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top tube/bike fit question(2 posts)

top tube/bike fit questionjbw
Jun 14, 2002 9:38 PM
okay... i'm about to order a frame. i can't find one to ride that has the exact specs i am purchasing. the frame is made in (top tube) 57 or 59. the 57 is way too small. the 59s i have rode all feel a bit big, but they also all have had at least a 120 stem on them. i infer that a 59 with a 110 will work, but i am not 100% sure. what to do?
Define termsKerry
Jun 15, 2002 5:50 PM
If the 57 is "way too small" that implies that your seat post would be out beyond the minimum insertion. Going to a 59 (it seems) would put the post at at most 2 cm below the minimum insertion - hardly what most would call too big. You need to look at the combination of seat tube angle and top tube length. A frame with a lower STA will effectively have a shorter top tube - each degree of STA in a frame this size will move the the bars about 1.5 cm. E.g. a 72.5 STA with a 57.5 cm TT puts the bars in the same place as a 73.5 STA and a 56 cm TT. In a 59 cm frame, 120-130 mm stems are quite the norm. In a 57, more like 110-120. But you need your total body dimensions to sort this out, none of which you provided.

Try some of these sizing calculators to make sure you've got your starting point right - it seems a bit confusing from the information supplied.

http://www.bsn.com/cycling/ergobike.html
http://www.coloradocyclist.com/BikeFit/index.cfm
http://www.sheldonbrown.com/harart-frames.html
http://www.rivendellbicycles.com/frameinfo/Frame_Sizing.htm
http://www.peterwhitecycles.com/fitting.htm