Wow A Best ever MPG!

[theholycow]

Question: Is the hole inside necessary, or if the vehicle's sides were shaped that way and the rear window was at the back of it, would it still work as well? If that Metro's rear window was more vertical would that do the same job?

I always thought that the reason hatchbacks and wagons had the sloping rear window was to reduce drag, but the kammback essentially makes it shaped like an older one that's more straight.

[groar]

Thanks theholycow for the pictures I wrote my message rapidly as I had to deal with the baby

cautious : I'm only the owner of an aero book and read only a few random pages by now... This is my naive interpretation

The angle between airflow and horizontal mustn't be greater than some value (11? is often cited) else the airflow detaches from the car. The way the airflow detaches participates to the drag.

The kammback permits to lower the rear area where the airflow detaches from the car, and so to lower the drag. The longer is the kammback, the lower is the rear area and the lower is the drag.

Intuitively I would say that adding a vertical glass to the additional kammback on the metro will not change the aero. The case of strong side wind may be different, noticeably in a safety point of view. Now if a constructor designs a kammbacked car (prius, insight, c4 coup?...), they will certainly put the glass at the rear of the kammback to have additional internal room and a greater solidity.

Denis.

[theholycow]

That's interesting. So the design that's almost universal among hatchbacks and wagons (and pretty common among SUVs) is neither the most aerodynamic nor the most spacious. By sloping the roof a few degrees and letting the rear window stand straighter, it would be possible to both gain space and lower Cd.

This puts a whole new light on the Matrix/Vibe.



That seems to put the kammback shape on a wagon and have straighter rear glass, since there's nothing to lose aerodynamically and cargo space to gain.

I never really gave it much thought, and if you asked me I would have guessed results similar to the PT Cruiser...but searching our garage, I found a lot of great results from Vibes and Matrices. I did find a few surprising results from PT Cruisers, but it looks like the Vibe/Matrix generally does better.

[groar]

Originally Posted by theholycow

That's interesting. So the design that's almost universal among hatchbacks and wagons (and pretty common among SUVs) is neither the most aerodynamic nor the most spacious. By sloping the roof a few degrees and letting the rear window stand straighter, it would be possible to both gain space and lower Cd.

A few days ago in a parking I saw a woman trying to open the 5th door of her compact MPV (can't remember the model). She couldn't open it because another car was too close from her's. I thought that I would have been able to open the 5th door of my MPV (Renault scenic 2001). I then remarked that the rear glass of her car was vertical, so she was needing more space behind her car.

Looking at my car, the rear end is upward. From what I understand, this permits to add downforce to improve stability.



In both examples, I think it's usual compromises that are more useful to most people than a few percentage of aerodynamics.

Denis.

[collegekid01]

hmm so that's an interesting thought on the larger diameter tires. But I think the fact that they're snow tires with large tread and low rr is gonna nix any artificial gains I would see from that. plus like I said it's higher so more air under the car too. Let me find a pic of what I was talking about too. I was basically thinking of a small kamback

[collegekid01]

so I think I would build something like this... only a little bigger




and here's a bad example of what you see on production cars. I challenge you to start looking at these parts on the back of suv's and what not. especially on the ones that are more rounded at the back

[theholycow]

My VW has a small similar thing from the factory: