Kickstarter product campaigns often aren't that promising, but this one caught our eye. The Datum from Digit Bikes is the brainchild of Tim Lane
, the man behind DirtBaggies
and several successful road bike designs. It's a trail bike with a pretty interesting suspension arrangement. The bespoke rear shock/strut is housed inside the top tube and is held rigidly in place with a pair of fork bushings; it forms a structural and integral part of the suspension system. The rear triangle is attached to this with a pivot, while a short link connects the bottom of the rear triangle to a bottom bracket concentric pivot.
Digit Datum Details
• 140mm Analog suspension with shock strut claimed to be lighter, stiffer and simpler
• Intended use: Trail
• Wheel size: 29" front / 27.5" rear
• Designed for 150mm-160mm fork
• 12" shock with 2:1 leverage ratio claimed to offer more consistent damping and spring rate
• Made in the USA
• Pricing TBC
The design is called Analog because the sliding strut is an analog (equivalent) of the rocker link at the top of a conventional four-bar design. Digit aren't the first to use a sliding element in place of pivots as part of the suspension linkage: Naild
and Yeti have done that before with their R3act and Switch Infinity designs, respectively. But Digit's design is different in that the strut is both a structural element and a shock, which cuts down on the number of parts required.
Sliding suspension elements have been proven to work before.
Digit aren't the first to do this either, as Resistance Bikes
, Maverick's Monolink
and Boulder Bicycles
all used integral shock struts, but the Datum is a little different to all these designs.
When asked to categorize his design, Tim Lane says he started out referring to it as a "3-bar link". He admits that's "not quite engineering correct [but] it's a snappy name that conveys the point that there are fewer parts." He added, "I think it could be called an 'offset slider-crank mechanism with the wheel riding on the connecting rod
'." Probably a good marketing decision not to call it that.
There are three pivot locations in total - two on either side of the short lower link, and one where the swingarm drives the shock/strut. That may sound more complex than an Orange-style single pivot, but even those have three pivot locations if you include the two rotating shock bushings. Conventional four-bar bikes (including Horst-link and twin link designs), as well as "faux bars" like Kona use, have four bearing pivot points plus two on either side of the shock, so six in total.
Digit claim that fewer rotating parts mean they can save almost a pound when compared to a four-bar or faux bar design, plus superior stiffness, reliability and lower environmental impact due to the lower part count.
The design also makes it possible to use a straight seat tube, which makes room for long dropper post insertion lengths and two water bottle mounts inside the frame. There's also very little seat tube offset, so the effective seat angle is almost the same no matter the saddle height.
One thing which could be seen as a downside is the need to design a proprietary shock that also functions as a structural frame member. Digit sees this as an advantage, however; because there are no conflicts for space inside the main triangle shared with rockers and water bottles, it allows them to make a bespoke super-long shock.
The shock strut is 12" long, which apparently allows for larger oil volumes for better damping consistency and larger air volumes for a more linear spring curve, meaning less beginning-stroke stiffness and more mid-travel support. "Because my shock is so long, life is easier for the oil and there's much more of it," Lane explains, "I can have a nice long air spring, and the low leverage ratio puts much less load into the frame and pivots, plus the shock is supported by fork bushings so there's no risk of sideloading the shock shaft."
The damper offers external low-speed compression and rebound adjustment, while the air spring can be fitted with volume spacers to adjust progressivity. The shock is said to be fully self-serviceable using no proprietary tools, and the first service is free to frame buyers. The average leverage ratio is 2:1, meaning the shock moves 70mm over the 140mm of travel. That's a lower leverage ratio than most bikes, which should improve reliability but could increase friction.
The aluminum frame is mullet-specific, offers 140mm of rear travel and is designed to be paired with a 150 or 160mm fork. With a 65-degree head angle and 75-degree seat angle, the geometry is modern without being boundary-pushing.
If the funding round is successful, Digit will make the frames in Southern California and hope to ship the first frames in March 2022. Pricing is still TBC.Check out digitbikes.com for more