Tire topics have been written about over and over --- however, most thinking about modern tires is based on understanding the original tires. Hence this post about questioning our understanding.
Recently there has been quite a bit of chatter regarding original tire sizes and the sizes of tires available today.
When Rolf-Dieter, on another thread, mentioned that the 195-75-14’s looked really large compared to what he had on his car it got me thinking as I felt the same comparing my 280sl to my 250sl. The 280sl has 195-75-14’s and the 250sl has the Coker Phoenix’s. The 280sl tires look much larger then the repro Phoenix tires. Many have mentioned that the 195-75-14’s are closest to original. I’m not so sure anymore and am thinking otherwise. Would appreciate your opinions.
I am questioning the thinking that Pagodas originally had tires with an aspect ratio of 78 & 80 (per our tech manual) or to put it simply, had a diameter of 25 ½ to 25 ¾ inches. On a 14-inch wheel an aspect ratio of 78 or 80, with a 185 tire, equates to a diameter of about 25 ½ to 25 ¾ inches respectively. This is very close to the 195-75-14, a commonly referred to equivalent in our forum and tech manual.
The reproduction Coker Phoenix tires are listed by the manufacturer as having a 25-inch diameter, ½ to ¾ inch smaller than a 78 or 80 aspect ratio for these tires and smaller than the 195-75-14’s. A 25-inch diameter on a 14 inch 185 tire equals to an aspect ratio of about 75.
I have Coker Phoenix tires on my 250sl and can confirm that the diameter measures just below 25 inches (they have about 2,000 miles on them).
In addition, my 1971 280sl came with an unused original Continental Spare and today I measured this original unused tire that was delivered with the car when new. If it was driven on, it must have been very few miles as the tire still retains the striping down the center of the tread.
This original Continental has a diameter of 24 ¾ inches. It has a circumference of 77 5/8 inches (which also converts to a diameter of about 24 ¾ inches). See photos.
(Sorry, to keep things easier to read, I’ve not included metric equivalents, apologies)
So, based on measuring an original Continental and a Coker Phoenix, the diameter of these two tires suggests that they are closest to modern tires that are 185-75-14 and not 185-80-14 nor 195-75-14 as commonly perceived.
Put simply: the Original Continental and Coker Phoenix are about 24 ¾ - 25 inch diameter while the 185-80-14’s and 195-75-14 are 25 ½ – 25 ¾ . About ½ - 1 inch larger in diameter. This may not sound like much, but it’s clearly noticeable on the cars.
I would also comment that the TomTom GPS miles-per-hour match spot-on or within one mile per hour on the 250sl with the Coker Phoenix at all speed ranges.
Would appreciate others comments as I would not want to steer our members wrongly if my deductions are not valid.
Thoughts would be appreciated.
