For commuting, you need an extra-long seatpost. Most normal seatposts max out at 400mm in length. To commute on a BMX, we need to go longer.
For comparison, here are some folding-bike seatposts:
model | diameter | length |
---|---|---|
Brompton | 31.8mm | 530mm |
Dahon | 39.3mm | 650mm |
Tern | 33.9mm | 585mm |
Brands known for making longer-than-average seatposts: