UNDERSTANDING FRAME GEOMETRY
BMX frame geometry can look daunting, but thanks to our handy guide below you will have it figured out in no time. Remember, we're all BMXers here so if you have any questions just ask.
Keep reading to find your perfect frame, or click below to watch the buyers guide video.
FRAME SIZE CHART
Frame sizing is very much a personal preference: some riders like them longer, others shorter. Here's a rough guide - if you have any questions remember we are here to help!3ft - 3ft 8" - best suited to a 16" BMX bike
3ft 8" - 4ft - best suited an 18" BMX bike
4ft - 5ft - 18" to 20" top tube
5ft - 5ft 4" - 20" to 20.25" top tube
5ft 4" - 5ft 8" - 20.25" to 21" top tube
5ft 8" - 6ft - 21" to 21.25" top tube
6ft plus - 21" top tube or longer
| Rider Height (in) | Rider Height (cm) | Top Tube Length |
|---|---|---|
| 5' | 152 | 20" |
| 5'3" | 160 | 20.5" |
| 5'6" | 167 | 20.75" |
| 5'9" | 175 | 21" |
| 6' | 182 | 21.25" |
| 6'6" | 200 | 21.5" |
FRAME GEOMETRY
Frame geometry can take a bit of understanding - but here 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!
Headtube Angle (HT)
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!
Seat Tube Angle (ST)
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.
Chain Stay Length (CS)
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.
Stand Over Height (SO)
Stand over 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.