Tamer Tricky Dick/Pivot Plus engineering mods
Does anyone have the new style (hollow, pressed in pins) Tamer seatpost, and have a good understanding for how the pins are designed/installed?
The reason I ask is I had the original style Pivot Plus that held up well, except for two design flaws....the pins were hollow, and there's no bump stop to absorb severe shock when bottoming out. My post finally failed when I bottomed out (only an 18" drop). One of the pins sheared, all the others were bent, and the ears of the aluminum block mounted on top of the post bent out. This could have been prevented if the pins were solid, and there was a way to incorporate a bump stop.
I figured out what I could use and how I could replace the pins with solid high strength precision shafting, and how I could incorporate a bump stop on this older model, but the new style seatpost is different. I'd like to buy and modify a new one, but I don't know how it's design is, and I don't want to by another post that will break on me unless I can figure out how to modify it. Can anyone send me super close-up pictures of the pivots, or explain to me what parts are in and around the pivots?
I have had ten Tamer Pivot Plus XC seatposts, 5 new, 5 factory rebuilds. The very first unit was built before EKO/MRP bought the co. and had solid pins which I could tighten with allens wrenches. This one lasted two years, the rest only two months each. You can check my reviews under Tamer PP XC and under Cane Creek ThudBuster LT, which I switched to and got 1900+ hours before one of the bottom pins compressed. CC rebuilt the unit for $36.75. While the TB was in the shop, I installed another factory rebuilt PP. Within 60 hours the bottom pin broke in half and popped out and within 120 hours the torque became too excessive. I would recommend going with the TB because the pins are bevelled preventing torque and popouts and it has more travel (3"). I have dicussed the PP problems with the EKO/MRP owner and employees and gotten nowhere and was told that they would no longer honor their warranty on any of their products that I returned to them.
Thanks for the reply. Because the seatpost sounds like such a low quality product, designed by engineers who probably couldn't pass the machine design portion of the PE test, coming from a company with such poor support, I'll choose not to buy another one even if it's cabable of modifications to improver perfomance, because I wouldn't even want to give them a stale Grape Nut. A shear load calculation on a hollow pin is fairly easy for an engineer to do, why don't they? To estimate the loads, it's a four bar linkage mechanism which should be in an example from their books in college.
For those who are already stuck with the product:
the spring is hollow, making it the perfect location for a bumpstop to reduce/dampen shock loads when bottoming out. Use automotive fuel hose or thick wall vinyl hose (from OSH) inside the spring. If you use vinyl, do a "chemical compatibility" search on the internet with any grease you're using inside the post.
You're essentially putting a high rate spring (the hose) within a low rate spring (the original spring). The hose OD should be slightly loose within the spring ID. The length of the hose will be TL-PSL-LAB-DAB-DT+1/4"........where....
TL=total length from the bottom of the post to the top of the top nylon cup (when no sitting load is on the seat)
PSL=total length of the top nylon cup and internal plunger
LAB=length of the preload adjustment bolt
DAB=depth of the adjustment bolt from the bottom of the post (at your desired preload setting)
DT=full depth of travel of the top nylon cup comparing the linkage in the fully extended position to the fully compressed position (you'll have to loosen you preload or remove the spring to measure this easily).
The 1/4" value I picked as a starting point, change the value as you see fit. You may want to make three different hoses..using 1/8", 1/4" and 3/8" as you various values to plug into the equation. When you land on the seat hard, you should feel the spring rate suddenly increase when you "squish" down and you hit the hose, before you feel the harsh "clang" when the seatpost reaches it's travel limit.
The disadvantage of this setup is that you increase the height when the hose "spring" is engaged if you decide one day to tighten your preload....this could be an advantage, though because you're ensuring more bottoming-out resistance. Unfortunately I can't test this out because my seatpost is already broken, but this will definitely decrease bottom-out loads.
Drill bits are available in more than just fractional sizes...machinist bits are available in numbers and letters to cover all sorts of diameters, and the portion of the shank between the cutting flutes and the stamped size designation qualifies as precision shaft material. Using the cut shank of a correctly sized drill bit would work..using small cross drilled holes on the ends with bent retention pins to ensure the pin doesn't fall out (do not use hairpin style cotter pins here!!!!). The trick is trying to drill a hole through the side of a drill bit shank.....a machine shop should be able to do this, and somewhat cheap, too.