You are probably running those tires under-inflated especially for the rear. That tire needs the full 50 psi for the 1520 pound load capacity. The problem is the heat generated by the stiff sidewalls flexing. That tire only has a 95 load index. For highway travel a 205/70-14XL with the 97 or 98 load index would actually be a better choice.  

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Dan N
Sent: Friday, September 11, 2015 11:24 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Highway driving

1990 Carat - rebuilt WBX - 27x8.5 R14 General AT2 - 40psi Front, 45psi Rear

fully loaded for long trip - average 20 mpg on highway - 18 mpg on other roads - average speed 62 to 65 mph @ 3400 to 3600 rpm