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For use with Mr Whirly cranks or super tough rings for any standard 58 BCD fitting
£29.50
When buying chainrings you need to know the BCD aka Bolt Circle Diameter. This is the measurement of an imaginary circle on the chainring hitting all the bolt holes. The best way to calculate this is by measuring the exact distance (center to center) between 2 neighbouring bolt holes. Then find that number on the correct chart below to determine the BCD for your chainring and cranks...
| BCD chart for 5-bolt chainrings | |
| Bolt to Bolt (measure center to center) | BCD Bolt Circle Diameter |
| 32.9mm | 56mm |
| 34.3mm | 58mm |
| 43.5mm | 74mm |
| 55.4mm | 94mm |
| 64.7mm | 110mm |
| 76.4mm | 130mm |
| 79.5mm | 135mm |
| 84.6mm | 144mm |
| BCD chart for 4-bolt chainring | |
| Bolt to Bolt (measure center to center) | BCD Bolt Circle Diameter |
| 41mm | 58mm |
| 45.3mm | 64mm |
| 48.1mm | 68mm |
| 73.6mm | 104mm |
| 79.2mm | 112mm |
Choose your ring size below...