Originally Posted by T-Mar

The Sugino AT and TAT (Triple Aero Tour) came out in 1981. The TAT's claim to fame was the introduction of the 74mm BCD allowing for a 24T granny gear. Prior to this, the smallest Sugino chainrings, without going to adapters, was 32T. However, the true brilliance was incorporating both bolt circles on the spider, allowing for a larger spider and less chainring deflection. Prior to this, triple cranksets mounted all three chairings to the same bolt circle or used the TA approach and bolted the middle and inner chainrings to the large chainring. These approaches compromised the granny gear size and/or chainring deflection.

Shimano released the FC-6207 New 600EX crankset in 1984. However, it's not really fair to compare it to a TAT, as it was a double crankset. Shimano's 6200 series triple was the FC-6206. It also used a 74mm BCD for the granny gear but was typically spec'd with a 28T, as Shimano was pushing their Biopace chainrings and this was the smallest Biopace chainring that a 74nn BCD would accommodate due to the ovoid shape. I can't recall seeing any specs as to construction but weight was comparable to the TAT, so I'm assuming it was also cold forged. So, the TAT had a smaller granny gear but the FC-6206 had Biopace.

Early 1980s Japanese grand touring bicycles were typically SunTour equipped due to several advantages. First, they shifted better, courtesy of the slant parallelogram rear derailleurs. While they shifted better at all gear ranges, it was more noticeable as the gear range got wider. Also, the SunTour wheels were more versatile If you wanted, you could get 38T. Shimano topped out at 34T. Finally, you could a 34T Ultra-6 from SunTour, so you could get an extra cog without giving up wheel strength, which is important on heavily loaded grand touring bicycles. Things would skew in Shimano's favour in 1986, when they brought out index compatible, wide range derailleurs with slant parallelograms. The mid-1980s seal failures on the SunTour Mountech rear derailleurs certainly didn't help.

Normally you'd think that with SunTour's supremacy, that Sugno cranksets would also hold the high ground in the grand touring world. However, this was not the case prior to the TAT. Many Japanese grand touring bicycles of the very late 1970s actually spec'd the SR Super Maxy Tour, simply because it could accommodate a 28T granny gear. Personally, I believe this was the real impetus behind the development of the Sugino TAT. They simply wanted to one up SR and gain market share by going 4T lower.