Digit Bikes Displays Prototype 125mm Trail Bike

 Old Mike Ferrentino likes it:
www.betamtb.com/bike-tests/trail/crowdfunding-a-better-moustrap-a-first-ride-on-the-us-built-digit-datum

 Yeah, with no upper linkage to take the side loads, the shock’s internal bushing takes all of the side loads exerted on the whole upper portion of the rear end from cornering, leaning, slapping corners, etc — all the way from the rear axle to the shock, along the 450mm+ “seat stay” element.

A bunch of mid-90’s bikes had MacPherson strut setups that loaded the shock that way, like Amp (and the many companies they sold their rear ends to) and Intense’s original M1...it’s hard on the shock bushings, and can be relatively flexy compared to many other linkage designs (and with more rear shock friction or “stiction” when side loaded — which is why most companies went away from that Mac Strut shock/rear-end design).

 Yep, that side-loading could be a problem
Some designs use a swing link to reduce side loading

With a fixed-orientation shock in the top tube you'd want a swing link pair similar to FOES for example: www.bikeradar.com/features/foes-21-xct5

 Yeah, it's a shame that a custom designed strut still gets compared to those old hack jobs from the mid-90's. It's a good thing that forks don't take side loads. Otherwise they'd fail all the time due to the side loading. Since it's impossible to design a strut to take side loads. Besides, if it's in the back of the bike it's a shock, not a strut.

 @gaberoc:
Forks have 2 sliders to distribute side loading / twisting. This strut has one, but it's pretty far from the bottom link which should help

This slider appears to be fairly small in diam compared to 1 fork stanchion

Just because it's in the rear doesn't mean it's a shock or strut. Struts are structural members of the suspension, shocks are not. Remove a shock and the suspension articulates the same path as it used to, remove a strut and the suspension no longer pathwise the same

It could be that this rear end can take years of side loading with minimal wear. But we the review board of PB armchair engineers just want to see the design study

 It doesn't matter how much space there is in the design of a frame, I won't ever stick a bottle in it and neither will I ever stop feeling incredulous as to why it is constantly mentioned as a standard by which frames are measured... Still each to their own I guess!

 Right?? They look great. I would love to try one.

 @WRCDH @chrod the slider uses bushings just like in a fork to resist side loads. So, just like in a fork, the damper shaft is protected from side loading.

Here’s some more on this subject: digitbikes.com/integer

 @bunjiman82: This bike proves that there is a person - in fact, perhaps many people - who would trade performance or durability for water bottle capacity. People to whom water bottle capacity is perhaps the most, nay only thing about a bike that matters.

It's only a matter of time before someone coats the inside of the frame with waterproof, food grade sealant and uses the entire frame as a giant water bottle. This my friend is peak water bottle engineering.

 @DirtBagTim: if you can't tell the difference in lateral load capacity between something 6" wide and something 1.5" wide then no amount of marketing speak will fix you.

 @Explodo, what part is 6" wide?

 @slumgullion: the distance between the fork legs.

 @DirtBagTim: Well, I bet that’s what their marketing information says — but comparing that rear end & shock to a modern fork isn’t a good comparison at all. Modern forks have a single-piece double-sided highly-reinforced magnesium slider casting, two stanchions spaced 6” apart, two bushings per leg for 4 total, a thru-axle to tie both slider legs together, a stiff crown (or double crown) to resist twisting, etc.

If the rear end of that bike had two 35mm shock shafts spaced apart a few inches, a 50% shorter lever arm (seat stays) relative to the position of the bushings, a bigger axle, and a stiff cast magnesium slider/seat-stay, then it would be a fairly accurate comparison.

 @gaberoc: Oh boy, where to start...

See my comment immediately above as well. But the comparison to 90’s bikes is drawing attention to Digit’s 17-inch-long lever arm that’s directly attached to the shock (just like a MacPherson Strut suspension design). The Digit design directly side loads a single-cylinder bushing-based shock — a custom planar needle bearing approach like in a Lefty fork would react those loads better.

This Digit bike and the old Mac Strut bikes have the same-length lever arm putting forces on the shock bushings (but the new shock has 2 bushings). That single-cylinder Digit shock will see vastly higher forces on the bushings than any fork, and vastly higher bushing loads / forces than almost any linkage bike shock. In fact, the Digit shock will see comparable loads to a 90’s Mac Strut bike, but the Digit shock distributes the loads probably 60/40 onto the two bushings. But if you don’t know what strut suspension is (for my comparison purposes), look it up. Obviously the Digit bike isn’t a MacPherson strut design — but the side-loading forces on the shock are comparable between a Mac Strut and this Digit bike.

And forks are a completely different load case, and see lower slide-side loading forces in general, and the forks have a single-piece 2-sided slider, a 15-20mm axle to tie both sides together and resist torsion, two stanchions / cylinders spaced 6” apart that are fixed on both ends, etc. Since engineering doesn’t seem to communicate the point, I’ll just say that comparing that Digit rear end to a fork is like saying eating with a single chopstick is comparable to eating with two.

 @chrod: Preach it man — refreshing to have informed commentary here. (But still, you’ll probably get downvoted by a bunch of people and the incorrect engineering commentary will get upvoted, haha).

 @WRCDH: yeah. So. I'm pretty sure @DirtBagTim is the marketing department. As in. He is digit bikes.......

 @WRCDH: how is it possible to vomit so much armchair engineering BS without taking a step back, to realize that half of your mechanical assumptions are wrong and that maybe, MAYBE @DirtBagTim has figured things out, just a bit more than you do?

I love how these bikes look. Never of fan or proprietary stuff, but someone has to push the envelope at some point for things to evolve!

 @WRCDH:

Ok you don’t like this bike, but the “engineering” based debunking you’re trying out makes no sense. Sure it’s got parts that resemble a fork… but that doesn’t automatically mean it should get two stanchions… it’s got pivots to deal with the side loads as well.

It’s like looking at a car, with an independent suspension setup for the first time after owning only leaf-spring vehicles— “Hey this things got no shackles, it’s going to eat itself!!”

 @WaterBear:

 @slumgullion: the part his ears attach to?

 @WRCDH: That's complete gibberish. The forces this shock is subjected to are completely different from what a fork is subjected to. To begin with, direct side loads are virtually inexistent, very much unlike a fork. What there is to be dealt with is whatever residual twisting motion comes trough from the lower axles. Whatever flex or play they have is what the shock will deal with, but dealing with it is much easier for the shock than it is for a fork leg to deal with whatever it deals with, assuming they are built the same way. I actually think this is the best suspension design, the stiffer and lighter suspension design that could be used for everything, from XC to DH. I envision a near future in which shock manufacturers sell models for designs of this type.

 @WaterBear: "This bike proves that there is a person - in fact, perhaps many people - who would trade performance or durability for water bottle capacity". I completely disagree with that. I think this design excels in performance and durability, compared to any other. Actually it excels in everything. Rigidity, weight and performance.

 @WaterBear: catch up bru.

www.scott-sports.com/gb/en/plasma-6

 @WRCDH @chrod @Explodo @dsut4392: in the fork analogy I’m referring to loads which push radially through the sides of the sliding bushings on each fork leg (such as braking loads), not to the lower fork arch/structure which ties the legs together to handle steering and synchronization duties. A better, though still imperfect comparison might’ve been an aircraft landing gear, which typically uses a single slider and a pair of torque arms to manage immense, critical loads. I chose to make the fork analogy because that’s what everyone here is familiar with, and because explaining the landing gear analogy also requires an explanation that the wheel on the Analog system is mounted to the element which is comparable to the landing gear’s lower torque arm rather than to the stanchion. Neither are a perfect analogy, they’re simply meant to illustrate with a familiar reference.

The Analog mechanism is a variation upon a slider-crank linkage. Slider cranks can be found in lots of reliable machines, including steam locomotives and combustion engines. The rear wheel on these bikes is mounted to the element which is comparable to an engine’s con-rod.. This all was covered last year ago if you care to catch up (review the design study), here are the notes and earlier discussion: pinkbike.com/news/first-look-the-digit-datum-has-shock-strut-suspension.html

The earliest prototypes of the Integer struts were made using needle bearings from a Lefty. This turned out to be unnecessarily over-engineered, some of that development story is covered here: betamtb.com/news-issues/why-its-ok-that-the-digit-datum-has-a-proprietary-rear-shock
The needle bearings were unnecessary because the upper and lower pivots of the rear triangle are about 12” apart. This wide separation provides a long lever arm, which begets low forces on the slider. When combined with the closed space-frame-like rear triangle these do a great job of keeping the rear wheel rigidly aligned with the front frame.

Obviously a theory as outlandish as this needs to be proven before it should be taken seriously, which is why I made bikes and proved the theory in lab tests and years of ride testing.

 @DirtBagTim: thank you for the excellent explanation and links all the way back to your initial prototypes (that is a fun and interesting read!)
You've clearly done your homework.
Can the PB armchair community bless this now?

 By lower axles I meant lower pivots, the word pivot seems to have taken a walk and axle was all I could think of.

 @lister11: holy shit lol

 @chrod: I have a question for you, as a member of the review board of PB armchair engineers: What does the design and engineering of armchairs have to do with bikes and bike suspension?

Office chair engineering seems much more relevant because of the gas strut, or la-z-boy engineering because of the recline mechanism. Their blessing seems more important to me than any of the lobbying groups for big-armchair .

 @DirtBagTim: literally spat out my coffee
PB's brand of backseat engineering is super special, you're right the traditional fixed-geom armchair doesn't do it justice.
Maybe a reclining chaise lounge from a psychiatrist's office? Super long, low, slack, and appropriate considering the implication for psychological counseling.

 @chrod: Roger that. The two sliders is important to resist twisting if the sliders are round. This strut is taking a decent bending moment, but this slider is also relatively a short to the first bushing, has good bushing separation, and the lower links will be helping to hold the load. I still have a 32mm 26" fork with 150mm travel that does ok..

As for the shock/strut my sarcasm tag wasn't working. I was calling out the post comparing this strut design to older side-loaded shock designs.

Armchair engineers and Monday morning Quarterbacks share a lot of traits. I try to avoid being either.

 @gaberoc: blast, my sarcasm meter was malfunctioning

 @WaterBear: username checks out

 Bikes with yokes on their shocks are becoming notorious for destroying said shocks with side loads. Sometimes it’s possible to mitigate that by allowing misalignment with spherical bearings, often not.

The Integer Strut uses bushings just like in a fork to resist those loads and keep things slippery. So, just like in a fork, the damper shaft on my bikes is protected from side loading.

Here’s some more on this subject: digitbikes.com/integer

 @DirtBagTim:

 Ring if you want back in.

 Why would the owner of the company say anything else??? lol

 A supercaliber?

 @mhoshal: I mean, the supercal suspension design is called isostrut, and is a structural component of the frame. It does seem fairly similar, the swing link at the bb being the main difference. Both appear to be structural in design, essentially supporting the rear end of the bike, and dealing with the side loaded forces of the rear suspension.

 @onawalk: AFAIK the Isospeed strut is serviceable with Fox parts. Maybe someone can educate me on the guts of this design-pretty cool regardless

 @Kiowa008: digitbikes.com/integer and betamtb.com/news-issues/why-its-ok-that-the-digit-datum-has-a-proprietary-rear-shock will get you started.

 The only bike I've wanted since the Swarf Contour. But I bought that, so I don't need this one :'(

 Mmmmmm swarf hardtails with paint splatter

 A fair concern. My recollection from previous articles is that anything you need to for service (seals, bushings, hardware), is all common items available at general purpose hardware stores.

 @pmhobson: If that is genuinely the case then I see this as the best of both worlds solution. The issue with these small manufacturers, is that they have a habit of going pop, leaving everyone in the dark.

 @Jaib06: after their first introduction, Rockshox were made by Dia Compe, I think there was an in between period before Sram acquired them. After Marzocchi went pop, Fox started making them.

 @DirtBagTim: I understand what you're saying, but there is a whole array of manufacturers who've just gone, disappeared with no support anymore, not to mention those still in operation with no support.

 @Jaib06: Yep. That could happen. There’s even a whole array of manufacturers who are still in business, from whom it’s nearly impossible to get spare parts.

 @Jaib06: here’s a little backstory on why I make the strut myself. betamtb.com/news-issues/why-its-ok-that-the-digit-datum-has-a-proprietary-rear-shock

 @DirtBagTim: That's hardly a convincing argument. If you can't get parts for a traditional shock, you can always just bin the whole unit and replace with an off the shelf part from any number of manufacturers.
If the damper unit in one of your struts goes, the options for repair or replacement are much more limited.

 @dsut4392: that's probably a worthwhile concern. I wouldn't be as concerned about breakage, but wear on the stanchion might be tricky.

Very rarely do folks bin an entire shock. Most of the time the only reason that happens is because the parts can't be sourced anymore. If Digit Bikes makes the parts relatively standard (say, a damper piston found in a Yamaha Moto Fork, common shim sizes, an IFP from Reverb, etc.) and provides it's buyers with a sort of "long after I'm gone, this is how you fix the Integer Strut" - then I wouldn't be quite as worried.

 @dsut4392: that is true, but frankly most people never do this, just as most people never replace the engines in their 4-wheeled vehicles and I think almost none buy a vehicle with that concern in mind. Sometimes people do need replacement shocks though, the replacement shock must have the correct e2e, stroke and tune, so the likelihood of that being on hand in an 'emergency' is relatively low. I offer complete replacement shocks, can offer loaners, and other options are available. I'm not selling outside of USA yet because I want to build a local service networks first.

 @PHeller: In a pinch, the pistons, glide rings, IFP's, etc can be switched out for parts from Rockshox, Fox, Manitou, DVO, etc. The seals are also available from industrial hardware stores. The stanchion is the most concerning item, but frankly, CSU's rarely need to be replaced for stanchion wear, nor did the shafts on Maverick monolinks. The stanchion is no more propriatary than the pivot screws on any other suspension bike. I will have spares, I guess worried customers could stock up on those, or keep a spare strut (which I have available).

 @DirtBagTim: I eat my words, you seem to have sorted everything nicely. Just a small suggestion as an (attempted) home mechanic, Hope Components do handy labelled exploded views of components with product codes, might you think of doing the same?

 @Jaib06: It's my list of things to do. I've not done it ahead of time because things change while still in development. The same was true for the early Hope components.

At present I'm in touch personally with every customer, if anyone needed a part I'm sure they'd contact me/Digitbikes directly and have me/us figure out what parts are needed.

 @DirtBagTim: Well despite the frame being out my price range, it sounds like you've got everything sorted, and I wish you the best of luck, we need more people like yourself who've actually thought things through!

 It's like feeding a Tic-Tac to a whale

 @Dogl0rd: it's like a mobile water bed.

 @ReubenSandwich: some broken ribs, a punctured lung, that's why I love it

 schaft

  Here's where I'm bookmarking the reviews of the Datum. They're all very positive: digitbikes.com/bikes/p/datum#Reviews

 Do you work at TSA and looked through my luggage as I flew out of SNA ?

 Probably digit = fingers, ring is a finger. How clever.

 @taskmgr: so is it "1 in the pink" or "1 in the stink"

 @Jedimtnbiker: 2 in the pink, 1 in the stink, thats called the shocker

 @slickwilly1: 2 in the pink and 2 in the stink, that's called the Spocker

 Don't forget to put this one up for the 2023 Enduro release.

www.bikepedia.com/QuickBike/BikeSpecs.aspx?item=72510

 Boulder! That's the brand I was trying to think of when I saw it. They had some sweet alloy frames that looked almost identical to this sans lower linkage.

 I'd imagine this integrated design results in less leverage against the shock since there isn't a upper eyelet

 the shock( or strut) is a load bearing part of the frame

 That's how I feel about my suspension fork too.

 The slider uses bushings just like in a fork to resist side loads. So, just like in a fork, the damper shaft is protected from side loading.

Here’s some more on this subject: digitbikes.com/integer