Is there anything i can do to make them work better, or failing that, something to use as a back up? they keep coming undone when the roof is fully back if i hit 50 mph, i don't mind but the rear view mirror is somewhat obscured and i use that quite a lot.

Pick your favourite hammer, and put it down in favour of a smaller one.

Then gently apply a beating to the male side of the poppers to widen them out a bit.

Works for me.

I know the poppers must be suitable for the use, as nothing on this car seems to be over or under engineered, but for peace of mind is there something more substantial that can be done?

I would go for replacing them, new ones that fit tightly should hold even at top speed.

But he was going above top speed

I find if you roll it back with the inside on the outside, and pack it tightly, it's a lot less prone to this happening. Not the ideal answer though. Sorry

haha, ill have you know that i have had this car off the speedo with the wind behind me down a hill. I think it works out at a scary rpm though!

Best to buy new straps, but in the mean time you can use a small flat screwdriver to 'close' the eyelets on the strap so they fit a bit tighter. Don't over do it though.

There's two very effective options which I know directly of.

My solution was to fit some one way press button studs: they look like the original fittings, but the button can only be lifted off by pulling upwards from one side only. When correctly fitted, the constant pull in use is from the long end of the strap and it resists it completely, but a quick pull on the short tab unfastens it. Unfortunately I found that they wore out quickly and so I reverted to standard, but I did 360-ish miles yesterday with the roof rolled back at speeds of up to (briefly) 75mph. But I do frequently check them in my rear mirror and a few years ago did find that one had come unfastened. The standard fittings usually work, most of the time, but as they have no failsafe they can never be fully trusted.

Ryo Hayashida's solution to the same issue was to fit Tenax fasteners. The female stud on the outer roof is replaced with a short male pin, and the straps have the male studs replaced with female receptacles. The permanently anchored end of the strap is just secured by directly screwing it to the metal with washers to spread the load and allow rotation. It doesn't look original, but on balance is a much better solution and doesn't look unsightly.

I have seen the results of a rolled roof suddenly letting go at speed and it's definitely something to be aware of, both for cost and safety grounds.

Ventflaps, thanks for the concise reply! I do recall seeing Ryo's thread a long time ago. i might pop down to hobby craft and see what i can find. it sounds like a good compromise with theses studs rather than what i was thinking of doing involving a load of bungee chords. etc.