Side mirror drag & effect on fuel economy - quantified

[MetroMPG]

Just picked up 2 of those round convex mirrors. Depending where you mount them, they could work fine.

One small problem with convex mirrors (particularly those round ones) is your vision has to adjust to their focal length. So on the driver's side, it takes a split second longer to check than glancing at a flat mirror (or even a mildly convex passenger mirror). Not a huge deal, but there you go.

[MetroMPG]

Are external mirrors legally required?

This question prompted me to check, and lo and behold, in Ontario...

66. (1) Every motor vehicle other than a motorcycle shall be equipped with [...] a mirror or mirrors securely attached to the vehicle and placed in such a position as to afford the driver a clearly reflected view of the roadway in the rear, or of any vehicle approaching from the rear. R.S.O. 1990, c. H.8, s. 66 (1).

[MetroMPG]

I wouldn't remove my driver's side mirror.

Occasionally folded back is a good compromise and will prove useful I'm sure when I need to use it to see behind (as opposed to beside, which the convex mirror mounted inside the car permits).

And knowing the law, now I don't have to re-deploy the mirror in a panic when I see the police (which I did today).

[MetroMPG]

I had near perfect weather conditions for doing a little experiment: light north winds, which are blocked by a ridge and tree line that runs along the north side of my usual "test" road, leaving the road in nearly still air.

I did an A-B-A, where A = both mirrors on, and B = passenger mirror off (with the hole covered) and driver's mirror folded, with my aero hinge insert in place (see pics, earlier in this thread).

Speed was 88 km/h / 54.7 mph, cruise control set once, cancelled with the brake and resumed for each pass. (Yes, an odd speed choice. I tried to set the cruise control right at 90k, but didn't quite make it. )

55.25 mpg (US) - average of first A runs (2 bi-directional runs)

56.51 mpg (US) - average of B runs (2 bi-directional runs)

55.04 mpg (US) - average of last A runs (1 bi-directional run)

For an average difference of 1.27 mpg between all A and B runs, or an increase in FE of 2.3% at this speed, for this car. Not quite the 2.94 mpg 5.19% improvement estimated earlier in this thread (for just one mirror removed!). But also not insignificant.

So there you go.

[MetroMPG]

FYI for those following this thread, I've posted a summary of the mirror information & road test on metrompg.com, correcting some of my sloppy pre-test drag estimates in the process:

Reflections on side mirrors: testing drag vs. MPG

[krousdb]

Ditto on the Prius....


I'm hoping Franklin at hybrid effects can make a A pillar cover to replace the OEM one that has the thingy sticking out.....



Although it takes time focusing, I can see headlights in both the rear and internal side view mirror simultaneously.

[Hybrid Effects]

Taking notes ,drivers side mirror cover

I really wish I was not having such a hard time finding cars that I can prototype on.

Franklin

[krousdb]

Originally Posted by Hybrid Effects

Taking notes ,drivers side mirror cover
Franklin

Actually, I was hoping for a passenger side mirror cover.

[dremd]

I wonder how much difference could be had from fitting more aerodynamic mirrors, rather than replacing them.

Reason I mention this is my 91 Celica GTS had/has very aero looking mirriors. Let me try and dig up a pic.

[krousdb]

Removing a mirror will reduce frontal area as well as lowering the Cd. A more aerodynamic mirror would only lower the Cd.