The fork spreading tool

Here are a couple of pictures of the tool I used to spread the rear forks on our Bromptons.

Brompton spreading tool

The assembled for spreading tool. The dropouts are clamped between the pairs of large washers.

Brompton fork spreader

The section of steel tube is just over 7 cm long. The ends of the threaded bar slide into the tube. Once the spreader has been bolted to the dropouts, the innermost nuts are then screwed in against the steel tube thus pushing the threaded bar sections outwards.

Tool to spread forks.

Detail view of the arrangement of nuts and washers on the threaded bar. The steel tube section slides on from the right.

Materials required

1 x piece of thick walled mild steel tube, outside diameter 12mm
1 x piece of M8 mild steel threaded bar (minimum length 40 cm)
4 x large M8 washers
2 x small M8 washers
6 x M8 nuts

Tools

Hacksaw or other metal cutting tool
File or sand paper

Instructions

1) Cut two 20 cm lengths of threaded bar. (I halved a 50 cm long piece of threaded bar)
2) Take the steel tube and cut of a piece 7.5 cm long.
3) Dress the cut end of the tube and threaded bar, if necessary
4) Screw on the screws and place the washers in the order shown in the third picture.
5) Slide the ends of the threaded bar into the section of tube as show in the first and second pictures

You are now ready to go!

How far do I need to spread my forks?

This is a bit difficult to say. You need to spread the forks further (under tension) than the 122 mm required to fit a modified Nexus 8 hub. The steel that the forks are made of will bend elastically before it starts to deform permanently.

With the tool in place I needed to wind it out to 138 mm on my Brompton which, when the tool was removed gave me a 122 mm opening. Damae’s Brompton needed the tool to be wound out to 140 mm before the Nexus hub would fit.

If in doubt start with a lower value, say 130 mm. Remove the tool and measure the distance between the dropouts. Then adjust as required.

You might need to bend the drop outs after spreading the forks so that they are parallel. Measure the gap when the dropouts are parallel again and adjust as needed.

Disclaimer – what happens if something goes wrong?

Use of this tool could damage you and your Brompton/bike. You are responsible for your bike and the modifications you make to it. I accept no responsibility for any damages or losses incurred by using the tool described in this post.


Note

I do not recommend opening out the forks to accept a hub with OLD of 135 mm. You will get clearance problems between the tread of the tyre and the cross piece on the fork near to the rear hinge. To fix this problem you will need to modify/replace the dropouts or find another way of increasing clearance between the rear tyre and the cross-piece.

8 Responses to “The fork spreading tool”

  1. rualexander Says:

    Great stuff, thanks for this information, its pretty much what I assumed from the photos on the other page describing the procedure.
    I think maybe you mean 132mm instead of 122mm though?

  2. syklist Says:

    No, I really do mean 122mm!

    As I said at the bottom of this article you will run into other clearance problems if you try and open out your rear fork to 135mm (I suspect the same will happen with an OLD of 132mm).

    So, you have to narrow the Nexus hub by removing the large locknut on the NON-drive side of the hub. Do not refit it. You also need to remove the dust cover and the nut behind it and then file down the nut by 1mm to get the OLD down to 122mm. Refit the nut behind the dust cover once it has been modified. The dust cover, both the black plastic bit and the metal outer cover then have to be modified if you want to refit them.

    Somewhere on the internet there is a “How To” explaining how you narrow the OLD for Nexus 8 hub. I can’t find it at the moment.

  3. John Gold Says:

    I used this method with great success.

    For the centre tub I used a length of copper plumbing pipe, double thickened by taking a second piece, slitting it lengthways and forcing it into the tube. This gave the tube the necessary thickness and rigidity.

    The ends do need straightening afterwards.

    I managed to fit a Shimano Deore hub into an old Dawes frame.

  4. syklist Says:

    Glad to hear that the method worked for you too. 🙂

  5. john Says:

    I have a trek 800 1994 cro-moly with 125mm rear space for 6 speed freewheel. I bought a 7/8/9 freehub wheel 135mm o.l.d. I stretched to only 129mm by pulling. I’m going to take a 3/8-16 bolt 6 inch long and thread 2 nuts on and torque them out to set to 135mm (or more if spring back) and let sit for a few days to set. Hope it centers out though.

  6. David Thompson Says:

    Fork Spreader…
    I have an old Dawes frame. The forks will only accommodate a modern wheel with difficulty, and removing a wheel on the road for a repair is an ordeal. Do you know if there is a tool that will just spring the forks a little to remove and replace a wheel? Should I just scrap the frame and forget it. Your advice would be much appreciated.
    Thanks, David.

  7. syklist Says:

    Hi John, I managed to miss your post all those months ago. Did you get your forks opened out OK?

  8. syklist Says:

    Hi David, I used the fork spreading tool described on this page to open out the rear forks on a pair of touring bikes with steel frames. The width was increased from 132 mm to 135 mm to accomodate Rohloff hubs. It seems to have worked fine on both bikes, which is good as we have a strong sentimental attachment to those bikes.

    But it is up to you to decide if you want to take the risk on your own frame, or not. Having said that, steel is a pretty forgiving material and, as you are planning to scrap the frame otherwise then it seems to me to be an ideal opportunity to try out the technique for yourself. Let me know how you get on.

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