Given the spatial constraints of a 31.8mm-diameter steerer tube and a 31.8mm-diameter handlebar, the shortest anyone has been able to go in terms of stem length has been just over 30mm – at least not without mounting the bar directly above the fork. Bike industry veteran Kirk Pacenti’s intriguing PDent handlebar concept, however, will allow for stems as short as 12mm and with no rise, thus opening the door for bike companies to further push the envelope of mountain bike frame geometry for better handling.
The key is a simple indentation in the center of the bar, which effectively wraps around the fork’s steerer tube and enables those two components to simultaneously occupy what was once mutually exclusive space.
“In CAD terms, the ‘dimple’ is a swept radial cut forming a pocket that allows the bar to wrap around the steerer tube,” said Pacenti in a press release. “The dimple is designed to allow for a range of head tube angles (63 to 69 degrees) plus several degrees of fore-aft rotation. By dimpling the handlebar we can make stems pretty much as short as we want. And unlike current sub-30mm stems, we can also keep stem and handlebar heights just as low as traditional designs.”
According to pacenti, the pdent ‘dimple’ allows the bar and steerer to overlap each other while still affording some rotational freedom to fine-tune the fit:
This small indentation is the key to Kirk Pacenti’s PDent concept
Handlebar strength supposedly isn’t compromised, either, and Pacenti says he has the finite element analysis and physical test data to prove it.
“The depth of the dimple has almost no effect on bar strength,” Pacenti told BikeRadar in response to some of our questioning. “We’ve tested dimples as deep as 15mm and have found no loss of strength. The reason for this is that there is nothing going on in the center of the bar from a strength standpoint. All the real loads are concentrated at the edge of the stem where the bar enters the stem.”
Mountain bike frame geometry has been trending toward longer top tubes, slacker head tube angles, and shorter stems. pacenti’s new pdent cockpit concept now might allow frame designers to push that idea even further still:
Long top tubes, short stems, and slack head tube angles have revolutionized mountain bike geometry in recent years
Although PDent will allow for stems as short as 12mm, Pacenti says the more practical lower limit is more like 15mm.
“The issue isn’t so much how short we can physically make the stem. Overcoming that challenge isn’t too difficult. The issue becomes with stems much shorter than 12mm and a swept bar, your hands can end up significantly behind the steering axis and create a very odd (bad) handling sensation.”
Production samples are supposedly scheduled for delivery next month with retail availability by the end of the year. All of the initial handlebars will be carbon fiber for now but aluminum ones may come later. That said, Pacenti ultimately hopes to license the PDent concept to other manufacturers – and he’s apparently already in talks with several major outfits.
Just in case you’re in doubt of Pacenti’s PDent concept, keep in mind that we’re talking about the same person who almost singlehandedly ushered in the 27.5in-wheeled mountain bike movement in 2007. If history is anything to go on, our guess is that we’ll be seeing PDent cockpits on bikes sooner than later.
For more information, visit pdent.pacenticycledesign.com.
Kirk pacenti’s rather ingeniously simple pdent concept uses a small indentation in the center of the handlebar that allows for stems as short as 12mm – and without any rise: