Seat Tube Size?

Asked by: Heather Nation

Seatpost diameters generally range from 22 mm to 35 mm in 0.2 mm increments. The most common size is 27.2 mm (1.07 in) for most bikes, especially for the higher-quality models. BMX bikes commonly use 25.4 seatposts. In some modern bikes with thicker alloy or carbon tubing, larger diameters such as 30.9 mm are used.

How do I know my seat tube size?

To find out the diameter of your seatpost, you must remove the seatpost from the bicycle frame and look for the size, which is stamped just below the “Minimum Insert” line toward the bottom. The number will be a three-digit number (such as 26.8 or 27.2 or 31.6).

Does seat tube size matter?

These days, seat tube length is still important in some cases: To understand the lowest position of a saddle, especially important when sizing up to a larger frame or considering a bike with a classic, level top tube. To determine the amount a saddle may be lowered when using a dropper seatpost.

Is seat tube length the same as frame size?

Frame Size



Bike frames are commonly measured in centimetres or inches representing the length of the seat tube. For example, a manufacturer may measure the seat tube length of a bike as 51cm, and then describe it is a small frame.

Are bike seats standard size?

While there are any number of post diameters out there, most modern road and MTB bike frames accept a seatpost of either 27.2mm in diameter (‘standard’), 30.9 or 31.6mm (‘oversize’).

Will a 31.6 seatpost fit a 30.9 frame?

You can fit a narrower post into a wider frame using a shim (a thin sleeve of aluminium or plastic), for example a 30.9 mm dropper post into a 31.6 mm frame. However, there is no way to fit a wider post in a narrower frame, for example a 31.6 mm post into a 30.9 mm frame.

What is the standard seatpost diameter?

27.2 mm

Diameters. Seatpost diameters generally range from 22 mm to 35 mm in 0.2 mm increments. The most common size is 27.2 mm (1.07 in) for most bikes, especially for the higher-quality models.

What is a good seat tube angle?

The trend we are seeing now is that a steeper seat tube angle actually compliments the longer reach, giving you a more balanced seated pedaling position. It seems like bike brands are landing on an optimal seat tube angle of around 76 to 77 degrees.

How does seat tube angle affect ride?

Seat tube angles range from about 70-75 degrees. A steeper angle moves the saddle forward while a shallower angle moves it back. Steep is fine for racers. It allows them to ride hard in an aero crouch, as the more open hip angle doesn’t constrain breathing or power transfer.

What is seat tube CC?

Seat Tube Length



“Centre to Centre” or C-C is the length from bottom bracket centre to the middle of where the top tube meets the seat tube.

Why do pro cyclists ride smaller frames?

In more modern times, pros often use a smaller frame that a similarly sized recreational rider because they want to ride a big drop to the handlebars. As head tubes continue to grow for a given frame size, pros are forced onto smaller frames to maintain their positions.

What length seatpost do I need?

Length. Make sure you have the correct length of seatpost for your needs. Seatposts are available in several lengths from 280mm to 400mm so measure the amount of post you have showing (plus the minimum amount of insertion that needs to be in the seat tube) before purchase. If in doubt, measure your old post.

How do you measure seatpost length?

1: Measure the seat tube from the center of the bottom bracket to the point where you want the seatpost to exit the seat tube. Subtract 1 cm. That is the seat tube length and reference point for the next two measurements.

Can I put a longer seat post on my bike?

Pretty much all you can do though is put a longer stem, possibly raise and lower it, use wider handlebars and adjust the saddle angle+ position a bit further back (which may be easier with a different seat post). The biggest things you have to do are get the effective top tube right.

Is 150mm dropper post enough?

The somewhere-in-the-middle 80-150mm travel posts are probably your best bet. Or are looking to spend a lot of time with your bike airing out over jumps, or dropping into super technical terrain where you just want the saddle completely out of the way? Then longer travel >150mm is probably your bag.

Can you shim a dropper post?

How To Find The Right Size Seat Post For A Bike

How do I know what size seatpost clamp I need?

Note: The seat clamp diameter needs to match the diameter of your seat tube rather than your seatpost, which is a little smaller. For example, a 27.2mm seatpost (a size commonly found on road bikes) fits inside a 28.6mm diameter seat tube, so it’s a 28.6mm clamp you need.

How do you measure seatpost length?

The length of the post that comes out of the frame is known as the stack height. This is the distance from the top of the seatpost collar to where the seat rails would be in the saddle clamp if the post was all the way inserted in the frame.

What is seat tube CC?

Seat Tube Length



“Centre to Centre” or C-C is the length from bottom bracket centre to the middle of where the top tube meets the seat tube.

What length seatpost do I need?

Length. Make sure you have the correct length of seatpost for your needs. Seatposts are available in several lengths from 280mm to 400mm so measure the amount of post you have showing (plus the minimum amount of insertion that needs to be in the seat tube) before purchase. If in doubt, measure your old post.

Can I cut my bike seat tube?

Unless it’s a really messy cut or you cut it too short then it’ll be fine. cutting your seat tube on your frame can weaken the frame. its designed to be a certain length for a reason.

Can I put a longer seat post on my bike?

Pretty much all you can do though is put a longer stem, possibly raise and lower it, use wider handlebars and adjust the saddle angle+ position a bit further back (which may be easier with a different seat post). The biggest things you have to do are get the effective top tube right.