jackyharuhiko has a Pacific Cycle Birdy, most Pacific Cycle Birdy are factory equipped with the 10.5 turn softer front spring while Riese & Müller Birdy are factory equipped with the harder 8.5 turn spring.

For me, the original front suspension with the 8.5 turn spring is perfect ( I am around 80kg), the softer 10.5 that was factory mounted on my Ti Birdy was too soft especially with a loaded Brompton front bag.

I tried the Multi-S G5+ suspension set (that seems very good with a front spring+hydraulic damper and sophisticated rear multi-rubber system) and it was bad.

The rear is ultra hard, there is almost no suspension. I couldn't compress it by pushing on it, then I put it in a vice and even so, the max compression I could obtain is about 5mm.

The front is also harder with a shorter spring that results in a shorter travel than the original and the top ring for the hook has a rectangular groove that doesn't fit with the shape of the frame hook (which is designed to hook a spring = a round object) with as consequence a continuous rattling noise coming from the front suspension.

I also tried the Ridea PU 100 hard rear suspension and it works slightly better than the original but the M3 very long mounting bold was broken several times, I eventually glued the several parts of this PU block instead.