Lengthening a classic bike steering tube
06-06-23, 09:26 AM
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Lengthening a classic bike steering tube
A moron of the month question. I have finally got around to swapping all the components from a 1979 Peugeot PK65 mixte bike with a 51 cm frame to a bare 57 cm version, actually a year older, a 1978 Peugeot PR65. Never having done this stuff before I optimistically (!) thought I could learn on the job. I got it all together as a trial fit, with the exception that - remember I haven't done this before - the threaded steering tube is (of course) too short. The donor bike front tube is 13cm and the lucky receiver is 17cms, so not only is the steering tube below the top of the front tube, but the threaded part is likewise.
My question is what is the best/easiest way to extend the fork tube length? A YouTuber cut the fork tube in half and added a section which was welded top and bottom. My front tube is perhaps 0.2mm wider than the fork/steering tube so in theory there might be about 0.1mm either side to be able to be thicker and still fit the front tube.
I apologise for the abject learner question, but wise advice would be treasured!
Guy Bagnall, Paris, France.
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My question is what is the best/easiest way to extend the fork tube length? A YouTuber cut the fork tube in half and added a section which was welded top and bottom. My front tube is perhaps 0.2mm wider than the fork/steering tube so in theory there might be about 0.1mm either side to be able to be thicker and still fit the front tube.
I apologise for the abject learner question, but wise advice would be treasured!
Guy Bagnall, Paris, France.
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06-06-23, 10:15 AM
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That’s the only way to extend a steerer tube.
06-06-23, 10:21 AM
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The best way to do it is to get a fork that is of the right size and threading what you could do is get a modern 1" fork and run a more modern 1" threadless headset and them of course a more modern threadless stem and make your life easier otherwise you have to find the proper length threaded fork which can be tough.
If you have a framebuilder you can have them make you a fork or cut and weld a new steerer tube (but I would just go the new fork route and keep the old fork with the old bike and sell it as a pair and make the next owner very happy so they don't have to do what you are doing).
If you have a framebuilder you can have them make you a fork or cut and weld a new steerer tube (but I would just go the new fork route and keep the old fork with the old bike and sell it as a pair and make the next owner very happy so they don't have to do what you are doing).
06-06-23, 10:54 AM
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Best course of action to complete your build....
1.. Measure the steerer tube on the fork from your old frame, from the "crown" to the tip of the threads at the top. ... now measure the head tube on your old frame(not the bearing headset parts/cups, just the FRAME tube at the very front of the frame)... now measure the head tube on your larger frame... add the difference between the two frames to the measurement of the old fork's steerer tube... that sum is the length of steerer tube on the fork you need to find..... and think in Millimeters.. these fork and frame measurements MUST BE VERY ACCURATE.
2.. find a local Co-op with a large stash of 1" threaded Road Bike forks..
3.. find a fork that will work in your larger frame.
4.. here's wishing you good luck.. Large frame sizes were sold at a much lower rate than medium or small frames, so the Forks for larger frames are kind of scarce... add to that the fact that larger bikes had larger, Heavier, riders,and that they crashed with more force than small riders,,, !
5.. a few mm longer can be dealt with by adding a spacer ring or two....a millimeter SHORTER is iffy, and 2 mm shorter should NOT BE TRIED without finding a headset with a shorter stack height.
I'd rather hear how nice your larger frame fits you instead of hearing a list of injuries sustained by you
1.. Measure the steerer tube on the fork from your old frame, from the "crown" to the tip of the threads at the top. ... now measure the head tube on your old frame(not the bearing headset parts/cups, just the FRAME tube at the very front of the frame)... now measure the head tube on your larger frame... add the difference between the two frames to the measurement of the old fork's steerer tube... that sum is the length of steerer tube on the fork you need to find..... and think in Millimeters.. these fork and frame measurements MUST BE VERY ACCURATE.
2.. find a local Co-op with a large stash of 1" threaded Road Bike forks..
3.. find a fork that will work in your larger frame.
4.. here's wishing you good luck.. Large frame sizes were sold at a much lower rate than medium or small frames, so the Forks for larger frames are kind of scarce... add to that the fact that larger bikes had larger, Heavier, riders,and that they crashed with more force than small riders,,, !
5.. a few mm longer can be dealt with by adding a spacer ring or two....a millimeter SHORTER is iffy, and 2 mm shorter should NOT BE TRIED without finding a headset with a shorter stack height.
I'd rather hear how nice your larger frame fits you instead of hearing a list of injuries sustained by you
Last edited by maddog34; 06-06-23 at 04:09 PM.
06-06-23, 03:19 PM
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I'd rather replace a steerer then extend an existing one.
This question comes up here (and in another forum I frequent too much) time to time. Like many situations there's a lot of opinion but few who reply have ever actually done the work. One of the details is the fork crown's finish. Painted/chromed. Adding a section mid steerer (or adding a longer top section complete) will allow the original finish to remain un harmed but does require more care in setting up the parts to insure a straight steerer. Another aspect is how deep into the longer steerer will the stem reach and if this would allow an internal sleeve/splint to be used. If not then the parts would need to be welded instead of brazed.
I strongly suggest that one doesn't try this themselves as the results of a failed weld (which will be out of sight and thus not able to easily check periodically) is pretty massive. If the old steerer was removed from the crown and replaced completely the risk goes down. Even with a failed braze the front brake or fender bolt will act as the safety pin. Andy
This question comes up here (and in another forum I frequent too much) time to time. Like many situations there's a lot of opinion but few who reply have ever actually done the work. One of the details is the fork crown's finish. Painted/chromed. Adding a section mid steerer (or adding a longer top section complete) will allow the original finish to remain un harmed but does require more care in setting up the parts to insure a straight steerer. Another aspect is how deep into the longer steerer will the stem reach and if this would allow an internal sleeve/splint to be used. If not then the parts would need to be welded instead of brazed.
I strongly suggest that one doesn't try this themselves as the results of a failed weld (which will be out of sight and thus not able to easily check periodically) is pretty massive. If the old steerer was removed from the crown and replaced completely the risk goes down. Even with a failed braze the front brake or fender bolt will act as the safety pin. Andy
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06-06-23, 03:44 PM
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