I am burning so much fuel I am going to need a super tanker. We are running full ballast + 1800lbs more. I just figured out where my tach was, so I am not sure what are RPM at 10mph is, but it has to be around 4500. I would like to get it around 3200.

Should I go OJ945 15X13 or Acme 2419 at 15X12 ??