Canvas Roofs

[bftstam]

What was the reason for the canvas section in the roofs in early cars? (up to the 30's)

[oldford]

Simple... Car mfg's just didn't have the technology to provide a large metal panel that would stay in place. The large roof would vibrate and 'drum' from the lift at higher speeds. Ever see the soft top on a modern convertible rise up at higher speeds. The same thing would happen to the metal roofs.

Frank

[Aanderson44]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Simple... Car mfg's just didn't have the technology to provide a large metal panel that would stay in place. The large roof would vibrate and 'drum' from the lift at higher speeds. Ever see the soft top on a modern convertible rise up at higher speeds. The same thing would happen to the metal roofs.

Frank </div></div>

Only partially. While it is true that a large, flat piece of sheet metal can "flutter" up and down (or in-and-out) with the slipstream of air over and around a moving car body, there were other considerations.

The upright, square, razor-edged sedan bodies (coupes too) that prevailed into the middle 1920's precluded the stamping of one-piece sheet steel roofs, due to both their shapes, and the type of steel available at the time, a high carbon grade. To have used a solid sheet of steel on such a roof in those days of composite (wood framed) automotive bodies would have put a lot of stress and strain on any joints around the edges of such a roof panel, resulting in cracking and leakage in rainy weather. Chassis technology was still very much in its infancy, with open-channel frame rails, riveted construction, and the lack of a suitable cross-member to resist the resulting twisting and flexing (the X-member didn't debut until 1929 on the L-29 Cord), making a truly rigid body structure a matter of both great weight and great cost.

With the softening of body shapes by the late 1920's, it was theoretically possible to create a sheet metal filler panel to be joined to the upper body sides, the upper rear panel and the windshield header--but again, cost was a consideration. The Walter Murphy Company built a pair of Berline bodies for Duesenberg Model J chassis having a full metal roof, those bodies being completely of metal construction, with no structural wood in them, but they were the rarity.

Streamlining and the Great Depression came almost hand-in-hand, which delayed the investment into the very large stamping presses and huge dies needed for stamping out one-piece roof panels. Additionally, until about 1930 or so, carbon steel sheet was pretty much the standard, mild steel sheet metal coming in about that time--but to stamp out a one piece "turret top", as GM advertized in 1936, had to wait for further softening of body lines, streamlining if you will.

Therefore, with all these factors, the fabric roof insert remained, given its low cost, and durability relative to the still flexible chassis being built, and the shortage of capital for such a major investment as stamping out one-piece roofs for closed bodies.

It was just an evolutionary thing, for the most part.

Art