Cross Turismo Roof Bars Pictures?

[WasserGKuehlt]

@WasserGKuehlt - would you mind measuring the actual bar width of the rear bar? The space between the boots, I'm trying to work out if my box will fit. I think my box is too wide for the actual width of the Thule bar. It seems the advantage of the Porsche system is that the feet are smaller horizontally so you have more bar to play with.

Looks like ~73cm - measured underneath the bar, from the edge one foot to the other. That's effectively the longest "clamping" span (as usually that's not adjustable for a given roof box); the top of the bar has more length available for a box to rest on it.

Here's a pic illustrating the measurement, and one with a detail of the underside of the bar.

HTH.

 

[Rusk]

Great, thank you. My box uses the T mount so I'm only worried about the useable width of the top side of the bar. From you pics I'm guessing it is about 80cm?

 

[WasserGKuehlt]

Great, thank you. My box uses the T mount so I'm only worried about the useable width of the top side of the bar. From you pics I'm guessing it is about 80cm?

I’d say you have about 7cm on either side, so 87cm total?

 

[Rusk]

I’d say you have about 7cm on either side, so 87cm total?

Then that is about perfect as my box is about 85cm wide total with the distance of the T mount in the rear being 55cm.

So, as much as I prefer the Thule lower profile and mounting method it looks like I will need the Porsche OEM bars.

I wish they came in black not just silver!!!!!

Thanks for all the help WasserGKuehlt

 

[Rusk]

Well it seem it is a very good job I went with OEM bars not the Thule ones as my box only just fits on with 3cm either side at the rear space!

Family wagon all ready for a holiday to north Wales. First trip with the EV and it is a barren wasteland in terms of charges after about Chester. Plan is to max charge at Chester Porsche and then hope the caravan can handle a slow charge for a few days

 

[ciaranob]

@Rusk
Remember you can always reset the opening height of the rear hatch if you feel its a bit too close or if you wanted to set the box slightly further back.

(Open hatch - manually set height - press and hold close key on remote or close and lock on door - hear a beep and its set).

 

[McgR]

Well it seem it is a very good job I went with OEM bars not the Thule ones as my box only just fits on with 3cm either side at the rear space!

Family wagon all ready for a holiday to north Wales. First trip with the EV and it is a barren wasteland in terms of charges after about Chester. Plan is to max charge at Chester Porsche and then hope the caravan can handle a slow charge for a few days

Like mentioned by @ciaranob I would shift it to the back. Should be more silent and stable. I did the same and you the decreased opening of the hatch is not a big issue.

Could you comment on wind noise? Mine is quite noticeable around 130 kmh with Thule. I wonder if it might be worse because it is closer to the roof.

 

[TDinDC]

Does anyone know the real aerodynamic impact of placement of the box on the car?

Aerodynamics do not seem to me to be naturally intuitive. Instinct tells me that we should move the box back as far as possible to improve aerodynamics. I don't mind adjusting the lift position for the hatch, but does moving it back really have a material impact? How can we find out? Is there anything out there about the ideal placement to maximize range? I place mine back far enough that I don't need to adjust the rear hatch. I have the Porsche high speed box and Thule bars, so I would expect Porsche to tell us about ideal placement, but, shocker, they say nothing. anyone know?

If I were "guessing" I would move this back so that the rear was lined up with the back of the black spoiler, which would really limit the ability to open the rear hatch, but would that matter? I mean, supposedly, the high speed box is optimized for aero, but why don't they provide info on ideal placement?

Gratuitous comment . . . I view cars like precision tools so I don't buy for aesthetics (e.g., I'm down with Toyota Sienna minivans -- apart from the sh@t brakes), but damn I think my Mamba station wagon looks bad @ss.

 

[Rusk]

Could you comment on wind noise? Mine is quite noticeable around 130 kmh with Thule. I wonder if it might be worse because it is closer to the roof.

it is obviously there and you can hear it but it really isn’t bad. I guess we’ve got used to the quietness of the Taycan so maybe people will notice it more. I really didn’t mind it. I also have a streamlined box so that helps with the wind.

 

[Rusk]

Oh and I should mention that I had our two and four year olds in the car so between the laughing, crying, shouting, playing, any animal sound that we see on the way and singing it is kinda hard to hear anything so maybe I can judge the wind noise too much

 

[Rusk]

I cannot stop looking at this thing, it’s so beautiful. On top of that it is amazingly practical considering what it is. Lots of people laughed at me for moving from an SUV to this as the family car but it’s working perfectly so far.

 

[TDinDC]

So, the second time around is so much easier. This is as far back as the box hooks allow me to go. I had to adjust hatch a bit, but honestly not as much as I had anticipated.

I do have a question. Not being an aero engineer, I assume that having the box as far back and as close to the roof as possible is ideal for range, stability and noise minimization. If that is true, why are the Porsche bars so high from the roof? It’s a pretty big difference. Is there a reason why that would be better for some reason?

 

[TDinDC]

So, I think I am on to something about the importance of the gap between the roof box and the car's roof. See this:

"Furthermore, it has been shown that the position of the roof box is a sensitive parameter to both Cd and Cl where Examining influence of a rooftop cargo carrier position on automobile aerodynamics found that the drag change compared to a base case of DrivAer estateback + roof box similar to what is denoted as Roof Box Cargo in this thesis, could be almost 30%. The primary reason was found to be that the interference drag between car wake and box wake can almost be removed if placed correctly, the essential parameter was the airflow between car roof and box bottom, which, if designed correctly, could shield the two wakes from each other[12]. This is not something that has been studied in this thesis regarding the two roof boxes due to time constraints. Thus one should take the values with a pinch of salt, however, the results found in this thesis fall into the same range as presented in Aerodynamics of Road Vehicles[8] and are deemed reasonable, and gives good insight to which phenomena that increase drag the most, and the differences between a roof box, and an IXTAbox."

"Reliable data on the impact on roof boxes is hard to find, the book Aerodynamics of Vehicles mention a 33% increase of Cd [8] for a roof box with luggage racks, but not much more information is given. For this reason, it was of interest to compare how two potential roof box models would compare, the results are reported in table 5.1. When comparing the reference only using the DrivAer Notchback to how the drag force increase when putting a roof box on top of the car, it is concluded that the adverse effects on the roof box is double-edged, as both the area and drag increase the power consumption significantly. By comparing the roof boxes to the reference, it can be seen that there are two primary reasons why Cd increase, the first reason is that the pressure recovery on the back window that could be seen for the car on its own, was negatively influenced by the roof box. The second reason is that it creates its own wake behind the box, as well as second stagnation point on the front of the box. Furthermore one can start to understand why roof boxes can pose a problem to the driver, it was discussed in section 3 on instabilities when using roof boxes. As the pressure on the surfaces of the car and a roof box change magnitude, the driving experience will be different compared to only using the car, as the direction of the force vectors acting on the car change. The drag force will likely increase the angle between the horizontal line as more wake is induced higher up on the test object, as well as the back window. Furthermore when introducing side winds, the moment will increase as the push occur at a much longer length away from the center of mass."

Aerodynamic study of vehicle mounted cargo boxeschalmers.sehttps://odr.chalmers.se › bitstream

Still not entirely clear on whether having flow between roof box and roof of car is good or bad, but this is interesting. I will have to do a comparison using both the Thule low profile and the Porsche high profile.

 

[WasserGKuehlt]

I’m not an aerodynamicist either (I did watch an F1 race once), but I think it’s not as simple as whether air flow between the box and the roof is desirable or not. What you don’t want is a bag of things: minimize turbulent air flow, minimize noise level/eliminate problematic frequencies (no whistling), optimize the impact on range vs usefulness of a big box up there, and, not least, allow for operational flexibility and safety (you need to be able to secure the damn thing to the roof cross bars somehow -> clearance). That said, laminar air flow between the box and the roof can’t hurt - downforce is not essential, especially in a 5k lb car driven on average at 35mph.

 

[TDinDC]

I’m not an aerodynamicist either (I did watch an F1 race once), but I think it’s not as simple as whether air flow between the box and the roof is desirable or not. What you don’t want is a bag of things: minimize turbulent air flow, minimize noise level/eliminate problematic frequencies (no whistling), optimize the impact on range vs usefulness of a big box up there, and, not least, allow for operational flexibility and safety (you need to be able to secure the damn thing to the roof cross bars somehow -> clearance). That said, laminar air flow between the box and the roof can’t hurt - downforce is not essential, especially in a 5k lb car driven on average at 35mph.

Yes exactly, which is why I’m mildly obsessed with wanting to know why Porsche made its cross bars sit so high as compared to the Thule. I wish we could do a test to compare impact of using Porsche crossbars versus Thule crossbars on range and noise . . .

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