Video: Can Skinnier Tires Increase Fuel Economy?

[naplm00]

Also, if you are goin to these lenghths why not just repack the wheel bearings?

[orange4boy]

The testing done in the previous examples showed changes in the CD of the vehicles so in these cases it had nothing to do with rolling resistance.

In these cases it mainly has to do with frontal area. In most road vehicles all four tires can be considered part of the frontal area. Generally, the front tires do not shield the rear ones. This kind of favouable shielding or flow control can be partly achieved with side skirts like on Basjoos civic. Without this kind of flow control, under car air flows slightly outward from the centre line of the car approaching the wheels at a yaw angle of about 15 degrees for the front wheels (sometimes much higher) and at a lesser angle at the rear.

There may be changes in the RR of the tires with changes in aspect ratio but in these cases it was not measured.

[euromodder]

Originally Posted by Piwoslaw

Going from wide to narrow usually means that the tire is not as tall. Could the Cd change have been from the vehicle's body being slightly lower, closer to the ground?

Dunno about Poland, but if we want to change our tyres, we have to keep to within a few % of the original diameter.
In order to get the same diameter, there will be more rubber around the rim.