Smarttop rear window question

shpritz · 08-08-2008

Is it possible to have all the windows up when the top is down. With the windshot installed it would be great on chilly mornings to be able to put the back windows up as well as the fronts to keep the wind out while driving. I have the Smarttop module installed and was wondering if there was a code that allowed this.

DansSlk · 08-08-2008

Nah sorry mate

FallintoCouture · 08-08-2008

If only life were that great :-/ I always wished you could, because I bet there wouldn't be any wind if there were just a couple more inches of glass...

shpritz · 08-09-2008

It is hard to fathom that there isn't some way of hardwiring a switch that would allow you to somehow activate the rear windows to rise. The only thing would be that you would have to remember to lower them again before raising the roof. Anyone know of a manual switch that could be installed to achieve this???? Dan any thoughts?

DansSlk · 08-09-2008

You could use a switch provided you prevent power backflowing into the control unit and you have up/down limits on the windows otherwise you will at the very least put them out of alignment and possibly even burn out the motors if you get the timing of the stops wrong.

I know they are only small but i have to wonder why MB wants them down with the roof and what the wind pressing against them at speed will do to them when they don't have the support of the roof.

**richard_leeds** · 08-09-2008

Roof up, the window is supported top and bottom, so stress is proportionate to h/8. That's a bit simplistic, since the window is a triangle supported on 2 sides, from experience (ie an educated guess!) I'd go for h/12.

With the roof down, the window is a cantilevered triangle, so stress is proportionate to h/3.

Conclusion is that window up and roof down gives 4 times the stress.

There are also aerodynamic considerations, I imagine a blade in an open airflow will be subject to higher forces and dynamic loading than a window forming part of a closed shell.

.... Having said that, the rear window is the same thickness glass as the door window, and that's much bigger, hence much higher forces.

DansSlk · 08-09-2008

The main side windows in the doors also have a tougher support structure and they actually have the support of the A-pillar up to the level of the cross member, even with that they get some serious flex going at the rear at cruise.

**etyu** · 08-09-2008

Quote:

Originally Posted by DansSlk

The main side windows in the doors also have a tougher support structure and they actually have the support of the A-pillar up to the level of the cross member, even with that they get some serious flex going at the rear at cruise.

Is it therefore a preferred option to drive with the main windows down when the roof is retracted while going at freeways speeds e.g., 60mph/100kph? What about 80mph/128kph?

DansSlk · 08-09-2008

I think the main windows would be fine up at any speed to be honest mate, they are well mounted and about half the window gets support from the A frame as i said so i wouldn't worry about them getting damaged or causing any damage, its just the pressure at speed trying to peel them in and it causes them to flex about.

Merc designed the car to close them when the roof goes down so it stands to reason that they will have tested them to be sure they are safe in that config, I'm just worried about the smaller rears since they open by design and don't have the same sort of support.

08-08-2008	#1 (permalink)
shpritz SLK World Member Join Date: Jul 2007 Posts: 42 Country: Thanks: 4 Thanked 8 Times in 3 Posts	Smarttop rear window question Is it possible to have all the windows up when the top is down. With the windshot installed it would be great on chilly mornings to be able to put the back windows up as well as the fronts to keep the wind out while driving. I have the Smarttop module installed and was wondering if there was a code that allowed this.

08-08-2008	#2 (permalink)
DansSlk Dude Join Date: Jun 2006 Location: Wales Vehicle: 05 B55S (Brabus 6.1 S) Posts: 6,752 Country: Thanks: 96 Thanked 221 Times in 173 Posts	Nah sorry mate __________________ One thing you will learn with German cars - If it's simple it ain't happening.

08-09-2008	#5 (permalink)
DansSlk Dude Join Date: Jun 2006 Location: Wales Vehicle: 05 B55S (Brabus 6.1 S) Posts: 6,752 Country: Thanks: 96 Thanked 221 Times in 173 Posts	You could use a switch provided you prevent power backflowing into the control unit and you have up/down limits on the windows otherwise you will at the very least put them out of alignment and possibly even burn out the motors if you get the timing of the stops wrong. I know they are only small but i have to wonder why MB wants them down with the roof and what the wind pressing against them at speed will do to them when they don't have the support of the roof. __________________ One thing you will learn with German cars - If it's simple it ain't happening.

08-09-2008	#7 (permalink)
DansSlk Dude Join Date: Jun 2006 Location: Wales Vehicle: 05 B55S (Brabus 6.1 S) Posts: 6,752 Country: Thanks: 96 Thanked 221 Times in 173 Posts	The main side windows in the doors also have a tougher support structure and they actually have the support of the A-pillar up to the level of the cross member, even with that they get some serious flex going at the rear at cruise. __________________ One thing you will learn with German cars - If it's simple it ain't happening.

08-09-2008	#9 (permalink)
DansSlk Dude Join Date: Jun 2006 Location: Wales Vehicle: 05 B55S (Brabus 6.1 S) Posts: 6,752 Country: Thanks: 96 Thanked 221 Times in 173 Posts	I think the main windows would be fine up at any speed to be honest mate, they are well mounted and about half the window gets support from the A frame as i said so i wouldn't worry about them getting damaged or causing any damage, its just the pressure at speed trying to peel them in and it causes them to flex about. Merc designed the car to close them when the roof goes down so it stands to reason that they will have tested them to be sure they are safe in that config, I'm just worried about the smaller rears since they open by design and don't have the same sort of support. __________________ One thing you will learn with German cars - If it's simple it ain't happening.

08-08-2008	#3 (permalink)
FallintoCouture SLK World Member Join Date: Jun 2008 Location: Northern Bergen County, NJ Vehicle: Alabaster White 2005 SLK350 Other Toys: Firemist Red 2001 SLK320 & Black 2005 CLK320 - R.I.P. :-( Posts: 19 Country: Thanks: 0 Thanked 0 Times in 0 Posts	If only life were that great :-/ I always wished you could, because I bet there wouldn't be any wind if there were just a couple more inches of glass...

08-09-2008	#4 (permalink)
shpritz SLK World Member Join Date: Jul 2007 Posts: 42 Country: Thanks: 4 Thanked 8 Times in 3 Posts	It is hard to fathom that there isn't some way of hardwiring a switch that would allow you to somehow activate the rear windows to rise. The only thing would be that you would have to remember to lower them again before raising the roof. Anyone know of a manual switch that could be installed to achieve this???? Dan any thoughts?

08-09-2008	#6 (permalink)
richard_leeds Elite SLK World Member Join Date: Sep 2007 Location: Leeds, UK Vehicle: 05 350 Posts: 203 Country: Thanks: 12 Thanked 10 Times in 7 Posts	Roof up, the window is supported top and bottom, so stress is proportionate to h/8. That's a bit simplistic, since the window is a triangle supported on 2 sides, from experience (ie an educated guess!) I'd go for h/12. With the roof down, the window is a cantilevered triangle, so stress is proportionate to h/3. Conclusion is that window up and roof down gives 4 times the stress. There are also aerodynamic considerations, I imagine a blade in an open airflow will be subject to higher forces and dynamic loading than a window forming part of a closed shell. .... Having said that, the rear window is the same thickness glass as the door window, and that's much bigger, hence much higher forces.

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