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85 MPH spedos were the norm on EVERY car in the US from the late '70s to early '90s. It has nothing at all to do with a car's top speed! Since drivers subconsciously (in many cases - UNconsciously) settled into a speed where the speedo needle pointed straight up, usually 60MPH, the maximum was dropped so the centre reading was a little over 45...slowing traffic...saving gas.
Those speed limiters are usually on light trucks and SUVs. It has to do with maximum allowable zoom on the tires the factory mounted. Cutout hits around 92MPH and engine restores around 89.
Now to the guy's original question: The pre-1990 Bertones (780)came with larger diameter tires (205/60-15 at 24.8" dia) than the 760 it was built from (which used 195/60-15). The speedometer calibration is different than all the other 200, 700, 1990-91 780s, 900 cars which came with 24.25" diameter shoes. Besides making a noticable jump in speed readings, if your 780 is built like mine, the taller 75 series tires WILL hit the bumper on turns. If you insist on getting off the 60 series at the expense of handling, the closest size you can go to is 205/65-15 touring at almost 7% larger. The smallest 75 series tire is 13% larger than standard.
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