So........if Mini thought there was no issue with shock tower movement, why did they think they needed to install the braces on the convertibles? How would anyone know that strut braces don't do anything? Came across this diagram some time ago, comparing a Machpherson car to a double wishbone car, something to think about :idea: With a machpherson strut, lateral loads go primarily through the lower A-arms, but because there is a moment about the hub, there is a smaller reactionary force going through the strut itself. That force can make the strut towers flex, making a strut tower bar helpful. With a double-wishbone setup, lateral loads go primarily through the lower A-arms, but again there is a moment about the hub. However, with a double-wishbone design, the reactionary force to cancel this moment comes from the upper A-arms and not the strut. The strut itself is free to handle vertical forces. Since a strut tower bar only is effective in stiffening the tower against lateral loads and since the upper A-arms don't mount to the tower, stb's do very very little in these cars.
The braces on the 'verts is not located in the same place as the aftermarket ones are. The 'vert braces are attached to the front of the chassis forward of the towers to help stop the NVH caused by the roof removal. The towers are located so close to the firewall that they should never move side to side enough to req any kind of bracing.
Pretty sure when MINI chopped the roof off they found they had a flexible flyer. A tin topped MINI has a much stronger structure. As I've said many times in many places. I'm sure the strut bars do something. I just can't feel it. Edit: The convertible also has under-body bracing in the rear suspension.