After visiting LH Thomson’s factory and talking with Dave Parrett in depth about their upcoming adjustable height dropper seatpost’s internals, it seemed clear they were on to something.
We covered the internals tech pretty well in that post, but the short of it is this: Rather than rely on mechanical clamps or an air chamber, Thomson’s post uses an oil cartridge to control height and nitrogen shock to return it to full height. The remote lever pulls a cable, which rotates a graduated cam that presses a release valve for the oil cartridge. As it’s depressed, oil is allowed to flow between the upper and lower chambers. Release the lever and it closes the valve. Since oil won’t compress, the post sticks in whatever position it’s in when you let go of the lever. If your weight’s on it, it’ll drop. If not, the nitrogen shock pushes it back up.
Drop in for our first impressions on how that all comes together, plus actual weights and more…
It’s important to note that this is a late stage prototype, not quite production. Most it is what you’ll see when they hit your local bike shop save that it’ll likely have different cable and housing. That said, it’s pretty darn close, and this particular one is Parrett’s personal post that he’s been trashing testing for a while. What’s impressive about that is there there’s zero play in it and the action is as smooth as can be.
The 400mm 30.9 post with cable, housing and remote lever comes in at 586g.
The drop and rise rate is preset, but you can control it by limiting how much you depress the lever.
The saddle clamp is classic Thomson.
The cable pulls a lever that actuates the cam underneath the saddle clamp’s lower cradle. If you routinely ride in muddy or wet weather, it’s probably not a bad idea to remove your saddle completely every couple months and clean out the top of the post (video in the Factory Tour post shows this close up). These pics show starting position (left) and with the lever fully pressed (right). There’s not a lot of movement, and that’s one of the reasons why it’s a little difficult to control the rate of descent or ascent by feathering the lever.
The post has 125mm of height adjustment, dropping all the way to the neck of the stanchion.
A plastic cable guide spins freely around the top of the outer post. This helps the cable housing move freely as the post goes up and down. A fixed guide might cause unnatural bends in the housing on a post like this, so it’s a good fix. We’d all like to see dropper posts with the cable entry at the base rather than the top, but at least cable management has been addressed.
The lever is machined in typical Thomson style and anodized black to match their stems and posts. It pulls a standard shift cable (or, at least, this prototype does…that’s one item they’re still finalizing), and action is smooth. It should ship with 60″ of cable and housing, and like any bike cable and housing, can be cut to fit. Just be sure to measure with the post all the way up and with enough slack at the front to allow for complete steering rotation. Parrett says the only catch with installation is not putting too much tension in the cable, which can result in the seat raising or lowering on it’s own, however slowly. We found one other catch:
While the lever is gloriously minimal, it also uses a straight cable exit, which can make placement either interesting or challenging. Shown here is the more likely placement, cable running forward with lever being depressed down and behind the bar. It’s not a bad spot, but putting it outside (from the stem, between the grip) of the shifter/lever clamps means the cable is running directly over the brake lever. It’s close enough to the lever’s pivot point not to interfere, but depending on whether you’re using i-Spec or Matchmaker clamps or not, you may have to jockey for position with the shifter levers.
Angle it to far down and it could tap the top of the shifter’s thumb lever. You could run it inboard of the shifter/brake clamps, but that moves it pretty far away from your hands.
The alternative is to flip it and set it up so you have to push it forward, but that absolutely requires placement inboard of the brake/shifter clamps to avoid having the cable interfere with your shift levers. Plus, it just doesn’t look right. None of these concerns are a deal breaker, just worth mentioning as you’ll likely want to have an extra 10 minutes or so to fiddle with the lever placement during install.
On the plus side, the attention to detail is exactly what you’d expect from Thomson. The mounting bolt threads into a captured swiveling nut, which eliminates any stresses on the bolt or the clamp, which should improve longevity and strength.
PERFORMANCE
Thomson knew they’d have to hit a home run with this one, and first impressions suggest they did. Even having received a well used test post, it’s a telling sign that its function remains flawless. It slides up and down smoothly and easily with no signs of stiction. There’s no noise when moving and minimal “clunk” when it hits bottom or tops out. You can control the speed, but there’s so little lever movement it’s tough. It doesn’t matter, the speed is good – dropping and rising fast enough but not so fast that you a) feel like you’re falling out of a chair or b) worried it’ll damage your sensitive parts on the way up.
We’ll flog this one for as long as David will let us have it (or until he swaps it out for a true production unit) and report back when appropriate. If you’ve been holding out for this thing, it should be available this month and personally I wouldn’t hesitate.
FUTURE DEVELOPMENTS
As Parrett told us before, they’re working on additional sizes and versions. The latest word is that progress is being made on the 27.2 version and the road-oriented Pavé dropper post. As for that Bluetooth remote control, well, time will tell.
