Honda Asymmetrical Wheel Hole Pattern; Why?
 

I was looking closely at the aero details on a Honda Fit yesterday.
When I looked closely at the wheels, I could hardly believe what I saw:
Ten large holes on one side, nine smaller ones on the other.
Irregular spacing of the smaller holes too: (Click to enlarge.)

Attachment 7025

Attachment 7026

Why is the hole pattern in the steel wheels asymmetrical?

The wheel is covered by a wheel cover, so I doubt it is directly aero related.
To reduce wind noise created by the wheel spinning?
To minimize structural resonance in the wheel itself?

If the latter, what about the untold millions of symmetrically holed steel
wheels on the road?

:confused:

Somewhat related thread: Why do most wheels have 5 spokes?

The devil is in the details. :rolleyes:

That is pretty odd -- where is the valve stem? I can't think that is could relate to balance -- are all four wheels this way?

I only looked at the two wheels on the drivers side. I don't know for sure,
but presume they were the same on the pax side.

(Folks don't like it when you prowl around their car, and look at it closely for
a longish time. They think you're scoping it out for a break in. Don't ask me
how I know. That time the security guard did buy my "Just looking at aero
details, Sir." story. :o
"Move along now." )

I think it was a 2010, it was very shiny with no chips or scratches... yet.

I poked all 'round the 'Net -- official Honda sites, Fit sites, etc -- looking for
info on this and have found none. The pix are of wheels for sale from the
'Net though.

Apparently, there have been many different wheels on the different levels of
the Fit over the years, many of them alloy. There have been other steelies
that have symetrical holes. This is allegedly on a Fit: (Pix from the 'Net.)

http://img26.imageshack.us/img26/4358/wintertire.jpg

The earlier pix were taken from the inside/backside of the wheel.
I guess the hole for the valve stem is in the cylindrical rim itself,
on the other side of the perforated disk.
(In the picture above, the valve is at 6 o'clock.)

That's all that I know at this point.

Could the asymmetrical hole pattern have something to do with
breaking up/randomizing the airflow through the wheel and minimizing
the turbulence downstream of the wheel wells?

The wheel cover had a five spoke arrangement, and the hole pattern roughly
divides the wheel in half. I guess you could get three or five different hole
arrangements/net hole areas in the five wheel cover openings.
If this is the reason, would it hurt or help aero to take the wheel covers off?

Inquiring minds are bebaffled, bebothered, and bewildered. :confused:

Interesting.

All I know is, you see asymetric blades on alternator fans for noise reduction...

Studies have shown brake rotors with 31 37 or 41 cooling vanes are quieter and smoother than non prime number vaned rotors.

Prime numbers are going to greatly diminish the even (and odd?) order harmonics, which are harsher on our ears.

My guess is to balance the tire pressure sensor mounted at the valve stem.

Ditto that, plus the prime number noise thing just because it sounds so plausible. :thumbup:

The second picture, with symmetric holes, looks like a generic rim - something one would purchase to mount winter tires for example.

Must be for wind noise.

My brother's 2010 Fit has these asymmetrical wheels, too. Still no closer to knowing why -- to vary the air flow through to the brakes? I wonder if the rims are out of balance -- it would not make sense if they were?

I vote for balance too. I doubt they would worry that much about wind noise on their entry model car, but a heavy sensor is going to make it a PITB for tyre fitters and be more of a problem for most owners.

Having tapped that I would also expect a dab of paint or something similar to indicate the best position of the wheel on the hub for balance.

Back in the good old days of British Leyland Mk2 (aka Austin-Rover) they used to balance the wheel on the hub and then mark the best position.

EDIT : Entry level - FIT of course, but the same issue applies - balance is more likely to be an issue.

I'm now leaning towards the balance idea too. Here's why...

I got to thinking that every OEM rim now must have the TPMS sensors. They
have significant mass, yet my wheels on my Touring model Prius -- 7
spoke wheels -- do not have a bunch of balance weights opposite the valve
stem. The rim section of the wheel is apparently trued on a lathe, little
chance for asymmetrical thickness there.

So I looked/felt around the spokes adjacent to the valve, and the spoke
directly across from the valve.

Surprise! The webs on the back of the spoke somewhat thicker than those
adjacent to the valve. (Note: The spoke essentially has the shape of a
"C-section" beam, kinda' like this: [ with the wide flat web facing outward,
the two flanges inward.)

Maybe this is to balance the mass of the TPMS sensor.

It remains for others to do a similar check on their alloy rims to see if this
feature/construction is widely used.

Edit: I just realized the balancing material in the opposite spoke/s could
also be in the thickness of the web... harder to find/measure.

well rokeby take the sensor out and see if the tire turns funny lol.