Genesis Croix de Fer 30 Seatpost Size: Separate Post and Clamp
Genesis Croix de Fer 30 seatpost size needs to be separated from seat-clamp size. For the GN21050 build, the manufacturer's sheet lists a 27.2mm seatpost and a 29.8mm clamp. Those two dimensions belong to different components. Ordering a post from the clamp number would answer the wrong question.
Genesis Croix de Fer 30 seatpost size: Match the number to its component
The component list describes the original post as Genesis Alloy 27.2 x 350mm. The first dimension identifies its diameter; the second is the listed post length. The additional-information table separately pairs seat-tube and clamp sizes as 27.2mm and 29.8mm.
Keep both component names in a replacement request. A shop needs to know whether you are replacing the post that supports the saddle or the external collar that secures it. Even when both are near the same point on the bicycle, their markings cannot be exchanged.
Do not borrow the handlebar dimension
The sheet also contains a 31.8mm figure in its stem description. That figure is associated with a different assembly. A page full of millimetre values is useful only when each value stays attached to its named part. Similar-looking numbers do not establish compatibility between those assemblies.
Separate length from permitted exposure
The specified 350mm post length is not an instruction to expose that amount above the frame. It is also not a dropper-travel measurement. The actual post and frame instructions must establish insertion and adjustment boundaries for the fitted combination.
A used bicycle may have a replacement post or saddle arrangement. Read the actual markings and preserve the relevant instructions rather than assuming the equipment still matches the original list. If a marking cannot be read, have the component identified before making a purchase or changing the setup.
Confirm the exact frame version
The photograph records a source-identified 2014 Croix de Fer in a 2018 scene. It cannot establish the diameter or approved insertion of the post in the GN21050 sheet. Its saddle position is a photographed setting, not a fit recommendation.
Include the bicycle's identity, the required component and any readable markings in your enquiry. The Genesis brand guide provides the range's background, and the Genesis topic offers other ownership questions. This guide supplies a documented distinction between post, length and clamp; it does not prescribe a torque, shim or unsupported modification.
FAQ
Which seatpost diameter does the GN21050 sheet list?
It lists a 27.2mm Genesis alloy seatpost for that specified build.
Is the listed 29.8mm clamp dimension the seatpost diameter?
No. The additional-information table assigns those numbers to different parts.
Does the 350mm length establish how far the post may be raised?
No. The permitted position must follow the actual frame and post instructions.
Sources
The component and additional-information tables distinguish the post diameter and length from the external clamp. Neither table supplies a safe exposed-post length or installation torque. Genesis Croix de Fer 30 manufacturer specification, GN21050, pages 1–2 (https://www.freewheel.co.uk/media/madison/product-files/525553/Genesis_Croix_De_Fer_30_VARGN21050.pdf). Original evidence retrieved 26 October 2026; saved document rechecked 27 October 2026; the code identifies the document, without inferring its model year.
Photograph credits and permissions
Photograph 1
Original title: Bike Resting at Ruillé-sur-le-Loir Campsite, France
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