Review on 🚴 BESNIN Alluminium Alloy Seat Post, 27.2mm/30.9mm/31.6mm Bike Seatpost 350mm - Adjustable Saddle Angle - Ideal for MTB Road Bike BMX by Logan Barela

Most bikes are 27.2mm in diameter so people know. This is the traditional size for most Walmart and Big Box bikes, as well as most older brand name bikes. Build quality was excellent and appears to be a great upgrade from stock. If you are unsure of the size of your bike, pull out the saddle and place it a quarter of the way up the seatpost. If your seat posts are a little over a quarter in diameter, your bike is 27.2mm in diameter. If you can fit almost a quarter in the seatpost then it is one of the larger sizes and you will need to use a caliper to measure.