The stock tire size on the SEC is 205/65-15. It has an overall diameter of 25.5". The car's speedometer is calibrated on the stock tires. So any deviation from that diameter will cause the speedometer to either understate or overstate the actual speed. The 245/45-17 tire has an overall diameter of 25.6" which is pretty close to stock. The 245/50-17 diameter is too far off at 26.6". If your car is lowered on shorter springs, clearance will be an issue.
For 17x8 rims ET11, AMG recommends 235/45-17 all around OR 235/45-17 for the front and 255/40-17 for the rear.
For 17x8.5 ET18-Front: 245/45-17 and 17x10 ET17-Rear: 275/40-17.
For 17x8 rims ET11, AMG recommends 235/45-17 all around OR 235/45-17 for the front and 255/40-17 for the rear.
For 17x8.5 ET18-Front: 245/45-17 and 17x10 ET17-Rear: 275/40-17.
