Terry Morgan / t_zmorgan@msn.com / June 6, 2001
The Mercedes-Benz Ponton shop manual indicates that 190 models came with either 6.40-13 or 6.70-13 tires and says the "effective radius, dynamic" for a 6.70-13 at 60 km/h is 307 mm and at 100 km/h is 313 mm. This is equivalent to a diameter of 24.17" to 24.65." (The 6.40-13 tires are 8 to 6 mm smaller in diameter) This is equivalent to the 185/80-13 size, according to the calculations in the table below.
The width of the tires under both old and new system is the width of the tire: in inches for the old system and millimeters for the new system. I believe the old-system tires had a varying aspect ratio near 80% (?). Under the current system, if there is no aspect ratio given, it is 80 by default; these are slowly becoming extinct.
I measured the circumference of my new 185/80-13s with a tape and I got exactly the same as the calculated circumference. However, there are probably small differences between tire brands. I also measured the section width (widest point of sidewalls) and it corresponds with the width (185 mm).
The "% diff" column shows the difference in circumference from the 185/80-13 size (first row) and indicates the change you will get in engine rpm, odometer, and speedometer readings.
Tire Size Guide |
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| width | aspect ratio | size | diameter | circumference | % difference | revolutions/mile |
| 185 | 80 | 13 | 24.65 | 77.45 | 0.00 | 818.06 |
| 175 | 70 | 13 | 22.65 | 71.14 | -8.14 | 890.6 |
| 175 | 80 | 13 | 24.02 | 75.47 | -2.56 | 839.51 |
| 185 | 70 | 13 | 23.20 | 72.87 | -5.91 | 869.43 |
| 195 | 70 | 13 | 23.75 | 74.61 | -3.67 | 849.25 |
| 195 | 80 | 13 | 25.28 | 79.43 | 2.56 | 797.68 |
| 205 | 70 | 13 | 24.30 | 76.34 | -1.44 | 829.99 |
| 215 | 70 | 13 | 24.85 | 78.07 | 0.80 | 811.58 |
| 195 | 60 | 14 | 23.21 | 72.92 | -5.84 | 868.84 |
| 195 | 65 | 14 | 23.98 | 75.34 | -2.73 | 841.03 |
| 195 | 70 | 14 | 24.75 | 77.75 | 0.38 | 814.94 |
| 195 | 75 | 14 | 25.52 | 80.16 | 3.50 | 790.42 |
| 205 | 60 | 14 | 23.69 | 74.41 | -3.93 | 851.51 |
| 205 | 65 | 14 | 24.49 | 76.94 | -0.65 | 823.45 |
| 205 | 70 | 14 | 25.30 | 79.48 | 2.62 | 797.18 |
| 215 | 60 | 14 | 24.16 | 75.89 | -2.01 | 834.86 |
| 215 | 65 | 14 | 25.00 | 78.55 | 1.42 | 806.60 |
| 215 | 70 | 14 | 25.85 | 81.21 | 4.85 | 780.19 |
| 195 | 60 | 15 | 24.21 | 76.07 | -1.79 | 832.96 |
| 195 | 65 | 15 | 24.98 | 78.48 | 1.33 | 807.36 |
| 195 | 70 | 15 | 25.75 | 80.89 | 4.44 | 783.29 |
| 205 | 60 | 15 | 24.69 | 77.55 | 0.13 | 817.02 |
| 205 | 65 | 15 | 25.49 | 80.09 | 3.40 | 791.15 |
| 205 | 70 | 15 | 26.30 | 82.62 | 6.68 | 766.87 |
| 215 | 60 | 15 | 25.16 | 79.03 | 2.04 | 801.68 |
| 215 | 65 | 15 | 26.00 | 81.69 | 5.48 | 775.58 |
| 215 | 70 | 15 | 26.85 | 84.35 | 8.91 | 751.13 |
Notes
Some of these tire sizes may not be available
How these values were calculated
a) Diameter (in): width (mm) / 25.4 mm/in * (aspect/100) * 2 + size (in).
b) Circumference: diameter * pi
c) % diff: percentage of increase or decrease (-) from the 185/80-13 size.
d) [circum - (circum of 185/80)] / (circum of 185/80) * 100
e) revolutions/mile: (12 in/ft * 5280 ft/mi) / circumferenceBy today's standards, the 80-aspect-ratio tires give very mushy handling and lower road-holding limits. One of the first upgrades for better handling is to go to larger wheels and tires with a shorter sidewall. I am planning to install 14" wheels and I might want to increase the overall gearing for more relaxed cruising while keeping up with modern traffic. Use the table above as a guide for selecting a size.