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08-11-2015 11:07 AM - permalink

cycleguy55

My thought was to mount 6 (or so) angle aluminum tabs (1" x 1" angle, cut 1" long) to the roll bar, using rivnuts. The Lexan, Duraplex (or similar) sheet would be mounted to the tabs with 1/4" bolts through rubber or vinyl grommets.

08-12-2015 02:14 PM - permalink

Xack

I hear you on the angle tabs. Consider this, What about a square bar of aluminum along the top, underside where the roll bar is straight. Also a bar on both inside vertical sides where the roll bar is also straight. Countersink/drill the bar so you can hide the screw or bolt heads. Then you have a flat surfaces to mount the window to the back. You can drill and tap the aluminum to hold the mount screws and keep it all clean. You can also use the back underside top of the glass to mount a 3rd brake light and make it look less like an afterthought. The added aluminum bracketing should strengthen the roll bar, not degrade it.

08-13-2015 11:12 AM - permalink

cycleguy55

One thing I have noticed about most OEM wind blockers (e.g. BMW, Mercedes, etc.) is they're not solid - they're typically made of a fabric screen of some type. It would seem they're trying to block the worst of it, not all of it, so I'm not concerned about getting the Lexan tight to the roll bar, even a 1/4" or 1/2" gap would let some air through and perhaps relieve pressure that might otherwise occur from air 'trapped' against the roll bar or body. I may even go looking for a material similar to what the OEM screens are made of and have a soft screen I can un-fasten, roll up and tuck away when I don't need it.

08-13-2015 03:13 PM - permalink

BOBOCobra

Cycle, I did the fabric screen and hated it. I got the idea from my wife's MB and had one made and its sitting in the garage on the bench. Regarding the air flow, you are 100% correct. I typed up an explanation the other day and the forum limits my characters and I did not have time to do it again in separate posts. Bottom line is you need to let some air in to break the negative pressure in the cabin. If you don't it will hammer/whistle/buffet and drive you crazy. I made several test screens and it was very interesting what I found. This assumes you have wind wings positioned correctly. If you don't there is no point having a back screen because the side air gets pulled right in on your face. Remember as the air flows over the front screen it creates a negative pressure in the cabin, just like an air dam does under your radiator on your old factory muscle cars. that negative pressure wants to equalize as quick as it can on your head, face and neck.

08-13-2015 06:01 PM - permalink

Xack

A gap in the glass to roll bar is not going to be a factor. The reason is there is nothing to trap air. Any pressure is going to force air around the roll bar. There is open space on the other side of the bar. If the gap makes any difference I would be greatly surprised.

Edit: Perhaps my comment was assuming and indifferent. I do not mean to argue, The physics involved puzzles me and my assumptions could very well be wrong. It would be nice if we could do a quick test when the time is right for BOBO to use some indoor masking tape, or some sort of easy to remove tape and block off the gaps around his roll bar and glass. It would be interesting to me to note the differences at highway speed and if an adjustment in the wind wings is necessary.

08-14-2015 01:11 PM - permalink

BOBOCobra

I've done it already,gave me an excuse to drive all over and back.I made a tight fitting screen. t whistled.Not sure if air going in or out. Taped it off and there was air hammer like when you drive your pickup with the window open and if you open the back window it stops. Not bad but I noticed it. With a 1/4" gap it went away. I believe the air is getting pulled into the negative cabin pressure from behind the back screen. Adjusted wind wings all the way in and it is a nice face wash. adjust all the way out and it is much better. There is a sweet spot when the conditions are right and there is no wind at all,the negative pressure makes my ears pop and all you hear is the side pipes, it is like hearing music for the first time. I have my theory on all this but too long for this forum. The air column above crashes in and without the screen it hammers the back of your head and rolls forward. With it,it buffets the screen,you can see it vibrating the screen,but it is not as severe.

08-15-2015 06:25 AM - permalink

Xack

So the ideal would be at least a 1/4", but no more than 1" gap all the way around the glass? It would also matter how high the roll bar is mounted.

08-17-2015 02:11 PM - permalink

BOBOCobra

YES! I raised the roll bar about 1.5". It may be better if it is raised a little more and all of my observations are out the window (pardon the pun). It still does not change the fact there is a negative pressure in the cockpit but how it tries to equalize the pressure. I would not put too big a gap as aesthetics also needs to be considered. Too big of a gap would not look good and your mounting "tabs" would need to be huge to engage the glass.

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