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. I'll be building a wheel using a Velocity USA dic hub.

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.

Wheels

• Velocity USA 'Road Disc' 130mm rear hub. 32 hole.
• Formula CL-91 Adapter Front 100mm hub. 32 hole
• Velocity USA 650B Blunt rims. 32 hole
• DT Standard 1.8x12mm Alloy Nipples.
• DT Competition 1.8/1.6/1.8 spokes.

The Fork

650B fork 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.

Since I need a light stiff fork with a minimum of 130mm of travel, my choices are poor.

Kirk Pacenti did have a run of White Brothers forks made specifically for the 650B wheels. I'm not really a fan of these forks, but at least something is available.

Rock Shox Pike forks have 42mm of offset and 130 and 140mm options. Tire clearance needs to be confirmed.

Marzocchi XC600 TST2 forks have 44mm of offset and a reported 140mm option. The XC700 ATA has 44mm offset and 100-140mm of travel. The 55 TST2 fork has 44mm offset a 140mm travel option but is heavy and clunky with it's 20mm thru axle. All of these forks need tire clearance confirmed.

Rumours of 2008 fox forx with 44mm offsets exist. The F29 is limited to 100mm of travel

The Print