I was wondering if the trunk deck spoiler that is standard on the HCH-II (it's on my 2006) creates more drag or less drag at highway speeds.

My first thought was that it would add more drag. But then maybe it actually reduces drag by reducing turbulence at the rear of the car.

Has anyone looked into this?

I'm sure Honda did, which is why they put the spoiler on there. It's not there for looks.

2006 HCH Alabaster Silver w/Navi
2003 Honda Accord LX

I agree, if they wanted it to be for looks, they would have used the same one offered on the standard Civic, instead of engineering a different one.

I do think it looks much nicer than the standard Civic spoiler.

I think it directs the air to leave the car more easily instead of being sucked into eddy currents behind the car.

Need fewer troops to support.
Drive a hybrid.
Best tank 71.65 MPG.

Before this car I spent two years learning hypermiling on my 2004 HCH1.

Things like this sometimes have unexpected results. While it may appear to create drag, it probably reduces drag.

A recent mythbusters did a report on pickup truck tailgates, and they found that they get better mileage with the tailgate up. Putting the tailgate down or replacing it with a net, which one might assume would reduce drag, actually increases drag. Why? Because the bubble of cycling turbulent air that develops in the truck bed with the tailgate up actually acts like an air pillow that deflects air coming over the cab. Strange and unexpected. Things are not always what they seem.

My car is all of one week old! What is very noticeable is that after rain the front, roof and sides are still spotless but the tail end, number plate, trunk lock etc., are really dirty. I have never experienced this with a car before and I think the spoiler creates a minor vacuum behind the car allowing the front to cut its way through the world.

One thing is certain, Honda will have had it or a model in the wind tunnel for analysis!

Most likely it is reducing drag. Small lip spoilers like that are generally put there to help clean up the air flowing off the trunk. The only way to really know for sure is to
1. Talk to a honda aero engineer that worked on the hch
2. put the car in a wind tunnel
3. get a 3d model of the car and use CFD (computational fluid dynamics, program like Fluent) to analyze the effects of the spoiler on the boundry layer over the rear of the car. These programs can do wonders for aero engineers, once you have a model you can see exactly where your turbulent areas are.

You'd be amazed at the amount of aero work that is put into cars these days. The under tray helps maintain a cleaner flow of air under the car. This is why most cars these days are starting to use those under trays. You will also see a lot more rear diffusers on sportier cars, they not only clean up the air flow but help reduce the low pressure area behind the car. They are generally used to help create negative lift (aka downforce) on performance cars. The dirty trunk is most likely a result of the "dirty" air behind the car.

06 HCH Mag. Pearl w/o Nav
05 wrx STi

Ricer spoiler placed on an HCH 1 spotted on I-10 this past week (LA area). You know who you are, 'fess up!

It was the funniest, trashy thing I have seen on a honda yet. That's saying alot considering the tin cans that pass for tail pipes...

Jesse

'06 HCH II w/Navi
'01 S2000

I agree it has to be useful in a positive way...if it wasn't they wouldn't have incurred the additional expense.

Retired: 2/11/06

Of course it's useful, it makes them look cool! (actually looks stupid and wasteful, but such is the folly of youth...)