I unlocked it on my fold XS,tops 25mph, but riding so for I can't crack 27.1.But definitely some major factors, weight,hills being the 2 enemies. Any hills you'll notice you can't push it but so far. I'm 6'2 225,I be moving but any hills small ones at that I'm pushing maybe 18-20mph unless you're peddling before the hill.Also you will probably think about changing the cassette. I'm new to e bikes, but I read something about running out of peddle, which I have done, so I change the cassette which then allowed me to push it to 27mph,so far.