Even pedaling backwards while riding, you flex the BB. Your legs are quite heavy, and their weight alone will flex the BB!
The amount of flex even in a relatively stiff frame is surprising. When we spent two days in the University of Washington wind tunnel for the big aerodynamics study in *Bicycle Quarterly* 21 <https://www.compasscycle.com/shop/print/issues/bq-21/>, our team noticed how much my old Alex Singer flexed while I pedaled on their special trainer at a very moderate effort. *"You should have seen Lance A. when he was here,"* was the response from the wind tunnel staff,* "his bike flexed just as much."* If you worry about chainring wobble, stop and spin the cranks backwards by hand. Then you can see just the chainring runout, without the confounding factor of the frame flexing. Of course, also make sure your BB doesn't have play, and that your chainring and crank bolts are tight... Jan Heine Founder Compass Cycles www.compasscycle.com On Thursday, September 27, 2018 at 7:05:20 AM UTC-7, Bill Lindsay wrote: > > One important point from Jan’s comments that I suspect may be overlooked > by some is that you should judge chainring wobble or run out on the > workstand. If you are riding the bike, look for it pedaling backwards. When > you are actually riding the bike, pedaling forward, everything flexes and > you can’t possibly separate run out from normal flex in your machine. The > OP indicated his 3mm of run out was on the workstand. > > Bill Lindsay > El Cerrito Ca -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at https://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
