Your MPGs would improve slightly, my guess .5 ~ 2.0.
Do you have the standard size tires on your car? When I owned a 300D Turbo when the tires needed replacement I changed from over sized tires back to the factory recommended sizes and it upped the MPGs.
Compression contributes alot to MPG, have the valves been adjusted recently?
Keep us posted,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)