One of the long-held beliefs of cyclists is that bottom bracket drop affects the handling. It makes sense - you lower the ride, and the bike should turn better. However, you need to look at what the important variable is: It's not the BB drop, not even the BB height, but the center of gravity of the rider. That is about 3 feet (90 cm) high for most riders. It's hard to see how 3 mm could make a difference.
In practice, that is how it tends to work out. For *Bicycle Quarterly*'s tests, I have ridden a lot of low-trail 650B bikes with the same front-end geometry, same Hetre tires, but one was an outlier with a BB height that was way lower. (I suspect an error by the builder, who was new to making bikes.) The bike handled exactly the same as other bikes with similar front-end geometry and wheel/tire combination that had BB heights of 265-275 mm. Even 30 mm didn't make a noticeable difference. (Note that I rode the bike first, then measured its geometry, to prevent the placebo effect of knowing that the BB is lower, and hence feeling a difference that may not be there. It wasn't quite a blind test, but the best we can do with test bikes.) Most modern 'cross bikes have a very different front-end geometry – more like mountain bikes – from road bikes, which probably explains their different handling. My old Alan<http://janheine.wordpress.com/2013/10/15/cyclocross/>has a very high BB (back then, you had to be able to pedal with toeclips facing down and not scrape the mud), yet its handling is remarkably "normal." Since we are in myth-busting mode, wheelbase is another factor that is overrated. The wheelbase of a modern bike varies between 995 and 1040 mm. That is between a Trek Madone and a touring bike with very long chainstays. It also amounts to just 4.5%. Once Peter Weigle and I rode two bikes with identical front-end geometry, but very different chainstays: A 1954 Alex Singer with 430 mm chainstays, a modern Peter Weigle with 450 mm chainstays. We switched back and forth between bikes and could not detect a difference in their stability or handling. (Chainstay length can affect comfort, because 20 or 30 mm difference in chainstay length will push your saddle significantly closer to the rear axle line.) We did a detailed article in *Bicycle Quarterly* Vol. 10, No. 2<http://www.bikequarterly.com/bq102.html>on bike geometry and how it affects the bike's ride, performance and handling. Jan Heine Editor Bicycle Quarterly http://www.bikequarterly.com Follow our blog at http://janheine.wordpress.com/ On Friday, November 1, 2013 9:14:36 AM UTC-7, ttoshi wrote: > > Lacking any hard data, we can only play with the numbers. 3 mm is > 25% of 12 mm, which is probably the average difference in bottom > bracket height between cyclocross and road bike bottom bracket > heights. People have argued that road bikes noticably turn better than > cyclocross bikes due to this difference, so perhaps the princess on 4 > peas would notice the difference! > > Toshi > > > On Wed, Oct 30, 2013 at 5:01 PM, Jan Heine > <hei...@earthlink.net<javascript:>> > wrote: > The difference in tire height (about 3 mm) will lift your center of > > gravity by about 0.3%. Even the princess on the pea would be > hard-pressed to > > notice that! > > > -- 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 http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out.
