Spinner fork actually compatible with 27.5” wheels

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Tanatos frame actually compatible with Shimano cranks

When we conduct street interviews on Tanatos, the ultimate street MTB frame from our very own Libido Bike Co., we hear voices like these:

  1. “What’s street mountain biking anyway? I’m only interested in pump tracks, dirt jumps, slope style and skate parks, but not that one.”
  2. “They say the top and down tubes are triple butted and the whole frame is post-weld heat-treated to ensure optimal strength and toughness to be expected from chro-moly, right? Yet, the 2.5 kg weight of the frame is way sinful from my lightweight equipment fundamentalist’s viewpoint and thus to be persecuted.”
  3. “Yeah, that one. That stuff with all the nightmares when it comes down to parts to assemble on, huh? Especially, the BB and crankarm area are designed with BMX parts in mind, but I’m a MTBer so I’m clueless.”

Certainly. Let me explain.

  1. Street riding is literally where you jump off stairs, ride walls and so forth in the streetscape. Key points and features in equipment design are almost perfectly identical to those for pump, dirt, slope style and park. Spot on.
  2. Sorry, that was a design error. If only we designed it to weigh around 2 kg just like other aluminum frames intended for similar use, folks would have snapped the frames in several months to several years just as in other companies’ frames when ridden on the street, making us richer thanks to replacement demands. However, many who have had a chance to hop on ours have said “light and agile,” while none has said “heavy.”
  3. We’ve got great news for you today. The Shimano cranks fit.

Yes, you heard me right. Tanatos can actually accommodate MTB cranks made by Shimano. That also means there are rooms for you to try and fit other stuff like RaceFace as long as the spindle size is the same 24mm. Let’s take a look at some photos from our installation test.

Here are the parts required and points to note for the setup:

  1. Grab a 6805-series BB bearing set (= basically Shimano BB minus cups) for the bottom bracket
  2. 24mm ID spacers are needed for crank position adjustment
  3. Use a “Chain Line 3mm Outboard (2×11-speed)” crankset, a.k.a. Boost-compatible model, available in XT and SLX component series
  4. Use the original 24T or 26T front sprocket
  5. Choose any rear sprocket, typically 11 to 12T

Now let’s cover all the details.

#1, BB bearings.

Though you could hammer the bearings out of threaded Shimano BBs, there are tons of identical bearings w/ ID sleeves sold after market, so why not get them? If unsure what fits, whisper these magical words: “for Trek’s BB90.”

On the right you see the bearings with 24mm ID sleeves I got for this.

The plastic sleeves had a flange larger in diameter than the bearing, which need to be trimmed. To any size smaller than bearing OD. There seems to be a design intent to add extra sealing, but it’s just optional. The definitive sealability is ensured by the bearing itself.

Thus, there is no need to fine-trim it like this. I just wanted to, being hyped for the demo assembly this time. Then, press in the bearings and you’re done. Much easier than BMX-type BBs where you need to insert a metal sleeve between the bearings.

#2, spacers.

You will also need some 24mm ID spacers, which, again, you can just buy anywhere, whether being genuine Shimano parts or aftermarket. Your BB kit may also include some. You’ll need about 10mm thickness in total. If you’re a handy type, you could chop some 24 ID piping into spacers, turn stuff on the lathe, or even find 15/16″ washers that fit. By the way, 15/16″ may sound like but not really is such an odd number: you’ll find it in most BMX sprocket bores as well as brake master cylinders on some sports cars like 32 skyline, JFYI.

Sorry for the messy notes, as I was juggling between Boost-compatible and non-Boost cranksets. Anyhow, the final spacer setup was 7mm on the right and 2.5mm on the left. Though slightly dependent on individual frames, these are about the right numbers that ensure sprocket-to-frame clearance, correct chain line, equal Q-factors between right and left, and maximum engagement of the left crank arm onto the spindle. Which means, you can add a few millimeters worth of spacers if desired.

You get this much clearance with a 26T. As bike frames and parts deflect under stress, you’ll need at least about 1mm gap here. Currently it’s around 1.2mm.

Chain line measures at 49mm, matching that of 50mm at the hub. Roughly put, larger differences like 3mm or 5mm may (depending on the chain and sprocket) cause issues. Although, some people ride with like 10mm offset, and no instant failure is likely. That 1mm here is, from the bike engineering point of view, within the tolerance range of zero.

Then #3, the entree, the crankset.

B is your lucky letter of the day. It means it’s dedicated by the global giant Shimano to Li”B”ido Bikes.

This Boost specification is essential, as sprocket/frame interference will be an issue otherwise. If you avoid it by adding more spacers, you’ll run short of the engagement margin on the left crank. So just stick to the gift of “B.”

That’s it.

I kind of over-elaborated on it for the fear of misunderstandings, but it’s nothing more than a breeze for pro shop mechanics to assemble Shimano cranks on our frames.

*More unnecessary extra information from here on*

So for the black magic approach to just make it work, you’re all set. In case you had more whys and hows in your curious mind, I’m addressing further details below.

The keys here are BB standards and bearing compatibility.

Let’s start from basic industrial knowledge. Industrial bearings are standardized respectively for metric and imperial series with several selected ID and OD sizing. Application-specific standards like bike bearings may come with larger or smaller ID than normal, but still are based on some standard sizes in most cases. Among such standard OD sizes is 37mm, which applies to both “Spanish” BB bearings employed on Tanatos and Shimano’s Hollowtech 2 bearings, albeit the different IDs.

Now about BB standards on frames that accommodate them. I actually learned recently that the BB shell I designed for Tanatos is quite similar to the “BB90″ standard from Trek.

Here’s my take on what BB90 is. It’s an integrated BB shell combining a threaded shell and outboard bearing cups. Historically, 68/73mm threaded shells were the golden standard for some time, which housed loose-ball bearings inside. However, through the transition from skinny, square tapered spindles to the fat and hollow ones for the sake of greater rigidity marketed by Shimano, the bearings were eventually chased out of the shell and found home outboard. The Hollowtech 2 era comes. In terms of bearing placement, it’s similar to traditional headsets, despite the difference of press-in and thread-in cups. Now, someone may have thought, “why not integrate the external bearing housing part into the frame as in the recent headtube innovations?” and voila, that renders about the exact dimensions of BB90 on the drawing board.

The BB90 and the “Spanish +” on Tanatos share the same 90mm shell width and 37mm bearing OD, with the only difference being the press-in depths. 7mm-wide 6805 bearings are used for BB90, while we use 9mm-wide 6904-based Spanish bearings. BB90 features flush mounting, while we press bearings 10mm in (1mm recess from shell edge), so there is just 3mm difference on either side if 6805 is pressed into our shell. Now, it’s so simple – just add spacers.

There also is an opposite hack called “Shimanish BB” where you press 6904-series bearings onto Shimano’s outboard BB cups to accommodate BMX cranksets. Either way, parts selection is key to success, in such manner as to ensure proper chain line, Q-factor, etc. For Shimanish, BB spindle length is probably the biggest requirement. For our case, front sprocket/frame interference was the highest hurdle, which just became solvable thanks to the release of the Boost-compatible cranks. I really appreciate all the requests, hints and information I have received from people that led to this fitting test.

The parts needed for this setup, like the BB bearings, are not our regular stock. However, there may be cases we can help you with if procurement is too difficult for you. Please don’t hesitate to ask.

Happy press fitting, everyone!

Spinner Cargo 34 fork travel reduction guide

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Ain’t Boost standard nothing but a joke?

This talk will involve some technical stuff about MTB. It may not be interesting without relevant knowledge, but we’re sorry, we are not elaborating on all that because there is just too much.

Back when MTB was born, component standards were pretty simple, with dimensions of parts unified in most cases. Like if you buy MTB stuff somewhere, you can put it on yours. It was easy to mash two bikes into one. In the last decade or two, though, bike companies started coming up with their own standards, making it a nightmare for you if you wanted to build your own bike from scratch. The kind of diversification as seen in the wheel size starting from 26″ to also include 29″ and even 27.5″ later has happened to virtually every part of the bike and fitting standards therein.

On one hand, this is great. It has made it easier to build a bike that suits the rider’s build and preferences. It’s also just necessary sometimes to step out of existing standards if you are striving to create the ultimate industrial products. Without such attitudes, the Ahead system deriving from the MTB world would not have taken over all sport bike segments including road racers and BMX. We, too, employed our original BB standard for our Tanatos frame because it would just make some industrial sense to us that way.

On the other hand, as bike designers, we are skeptical about “new” standards without reasons. Case in point: Boost standard for MTB front hubs (accompanied by the new rear hub design, which we’ll skip on as there is just too much to mention).

Front hubs of sport bikes, mainly those equipped with multiple speeds, namely road and MTB, typically used to have a 9mm shaft with quick release. The width, called the over lock nut (OLD) length, was 100mm. In line with standardization of suspension forks and disc brakes, however, mountain bikes especially those in mechanically demanding usage such as downhill saw the rise of 20mm axles in 110mm width since around the end of the 20th century. The thicker axle was to compensate for the loss of rigidity owing to the structural limitations of suspension forks. The wider hub contributed to maintaining the lateral rigidity of the wheel with its greater spoke flange widths compensating for the space given to the disc rotor.

Then about a decade ago, the next standard with 15mm shaft and 100mm OLD appeared, claiming its merit in weight saving thanks to downsizing. I would say it’s 99% nonsense, with the remaining 1% being stingy reasons about stimulating new demands out of saturated markets. That’s what we suck at anyway hence is what we don’t care much about.

To put the design problem simple, the claim that the thinner tubing makes it lighter will get you something like the Alan road frame back in the day. Sure, it’s easier to make it light with smaller diameter, as long as you don’t care about rigidity. Those 20mm and 15mm hub shafts are usually made of aluminum, a material that usually has a better balance between weight, rigidity and strength if designed with a larger diameter with thinner wall thicknesses (specifics depends on material characteristics, but aluminum performs better with ever larger diameters typically). If they were serious about ultimate cross-country performance, it would have made more sense to create a thin-wall 20mm shaft. Sorry it’s not even theoretical analysis but pure gut feeling of mine, but I’d guess that’d be lighter and stronger than regular 15mm shafts. On a side note, hub manufacturers offer a bunch of hubs compatible with both 15/100 and 20/110, which realistically means there are’t many of those optimized for either standard.

Now, the industry has come up with new stuff, the Boost standard with 15mm shaft and 110mm OLD. If I’m to elaborate, the wider flange width ensures plenty of strength for large wheels, with proven lightweight. All the better than the previous 15/100, so why not replace your current one? To put it simple in my own words, that’s the death of 15mm standards. Lightweight-minded with all the sacrifice you could ever think of, as if in a case of a boxer with his hair shaved and teeth pulled out for weight loss, and he’s saying, yeah let’s go back to 110 heavyweight, I’ll show em what I’ve got. He’ll die. The longer span means more diameter needed to ensure rigidity anyway, right?

So here is my conclusion, full of biases based on personal preference so it’s up to you whether or not to swallow. The 15mm standards have gone in a full circle and are going to die off, handing their foothold back to the good ol’ 20/110. If the industry was serious about optimization they may land on something like 25/120, but it’s going to take a lot to rewrite whatever exists. We may witness the scene revert to 20/110 in a few years, and see a new struggle for the very best that may likely entail not only the dimensions but also the hub fixing mechanism in a decade or so that follows.

Tire bead breaker build (1)

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