Switching to 650B

I am considering fitting a pair of 650B wheels to my 700C-wheeled Planet-X London Road hybrid to extend its capability on canal towpaths etc. Perhaps Mavic Crossrides with Grand Bois Cyprès (32mm), Lierre (38mm) or Hêtre (42mm) tyres. As a 650B expert, I'm wondering if you could advise if these are reasonable options.

Mike Young

The Grand Bois Hêtre is a great choice for this purpose, as is the Lierre. There are, however, two obstacles. Firstly, both tyres are smaller in radius than a 700fi23c tyre, by about 10mm and 15mm respectively. This will lower your bottom bracket height by the same amount, which may or may not cause problems with pedal clearance depending on crank length, pedal type and terrain. The stated BB drop of 70mm translates to a BB height of 260mm with the Hêtre.

Secondly, while the London Road’s fork may have enough clearance for 650fi42B tyres, the chainstays may not. If that's the case, why not try 700C wheels fitted with the 700fi32C version of the Cyprès? 

Richard Hallett, Cycle Technical Editor

This Q&A was published in 'Cycle' the magazine for members of Cycling UK. To contact the experts, email your technical, health, legal or policy questions to editor@cyclinguk.org or write to Cycle Q&A, PO Box 313, Scarborough, YO12 6WZ