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Old 07-18-2013, 07:46 PM   #23 (permalink)
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Location: Ann Arbor, MI; Madison, WI; Bloomington, IN
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Vansquish - '06 Mazda Mazdaspeed6 Grand Touring
90 day: 32.63 mpg (US)
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If your suspension hasn't been modified, then your wheels are having similar impact on your crash-bar height.

A 175/50/13 tire should have a height of about 19.9", or more usefully, a radius of 9.95". The original wheel/tire package on your car was a 185/65/14, meaning a diameter of 23.5" (radius of 11.75").

So, what does this mean? Obviously you're playing the semantics game. OK, your suspension hasn't been modified, but you've effectively lowered your car by slightly less than 2 inches (11.75-9.95=1.8"), thus lowering your crash bar height by an equivalent amount.

I'm not arguing that you're a bad driver, or that you're driving in an unsafe manner, I'm suggesting that the car itself is no longer able to withstand impacts the way it was designed to.

The most likely (and problematic) impacts are the ones over which you have no control.

As for the overinflation, I'm sure the subject has been discussed ad nauseum on here, so I'm sure you have a reasonable basis for your argument. My justification for saying that your 60psi over-inflation is unsafe was based on the listed maximum inflation pressures, for the tire type, size, speed-rating, and load capacity.

Additionally, with a tire so over-inflated, your braking distances will be negatively impacted, as will your ability to make evasive maneuvers if necessary. Of course, some of this will be negated by the fact that you're running smaller-diameter wheels which carry less angular momentum and less lateral inertia.

Last edited by Vansquish; 07-18-2013 at 08:12 PM..
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