tire width vs. drag (Cd)

[ngrimm]

If I have two bicycles with the same tread but one with wide tires and the other with narrow tires, would doing a coast down comparison be a fair test of the theory?

[aerohead]

Originally Posted by ngrimm

If I have two bicycles with the same tread but one with wide tires and the other with narrow tires, would doing a coast down comparison be a fair test of the theory?

My opinion is that it would take a wind tunnel with extremely accurate load cells to be able to pull out the difference.Your own body is the largest drag contributor and its interference drag would play into at least the drag of the rear tire.
Technically however,the narrow tire would tunnel out with the lower CdA.

[tjts1]

There are several MB models where they specify different CD numbers for the base skinny tire version vs the optioned up big engine big tire version.
C220 coupe 0.24
C350 coupe 0.27

[aerohead]

Originally Posted by tjts1

There are several MB models where they specify different CD numbers for the base skinny tire version vs the optioned up big engine big tire version.
C220 coupe 0.24
C350 coupe 0.27

Yeah,my CRX was that way.Porsche 911s ditto.Trans Am Firebird.
One caveat.The wider tire may get it flush with the flanks of the car,reducing some turbulence,buying back some gain over the increase in frontal area.

[trooper Tdiesel]

comparing 33"X12.50X15 to 33"X9.50X15 tires on a older SUV with about 100hp.
the tires had the same tred lay out, and where very aggressive about 20/32" of tread.

there was on average a 3 mpg difference


0.01C

[MetroMPG]

Just adding this relevant tidbit to the thread for further consideration:

Toyota's latest Avalon was designed with weight reduction as a goal. It is 110 lbs lighter than its predecessor, which permits narrower tires to retain acceptable grip:

“Less mass makes Avalon more responsive and engaging near handling limits,” Katarzynski [Program Manager of Avalon Vehicle Development] explained. “Also, with less mass, less tire width is needed to reach competitive grip levels. The smaller width helps minimize drag losses to help enhance fuel economy, too.”

Source: Toyota's weight reduction strategy makes 2013 Avalon lighter, more fuel efficient

[camaroman101]

extra fact supporting the narrow tires,

the new malibu ls has a cd of .29 w/215s on 16s but the maibu eco has a cd of .30 because of the change to wider 225 on 17s

[Otto]

Seems like the wider tires cause the lion's share of increased drag, eclipsing reduced rolling resistance, if any.

Maybe we need to work on fairings for the tires, as an adjunct to belly pans, with an eye per Hucho's Calibra wind tunnel photo, which shows airflow hits the front tires at an oblique angle.

[CapriRacer]

Originally Posted by Otto

Seems like the wider tires cause the lion's share of increased drag, eclipsing reduced rolling resistance, if any.......

I don't know about that. My calculations say the opposite.

Barry's Tire Tech

Last bit on the page.

[ConnClark]

Reducing tire width isn't always going to give you a lower CD. If you go too narrow your wheel wells become big gaping holes in the side of your car that cause drag.