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…

front-of-bar040715-3 Bar Top-Down Pacenti_040715-2_lowalt crop

Pacenti-1-crop-Lo

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.

pdent-diagram-1024x397

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.

Pacenti-2-Lo
Matt Hartwig of Push Industries rides it. Photo: Thomas Licht

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.

35 COMMENTS

  1. @ Tim, I expect we will eventually end up with 0mm reach stems just like MX bikes use. Behind the steerer would certainly making leaning into corners… exciting.

  2. The same thing could be accomplished with oddly swept-back bars. But the advantage of this system is that the bars can still be used with normal stems and “normal” geometry frames.

  3. the front center dimension is the distance between BB and front axle, it is independent of stem and top tube length.
    If shorter stems increase “control”… man, trials riders are going to feel soooo dumb. Perhaps you meant something less absurdly vague?

  4. This is both clever and stupid at the same time. Why not just made a one piece stem bar combo? it would be lighter and the lenght could be zero.

    Short stems are nice and all, but this contraption is really unnecesary.

  5. The bars have no forward sweep, it’s an optical illusion in this particular photo.

    The bars are pretty standard 5 x 7 riser bar. The radial “dimple” in the bar was designed to accommodate head tube angles from 63* – 69*, plus a few degrees of additional rotational adjustment on either end of that range. More than enough adjustment built into the system for contemporary frame geometry.

    0mm stems really aren’t where we want to go… something north of 12mm but less than 30mm should be about perfect.

  6. Pay attention here folks… Motocross and Supercross have been doing bars-above-steerer for years… there is no such thing as a “stem” on motorcycles. Stands to logical reason that MTB should follow. MX and SX carry a helluva lot more speed/power than MTB.

  7. Okay, so why not just have bars where the backsweep starts earlier, or add a little extra backsweep between the stem and the grips? That way you don’t have to buy both a proprietary bar and a proprietary stem. It’s not the stem you’re holding onto, it’s the bar. I’m not seeing the FEA showing this is a stronger or stiffer setup than a non-dented bar either.

  8. Fair enough concept, but how is this worthy of a patent? That’s a system that’s seriously broken. The dent is just as obvious as doing rearwards “rise”, or any other way of bending the bars around the steerer, or for that matter placing them on top.

  9. Kirk was telling me about this stem and bar last year. I think it’s a pretty good idea. While it may not be what I need in a stem and bar, I do have customers who could benefit.

    Kirk, don’t worry ’bout them. License that design to other companies and watch these ppl totally drink it up then.

    Ronald from RCB

  10. I’m usually for more open patents too, but this isn’t totally obvious and is likely patentable. At the very least the “pat. pending” offers some protection and can be a business advantage even if in the end no patent is issued.

    It’s not just a simple dimple. It still allows some rotation, and they somehow have made it so the rest of the bar in that area is nice and round and still works in normal stems.

    Try dimpling a round tube yourself -this is not as easy as it looks to accomplish.

  11. @typenschilddelete I’m sure it’s legaly patentable, I’m just saying it shouldn’t be. How hard something is to manufacture doesn’t/shouldn’t have any effect on patentability. AFAIK you patent the end product, not the manufacturing process. And the shape of the end product is trivial. A system that produces millions and millions of patents causes more harm than benefit to innovation, it benefits only lawyers and trolls.

  12. @advcyclist @J N H etc. re MX mounting. MX bikes don’t really use 0mm mounting (5mm to 30mm is the usual range) and there are a host of geometry relationships in play
    ( >20″ travel affecting angles, much larger caster, very different bias, much lower COG etc.)

  13. please to be explainin’ how a 15mm stem is ideal or “the future” for any normal shaped human on a mountain bicycle with standard/normal geometry.

  14. @ Gunnstein: >AFAIK you patent the end product, not the manufacturing process.

    Nope. You can do either or both a product or method patent. Usually the examiner won’t let you do them both in the same application, but sometimes.

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