Carbon bike shaft extension

Cut off carbon lengthen racing fork too short
Cervélo Aero carbon fork shaft extension by 40 mm

Despite all the attention, it happens again and again that you shorten the steerer tube too short and it lacks the deciding millimeters for the right handlebar position, or you take over a used frame, a complete bike, but the handlebars can not be mounted higher. 


We recommend at first always to check the new or additional purchase. Often, however, this is no longer an alternative, as the original fork is no longer available due to old models from the manufacturer. 


If all possibilities are checked, this is no reason to write off the bike. Based on our many years of experience in manufacturing, repair and modification, we can easily realize an extension of a carbon shaft.



Extension of carbon fork stems

The fork stem of a carbon fork cut too short!

Review of process and processing technology according to ISO standard 4210

Safety carbon fork - fork stem cut too short
Examination of a fork stem extension on an older Smolik Motivation Race SLX carbon fork according to ISO Norm 4210 by EFBE Prüftechnik

The procedure and processing technology of our offered fork-leg extensions of carbon forks for models no longer available on the market, we have tested successfully without complaints at the company EFBE-Prüftechnik independently, objectively and transparently according to the ISO standard 4210-6: 2015 for forks of the category racing ( RD) to the corresponding critical load cases . 


Our test specimen was an older Smolik Motivation Race SLX carbon fork, which was extended by 2 cm for test purposes. In the picture on the right you can see the shock test backwards - torsion test of the steerer tube.


Safety carbon fork shaft too short - repair carbon
Tensile test of the Smolik Motivation Race SLX carbon fork to ISO standard 4210

In another test case, see picture left, you can see the test for tensile load of a non-welded fork in accordance with ISO standard 4210 of the Smolik Motivation Race SLX carbon fork supplied by us. 


Overall, the test was successfully carried out without any complaints, and no parts of the unit relaxed or separated. In addition, there was no evidence of fatigue in the form of cracking.

Technical realization of a fork stem extension

Carbon fork cut too short Shank extension Carbon
Carbon fork shaft separating cut according to the given head tube height and desired final length

The extension does not take place by a preparation / extension in the true sense, but by the technologically correct incorporation of an intermediate piece. Here, the position is selected so that the interface is largely stress and load free at a certain position with respect to the height of the head tube, and the desired final length. 


For this reason, the specification of the head tube height is a prerequisite for the technically perfect implementation. 

carbon repair modification bike stem fork
the same fork after carried out carbon shaft extension

The maximum extension, which we offer and give warranty, are 40 mm. This limitation is based on the fact that the max. spacer height generally are 40 mm to the standard value. 


Likewise, the warranty is limited to the specified parameters, ie head tube height and protrusion / extension. The fork is therefore no longer for a different configuration than the frame dimensions and the desired height you specify universally to use, but is then tailored to your specific frame, modified.

Share with friends

Start your request  help(at) via e-mail or via online form on our  CONTACT page.


Kommentare: 7
  • #7

    Carbon Bike Service (Mittwoch, 12 Juni 2024 08:40)


    For the calculation of a fork steerer extension, we need the following information. Please send it via email to

    Height of the head tube from bottom edge to top edge in mm
    Final fork steerer length measured from the bottom edge of the head tube in mm, maximum extension from the top edge of the head tube is 40 mm
    Length in mm or depth of the compressor, indicating how far it extends into the steerer tube
    Inner diameter of the steerer tube in mm

    With this data, we can geometrically determine the cut for the extension, the maximum length for the inner sleeve, as well as the cost.

    Best regards Carbon Bike Service

  • #6

    Thomas cooling (Montag, 10 Juni 2024 15:43)

    Hi, can you tell me how much you charge to extend a carbon road bike fork by 40mm please?

    Kind regards
    Tom Cooling

  • #5

    Dirk Brouns (Freitag, 15 September 2023 18:33)


    Can you extend a d-shape fork of a Colnago V3rs ? And what would be the cost of such extension ? The fork has still 46mm left above the headtube 153mm including bearing ring.



  • #4

    Carbon Bike Service (Freitag, 29 Juli 2022 09:07)

    Guten Tag Martin,

    Wir empfehlen immer zuerst den Neu- / Nachkauf zu prüfen.

    Bei weiterem Interesse gerne eine Anfrage über unsere Kontaktseite / E-Mail. Wir benötigen folgende Angaben zur Prüfung vorab:

    aktuelle Länge Gabelschaft xxx mm
    gewünschte Endlänge Gabelschaft xxx mm
    Höhe Steuerrohr Unter- bis Oberkante xxx mm
    Länge Kompressor xx mm
    Innendurchmesser xx mm

    Mit sportlichen Grüße der Carbon Bike Service

  • #3

    Martin Lessing (Donnerstag, 28 Juli 2022 19:17)

    habe eine Carbongabel dessen Schaft etwa 3 cm verlängert werden sollte. Ist das möglich und was kostet das in etwa?
    Es handelt sich um eine Whisky No 7 Carbon Gabel.
    beste Grüße

  • #2

    Carbon Bike Service (Montag, 20 Juni 2022 14:18)

    Good day Luan,

    for a offer please send us photos of the fork, as well as

    - height head tube from bottom edge to top edge in mm
    - final dimension steerer tube length measured from lower edge head tube in mm, max. protrusion from upper edge head tube are 40 mm
    - length in mm, or depth of the compressor how far it reaches into the steerer tube.
    - Inner diameter of the steerer tube in mm

    E-mail is

    Sporty greetings from the Carbon Bike Service

    Translated with (free version)

  • #1

    Luan Vella (Sonntag, 19 Juni 2022 08:14)

    Dear Sir ,

    I have a scott carbon fork which I need to extend to 1.5cm to 2cm.
    Can you do it ? Can I ship it and you ship it back ?
    What is the cost ?
    I Live in Malta.