Joined: Sep 2009
Posts: 4,697
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Bikes: Masi, Giant TCR, Eisentraut (retired), Jamis Aurora Elite, Zullo, Cannondale, 84 & 93 Stumpjumpers, Waterford, Tern D8, Bianchi, Gunner Roadie, Serotta, Serotta Duette, was gifted a Diamond Back
What gear range are you planning on using? What range of cogs? that will determine short or long.
to look up the ranges google on ""Shimano.com" go to proper country, under products select Tiagra, select the RD and it will show the sprocket range, FD range and total capacity.
You will need to decide since you didn't provide enough information.