Correcting Speedo after Wheel change.

X 2 on the recommendation to use powered graphite on the speedometer cable. Get it at Home Depot or Lowe's.

A general rule of thumb to correct a speedometer (assuming it was accurate before tire/gear change) is one tooth per 3 miles per hour. Using this rule, the transmission would need six fewer teeth on it. I'd prefer to use Tony's chart, however.