Folding Bikes - Lateral play in Swift hinge
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law4jba
09-26-08, 08:54 AM
While folding my swift folder today, I noticed about 1/4 to
1/3 inch lateral play (at the bottom bracket) in the rear
triangle when folded under the toptube. More particularly,
when the bike is folded, I can lightly press on the crank
bolt and induce about 1/4 to 1/3 inch of travel in the
triangle perpendicular to the maintube.
Is this normal?
timo888
09-29-08, 01:58 PM
While folding my swift folder today, I noticed about 1/4 to
1/3 inch lateral play (at the bottom bracket) in the rear
triangle when folded under the toptube. More particularly,
when the bike is folded, I can lightly press on the crank
bolt and induce about 1/4 to 1/3 inch of travel in the
triangle perpendicular to the maintube.
Is this normal?
I am not at home to check, but believe so. But make sure the pivot bolt in the main tube is tight. You might contact Xootr for torque recommendations there. See what they say :)
When the seatpost is removed from the bottom segment of the seat tube, the rear triangle is connected to the main tube only by the pivot bolt. Any slop there would translate into lateral movement at the rear dropout.
Consider the pivot bolt as sitting at the centerpoint of an imaginary circle. A small amount of wiggle at the centerpoint translates to much larger distances at the circumference of this circle, i.e. at the rear dropout ... just as moving a telescope a millimeter on its tripod can result in huge shifts a mile way....or across the cosmos :-)
PIVOT
a
-
-
-
-
-
-
-
-
-
-
-
b.......c
DROPOUT
ab is the distance from pivot to dropout
arc bc is the wiggle distance to one side (hard to draw with a keyboard)
ac is the stay at max wiggle
angle b-a-c reflects any slop in the bolt
Regards
T
law4jba
10-01-08, 10:40 AM
Your description is spot on. Alas I'm a chemist not a mechanical engineer by training.
Anyway, I spoke to Peter Reich about this issue.
There are no cracks in the any of the tubings or welds (good news).
The wiggle occurs when folded or when unfolded without the seat post inserted.
Peter has requested I check for lateral play when the seat tube is inserted. I'll do this tonight and report back....