Found this online:
"You can find the speed for the maximum lift to drag ratio (L/Dmax) right in your Pilot's Operating Handbook (if you have one). Look under emergency procedures for engine failure. Find the recommended glide speed for maximum range. This glide speed is the speed for L/Dmax (I'll save you the derivation). This speed also corresponds to the bottom of the drag polar. After all, if lift is a constant for level flight, L/Dmax will occur at the minimum drag. According to Carson, these three speeds are related by factors of about 1.316. So this means:
Vmax endurance = Best Glide Speed ÷ 1.316
Vmax range = Best Glide Speed
Voptimum cruise = (Best Glide Speed) * 1.316
So now you can find these speeds for your airplane."
Here's the link to the complete article. Came from EAA website.
Maximum Endurance, Maximum Range, and Optimum Cruise Speeds