Although I'm not an expert, I've been around Thunderbirds since I was little (My uncle and cousin have a 64, two 66's and a 69 and all the original brochures we used to look in all the time), and I don't think they offered wire wheel covers on 67 Thunderbirds and not on any earlier years either (although they did offer real wire wheels in 62-64).
It's probably some other T bird wheel cover (or Galaxie maybe?). All in all, the whole suspension looks much like what the Shelbys came with: they also used stiffers springs, adjustable Gabriel shocks and Thunderbird wheel covers (Kelsey Hayes mag wheels optional).
A plausible scenario is that Ford just installed the Shelby suspension parts and offered it as an option on Mustangs. The parts were already there and just could be installed without further development. Or maybe Shelbys were fitted with this option as standard equipment? Just a guess of course.
BTW: maybe you know this already, but the <b>load rate </b> which is often mentioned for leaf springs has nothing to do with the stifness. It is the amount of load that is required to compress the spring a certain amount (usually so that it's flat). That's why a fastback leaf spring typically has a higher load rate than one for a coupe. It is heavier in the back, so the load rate is higher to achieve the same ride height.
A higher load rate without increasing the stifness can be achieved with a larger arc. That way, it needs to be compressed more inches before it's flat, and since the load/inch is the same, a higher load is required to flatten it.
Edited by - Helmantel on 06/01/2007 03:23:47
