Joined: Feb 2012
Posts: 19,288
Likes: 5,381
From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
The rear der will have a part number on the cage's back side. Looking up the specs for that part will tell you what its largest cog capacity is. Ultegra has had 27 and 28tooth large cog limits for decades depending on the version. Fitting a too large rear cog can result in pulley knock and not being able to shift off the large cog.
But for a trainer stand bike this is moot. I still suggest looking at future uses and not limiting this bike to never being on the road.Andy
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AndrewRStewart