Getting some lower back pain and was playing with the idea of a light weight carbon fibre vibration reducing seat post. The problem is, Scout will only take a 300mm length max. The one I was hankering after is the Specialized COBL GOBL-R Carbon Seatpost (https://www.evanscycles.com/specialized-cobl-gobl-r-carbon-seatpost-EV180943) but it's 350mm. Just that bit too long.
Any thoughts or should I give it up as a bad idea?
This is a bad, bad idea.
ANECDOTE WARNING. A few years ago a man in lycra waits for me at my parked bike in front of the library to ask directions to the LBS for an emergency component purchase. It turns out he came off the plane and started riding, and shortly his carbon fibre seatpost splintered and shafted him. Looking at his bike, on which everything, including the bolts, were from some boutique brand that I wouldn't have on my bike for fear that the local tradesmen would start thinking I was gullible, I explain that the local LBS is in his eighties, from the blacksmith age of bike mechanics, and won't have any stock he'll want, or know what to do with it if he had it. I take the wounded cyclist home with me to call around and find him a place to stay (tourist town in the middle of the summer, not callousness about his wounds; I couldn't put him up as I already had friends staying) and, most important, to call the bike shops in the city before they closed to find him a suitable seat post. Then I took him downstairs to the surgery to have the wound in his bottom seen to. The guy was a physician himself (Scottish GP, retired early from the NHS to tour on his bike) so I reckoned he would tell me if he was in so much distress or even a dangerous condition that he couldn't wait for attention. It turned out when I got him to the surgery to be quite a serious wound, though not so debilitating that, after a side trip to the city the next morning to buy a new seatpost, he couldn't ride on in the afternoon. Received a nice note from him a while later from which I gathered he was fully recovered and reconsidering carbon seat posts.
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Jags has already mentioned the importance of correct posture on the bike. On a badly fitted bike when I started cycling I paid for my physio's new BMW. Then, over three new bikes I gradually sorted out a proper fit. The first thing is to raise the bars as far as they will go, using an extension if your steerer tube has been sawn short. The next thing is to buy or borrow an adjustable stem; you can always replace it with a fixed stem later if you ride with weight weenies and must fit in. (They don't try to patronize me twice but you may be more socialized than I am.) Rotate the stem for further height and also to bring the bars closer to you and thus to reduce the angle on your back. Now move the seat back as far as it will go; the ideal effective seatpost angle is 68%. Then rotate the bars until the grips are at a comfortable reach (slightly bent elbows) and angle (very nearly straight wrists)s If at this point your back is still at too acute an angle, first try a shorter stem, and remember, it is only habit that the stem points forward -- there is no engineering reason you can't reverse the stem.
Next, remove all sources of transmitted vibration (and noise, which is psychological vibration) from your bike. A far better idea than a carbon seatpost is fitting low pressure tyres, as wide as the forks on your bike can accommodate. (I seem to remember a thread which concluded that the Thorn tourers can take 55mm/2.15in Big Apples.) Unless you ride in mud offroad, zero tread is best, and will together with the width and low pressure, surprisingly to many, give you lower rolling resistance, which again is less strain on your back (and more security in the roadholding and handling at huge speeds, if you care).
In the same line of thinking, removing vibration from your spine, a hammock type Brooks leather saddle is far superior to gel saddles and suspended seat posts, and a hammock with additional helical (coil) springs is better still. I ride on a Brooks B73, which has triple rail (those rails are straight springs) plus helical coils at each of the three corners. SJS sells them for a reason but they are difficult to fit to standard micro-adjustable seat posts (out of the box they come with a fitting to attach them to a so-called "candle" seatpost, which is not hard to get but today limited to Brooks saddles). The more common, less extravagant-appearing (but not much cheaper) style with two helical springs and fewer rails, also available with a micro-adjustable fixing for modern seat posts, is the B67/68. One of those is a lady's model, somewhat shorter in the nose. If you have no Brooks experience, don't be put off by the mansplaining about how painful it is to break in a Brooks; cyclists just love to brag about how they suffer for their hobby. Soak the entire saddle in neatsfoot oil (about a fiver from a saddlery near you) for twenty minutes, let it sit overnight, wipe, ride in old clothes, and soon you will only let it go over your dead body. My B73 was hugely more comfortable than any gel seat right out of the box.
The tyres and the saddle will remove most vibrations, but microvibrations might still get into your hands and via your arms into the muscles that cause pains in the lower back. I use Brooks grips of thick leather rings at right angles to the bars, held together by mini-bicycle spokes seated in custom-cast stopper ends, to isolate my hands from the steel bars (these grips also came from SJS and I soaked them in neatsfoot to match the saddle visually) but all kinds of gel grips are available; an excellent, inexpensive gel grip is made by Herrmans of Finland, fitted to many upmarket German touring bikes. My grips are pretty hard, but nonetheless I cycle in dress leather gloves, without any gel or padding whatsoever because there is zero transmitted vibration through the compressed leather so I hold the bars very lightly.
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It's been about fifteen years since I put together my systems approach to specifying my bicycle, starting with the fit and proceeding to eliminate all vibration and noise, and it's been fifteen years since I last paid a physio a penny. My back feels no pain, nor do my hands ever go numb. Since I'm old and my cardiologists and GPs are all convinced that it's cycling which has kept me alive, it's been a worthwhile journey. If I had to put up with constant back pain, I'd have stopped cycling long since.
