My 1958 550 has original regular red rims on the rear. Apparently these were only on the first 550's made. They may have been the one's with the 144 cubes and 35 HP. Later ones had white rear rims and 155 cubes and higher comp and 43 HP. Does anyone know when the red rims were stopped. Mine is serial 64069. The serial numbers for 1958 went from 60501 tp 72632. These smaller cubed red rimmed 550's may be the rarest of all 550s.  Contact me if you have a 58 with red rear rims or the 144 cubes. l'll be glad to update everyone later. Thanks.