One of the most significant new components to come along for mountain bikes in recent times has been the adjustable seatpost. An adjustable seatpost allows the rider to lower, or "drop" the seat on technical or high speed descents, lowering his/her center of gravity and making it easier and safer to negotiate steep downhill sections. When raised to its full extention, the seatpost allows the rider to fully extend his/her legs for more pedaling power.
There are a number of companies that make adjustable seatposts, but they come in two basic flavors; hydraulic and mechanical. Hydraulic seatposts use hydraulic pressure to extend the seatpost, the rider's weight compresses it. Mechanical seatposts use some kind of spring to raise the post, same as with the hydraulic version, the rider's weight is used to compress the post. Most hydraulic seatposts are infinitely adjustable; the seatpost height can be set at any point in the seatpost's travel distance. Most mechanical seatposts have predetermined "stops", the seatpost height is determined by the position of the "stops". Most mechanical posts have at least two or three "stops".
The seatpost travel is controlled by a lever under the seat at the top of the seatpost, or as is becoming the more popular setup; a remote switch or lever that mounts on the handlebars so the seatpost can be activated without taking the rider's hand off the bars; a pretty good idea when negotiating technical terrain. Some seatpost remote levers use a cable to actuate the seatpost, much like mechanical brakes or derailleurs and some use hydraulic levers, like hydraulic disc brakes.
KS Adjustable Seatposts
KindShock is a Taiwanese/Chinese company that makes three adjustable seatposts; the i900 and i900r, the i950 and i950r and the i7 and i7r. The part number with the "r" means the seatposts come with a remote lever that mounts on the handlebars. The i900, i900r, i950 and i950r come in 30.6mm and 31.9mm seatpost diameters, which should fit the majority of mountain bike frames. The i900, i900r, i950 and i950r are basically the same seatpost except the i900 and i900r have a 30mm setback seat clamp, the i950 and i950r have zero offset. Both come in 75mm travel, 300mm overall length and 125mm travel, 400mm overall length models. The i7 and i7r come in 27.2mm seatpost diameter with 100mm of travel and 350mm overall length.
Installing the KS Adjustable Seatpost
Since the stock seatpost for our bike had a setback seat clamp, we went with the KS i900r. The remote lever and cable add about 25 grams but to be able to work the seatpost without taking a hand off the handlebars to fumble around with a small lever under the seat seems worth an extra ounce of weight. If you have an interrupted seat tube or have a bend in it, be sure the seatpost will go into the seat tube far enough so when the post is fully extended it won't be too high. Our Giant Trance X has a bend in the seat tube, after careful measuring we figured the 125mm travel model would just fit. It turned out that because of being able to adjust the seatpost height, we were actually able to run the maximum seat height a couple centimeters higher than the standard seatpost so it worked out fine. If you have any doubts if it will fit or not, you might consider the 75mm travel version.
We ran the remote cable under the top tube of the bike and secured it with zip ties. Make sure there is enough cable near the seatpost so the post can travel without yanking on the cable or getting caught in the rear suspension. This version of the remote replaced one of the lock rings on the ODI grips so the shifter and brake levers could be left were they were. Once the seatpost, remote lever and cable are installed, adjust the cable with the set screw on the seat lever and it's good to go.
On The Trail
It takes a few rides to get the hang of it, but once you start riding with an adjustable seatpost, you'll wonder how you ever rode without one. Being able to adjust your riding position without taking your hands off the bars, let alone getting off and adjusting your seatpost, is a huge advantage. Lowering the post gives you much more stability and control over technical sections and by lowering your center of gravity, you can really fly on the downhills. Raising the seatpost to it's maximum height gives you all the power you can generate for those long uphills. Of course you can raise or lower the seat anyplace within the seatpost's travel distance.
A Few More Things.....
Overall, this adjustable seatpost is a great thing, however, now that the seapost contains moving parts, it will require a certain amount of maintenance and there could be some problems you won't have with your normal seatpost. Most of the time you won't have any problems, most of the minor issues are easily repaired. KS customer service is pretty good, they have a two year warranty, any major problems are taken care of pretty quickly.
From time to time, it is a good idea to lubricate the shaft that slides up and down within the seatpost. After a period of time, there will be noticeable stiction when the seat slides up and down; that's when it's time to lube it up. The seatpost will also need to be disassembled, cleaned and re-lubed from time to time. You can find out how to maintain and rebuild the KS seatpost on in The Bike Shop section of this website.
Adjustable seatposts are in their first generation of existence, you will see a great deal of development and new products in the years to come. Despite a few minor annoyances, adding the KS seatpost is probably the best upgrade to our bike since it was new. If you are a downhill or freerider; an adjustable seatpost is a must. For trail and XC riders; you'll be able to tackle sections you had to walk before and it will be a lot safer. No reason not to have one on your bike.
UPDATE 5-1-2013 This KS i900r has been used for nearly four years and hundreds of off road miles, here are a few observations on the durability of the seatpost.
Overall, the KS i900r has been very reliable, other than the seatpost clamp coming loose, there have been no problems with it and while it is not as smooth as it used to be, the post is still in regular use. The post receives regular maintenance whenever it gets a little sticky. It only takes a few minutes to grease the seatpost. It has been completely disassembled twice for complete maintenance.
There is no scoring on the telescoping shaft and no signs of significant interior wear. There was a small amount of oil at the bottom of the seatpost when it was disassembled for maintenance, it is most likely hydraulic fluid that has leaked from the seatpost's hydraulic cylinder. The seatpost locks in position without issue, but at times, the post will not move all the way up, it has to be pulled up the last centimeter or so by hand. Perhaps the fluid leak has something to do with the insufficient hydraulic pressure, the cylinder may be wearing out. The post will also extend if the saddle is pulled up, like when you lift the bike by the seat. At this point, the post is still fully functional, but seems like it is wearing out. There are no serviceable parts from KS, so when the post fails, it's in the trash.