[Vekke]

Tested tires savonlinna route 100km:
Measured fuel consumption @ 100km/h gps speed/ speedo error/ trip error/ corrected values/tire model
235/65R17 6,2/2%/ 0%/6,2l Nokian hakkapeliitta 7 suv 6mm thread left 3,5 bar, studs removed (no hubcaps)
205/75R16 C 6,1/5,28%/3,28%/6,3l Nokian Hakka C2 205/75 R16C 113/111S, new tires 5,0 bar
225/70R16 5,6/4,2%/2,2%/5,72l Nokian Hakkapeliitta R 225/70R16 4mm thread left, 3,5 bar

Tested tires Lappeenranta route 51km:
235/65R17 5,9/2%/ 0%/5,9l Nokian hakkapeliitta 7 suv 6mm thread left 3,5 bar, studs removed (no hubcaps) temp 26,5 celsius

235/65R17 5,8/2%/ 0%/5,8l Nokian hakkapeliitta 7 suv 6mm thread left 3,5 bar, studs removed (with hubcaps) temp 24,5 celsius
Hubcab effect 1,7% with touareg oem 17" wheels. Hubcabs did not fill the whole wheel.

235/65R16C 5,7/5,77%/3,57%/5,9l Continental VanContact Eco 235/65 R16C 115/113R (with hubcaps) plus new mirrors and smoother upper grill block temp +18 celsius

235/65R16C 5,7/5,77%/3,57%/5,9l Continental VanContact Eco 235/65 R16C 115/113R (with hubcaps) plus new mirrors and smoother upper grill block. Siped my tires to halve the pattern. temp +14,5 celsius 5 m/s sidewind, Parks ligths on

235/65R16C 5,6/5,77%/3,57%/5,8l Continental VanContact Eco 235/65 R16C 115/113R (with hubcaps) plus new mirrors and smoother upper grill block. Siped my tires to halve the pattern. temp +15 celsius 3 m/s sidewind.

235/65R16C 5,5/5,77%/3,57%/5,7l Continental VanContact Eco 235/65 R16C 115/113R (with hubcaps) plus new mirrors and smoother upper grill block. Siped my tires to halve the pattern Adjusted rear front tire deflectors. temp +21 celsius 3 m/s sidewind

235/65R16C 5,5/5,77%/3,57%/5,7l Continental VanContact Eco 235/65 R16C 115/113R (with hubcaps) plus new mirrors and smoother upper grill block. Siped my tires to halve the pattern Adjusted rear front tire deflectors. Put on front lower A-arm plastics, smoothed front bumber lower parts and adjusted front tire deflectors. temp +21 celsius 3 m/s tailwind. Was wet road for 5km distance which dropped tyre temps in halfway of the test.

235/65R16C 5,4/5,77%/3,57%/5,6l Continental VanContact Eco 235/65 R16C 115/113R (with hubcaps) plus new mirrors and smoother upper grill block. Siped my tires to halve the pattern Adjusted rear front tire deflectors. Put on front lower A-arm plastics, smoothed front bumber lower parts and adjusted front tire deflectors. temp +22 celsius 2 m/s sidewind. Cutted smaller the rear tire deflectors heigth to about 60mm from body.

Tail/headwinds are worse for fuel economy than sidewinds based on my own testing. Reason is that max speed is increased more on headwinds that increace the fuel consumption more than what you gain by going "slower" on tailwinds.