PVD 650B

650B

A standard 26x2.2" wheel has a diameter of approximately 670mm. A 650B wheel with one of Pacenti's 2.3" 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 changed 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. Actual weight (no QR) - 349g.
  

The dished wheel.

• Formula CL-91 Adapter Front 100mm hub. 32 hole
  

-Flange Distance from Center: L- 27.5mm, R- 17.5mm
-Pitch Circle Diameter: L- 44.5mm, R- 44.5mm
-Spoke Hole Diameter: 2.5mm

• Velocity USA 650B Blunt rims. ISO 44-584. 32 hole. 560 ERD. Claimed weight 459g. Actual weight 464.8g. This is a 53.7 gram reduction from my usual rim, the mavic tubeless 819 disc rim (518.5g. with special nipple nipples). This will help offset the increased rolling weight of the larger wheels.
  

• DT Standard 1.8x12mm Alloy Nipples.

• DT Competition 1.8/1.6/1.8 spokes. Rear, 270mm both sides. Front, ???. Using the online DT spoke calculator produced the 270mm spoke numbers for the rear wheel. After fully tensioning the wheel, It was clear that the spokes should have been longer, 272 or 273mm. I am tired of the DT calculator producing off spoke lengths and will find another system.

Front spokes calculated to be 272mm left, 271mm right.

Tires

Only one choice exists at this point (9/25/08) Pacenti Neo-Moto 2.3" (formerly known as Baby Bear), 584x58, actual weighed sample - 715.3 grams. Kinda like a Kenda Nevegal, the best 26" tire ever. Would be better if this tire was 2.1" and UST with a hearty carcas.

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. Although the Fox F120 RL from a G2 Hi-Fi is reported to be 46mm offset, clearance needs checking.

The Print

Tubes and Parts

• Down Tube - Nova 29er DT 35 x 8/5/8 $16.20
• Seat Tube - NOVA EXTERNAL BUTT SEAT TUBE 28.6 X 460 $13.80
• Top Tube - Tange Pretige DT 28.6 X 7/4/7 X 650 $24.54
• Chain Stays - NOVA CRMO 22MM OVAL 425 - 12 DEGREE BEND $18.50
• Seat Stays - DEDACCIAI 12.5 16mm X 0.6 SINGLE TAPER 560 $18.71
  
  

• Paragon Slider-light dropouts.
• Paragon 1.5" bb shell, 68mm wide. I really need to start using 72mm bb's.
• Pacenti SS StampedHydo Stops:Bikelugs.com
• PVD Integrated IS Head Tube

• 27.2 Seat post

The Ride

The improved geometry from my last 26 inch bike made a huge difference climing. 69.5 degree head and the 12.25" bb height makes a night and day difference.

I was right away comfortable with the wheel size. It's not a dramatic change. It still seems like a 26, only meatier.

Riding the 650B wheels is much like riding a set of heavy 26 inch wheels. A slightly sluggish feel on accelleration and once up to speed, a very powerfull feel. It's hard to tell if a real improvement is gained by the wheel size. The difference is not amazing. It's very subtle.

I wish that some 2.1" versions of the same tread was available in a UST tubeless version. The 2.3" tire is just too big.

Rear tire clearance and front derailure clearance are huge issues to deal with. This is the hardest thing to deal with with these wheels.

130mm rear spacing was indeed a mistake. I will be respacing it to 135 once I get another wheel. Chainline is lame. The 2x9 gearing needs some refining...I think.

My Rock Shox Revelation did not have enough clearance for the larger tire. I had to use the Fox Float 140, not as good.

Sadly, on the thrid ride, the rear tire sidewall got slashed. The slash was huge, about 1.5" long. I have not had this kind of problem in years. The Kenda UST tires that I'm used to would never have done this. These tires really need to get something more stout for a carcass and sidewall.

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