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Is there an effective, non-destructive way to mark the seatpost position?

We share some bikes within the household, meaning that the saddle height is adjusted often. When I had an affordable Decathlon bike, it came with a seatpost that had centimetre markings on it (like this). This was very helpful in quickly setting the preferred saddle height for any family member. Unfortunately, most other manufacturer's don't include this feature, and Decathlon's own seatpost is not great (no angle adjustment for the saddle).

Is there a reliable and ideally reversible (or at least non-destructive) way to mark certain positions on a seatpost? A hard scratch would work, but it is not reversible. I have not found a marker pen that works because of: (1) black background (2) it rubs off easily when the seatpost is slid down.

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    I wonder if it is actually harmful at all to lightly score the surface of the seatpost and make a clear mark? The top position is the difficult one to get right. It wouldn't take much to make a visible mark.
    – SamA
    Commented May 31, 2023 at 3:23
  • @SamA For thick-walled aluminum seatposts, it won't make much of a difference. Sure, there's some theoretical increase in crack likeliness due to the stress concentration and whatnot, but I don't think that's going to present itself as a problem in the lifetime of the bike. Also, I would expect bikes in this category to have enough safety factor to handle normal everyday wear and tear. Of course, scratches (intentional or not) pose an aesthetic problem if that is one of your criteria.
    – MaplePanda
    Commented May 31, 2023 at 5:54
  • Because of a fear of stress concentration I have have always been reluctant to scribe a mark on a seatpost. However the maximum stresses will be at the front and back of the tube so scribing on the side would be safer. An additional factor is how far out you have your seatpost as the stress is much greater if it is fully extended.
    – Ken Mercer
    Commented Jun 1, 2023 at 9:10
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    Is the bike always in the same place when the saddle height is adjusted? If so, could you hang up an ordinary plastic or wooden ruler next to that can be butted up to the underside of the saddle when needed? Commented Jun 1, 2023 at 13:12
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    @Mazura That will come off as soon as you slide the saddle down and back up once.
    – Szabolcs
    Commented Jun 2, 2023 at 7:53

8 Answers 8

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Not a strict answer to the direct question, but an answer to the question of sharing between different people. If you are ready to change the seatpost, having a dropper post is a nice solution when sharing a bike (these are sometimes fitted on shared/rented bikes).

The less fancy ones have levers under the saddles (so no need to mess around with internal or external cable routing), which is not perfect when using it offroad, but when sharing a bike, that is perfect.

The seatpost is adjusted for the tallest person, and for example, with a ribbon of tape, you can mark the position for the smallest one. Then, when you need to change the height, you just need to actuate one lever and adjust the seat (and the saddle remains correctly oriented).

A side benefit of this solution is that such seatpost avoids the use of a quick release (it also works with anti-theft collars), which is a benefit in areas where components theft is an issue.

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    The neutral bikes at the TdF and whatnot have droppers to accommodate different rider heights. Pretty cool application of the technology.
    – MaplePanda
    Commented May 30, 2023 at 19:05
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    Not all droppers are created equal in this respect. I've had at least one (all be it a very entry level OEM dropper) where it was advised not to sit on it for extended periods when not fully extended
    – Hursey
    Commented May 30, 2023 at 22:55
  • @Hursey That's very interesting. Do you know which model it was, and who told you this advice? Perhaps there's some nuance I'm missing, but from a hydraulics perspective I'm not sure what the difference between fully and partially extended would be. If anything, less extension = less leverage = less stress on the bushings. Intriguing!
    – MaplePanda
    Commented May 30, 2023 at 23:09
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    It was a KS Lev e30 I think or something very like. Was in the docs for it when I got the bike, no explanation of why. I only remember reading it because I too was "that seems odd". Truth be told the less vertically gifted in my family still rode that bike with the dropper down anyway and didn't seem to affect things.
    – Hursey
    Commented May 30, 2023 at 23:22
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Some marker pens are more robust than others (especially if there's grease around), and on a black background it's often possible to catch the light and make it much more visible. Taking that a step further, security marking pens that glow under UV light would show up nicely with a suitable lamp.

What I really suggest though is that you mark it as the one you like was marked, with a scale. For black anodised aluminium, you can use a scriber instead of the factory's laser engraving. Better still, a carpenter's marking gauge can transfer a measurement from a ruler to make a nice line around the post, perhaps al the way round every 5cm, with smaller markings every 1cm, starting from the minimum insertion mark.

I keep meaning to scribe my MTB seat post, because I want to mark one height for road (and gravel) where I want to ride seated for a fair distance, and a lower one for proper trails. I'd just mark 2 positions as tidily as I can, but if you've got kids who keep growing, a ruler scale is better.

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Rather than marking the seat post you could use the fingers on your hand.

For example:
Nancy's seat is three fingers high.
Bob's seat is eight fingers high - four fingers plus four more.

Each person doing the adjusting would have to remember how many of their fingers were used.

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Both permanent silver metallic markers and permanent gold metallic markers work well. They leave a clearly visible mark on the (usually black) seatposts.

After finding that my own handwriting, of lines and numbers, looks less than very elegant on the seatpost of one of my bikes, for my second attempt (image below) I used painter's masking tape and a permanent marker from a popular brand sold in my area.

stenciling permanent metallic marker

As you see, the mark itself is perfectly opaque, but the masking tape left streaks. Hence it appears that masking tape is not the right tape for this task. You may want to experiment with simple adhesive tape.

"Why just two lines; and why such fat lines?", you may ask.

This is for the seatpost of a child's MTB (hot off the assembly line).

The two lines mark the recommendation of the trails coach, as well as the child's own preference for a setting that is not as high as the coach suggests.

Why fat lines? Because although nominally permanent, the mark consists after all of just particles on the surface. It will get abraded from inserting and taking out the seatpost. I'd like it to remain visible even after some abrasion.

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    "not particularly pretty" - if OP makes sure to use something which wraps around a curve and acts as a straight edge, they should be able to make a very clean, straight, level line. I wouldn't see a problem regarding prettiness? Or do you mean some other aspect about this?
    – AnoE
    Commented May 31, 2023 at 9:10
  • Those are just sharpies. You want the ones with the little rattle can ball in there because it's actually acrylic paint. However that stuff is permanent. You can mark bk on bk /w a sharpie; it'll show up as a different sheen if you catch the light right. Sharpie, acrylic pen, grease pencil, an awl, and good 'ol graphite. Bikes are neither here nor there, +1; that's how you mark stuff.
    – Mazura
    Commented Jun 2, 2023 at 17:51
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String and knots

Attach a piece of string somewhere on the underside of the saddle, then add a knot to it for each person that wants to use this system. The knots are spaced so that at the correct height for each person, their personal knot just about touches the quick release (or whichever point of reference is convenient).

Obviously you will have to remember which knot is yours, unless you go with a more sophisticated system that makes them distinguishable. Although realistically, you might very well be the only one using it anyway :)

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    I'm going to give this a try, at least until I can get my hands on some light-coloured permanent markers. Light-coloured string can me marked in red, which is easier than tying a knot at a specific position.
    – Szabolcs
    Commented May 31, 2023 at 14:49
  • @Szabolcs light coloured permanent markers won't be much good unless they're paint-like. They're translucent and the black shows through
    – Chris H
    Commented May 31, 2023 at 17:58
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    @Szabolcs I think knots are more convenient than color marks because you can feel them, so you don't have to keep looking at the mark while adjusting the saddle. But sure, whatever works for you.
    – MaxD
    Commented Jun 1, 2023 at 10:34
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String and knots has been suggested (and similar) but if you're doing this often, you may want to make a jig. This is a common trick among woodworkers.

Take a single piece of wood, cut everything at the correct angle and so on that it mates cleanly with both ends. It should sit cleanly on the frame seat tube and possibly have some sort of cutout for the saddle rails.

If you are adjusting for multiple people who have known-good seat configurations, each can have their own jig. They could be made out of plastic as well. I have done this in the past with both plastic and wood and it has worked.

I have also scored aluminum seat posts and I've never had a problem with one in over 25 years of competitive riding. The only seat posts I've ever seen shear, other than accidents, were carbon fiber.

I appreciate over-caution but sometimes it just makes things unnecessarily complicated. My bike mechanic always carried a knife in his pocket and he'd mark the post at the frame with it after each fit. But that's your personal choice.

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  • I was going to make a suggestion like this, but I think you could even do with a single jig and mark on it the length/height for each person. Commented Jun 2, 2023 at 2:22
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A separate saddle/seatpost for each rider, and a QR in the frame.

For exact height setting, put a piece of tape around the seatpost just-above where it enters the frame, or a better solution is to clamp on a band-on reflector so it rests on top of the frame and acts as a hard-stop.

Do all of you have exactly the same preference for a saddle and saddle angle too? That's unusual, especially across genders.

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    That's a bit expensive and inconvenient compared with changing the height, don't you think? I share a cargobike with my wife and I hate the saddle but I'm much to impatient to swap the whole post and saddle. And my wife would kill me if I ever forgot to put it back.
    – SamA
    Commented May 31, 2023 at 1:34
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    @SamA yes it would have some cost compared to simple markings. Personally I'd have a bike per-person, myself. One advantage of a stop-collar is that each seatpost will end up at the right height immediately without reading a gauge or tape measure or looking for a mark on the metal. Also allows each rider to have the saddle they fit, rather than everyone compromising on one.
    – Criggie
    Commented May 31, 2023 at 2:06
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    @SamA also, popping a seatpost out and putting a different one in is only slightly more effort than adjusting the height.
    – Criggie
    Commented May 31, 2023 at 2:07
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    I agree that it is preferable to each have own bikes, if not always practical. I have never heard of this particular solution before, but I suppose it could work. You'd need someplace to hang your extra seatpost and saddle. A decent bike shed...
    – SamA
    Commented May 31, 2023 at 3:21
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    @Criggie I did that at some point when sharing the e-bike of my wife. It's indeed more convenient than adjusting the position of the saddle. But it's only because I had a seatube and a saddle in my spare parts. I wouldn't buy a seat tube and a saddle just for this reason (I'd rather buy a dropper). Also considering that shared bikes are rather the utility ones (that are usually not used for long rides), there's no need to have the most suited saddle.
    – Rеnаud
    Commented May 31, 2023 at 5:21
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Assuming that etching your seatpost is out, because you do not want to reduce its strength, writing on the seatpost — even using a permanent marker — is not really a workable solution. After a few times even a permanent marker will be abraded and then smudged. Soon enough, it will be necessary to repeat the marking, but then the seatpost will not be very pretty.

An alternative is to observe that the crankshaft-to-saddle is a fixed distance for each cyclist. You would use that distance for multiple bicycles for the same rider. It is thus well worth it to cut a stick of wood to the requisite length. When you adjust the saddle, you'd grab that fixed measure and use it.

Well, this idea would not work very well for growing youths. It's a way to solve the problem for adults. For those still growing, you'd use a long ruler or a tape measure.

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