Cross Turismo Roof Bars Pictures?

[Poshfpg]

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 . . .

If it helps I have Thule wingbar edge and Thule roofbox with the claws and on a long trip, bikes on the carrier too, I was getting 2.2mi/kWh in May v 2.8-3 generally on similar trips. Just with bikes I seem to get 2.6/2.7.

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[TDinDC]

Hey, look how I just did Not bad I would say for Thule aero bars and Porsche performance box pushed as far back as I could. Silent until 85 mph. Between 85 and 105, mild noise. I was on range mode for most but misbehaved in sport plus when needed to pass.

 

[McgR]

I have Thule wingbars and a Vector M box. Both look very aerodynamic. I find mine quite noisy above 100 km/h and almost annoying around 130 km/h. Last year I tried to go a bit faster in Germany and the noise seemed to decrease above 150 Km/h.

The reduced range is not so much the issue for me it is more the noise. Even with insulated glass. We are going to try to pack a bit lighter and go without roofbox this summer. Maybe take out the cover and pack till the roof.

I have wondered the same. Why did Porsche make the bars so high. If they are more silent I would consider buying them.

Another difference between both is that with Porsch they are leveled and with Thule they slope down 3 degrees with the roof.

I think for noise and drag it may be better if the air has more room between the box and the roof. But no expert on this either.

maybe @f1eng could have an opinion on this frame his race car engineering

 

[TDinDC]

I have Thule wingbars and a Vector M box. Both look very aerodynamic. I find mine quite noisy above 100 km/h and almost annoying around 130 km/h. Last year I tried to go a bit faster in Germany and the noise seemed to decrease above 150 Km/h.

The reduced range is not so much the issue for me it is more the noise. Even with insulated glass. We are going to try to pack a bit lighter and go without roofbox this summer. Maybe take out the cover and pack till the roof.

I have wondered the same. Why did Porsche make the bars so high. If they are more silent I would consider buying them.

Another difference between both is that with Porsch they are leveled and with Thule they slope down 3 degrees with the roof.

I think for noise and drag it may be better if the air has more room between the box and the roof. But no expert on this either.

maybe @f1eng could have an opinion on this frame his race car engineering

For what it’s worth, I think I have the same bars, but the Porsche performance box. Honestly, mine was not noticeable until above 145 kmh. Even then, it wasn’t unbearable but was definitely noticeable

 

[McgR]

For what it’s worth, I think I have the same bars, but the Porsche performance box. Honestly, mine was not noticeable until above 145 kmh. Even then, it wasn’t unbearable but was definitely noticeable

So I should buy the Porsche box. Quite a bit more expensive option ?. Maybe I should give it a try first.

 

[mikezhang31]

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.

"The drag penalty compared to the DrivAer model on its own is largely attributed to the stagnation that occurs on the IXTAbox surface, facing the car. For that reason it was found that sensitive parameters to the increase of CdA is both the height above the ground, as well as the size of the IXTAbox. "

Also i was thinking jokingly that if the box is too close to the roof, it will create a zone of compressed air at speed where you can ignite it and let it act as a scram jet lol

 

[f1eng]

maybe @f1eng could have an opinion on this frame his race car engineering

Anything which increases frontal area is bad. Anything making the wake bigger is very bad, so the shape of the top of the box and how it merges the flow into the flow over the car roof to keep it attached may be less bad.

I haven’t looked into the detail of what boxes are available since I don’t need one, and didn’t specify even the rails myself, to reduce drag!

Generally the front shape makes far less difference than you think and the top, sides and back, far more since keeping attached flow and a small wake makes the least drag.

 

[TDinDC]

So I should buy the Porsche box. Quite a bit more expensive option ?. Maybe I should give it a try first.

So, semi-interesting discovery. Yesterday, the box was empty, and it did start to make a noise above 85 mph/145 kmh.

Today, the box was full, and it made no appreciable noise all the way up to 110 mph/177 kmh. I think the noise yesterday was likely a vibration in the empty box that the load dampened or prevented from happening. Nice!

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