The PRO Tharsis Dropper Post is lightweight with 100mm of travel, designed for cross-country riding or potentially gravel bikes. The seatpost offers very smooth action and no sideways play. Multiple remove levers are available, although these are extras, not included as standard.
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With dropper seatposts offering an increasing range of movement, with up to 200mm now available, it may seem off for a new post to be released with only 100mm of travel. However, the PRO Tharsis 3Five is designed primarily for cross-country riding and racing, where weight is still essential to many. With a claimed weight of 405g for the 27.2mm version (without lever), the Tharsis is one of the lightest posts available.
The seatpost features internal cable routing. I chose to use a more minimal PRO Koryak inline lever compatible with both single and double drivetrain options, with an alternative under the bar thumb-activated PRO Koryak command lever, which might suit some 1x drivetrain options. However, for me personally, a fork lockout lever would have interfered. The seatpost could also be used on a gravel bike or other drop-bar bike and matched to the Shimano GRX LA shifter, which again would be for 1x bikes.
The fitting of the seatpost and removal was not straightforward, but this may change on different bikes, depending on the specific internal routing. I found it difficult to know if the gear cable outer was fully fitted into the required port when placed into the seatpost, making fitting a slower process. One benefit of the system, which clamps the cable inner at the lever end, is that any hose shortening required after the initial fit is a much easier process.
The seatpost tested was the 30.9mm version with the seatpost itself weighing 448g with the lever and cables at 95g, taking the total fully fitted weight to 543g, which still makes it one of the lighter seatpost options available, but less of a headline with the popular RockShox Reverb, for example, weighing under 600g for the 150mm travel version, with the 100mm version that is also available likely to be much closer to the PRO Tharsis. Riders looking to save every gram possible will likely be pleased to see the seatpost features titanium bolts, which themselves will save approximately 15g over the same length steel bolts.
The action of the dropper is very smooth in both directions, with enough movement in the lever to allow for adjustment in the speed and amount of drop/return. So, if you only want to drop the post a small amount, the travel is also infinite in the movement from top to bottom.
Throughout the use, it has remained smooth with no sideways play, which suggests that the oval internal shaft is working as it should. While fitment wasn't the quickest, once fitted, it has become a fit and forget component and has been used in a wide range of conditions from the heat of summer to the cooler, wetter weather we are experiencing now.
With many dropper seatposts increasing in the amount of drop that they can achieve, which will be a benefit to some riders and styles, for cross-country or gravel riders such as myself, 100mm is all that is needed, and they are becoming harder to find, especially high quality and top-performing seatposts such as the PRO Tharsis.
The PRO Tharsis retails for £299. However, this doesn't include the lever, with multiple options available. The PRO Koryak command lever used for the test, for example, is another £40. While this combined price is cheaper than the RockShox Reverb Stealth at £395, there are other more affordable seatposts available such as the PNW Loam that Liam tested recently at £144. However, that was a little heavier at 524g.
Having less travel might seem like a backward step, but if you have an XC or gravel bike and don't need a huge drop, the PRO Tharsis is lighter than most of the competition but still keeps a smooth action with good seals and an oval shaft design that eliminates sideways play. The lever is extra but gives options for different styles and help create a setup that suits your individual preference.