Most trifold bikes stock seatpost clamp lever are made of plastic, sooner or later due to wear and tear it won't be able to hold the seatpost properly, sure it will slide down few centimeters which will make your riding so uncomfortable. Even you tighten it well, still, will slide down. I experienced this after 1 1/2 years of usage. I was thinking of replacing the plastic sleeve to aluminum sleeve, but this will be a trial and error because obviously, the problem is the seatpost clamp lever which is made of plastic.
So I decided to replace the whole seatpost clamp and I found one online, which is cheaper and made of aluminum & stainless. No plastic part, so it's more solid than the stock one.
Here's the link where I bought mine;
shope.ee/3poUc...
#3sixty #pikes #camproyale #brompton #trifoldbike #seatpost