If you dont know the wheel radius, or cant be bothered to go and measure, fill in the tyre width/profile and rim diameter, hit calculate and then copy the number you get from the radius calculation, return to this page and paste the radius in. If you are unsure as to which gearbox you have then these links might help Nova gearboxes Corsa B Gearboxes Corsa C Gearboxes Big block boxes Mk4 Astra Boxes Box ID (F number and FD id)

With regards to the F20 choices, its only 5th and the FD thats different between the 3.

Also bear in mind that using the tyre profile info will yield a larger radius than if you were to measure it since it assumes that you have tyre pressure to hold it perfectly square.

If you wish to use your own gear ratios please click HERE

  Units  
   

Use Tyre Size rather than Wheel Radius

Use Wheel Radius (ive gone and measured it)

 
Wheel Radius mm (centre of wheel to the floor)
     
     
GearBox  
Final Drive Ratio  
   
Tyre Width mm
Tyre Profile %
Rim Diameter Inches
     
Rev Limit Rpm

DISCLAIMER : If you get caught for speeding and then try to blame this calculator its not my fault. This relies on the fact that your revs and wheel size is accurate... its purely for indication purposes only.

Thank you.

If you wish to Email me, please do so here