Speedometer Error: 185/55R15 → 205/45R17

What this means for your vehicle

Changing from 185/55R15 to 205/45R17 shifts overall tire diameter by +5.44%, which produces a proportional 5.44% error in the speedometer and odometer readings. Because 205/45R17 is taller than 185/55R15, each tire revolution covers more ground, so the factory speedometer reads low — you are actually moving faster than the dash shows. At an indicated 30 mph (city driving) your actual speed is 31.6 mph; at 60 mph (highway) it is 63.3 mph; at 75 mph (cruise control) it becomes 79.1 mph. The odometer drifts at the same rate — over 12,000 indicated miles per year, you actually travel 653 miles more than the dash shows, which matters for lease-mileage caps and warranty tracking. Over 5% is outside most factory tolerance windows. Recalibration is essentially mandatory, and ABS, traction control, and TPMS may throw codes or behave incorrectly. If you plan to keep the 205/45R17 setup long-term, an OBD-II programmer or dealer recalibration costs roughly $50–150 and restores accurate readings across the instrument cluster.

Odometer impact

For every indicated mile, you're actually traveling 1.0544 miles. Over 10,000 indicated miles, that's 10544 actual miles. Check your warranty and service intervals accordingly.

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