Seat Posts

BMX race seat posts: diameter, head, length

A seat post is unforgiving of guesswork: the wrong diameter will not go in, an incompatible head will not take your saddle, and a post that is too short forces you past the minimum insertion mark. Three measurements are enough, as long as you take them in the right places.

The common diameters

Diameter is dictated by the frame's seat tube, never by the saddle. In BMX Race, three figures cover most bikes in use:

• 25.4 mm: the historic size, still widespread on older frames and on Micro and Mini bikes
• 27.2 mm: the most common on modern frames from Junior to Pro
• 31.6 mm: found on certain frames and on Cruiser builds with a large seat tube

Measure the inside of the seat tube with a vernier caliper, or read the figure engraved on the old post. A post narrower than the tube cannot be made up by clamping harder: it needs a shim, which you will find in our BMX adaptors.

Head types: Pivotal or cradle

• Pivotal: a splined top and a through bolt. The saddle clamps onto the splines, angle is set in steps and nothing can rotate. Quick and reliable to fit, and the majority standard.
• Railed cradle: a clamping head that grips two 7 mm rails. Angle adjusts continuously, and so does setback, for fine-tuning the seated position.
• Integrated saddle and post: a one-piece unit, lighter and stiffer, but with no setback adjustment.

A Pivotal post only takes a Pivotal saddle, and a cradle head only a railed saddle. Check that first, then choose the matching saddle from our BMX race saddles.

Lengths and minimum insertion

Lengths typically run from 200 to 400 mm. A short post is enough on a Mini or Junior bike, where the saddle sits low; a long post is needed on a large frame, on a 24" Cruiser or for a rider who spends time seated. Respect the minimum insertion mark engraved on the post: beyond it, all the load concentrates at the top of the seat tube. If the mark shows once you have set your height, go up a length.

Aluminium or carbon

The vast majority of BMX race posts are 6061 or 7075 aluminium, often machined out internally to save weight without losing stiffness. Carbon takes off another few tens of grams, at the cost of a more delicate clamp: low torque is essential, and friction paste rather than grease. On a training bike, aluminium remains the sensible choice.

Fitting: the clamping that matters

Clean the post and the inside of the tube, apply a film of grease on an aluminium post or friction paste on a carbon one, then insert to the height you want. Retention comes from the seat clamp, whose diameter follows the frame tube and not the post. Tighten to the stated torque with the torque wrench from your BMX tools kit: overtightening crushes a carbon post, undertightening lets an aluminium one slip on the first landing.

The brands available

• Tangent: lightened Pivotal posts, a wide choice of colours and lengths
• Box Components: a full range in 25.4 and 27.2 mm, a good weight-to-price compromise
• Insight: accessible posts, with short lengths for Mini and Junior
• Elevn: careful machining for matched builds
• Pride: hard-wearing posts, suited to intensive training

The BMX RACING advice

Give us the measured diameter of your seat tube, the height you are after and the mounting type of your saddle, and we will confirm the compatible post, its length and, if needed, the shim. Being multi-brand, we compare posts on real measurements. Dispatched within 24 to 72 hours, you can spread the cost over 2 or 3 payments available; the rest of the range is in our BMX accessories.