Tonneau Top Flapping

I was talking Porsche with a friend that has an old 911. He told me that the tonneau tends to flap up and down and his 911 has a strap about midpoint that allows him to connect it to the floor to provide some downward tension. Does anyone have this problem, and, if so, have you done anything to solve it. I'm in my final build week and may throw one last spec change at Carey :)

You can do a couple things. I assume you're talking about a half-tonneau?
Have the leading edge made about three inches longer than it 'should' be, and ask Carey to fold in a one-inch-wide piece of either leather or light metal to sew into it. Fold the material around the add-in piece, and use a jean-stitch to retain the excess cloth. Should work like a champ.
Option two is to use a full tonneau - the kind that zips up the center of the car - and fold the front half in between the backs of the seats. I used option two when I had a tonneau. It worked beautifully. In fact, it was the ONLY thing that worked beautifully.

Thanks Cory. I was talking about a full tonneau driving with one side open and the flap tucked behind the drier's seat. I was watching a video from Carlisle that MUSBJIM posted this weekend showing Lane Anderson's car (I think) and the tonneau was flapping pretty good. This increased my awareness. I was thinking about taking something like a computer bag strap, cutting off one end, sewing that end to the bottom of the tonneau right behind where the zipper starts and putting an eye on the floor and using the adjustable feature of the strap to apply the desired tension.

Thanks Cory. Good thoughts. I'll hold off.

Tom, I think you'll be disappointed over time if you add anything that provides external tension. It might be better to reinforce the zipper on just the passenger's side -- add a heavier material in along the same path that the zipper follows -- instead.
I think most people here who drive their cars that way will agree; it doesn't take much temperature difference at all for the tonneau to stretch or shrink, and those (relatively mild) stresses lead to cracks in the fiberglass where the snaps are screwed in.
If you're planning on driving your car with that cover in place, the buffetting will provide similar stresses on the fasteners. Putting a strap in might seem to solve the flapping problem, but I bet it's going to pull on those snaps like shroud lines pull on a parachute.

EDIT -- Maybe if Lane drives that way routinely, we should ask him to have a look at his snaps to see how they're holding up. The Hoopty was a CMC body, and they're not known for being the best ever produced. I'm pretty sure a Beck is far and away a better bit of workmanship.
On my car, the snaps all had hairline cracks that went right through the centerline of the fasteners, leaving small breaks in the paint on an axis radiating outward from the center of the car. They were about a quarter-inch long on both sides, and cost more than $500 to repair.

Yeah, the full tonneau flaps a lot. That's one reason I don't use it much. The center snap on the dash is holding up well so far, but I'm thinking of removing it and putting a big washer underneath. The car doesn't really have a half tonneau. Instead it has a full boot over the folded top. The boot is held in place on the bottom by velcro and on the top by snaps. It doesn't move much at all.

The only solution that I can come up with for the tonneau is a piece of wood or metal running the length of the tonneau from the dash to the back of the passenger compartment. You could fasten it to the cover with velcro. It would also reduce sagging in rain that catches water and makes a big mess in the car when you open it. Haven't figured out all of the particulars yet. The easiest solution is to do like Cory says - just fold both sides behind the seats when you're driving and only close it up when you're parked.

Thanks Lane. The folks on this site are all awesome. I'm so disappointed that I can't come to Carlisle this year.

Got bid'ness obligations? Tell 'em you're having quadruple bypass and will be out for a week. They'll be too impressed by how quickly you recover to ask questions.

By the way: When you get your car you should expect to have some sorting issues to deal with. It's a test to see if you're really committed (or should be ;-). That's normal, and nothing to get worried about. The folks here will walk you through any that you can't fix immediately.

Tom - Dusty Johnson fabricated a strap on his tonneau cover that snaps to the underside of the door strip (this is snap that the strap of the side window would normally attach to). It works REALLY well!

Lane, new baby on the way. Next year. It will be good ro get through the break in period and sorting out period, anyway, before taking such a long drive :)

Jim, thanks, but I can't visualize that. Maybe he will see this post. I'm going to hold off for now.

I think he's talking about the middle, Jim.

OH, I see.

O.K. then, how about taking the tonneau to a boating supply shop or your local sail-maker and have them install a couple of (removable) battens in a front-to-back direction on the underside of the tonneau. This probably wouldn't totally eliminate the flopping around of the center of the tonneau, but it should reduce it quite a bit.

The flapping tonneau cover...Flap!

I added another Tenex fastener just to the right of the Velcro/zipper flap combo. I now have 3 fasteners on the dash. I converted to all Tenex fasteners all the way around including the tonneau and boot covers. Each stud has a nylon washer that prevents the hexagon portion of the Tenex from damaging the top. No fiberglass cracking around the tub where the Tenex studs are located. Makes life easier and I don't have worry about the plastic snap tops being damaged by the weather or the ultra-violet sun rays. No fading or cracking. Tenex shine all a round.

I've had no problems with water...the weather covers have to be stretched every time for installation! The top also has the same shrink attitude.

Be sure to wash all the weather parts with a very good convertible cloth top cleaner and add an excellent waterproofing compound. Carey can recommend one. I use 303 products per Carey's recommendation.

Sail battens may work, but remember they are designed to bend and form the aerodynamic shape of the sail luft. May be well worth the try. Check out the ones used on the larger Hobie Cats and C-Scows.

I've been driving with a full tonneau for over 9 years. In fact I have never driven the car without the tonneau (never driven the car with the top up). Most of that time the passenger side was covered. I have NO flapping issues. I do have a roll bar sticking thru the tonneau and sealed with a velco strip. This may change the "dynamics" of flapping.

This one doe's not flap.

David:

On open-top cars, the wind is actually 'reversed' more than one would think - Top Gear (an UK TV show about cars) actually had a test to see which car would make a toupee fly away faster, and the wind patterns seemed to prove that - wind is stronger coming from behind, after having "rolled" and accelerated by the window, and hitting the smooth wind on top, thus coming into the car.

When you have a wind-stopper like you have, that phenomena is reduced, and should help immensely in preventing flapping.

However, it isn't easy to do in speedsters without the roll-bar, and the aesthetics on the roll-bar do vary according to personal taste.




I'd say (with no experience) that a heavier material lines on the wind-facing sides, and probably also reinforced 2/3 centimeter lines of said heavier material, forming an "X" or some sort of pattern, should help stabilize the tonneau.