Hi Dave!
Though your initial post was about seatpost diameter and length, it seems to have morphed into a larger thread on seatpost selection for a new bike. Since Anto/Jags has mentioned my experience with the Thudbuster parallelogram suspension seatposts, I suppose this is a good time to weigh in.
As Anto mentioned, I have indeed installed a Thudbuster LT (Long Travel) suspension seatpost on my Nomad Mk2 expedition bike and Thudbuster ST (Short Travel) versions on two of my randonneur (Audax) bikes.
Each has performed as expected or better, and I remain very pleased to date. Each kind of Thudbuster is available in a varietyof sizes to be fit with shims; there are also some sizes that are milled to fit without the use of shims. They are available from two primary sources, either Cane Creek (
http://www.canecreek.com/products/seatposts ) or from the inventor, who has an arrangement for orders to be drop-shipped by Cane Creek (
http://www.thudbuster.com/ ). The inventor's site includes a neoprene cover with the seaposts, a good value. The posts are also carried by a number of vendors including SJS Cycles, but sometimes not all sizes are available from third parties. You will need the 27.2mm model for a Thorn Raven.
I installed the LT version on my Nomad because the very robust frame rides harshly for me in my use when off-road, cross-country, or on rugged logging roads unladen. This is to be expected of a frame with its weight-bearing capabilities and so no surprise; with a load all smooths out nicely. Using the TBLT while riding unladen off-road has made the bike pleasurable for me in all uses, and completely addressed the problem of road shock on my neck, back, and shoulders.
If pressed for an analogy, I will draw one from marine use: If a rigid post feels like a boat in heavy chop, then a sus-post feels like the same boat in moderate to heavy swells. The "bumps" are still there, but moderated and smoothed over time so they are not as abrupt.
Like you, I was initially concerned about introducing an additional point of wear and potential unreliability, but most of those can be forestalled by fitting the Thudbuster neoprene cover appropriate to the model being used and occasionally removing it to oil the pivots (I do so quarterly with heavy use, and it takes seconds). Once a year, I re-grease the elastomer stack on the Nomad's TBLT. My TBLT developed an unpleasant click shortly after installation and I contacted Cane Creek about it, detailing all the steps I had taken to address it according to their service manual and my own experience. Immediately and without quibble, they sent me a pivot bushing replacement kit and tool. Installing a single new lower pivot bushing completely solved the problem, which has not returned to date. The original bushing appeared to be slightly distorted and had a small burr on it, so was apparently defective.
A few points if you go with a Thudbuster LT:
• The TBLT has a much larger parallelogram, so requires more free space between the seatpost collar and saddle. It is very unlikely you will have sufficient room on a properly fitted Raven to use this model; a Short Travel version would be indicated if there is sufficient room. See:
http://www.thudbuster.com/details.html• The one point of potential failure for the TBLT is the bolt that serves as a free travel stop for the elastomer stack. I have read very few, very isolated reports of this bolt failing after extensive use due to shaft wear caused by rubbing of the elastomer stack and by cumulative shock loadings. I simply carry a spare bolt, washers, and locknut as part of my long-distance touring kit. Proper maintenance will greatly reduce any possibility of failure.
• The TBLT has much greater travel than the TBST, and is more finely tunable because it allows the user to mix elastomers in the compression stack.
I fitted the Thudbuster ST models to my two randonneur bikes simply because they take the "edge off" the buzz of road shock, particularly on roads that have been chip-sealed (gravel pressed into hot tar, then rolled). These bikes are my choice for long-distance (300-400km) day rides mostly on pavement, and don't require the long travel off-road shock absorption the Nomad does. Also, these bikes have horizontal top tubes and so lack sufficient room to fit the bulkier LT model, which really isn't required in their use.
The Short Travel versions use a single rubber puck for suspension and rebound control instead of the LT's stacked urethane elastomers. It is not as finely tunable to rider weight and preference, but has worked well for me.
Neither model has the full actual travel claimed, which I could only achieve in my measurements by removing the elastomers and exercising the mechanism through its entire range. However, both styles have more than enough travel for my needs and I can't envision needing more. I still stand for really big bumps and thereby avoid any "launch into space" rebound effect caused by heavily compressed elastomers.
Unlike telescopic suspension seatposts, the parallelogram linkage of the Thudbusters keeps the distance between saddle and bottom bracket essentially constant and is nice for people like me, whose knees are sensitive to even slight changes in saddle height.
However, because the saddle moves by declining downward and rearward -- and I found the suspension medium tended to compress slightly or "bed in" shortly after use -- I introduced some "positional preload" by moving my saddle 5mm forward on the clamp to take up the initial slack when sitting on the saddle. This restored my initial, static position to what it would be with a rigid post and all is well.
Also, I found with my preferred riding position -- compact-reach drop handlebars on a stem placed so handlebar-tops are as high as the saddle-top and with my back bent at 45° with my hands on the brake lever hoods and elbows slightly bent -- I was not weighting the saddle enough to compress the indicated Medium rubber puck on the ST models, so I substituted the included Soft model and all works well. The prescribed Medium elastomer stack worked well for me out of the box on the Nomad's TBLT, so no adjustment was needed there.
I concede I have introduced additional wear and maintenance points with the Thudbuster suspension seatposts, but I have benefited enough from the reduction in road shock and shock-induced fatigue to make them well worth it. I have ridden a lot over the years, and it does take a toll by this time (I am 55 years old). I wish they had been available when I started riding "with intent" 38 years ago; I might not have some of the problems I do now (particularly with road shock-induced nerve damage in my hands; damping shock transmitted through the seatpost means I am thrown forward onto my hands less, so they are spared at fair measure of overall vibration and impacts). With the sus-posts, I end each ride feeling more rested, fresher, and less beat-up by road shock. The difference is more apparent the longer I spend in the saddle, so really makes itself known on very long day-rides.
I was initially concerned that any of the sus-posts would bounce under me, but in practice that has never been a problem, perhaps thanks to my very smooth, round, light, high-cadence ("hummingbird") pedaling style. I do think it might be a problem for "mashers" -- those who prefer to primarily ride in higher gears and use a low cadence to mostly press the pedals down vertically. I don't think suspensioon seatposts are for everyone, but if you find your neck, back and -- surprisingly, hands -- are bothered by road shock (and your pedaling style is a match), I think they can be a good solution if other more ready changes fail to bring relief.
If you choose a Raven (with tube diameters tuned for more general use than my SuperDuty expediton Nomad) and fit it with fat (1.75-2.0in) tires running reasonable pressures, you will have much less need for a suspension seatpost. I would suggest you try it with a rigid post first and then fit a sus-post later if required. Simpler is generally better for long-term reliability and a sus-post might not be indicated. Forum member AndyBG kindly loaned me his Raven Tour (a slightly more robust version of the current Raven, with larger tube diameters and a bit higher cargo capacity) for my ~9,000km double-crossing of all Eastern and Western Europe. It was equipped with Thorn's supplied rigid seatpost, and rode on 2.0in Marathon Deluxe tires aired to reasonable pressures. I fared well without a sus-post even on Bulgaria's sometimes exceptionally rough roads. However, by summer's end, I was awakening with some lower backaches that I feel would have been absent had I used a sus-post, but who's to say for sure? All I can say is I now find riding much more pleasant and comfortable with a suspension seatpost, and I was a pretty hard guy to convert, having ridden forever on rigid seatposts and handling the larger bumps by posting (standing on the pedals).
One last note, keyed off Anto's comments: For my own use, I have found Brooks B.17 saddles and either Thudbuster ST or LT seatposts to be a sublime combination. The B.17 is my preferred saddle and still feels the same to me as on a rigid 'post, but less road shock is transmitted through it to me when it is mounted to a sus-post. I suspicion my leather saddle-tops will last a bit longer as a result, and it can't be a bad thing to extend the life of saddle rails. I've broken three of the chrome railsets (due to hydrogen embrittlement as a result of the plating process; no powdercoated rails have failed on me yet), but it can't hurt for them to have shocks dampened and eased. Also, I have found no mechanical interference between Brooks B.17 saddle rails and either of the TB sus-posts; the parts all clear each other fine. There are other sus-posts out there, both telescopic and parallelogram in design. SunTour make a very nice model, but it can sometimes interfere -- at least initially -- with Brooks saddle rails. Among its virtues are a roller-guide-aided spring travel that is highly tunable even compared to the TBLT's elastomer stack and the TBST's rubber pucks.
If you want to read more about my selection and experience with these sus-posts, you can use the Forum's search function. I posted a little tutorial showing how to quickly find things here:
http://thorncyclesforum.co.uk/index.php?topic=4390.0Related threads are listed here:
http://thorncyclesforum.co.uk/index.php?topic=5709.msg71061#msg71061Best,
Dan.
