How short can we (or should we) go? Based on the current trends in mountain bike geometry, that seems like a question worth asking. It’s also a question that got Kirk Pacenti thinking. Shorter stems and longer top tubes have a number of benefits – increased control, longer front center for better stability, and the ability to run wider bars with effectively the same reach.
But as geometry has changed to adapt to shorter stems and wider bars, the limiting factor to going shorter has been the stem itself. Sure, stems shorter than 30mm have been available for awhile, but each comes with at least a 30mm height penalty which itself becomes a problem when you’re trying to get the front end as low as possible. At this point a few companies are offering stems as short as physically possible – basically adding just a millimeter gap between the steerer and the handlebar.
Pacenti thinks even shorter is better, and knows exactly how to do it…
The only thing preventing current stem designs from getting even shorter is the interference between the handlebar’s center and the steerer tube. The answer? Put a dent in it. After apparently coming to Kirk during a ride, the thought was turned into reality with the new patent pending PDent bar and stem from Pacenti. While the first version of the stem measures in at 25mm long, Kirk says the design will allow stems as short as 12mm and their IP will allow them to go even shorter, though Kirk’s keeping that part of design secret for now. Truthfully though, he feels that the ideal size range for the future of mountain biking is between 12-27mm which until now hasn’t been possible without the height penalty.
Designed to allow for head angles from 63-69º and plenty of fore/aft rotation, currently the Pacenti PDent bar must be used in order to run the PDent stem. The PDent bars can be used on other stems, but the 25mm stem requires the PDent bar.
Initially concerned about what the dent would do to the structural integrity of the bar, Pacenti ran extensive FEA and lab testing on the structure which showed that the dimple didn’t have any effect on the strength of the bar. Essentially, since the stresses are concentrated at the points where the stem clamps to the bar, the dimple inside those zones is unaffected.
Due to the radically short design, the PDent bar and stem isn’t for everyone. Kirk states that the set up can be used if your bike allows for the position, but it will also allow for riders between sizes to size up, and is especially good for bikes with longer top tubes like those from Mondraker, Nicolai/Mojo, and new bikes from GT. The system should be available for purchase in late 2015, and Pacenti is currently in talks with other manufactures about licensing so you may see this on some other brands in the time to come.
Make sure to check out the in depth theory behind the move to shorter stems on the Pacenti site.
