PVD 650B

650B

A standard 26x2.2" wheel has a diameter of approximately 670mm. A 650B wheel with on of Pacenti's tires has a diameter of approximately 702mm. A 4.7% increase in diameter. A 29x2.2 wheel diameter is about 736mm, a 9.8% increase in diameter. 29" wheels are really to big for all around riding, the 650B may be an improvement. Only testing can say.

2x9 or 3x9

I like 2x9 gearing. It works well enough for all around riding, but makes me hit the pedals a little harder and more efficiently in general.

One real key to doing a nice 2x9 configuraion is by using a 130mm rear hub. Disc versions of these hubs are just starting to become available.

On a 26" bike, I've tended to run a 2x9 with 39-26 up front and an 11-32 cassette in the rear. This translates to a range of developement between 294.1 and 67.4 inches.

On a 650B bike, this gearing would be corrected to 36-24 up front with the same 11-32 cassette. The development range here would be 284.2 and 65.1 inches, a little wider which may be better and better front shifting. If 284.2 is too low, a 38 tooth ring could be used to increase maximum development to 299.9 inches.

Now the problem is chainrings. 104mm 4 bolt is the most popular choice for MTB. 2008 Shimano XT rings are incredible, but not available in the sizes that I need. Race Face Racerings are available in 36, 24, and 26 so I should be good there.

If staying with 3X9, stock 26" bike rings of 44-32-22 would have to be chainged to 42-30-20. That 30 tooth ring is not availble for 104BC cranks. This is when hard decisions need to be made.

The Fork

650B forks options face 2 challenges. Wheel clearance and offset.

26" wheel forks may be able to fit the 650B tire, but arch and crown clearance can go down to less than 1/4". Test fits are required to ensure a fork will work.

With regard to offsett, a fork with a 44-45mm offset is required to keep mechanical trail within reason.