Now that you know what size YOU are and what size frame should suit your body metrics, here is how you actually measure a bike frame, say a frame that you might be interested in buying.
Trust No One
But first, it's a good idea to not trust a seller's measurements. Too often you hear of people who thought they were buying a size X frame, only to find that the seller mis-measured or had a different idea of how to measure a frame and they wound up with a bike that was one size too small or too big.
Ideally you can take your own measurements. This page will show you how. But you might also have to be very clear with a long distance seller about what metrics you want and how they should take those measurements.
Ideally you can take your own measurements. This page will show you how. But you might also have to be very clear with a long distance seller about what metrics you want and how they should take those measurements.
Key Metrics
ST: Seat TubeST is the basic "size" of a bike as relates to the riders legs, or lower body length.
ST is the length from the middle of the bottom bracket axle (where the crank arms attach) to a point at the top of the seattube (the rear tube of the triangle, into which the seatpost fits.) ST is usually measured in cms (though English bikes were measured in inches and many sellers may not have a metric tap measure so be prepared to convert) ST can be measure either CTC (center to center) or CTT (center to top). Italian frames are typically measure CTC. English frames are typically measured CTT. ST CTC (A in the photo) is to the middle of where the Top Tube and the Seattube intersect. ST CTT is (B in the photo) to the very top of the seattube, to the TOP of the toptube. a third measurement is CTVT (center to Very Top) which would be to the very very top of the seattube. Often this is the same as B CTT but on some bikes it can be slightly longer. ST though only refers to a traditional frame with a horizontal top tube. While ST Seattube is basically fixed for any frame, a rider can adjust their saddle height (by raising the seatpost) somewhat to compensate for longer or shorter legs or the desired riding position. However a seatpost can only be extended so far before overrunning the "Limit" line, the minimum amount of seatpost still in the seattube to be safe. And obviously, a saddle can only be lowered so far. On a traditional bike a "fistful" of seastpost was considered ideal. You could grab the seat post and cover it with your hand. EST: EFFECTIVE Seat TubeThe advent of the sloping top tube (which most modern bikes have) made it impossible to use ST measurement on a modern bike. The point where the top tube and seat tube met was much much lower and was unrelated to the actual size of the frame.
a new metric EST: effective |
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TT: Top Tube
TT or Top Tube is the horizontal length of frame,
TT is measured from the middle of the headtube to the middle of the seattube, on the horizontal.
This metric is fixed and typically increases with frame size.
Too short and the rider will feel cramped. Too long and the rider feels too stretched out. A longer or shorter stem can be substituted to
On a bike with standard 700c wheels, there is a lower limit. A frame cannot have a TT of less than about 58cm
Frame sizes are traditionally expressed as ST x TT.
TT is measured from the middle of the headtube to the middle of the seattube, on the horizontal.
This metric is fixed and typically increases with frame size.
Too short and the rider will feel cramped. Too long and the rider feels too stretched out. A longer or shorter stem can be substituted to
On a bike with standard 700c wheels, there is a lower limit. A frame cannot have a TT of less than about 58cm
Frame sizes are traditionally expressed as ST x TT.
"Stretch" or "Projection"
Stretch is the distance from the middle of the seatpost to the middle of the bar clamps. Basically it is how far forward your hands will be
Since it can be adjusted, Stretch is more of a "fit" metric than a frame size metric but it can only be adjusted to a certain degree. A very tall rider cannot make a small frame size work just by using a very very long stem and seatpost.
typically a rider can ajust the stem from about a 95mm to 135mm. On an ideally sized frame a rider with a reasonably proportionte upper and lower body will usually use a stem in the 110 to 120mm range.
Since it can be adjusted, Stretch is more of a "fit" metric than a frame size metric but it can only be adjusted to a certain degree. A very tall rider cannot make a small frame size work just by using a very very long stem and seatpost.
typically a rider can ajust the stem from about a 95mm to 135mm. On an ideally sized frame a rider with a reasonably proportionte upper and lower body will usually use a stem in the 110 to 120mm range.
Traditional Bikes
Standard frame sizing terminology stemmed from the olden days of cycling, when frames had nice simple horizontal top tubes.
