User blog comment:SuperSaiyan2Link/Swampert Stats/@comment-25993979-20160705004813

Meaning Swampert can run 60% of Dodtrio's speed, putting Swampert at 39.3mph.

60% is a little over half. 39 is much more than a little more than half of 40. a closer guesstimate would be 22-23 MPH