Originally Posted by richardmasoner
I'm going by memory on the components so I could be wrong about the 105. I remember it had Biopace chainrings and downtube shifters that could convert from friction to indexed shifting. I seem to recall 105 being the low-end back in the late 80s -- Sora and Tiagra didn't exist back then.
I didn't think Centurion still existed as a brand in 89 -- When did they change the name of the company to Diamondback?
1990 was the first model year for Diamondback road bicycles. BioPace came out in 1983. Shimano 105 was lower, mid-range group when it first appeared in 1983 but gradually moved slightly upscale with increasing features. Until 1989, the Ironman Expert was typically the 105 model in the Centurion lineup. Shimano Light Action SIS derailleurs were a step lower and would be the most likely candidates on an Accordo. Exage was their successor. Both would have had shifters that could be switched from SIS to friction.