Hi All!
Next installment in Danneaux's Sus-Seatpost Saga...
Here's the
Executive Summary following extensive empirical comparative testing in a variety of terrain and conditions:
For me in my intended use, the Thudbuster LT has it all over the ST. For little additional weight it is far more tunable, quieter, and has much greater travel than the ST; taken together, this makes it a more versatile suspension seatpost for the money provided one has the clearance to accommodate the greater stack height. It really works well at reasonable speeds over bumps 1-2in/25-50mm in height and doesn't bob if ridden by a cyclist spinning with a smooth, fast, "round" cadence and can be effectively locked-out on smooth roads using an even pedaling technique. It will bob/bounce to a greater or lesser degree if one is a "masher" riding with pistonlike vertical stokes at a slow cadence.
In contrast, in my trials I found the Thudbuster ST to be much more comfortable than my Thorn/Zoom rigid large layback seatpost in all circumstances -- but not as much as the LT and not enough for me. It did not meet my goal of sufficiently attenuating bumps off-road or on very rough surfaces, but was very nice on rough-surfaced pavement including that bane of American road cyclists, chip-seal. It nicely softens bumps and irregularities .5 - .75in/12.5-25mm in height. The ST is largely immune to pedaling style and I think would be much better suited to a "masher".
I would say if one has the room to accommodate it, the LT is the preferred choice and will accommodate the greatest range of road surfaces, including off-road at reasonable (i.e. slow and touring) speeds. If space is limited and you only wish to "take the edge off" rough pavement as Thudbuster claim, then the ST would likely be a worthwhile substitute to a rigid post. Mine was noisy, however, and I put this down to the elastomers being made of rubber and formed so they are self captive within the parallelogram linkage and edge-actuated. Where the urethane-damped LT was bolt-captive, end-loaded and silent, larger bumps made the ST say "Squodge-squodge-squodge" a bit like a rubber squeegee drying a window. I didn't add (silicone or other) lubricant to the elastomers of either 'post, choosing instead to test them as-delivered, though I realize lubrication of pivots and elastomers is a required part of regular long-term maintenance.
Why the difference?Again, in my own experience and testing with my two samples, I found I am getting nowhere near the published amount of travel -- and it is still alright. I weigh 172lb/78kg, appropriate for the "Medium" elastomers supplied with each 'post. Having tried combinations of the next softer and firmer samples included with each 'post, I feel the Medium is the best combo for me -- well-damped to prevent bouncing while remaining comfortable. Both 'posts reacted similarly within their respective available travel.
The difference between them is down to the available travel (and to a lesser extent, the medium used to make the elastomers). No suspension can really eliminate bumps, they're still there, of course. Holding constant for speed and weight, what suspension does is
attenuate the bumps, spreading out the force over time so they don't feel as abrupt. Given the bumps remain the same, the ST has less distance and damping material to absorb and slow them, so the bumps feel less well-damped to the rider.
I never came close to bottoming-out either 'post and I never had a conflict between the linkage and the rails of my Brooks B.17 saddle.
I found I never approached the published amount of travel for either seatpost. It is extremely difficult to measure actual travel while riding, so I made a little test rig with a hard rubber bead on a shaft to serve as a stop-marker when each 'post was at full compression; the actual measurement is in a diagonal from the steerer, so is a combined measurement of downward and rearward travel consistent with how the 'post's linkage works to absorb shock transmitted from the rear wheel when it hits a bump. My measurements show I am consistently compressing the ST about .5-.65in/12-16.5mm and the LT about 1.0-1.25in/25-32mm in heavy use. Curious to learn how CaneCreek got their published travel measurements, I emailed them and received the following reply...
There is really no full travel on the Thudbuster- it just varies based on how soft or firm you want the ride to be. If you want to experiment [for my given weight], trade one of the blue elastomers out for a gray elastomer and see how that works.
I suspect the published travel is the total amount available
without elastomers; in other words, the total "potential" travel. With elastomers installed, the potential is still there but isn't fully realizable 'cos the elastomers damp and prevent full compression thanks to their rising rate (they show every indication of becoming stiffer as they compress).
In any event, in my use each post fully accomplished its stated "mission" and made riding noticeably more comfortable by absorbing and distributing the effect of bumps through a combination of geometry, link length, and elastomer compression. I don't think more travel would have given a better result. CaneCreek/Thudbuster suggest a rider can use harder elastomers but should not use those for less than their weight. Given my weight and 45° back angle (which affects weight on the saddle), I have leeway to use a half-softer grey/blue combo on the LT and can adjust the preload bolt, but would be limited to only the Middle elastomer on the ST with no further adjustment possible. Heavier riders please note: The ST is limited to 250lb/113kg. I don't see a similar note on the LT.
The difference in travel also affects saddle placement to a degree. I found the equal-length parallelogram linkage meant the
distance between saddle and BB really varied little if at all throughout the available range of travel. However, as noted in a previous post, the rider's
position behind the bottom bracket can still vary as a function of the linkage's downward-and-rearward travel. This is important because it is generally a bit easier to spin at a high cadence if one is closer to the BB and it is possible to generate a bit more torque if you're behind the BB a bit. I found the LT's longer links and greater sag under my weight meant I needed to move the saddle forward about 5-7.5mm to compensate compared to my rigid post. The ST required no such adjustment.
So which is "better"?Neither, either, and both. The "best" is the one most suited to conditions and user requirements and depends in part on the bicycle's frame size and design; the shorter ST can be used on far more bicycles 'cos the suspension mechanism requires less room than the LT.
In terms of preference, I like the compact appearance of the ST much better and I really like the silence, response, and greater travel of the LT. For those needing to fine-tune saddle position, the LT's greater link length and inclination allows one to get the saddle further rearward than the ST even though they use the same clamp.
I'm thinking of someday fitting an ST to one of my road bikes that has a really harsh ride. I think I'd ride the bike more with an ST than I do now, simply because it would be that much more comfortable.
Why'd I choose the LT for my needs?The LT is the sus-post that will remain on my Nomad Mk2. It is a true expedition touring bike -- just what I needed -- and adding weight makes the ride smoother. It is simply such a nice bicycle I want to also ride it unladen on the rougher tracks it excels on, making it a sort of MTB for my purposes, the rough equivalent of a dual-sport motorcycle. The same stiff frame that carries weight so well often makes the ride uncomfortably harsh for me when hitting bumps unladen on really rough pavement, on poor gravel roads, and off-road. Adding the Thudbuster LT has nicely addressed all my concerns with no compromise while carrying a load or on smooth pavement. I can lock-out the post simply by standing when needed, and I always do on larger bumps to ease larger shocks to me and the bicycle. I take exceptional care of my equipment, appreciating fully the need for reliability and knowing what a breakdown would mean in the isolated areas I tour alone. The LT does not make the rigid Nomad the equivalent of a full-sus downhill or freeride rig, and I'm not going to "case" jumps in any event. Instead, it makes an already ideal expedition bike into a more ideal all-'rounder to use comfortably and enjoyably on my unladen day rides. I think it will also prove beneficial when touring fully-loaded, allowing me to remain seated on the smaller bumps I would otherwise have to stand for and I expect to end the day less fatigued as a result.
I really like how the bike itself remains unaltered; the only difference is a far more comfortable ride with no loss of handling precision or load capacity.
I am faster on the bike with either sus-post than I am with the rigid one, simply because I don't have to slow as much for bumps to remain comfortable and by remaining seated on rough, steep terrain, I achieve better traction at the rear tire. The LT has taken an already great bike and made it even better suited to my needs, more comfortable and more versatile, making it feel like the "next generation" in Nomads. I'm pleased with the result.
...Even though there's resolvable "challenges" in my applicationThe switch to a sus-post has required some adaptations in other areas. Until I can find time to mill a new rigid bag support from aluminum billet, my Ortlieb Medium underseat bag will ride supported by Ortlieb's quick-release webbing strap kit, intended for Brooks and spring saddles. It works alright but is not to my preference. Fitting spokes inside the ST is not possible and just today I came up with a way to make it possible on the LT (more in a later update). There is room on the LT's lower shaft for my alarm and pump peg, but I will need to find another place for my ring-lock's coiled cable mount. All in all, the LT will be well worth my troubles to adapt based on my thorough comparative testing to date. I'll be sending for the neoprene dust/rain cover for it soonest.
Best,
Dan.
