I want to upgrade my newly acquired Centurion Ironman to STI and dual pivot brakes. My first inclination was to keep it all in the 105 family like the bike originally came with, and go with a 105/ 1056 groupset. But now I come across a very complete RX100 groupset, and I am wondering- is there any really difference between the 8 speed RX100 groupset and the contemporary 8 speed 105 groupset? If you look at the components:


They are the same except the 1056 has grey powder coating(?) . Same with the crankset- it looks exactly the same aside from the grey powder-coating. Does anyone know if the RX100 had inferior bearings or something subtle like that? How did Shimano justify the price difference?

I've read they are the same with rx100 being polished and 105 painted. And from what ive seen, they are effecrively the same. Ive worked on 2 bikes that also had mixed drivetrains of the two groups.

I like the rx100 look more, actually.


As for difference in cost, I dont know what that was or how it was justified. Current 105 and Ultegra is in a similar murky situation as r7000 and r8000 are stupidly similar in feel/performance/weight/quality.

There is admittedly an insignificant difference in the current models, while the old rx100 and 105 seems to really be no material difference.

Marketing departments often find it useful to have products available at virtually every price point, so may create products with mere finish variations in order to give the higher-paying customer a feeling of getting more for their extra money.

RX100 was touted as a racing gruppo, but got almost no advertising money devoted to it. And perhaps for the same reason, RX100 was practically an OEM-only gruppo.

It was a great gruppo imo, I built my first STI-equipped bike about 25 years ago using a pair of RX10 levers I bought new at a swap meet, and I still have the late-60's PX10 with those levers on it!

For mechanical differences between RX100 and same-period 105, look at the hub bearing shielding. I think that 105 may have used plastic pieces and a more effective seals there.

Oh, and here's that PX10 that I pulled from The Off Ramp's dumpster in 1996 and rebuilt using RX100 levers, Roval wheels, Sachs rear derailer and Super68 calipers:

The 1055/1056 105 hubs have better seals than the RX100 hubs. The dual pivot 105 brake calipers have a ball bearing thrust bearing where the RX100 has a washer.

I can't tell much of a difference in braking operation. I definitely prefer the 1055 & 6400 hub seals.

Great info! The brakes actually look completely identical from the outside:


But looking at the documentation, I can see that the 1055/1056 has thrust ball bearings where the RX100 has a flat washer.

Same with the hubs- they have identical looking casting.

Pictures of a 2X6 RX-100 SIS groupset on a 1989 Fuji Club.

It's a good looking groupset and a great looking bike. Did the 7 speed SIS index with your 6 speed hub?

It was original equipment on the bike. So, AFAIK it was always just a 2 x 6 downtube SIS set up. I think this may be an example of the very first time RX100 appeared on a bike. I sold that particular bike last summer when the vintage market was pretty soft. (Probably could get $2X for it now........... dang!).

This is a very old Shimano 105 group on a 1988 Centurion Ironman.