SourceBMX is a 100% Rider-owned and run store - we live and breathe BMX! Thats why we know BMX bike frame geometry can look daunting, especially if it's the first frame you're buying. This handy guide has been created to give you all the tools you need to scratch up on your BMX frame knowledge and help you find the right frame to meet your needs.

We hope you find this guide useful and remember we’re always here to help - chat to us on our 24/7 live chat service, pick up the phone or get in touch through our Contact Us page

BMX BIKE frame geometry

BMX bike frame geometry can take a bit of understanding - but at SourceBMX, we are here to help! The first thing to understand is that BMX frame sizing is best measured by the length of the Top Tube - shown here as TT. Keep reading on to understand how the angles change how your frame will feel and check out our sizing chart below!


Head tube angle determines the angle of your forks. A steeper HT (i.e 75°and higher) will make the bike turn quicker than a mellower angle (i.e 74.5 and lower°). The more responsive the frame, the more twitchy it will feel, especially at high speed!


The chain stay is essentially the length of the rear end of the bike. A shorter CS length will make the bike more responsive and a longer one more stable. As a rough guide a 13.5" long chain stay is about average.


Seat tube angles don’t vary too much (around 71°) and affect the centre of gravity. The steeper the angle the shorter your bike will feel. Some frames have a mellower seat tube angle (example 69˚) which makes for a longer frame without actually being longer and reduces how fast your frame turns.


Standover height is essentially how high your frame is. A frame with a low standover height is more responsive and easier to ‘throw around’ whilst a high SO height is more stable; particularly useful when going fast.

BMX BIKE frame size chart

Frame Sizing is very much a personal preference, some riders like them longer, others shorter. Our guide is a great starting place if you're not sure and if you have any questions remember we are here to help!

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