This calculator will take your existing 700c tire size and recommend a 650b tire size that keeps the overall Outer Tire Diameter (OTD) as close as possible, which minimizes changes to your bike’s handling and geometry.
700c to 650b Wheel Conversion
⚠️ **Warning:** Always check frame/fork clearance and brake alignment before riding. Rim brakes are usually incompatible.
How the Calculator Works
The calculator uses a simple mathematical principle to maintain your bike’s geometry:
- Define Rim Sizes: It uses the standard ISO metric rim diameters: 700c = 622mm and 650b = 584mm.
- Calculate Initial Outer Diameter (OTD): It takes your input 700c tire width and calculates the total diameter of your current setup
- Determine Required 650b Tire: It then calculates the required 650b tire width necessary to achieve that same OTD on the smaller 584mm rim.
- Suggest Nearest Common Size: Since tires aren’t sold in every possible 0.1mm size, it rounds the calculated requirement up to the nearest common 650b size (like 42mm,47mm, or 50mm).
- Calculate Geometry Change (BB Drop): It shows the final small difference between the old OTD and the new OTD. A positive difference means your bottom bracket (BB) will be lower (more stable, more pedal strikes).