bikebreak

question on 650b conversions
How much lower to the ground would BB get going from 700x28 to 650x28?

Is there a general rule that going 700 to 650b adds about 10mm in tire clearance? eg a frame rated for 28mm in 700 would fit a 38.
I saw that somewhere, don't know how accurate it is

thanks!

Spoonrobot 

Andrew R Stewart 

And labeled width is not the measured width. Additionally rim width effects tire profile, But the differences are usually in mms, not a lot unless you are crazy in pedaling through turns. Andy

jlaw

To determine the approx. clearance for a 650b wheel measure 320mm from the axle (front and back) and then determine the available width at this point. An additional 10mm is not a bad guess, but it truly depends upon how the fork and the chain stays/seat stays/brake bridge are built.

Here are some additional guidelines re: 650b conversion from 'Bikeman' - I found them useful: 650B Conversion Guidlines

Hoopdriver

The point of converting a 700c bike to 650b is that the smaller wheels allow wider tires, which generally have a higher profile. I converted a 90s Bianchi road bike a few years ago and went from 25mm tires to 38mm. The difference in the wheel/tire diameter was about 1/2 inch (smaller for the 650b) so the BB height was about 1/4 less. Not all that significant.

jlaw

Re: BB height after conversion - looks like the consensus is that it's no big deal - just pay attention if you really lean the bike over in a high-speed curve while pedaling.

I converted a bike from 27" wheels to 650b and have not yet had a pedal strike - although I am generally not hammering down hill on curves.

I am a believer in 650b for certain bikes. I have only converted 1 bike but it is now my favorite because of the plush ride (38mm Panaracer Gravel Kings) that I get on a 'sport' frame.

If you buy or build a decent set of 650b wheels you can always keep them to try on other bikes if you do not like the results on your current bike. However, there is not a huge selection of rim-brake rims available for 650b. Fortunately, there are 2 or 3 good choices to try.

Andrew R Stewart 

Here's a recent thread on some of the same topic. https://www.bikeforums.net/bicycle-m...questions.html Andy

nfmisso

First of all, use ETRTO standards, and the math is then easy. 700c is 622mm BSD, 650b is 584mm BSD; (622-584)/2= 19mm about 3/4 inch for non-technical folks. Then take into account the tire size difference.

It would have to be a very special situation to convert from 622 to 584, and keep the same tire width.