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Tire Sizes

This component is part of Wheels and Tires.

Definition

The standard Pagoda Tire Size is a 185x14 tire. When these tires were originally made there were no variations on the Aspect Ratio (see Tires for an explanation). In those days all tires had the same sidewall height to tread width ratio, 80 for European tires and 78 for US sourced tires. Someone measured an original Continental 185SR14 and measured its rolling circumference as 2040mm or an aspect ratio of 79 3/4". Choosing a correct tire size will ensure that the speedometer and odometer on the car are accurate.

The original Firestone Phoenix 185 HR 14 radial tires had the following sizes:

  • Diameter: 650mm;
  • Rolling radius: 1983mm +/- 5% (1883 to 2082mm);
  • Sectional Width: 188mm;
  • Wheel width: 5 1/2 to 6"

With 185/80R14 Tires, the original look and height of the car is retained. Some people believe that it is important to keep the original tire size in the W113 to not destroy its balanced body design. Consider that when Dr. Rudolf Uhlenhaut (responsible for the racing Mercedes, the Silver Arrows) designed the mechanicals of the W113 car, he did it all around these tires. And most of us are not better engineers than Mr. Uhlenhaut.

If the tires - aesthetic matters apart - are changed, the balance of the car's suspension can be affected, and when the W113 was launched in 1963, it was considered as the car with best handling on the market.

As a result many people prefer to stay with the original narrower 185/80R14 tires, now that Michelin, Coker, and Vredesteijn produce tires in this size. Wider tires (especially 195/70R14 and 205/70R14) will fit but the resulting look is primarily a matter of taste.

195/70R14 tires became popular as 185R14 tires became hard to get. These tires give a speedo reading error of 3.5% while the 195/75 error is just 0.5%. 205/70 gives 1.4% error. However, since 195/70R14 tires were easier to obtain they became very popular on W113 cars.

With 205/70R14 or wider tires, there are incidental reports of:

  • speedometer differences (although small at 1.4%)
  • rubbing in the front wheel well
  • rubbing or too close proximity to the exhaust in the rear wheel well
  • suspension damage due to stress on the suspension components.

These may however be caused by incorrectly installed exhaust systems, aftermarket exhaust systems, old or incorrect shock absorbers or springs and many other factors. Before using wider tires it is recommended to verify these matters on your own car.

Calculating tire sizes

You can calculate the diameter of a tire by using the formula:

 diameter = 2 * (width / 25.4 x aspect) + rim size (in inches)
 circumference = diameter * pi = diameter * 3.1415297

For example for a 185/80R14 tire use 2 * (185mm / 25.4mm/in. * 80%) + 14 = 25.6535 inch. The circumference is then 651.6 mm * 3.1415297 = 2047 mm (compare with above measured circumference).

For a 205/70R14 tire this circumference is 2018mm.

Tire size and speed calculator http://www.miata.net/garage/tirecalc.html

Alternative tire sizes and report

Tire-sizeComments
185R14Standard size. Aspect ratio is 80 so more accurately named 185/80R14
185/90R14Available from Michelin as MXV-P tire with rub strip. Slightly taller look fills wheel-well and looks good.
195/60R14Lower profile, reported better handling in turns
195/70R14Frequently used alternative. Easier to source?
205/70R14Frequently used, slightly wider alternative that gives the same diameter (and thus preserves speedometer calibration and overall gearing). No rubbing experienced.
215/70R14One person confirmed that this size could work without rubbing, but note the caveat below. Your mileage may vary.
205/55R16One person runs 16 inch Ronal wheels with these tires on a 1964 230 SL. They work fine and there are no clearance problems.

Some people like the look of the wider 205/70's on the SL, but some don't. Some believe that using these wide tires put too much stress on the lower control arms at higher speeds. Since both Vredestein and Michelin have classic tires available in the original size with the rub strip (see Tires), and because those who own them are positive about the ride and handling, we recommend looking for these classics first. They are expensive however.

Pictures of cars and different tire sizes

  • Rob's car with 205/70R14 tires and Alloys
  • A car with 15 inch Alloys
  • 15 inch wheels as fitted to Classic Center 230SL Rally Replica, tires are 185x15 Dunlop Sports
  • These high-speed 215/45 'Z' 17" wheels are probably not liked much


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