires for cooler running and better fuel efficiency, although lower pressures are more comfy for boulevard cruising (espec. when you're trying to *sell* a boulevard cruiser), and higher pressures are desirable for tossing your car about in a sporting event. Use Of Tire Pressures In Competition ------------------------------------ In fact, at autocross/Solo II events, tire pressure manipulation is a very useful variable. Most drivers run their tires ~10 psi higher than normal in order to stiffen the sidewall somewhat (so that the tire will not roll over onto the sidewall or come off completely). Moderate overpressure will accomplish while still retaining pliant tire characteristics. When racing a non-modified sports car it is particularly useful to manipulate the tire pressures (since there is little else to tweak) to try to strike the right balance for the conditions. Many people will change tire pressures between runs (using a foot pump or portable compressor). Front vs. back tire pressures are manipulated to induce understeed or oversteer: relatively lower front tire pressures results in understeer ("plowing"), while lower rear pressures results in oversteer. happy trails, Robert Duncan AT&T Bell Laboratories @ Naperville, IL ihnp4!ihuxx!robert1 -- Robert Duncan ihnp4!ihuxx!robert1 AT&T Bell Laboratories @ Naperville, IL