Roof "ballooning" while open trailering (!!)

[1953M100]

Open trailered my '31 Coupe to a car show in Iowa a couple weeks ago. Headed down 35W interstate at 70mph until I noticed the soft top roof starting to "bulge" and "balloon" at anything above 60mph. Tried to keep my speed down to 55mph the rest of the way, but I don't like travelling 15mph below the speed limit on the freeway, forcing everyone to pass. Not safe. For the trip home I borrowed a few ratchet straps and some carboard to prevent the condition on the return trip, worked pretty well, but kind of a hassle to secure without causing damage. A fella at the car show mentioned there was a cover available for open trailer towing. Tried searching, not finding anything like he described (??). Any of y'all heard of this...?

[Cape Codder]

Would backing the car on help?

[nkaminar]

Good example of the Bernoulli effect where the pressure is reduced by fluid flow. Same thing happens in the venturi in the carburetor to suck gasoline into the air. Anything you do to reduce the air flow across the roof, like slowing down or some kind of deflector, will help.

[1953M100]

Originally Posted by nkaminar

Good example of the Bernoulli effect where the pressure is reduced by fluid flow...

Exactly! And the more the roof bulges, the faster the air flow, the faster the air flow, the lower the pressure. The lower the pressure, the more the roof bulges.
Lather, rinse, repeat.

Hoping I can find some kind of workable cover for safely open trailering on the interstate.
Lots of car shows and activities I want to attend beyond reasonable driving range for the Coupe.

[Keith True]

Yes,you've found the drawback to hauling a soft top car on an open trailer.My friend has a Dodge dually,when he has the cap on the roof fluctuates almost violently.With no cap on the truck it just flaps up and down a little.Air doesn't jump a very big gap,only about 30 inches,but it mixes back together with a lot of turbulance.Sometimes the turbulance is before the towed vehicle,sometimes right around it.I have a 96 Dodge 2500,single cab,flatbed,and a low profile trailer that I built.I hardly notice a ripple in an A roof at 70.But,if I put the side racks on the flatbed,I can feel the wind buffet the car and trailer around.

[updraught]

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Chop about 4 inches out of the roof like the hot rodders do.

[ModelA29]

Originally Posted by updraught

Chop about 4 inches out of the roof like the hot rodders do.

Or weld a solid roof section from a station wagon like the hot rodders in the 60s did. 57 Ford ones were popular.

[BlueSunoco]

I'd save up for a good enclosed trailer... problem solved plus protection from the weather

[1953M100]

Originally Posted by BlueSunoco

I'd save up for a good enclosed trailer... problem solved plus protection from the weather

It's not really a saving problem, more of a storage space issue. Garage is already maxed out, and doors are only 7', an enclosed wouldn't fit. I'm in a residential neighborhood lot, so no outbuildings, no room to store a trailer. I was towing with an open U-haul trailer. Haven't looked into availability of renting an enclosed... (??)

[Phil Brown]

Originally Posted by 1953M100

It's not really a saving problem, more of a storage space issue. Garage is already maxed out, and doors are only 7', an enclosed wouldn't fit. I'm in a residential neighborhood lot, so no outbuildings, no room to store a trailer. I was towing with an open U-haul trailer. Haven't looked into availability of renting an enclosed... (??)

Well.......you could always drive it to the show

[Planojc]

I would not tow a car with a car cover. There has been lots of discussion here on that topic.

[David in San Antonio]

As Cape Codder mentioned, towing the car backwards may have merit. Buckminster Fuller (and later, Chrysler / DeSoto) claimed that sedans were more aerodynamically efficient in reverse. Does anyone have experience doing this?

[Will N]

Originally Posted by David in San Antonio

As Cape Codder mentioned, towing the car backwards may have merit. Buckminster Fuller (and later, Chrysler / DeSoto) claimed that sedans were more aerodynamically efficient in reverse. Does anyone have experience doing this?

The problem with that is that you want the center of mass of the car ahead of the trailer axles. You want a couple hundred pounds of tongue weight on the trailer hitch. If you put the center of mass behind the trailer axles you will have lift on the hitch, which will lead to a very unstable trailer that will fishtail uncontrollably at speed.

[kbinde2]

When I first purchased my Special coupe I trailered it from Michigan to Delaware, on a U-Haul car trailer. I backed the car on, and made the trip with no adverse effects, except for a wheel strap working loose., the rachet strap had been cut and was just long enough to secure the webbing on the 21" tire.
If I had to trailer again, it would probably be enclosed..

[Bob Bidonde]

nKaminar has it right. More simply stated, the Bernoulli Effect is that an air flow over a surface produces a surface boundary effect that is a suction air load which increases with speed. The suction tends to pull the vinyl top upward.

[Dave in MN]

I had the same problem with a new roof. I had not stretched the top material enough during installation.
I replaced the top and pulled harder….No more problems.
Good luck!

[Tinbasher]

I would check the sealant around the edge of the roof material. especially across the front.
a little black sealant around the edge of the mouldings might fix it.
Also try leaving a side or rear window open if you have a roll down rear window. It's all about air pressure.

JP

[nkaminar]

I sympathize with your problem. Although the neighborhood where I live would permit our travel trailer to be parked at our house, there is no room. I have to rent a space at a storage lot. It is expensive. I envy my friends who have 40 acres and large storage buildings. But along with the space comes the collection of junk and who is going to get rid that when I am gone?

[1928Mik]

I was always told never to open-trailer a Model A any faster than the car could go, so I stay at 55 or so, never using the interstate. Of course mine's a Phaeton too. If I had a distance to go, then I'd buy an enclosed trailer, not use a cover..

[ronn]

who is going to get rid that when I am gone?

the scrapper! he needs to make a living too!!!!!!!!!!!!!!!!!