700C to 650B conversion tips

Things to be aware of when converting a 700c wheeled bike to 650b wheels.

  1. Hub spacing and axle type need to match or made to be compatible
  2. Front wheel axle type. My 650b wheels were 15mm through axle and the fork lowers were set up for 5mm quick releases so I had to get a reducer. The width is also important but most are 100mm but some are wider.
  3. The rear wheel hub spacing and axle type were 15mm screw in non quick release. I stayed within the same brand (Giant) so that helped since they matched.
  4. Clearance. Since I wasn’t converting a road bike frame with tight clearances to fat 650B tires everything fit fine as you can see. These are 2” wide tires. They are plenty wide for any application and only one 650b street tire is wider at 2.3”
  5. Hub and cassettes. I had a 9 speed cassette on the original 700c wheel but a 10 speed cassette on the 650b wheel. These have to match number of speeds and brand so I put the 9 speed cassette on the hub and it worked fine.
  6. If you change speeds from say Alvio 9 speed to Deore XT 11 speed, you will need a new shifter, chain, rear mech. Generally you would do this to get easier gearing since the 11 speed cassettes go up to 40, 42, 46 teeth!
  7. Brake rotor diameter has to be the same.
  8. Can usually find stock 650b wheels from your brand of bike for cheap from people who upgrade from aluminum wheels to carbon ones. I got pair for $120 with good tubes tires, cassette, and a screw release. Lots of deals on cl and eBay.

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What is the benefit of installing 650b wheels vs 700c wheels?

Giant has a good write up after years of research on this wheel size and in 2014 went all in on 27.5″ for their mountain bikes though in 2018 added more 29ers to their line.

  1. Lower center of gravity better handling.
  2. Lighter wheels.
  3. More cushion for the same overall diameter due to fatter 650b tires if you spec your tires as such.
  4. Faster acceleration.
  5. Easier to maneuver in tight spots like a switch back.

Harder to quantify, but I like the feel of 650B wheels better than a 26er or 700c wheeled bike. 700c wheeled bikes feel twitchy, this honestly has to do with the head tube angle being steeper on road bikes, but and I feel less in control on the 700c wheeled bike. I feel like I’m sitting too high up, like an SUV versus a sports car.

Disadvantages of 650b wheels compared to 700c?

  1. Lower B.B. height so higher risk of pedal strikes. This is only a problem if you pedal through a curve which I don’t.
  2. 650b has a smaller selection of road and street tires from Maxxis: 2.00″ 50-584, 1.65″ 42-584, and a 1.5″ 40-584 so 40mm, 42mm, and 50mm widths only. Schwalbe however has several 650b street tires from 25, 28, 30, 37, 40, 42, 44, and 50 mm widths with different tread patterns so you’re all set.
  3. 650b wheels don’t maintain momentum as well as 700c wheels
  4. 650b wheels don’t roll over bumps as well as 700c wheels. See this write up by Giant for a full explanation.

Changing speeds on a Shimano drivetrain?

  • 11 speeds: XTR 11-40, XT 11-40, 11-42, 11-46, SLX 11-40, 11-42, 11-46,
  • 10 Speeds: SLX 11-32, 11-34, 11-36, Deore 11-25T 12-28T 11-32T 11-34T, 11-36
  • 9 speeds: Alvio 11-25T, 11-28T, 11-32T, 11-34T, 12-36T

I’m currently running Alvio 11-34 with a 34 1x up front. I’m considering getting SLX 11-40 to get some easier gears and if it’s too easy then I’change the 34 to a 36 so I get a wide range. SLX rear mech $53, cassette $53, chain $25, shifter $30 so $160 for parts.