Originally Posted by berlinonaut

Moulton and Brompton both overcome the rolling-resistance issue by using high-pressure-tires. Alex Moulton has done years of engineering work on the topic and - according to him - small high-pressure-wheels in combination with suspension are the best of breed. The fact that the land-speed record for upright bikes is still (and for ages) held by a Moulton bke suggests that he may have been right.

If you do not pump up your Brompton's tires to the suggested 100 PSI but run on low pressure you'll suffer from a significant loss of efficiency (and therefore speed). If you do you are just fine. The only modern Brompton tire that is designed for less pressure is the Scorcher (due to it's width it has lower rolling resistance is therefor fast AND comfy already at lower pressures).