Ask Pinkbike: Bike Development Project, Fox X2 Bottom Out Point, Quiet Chain Stay Protectors
Here at Pinkbike, we get inundated with all kinds of questions, ranging from the basic "Can I have stickers" to more in-depth, soul-searching types of queries like if you should pop the question or what to name your first child. Ask Pinkbike is an occasional column where we'll be hand-picking and answering questions that have been keeping readers up at night, although we'll likely steer clear of those last two and keep it more tech oriented.
University Project - Developing a Bike
Question: A good friend is currently at university and has chosen to develop a bike frame as his final year thesis. He recently asked: Where do you find out information on the fundamentals of bike design and engineering? How do you go about figuring out the process for the first time?
 | This one is close to home, as I chose a similar endeavor for my university thesis. While it might seem like there is a complete lack of information, there are some bits and pieces out there. Bike engineering as a profession isn’t as established and recognized compared to the likes of aerospace and motorsport engineering. There’s interesting and relevant literature on websites like Linkage and i-track. It’s applied to bikes and explains the fundamentals really well. Lots can be found from Google with manufacturer's two cents and other academic documents from individuals who have done the exact same thing and set about designing their own bike. Pinkbike has also recently provided some information on suspension with the Behind the Numbers series, and we plan to offer more explainers and information in the future. Lots of literature is available from the automotive world looking at motorcycle suspension and chassis design. For example, Tony Foale’s book, Motorcycle Handling and Chassis Design. Many of the fundamentals and concepts are the same for bikes, but they do need to be translated due to the lack of internal combustion engine and also the lack of consistently smooth tarmac. There is, though, much less information about the process of bike development floating around. Most brands keep the exact process under wraps, and like most development cycles, it needs a couple of times around the Ferris wheel to understand and learn by actually do the necessary steps. However, here’s a really condensed version from concept to going about making something physical. Identifying the Concept – A bike doesn’t suffice. It needs a purpose, a potential rider, and potential riding terrain. The concept needs to be defined, no matter how obvious, and damn clear otherwise the coming steps will continue the haziness. Decisions always relate back to this concept and questions use it as guidance for an answer. Defining Ideal Geometry and Specs – You can define the geometry you would ideally want. It will change as you go further into development, but you need a starting point. Also defining all the parts you want to fit and be available to work with your bike. 2D of Geometry and Kinematic – Converting the numbers on a table into a 2D line drawing. Geometry is the first drawing, and you can add in as many knowns as you can to see how clearances and parts standards come into play. Adding in the kinematic is next, with a lot of time behind the scenes in deciding which layout, which characteristics and iterations of 2D design to put the pivots where you want them, and also in a place that works in the real world. 2D to 3D – Bit by bit you start to add in 3D volumes of parts and no-go areas of the bike. Important things like clearances and spec parts go in here and effectively narrow down the envelope that you have to work in. Rough volumes of your frame parts can go in here to. They help make the model look more like a frame, helping you see improvements or issues, and generally adding stoke as you can see a form you recognize as a bike. 3D Modelling – You can then start to model the parts of the frame properly taking into consideration your chosen material or production method. Tube by tube, forging by forging, bolt by bolt you’ll build up a full model of the bike. Iterations, Development and Refinement – Rarely does the first shot at modelling result in the final part. It takes time and many iterations to balance all the clearances, suspension layout, shapes, volumes, parts (I could go on forever here). These iterations can go back all the way to the geometry and kinematic as you tweak and dial things in. The more experience you have here results in fewer iterations between the first model and the final model. But this is usually the longest segment in development for the engineer, barring industrialization. Other factors like FEA or CFD can come in here and influence the development time and number of cycles round you go. Deadlines – Unfortunately, we can’t just develop for ever and a day. At some point we need to have a deadline and call it time to move onto the next stage in development. For my friend that will be when he has to write up the thesis. For brands it’s often moving onto industrialization or prototyping or handing the project across to a different department. As mentioned, this is a very condensed version. I honestly could write a book on the development process with all its factors and intricacies. And while the condensed version may put the process across as easy, it is anything but. However, the challenge and the final product are two of the most satisfying things ever. This question hit close to home and got me stoked to see someone wanting to develop a bike and perhaps pursue a career in the industry. Let’s get more smart people in the bicycle brain trust! |
Images from 77designz's We Develop a Bike Frame series show them moving from a simple definition of concept to a complete 3D model.
Fox X2 Bottom Out Point
Question: @sihotaman asks in the Bikes, Parts and Gear Forum: Trying to figure out if my X2 is bottoming out. Should it go right to end of the shaft/stanchion, or is it a few mm before, or does it vary between stroke lengths?
| RockShox have a patent on printing shock information on the shaft, which means other shock manufacturers can’t make it that easy. But most bike companies give you the specs for your bike including the shock length and stroke. Taking that and measuring your shock would give you your bottom out point on your X2. Another way would be to measure the eye to eye of your shock, and go check the Fox website to see what stroke is available for that shock length. Then you can do a quick measure on your shock to see where the max stroke is. On a lot of the imperial length shocks, the end of travel was easier to line up as the end of the shaft. But with metric shocks it’s not always as clear, since some shock lengths have multiple strokes. You can also let the air out of the shock (record your air pressure first), then compress the shock to see exactly where the bottom is. On the X2, there's a generous bottom out bumper that saves those last few millimeters of travel for really big hits. Always trying to get the O-ring to the end of the shaft might result in you compromising your setup for a bigger chunk of your riding, and getting full travel every ride shouldn't be a priority. The Fox website is really helpful for the information you’re after. And grabbing a measuring tape too will help implement that knowledge for your specific bike. |
The amount of shock shaft you have isn't necessarily the amount of available stroke. Finding out the actual stroke figure and measuring your shock is the best way to figure out when your O-ring is at the end of travel.
Quiet Chain Stay Protectors
Question: @rangerdanger2001 asks in the Mechanic's Lounge Forum: Anybody have a really quiet chain stay protector setup they recommend?
| For a long time, brands would include a chain stay protector with the frame. But some were more an afterthought with naff-all coverage and hard plastic adding to the potential bucket of bolts sound of your bike. Recently, more and more brands are doing a wicked job of covering up the chain stay and seat stay in good soft rubber, molded to the shape of the frame and including a ribbed design to deaden the chain slap. So now there’s less reason to buy Velcro or rubber tape to custom make your own. That being said, and looking at World Cup DH race bikes, we see a lot of custom setups still being used. Time and time again, soft Velcro and 3M tape seem to be the choice setups. Doubling up layers also helps add extra cushion for the chain. I’ve been a long-time fan of Velcro, and one of the best I can find, Tesa, comes with a 2m roll of the soft side and hooky side. Not one to waste the hooky side I often use it as the middle layer in the 3-part sandwich. First, I lay down a thin strip of soft on top of the chain stay. Then I cut the exact same piece of the hooky side and lay it on the first soft piece, hooks down. The final layer is the soft side and uses the full width of the strip to cover over the previous 2 layers and have good purchase on the chain stay. You can extend this as far back and as far forwards as you need and use a real sharp blade to trim that final layer into all the shapes you usually find at the yoke and drop out, and around the tire and heel clearance areas. 3M Rubber Mastic 2228 tape is also a really good option and a favourite on the World Cup circuit. It can be trimmed to all shapes and sizes and even molded to itself with a bit of warmth and thumb action. It can be a pain in the arse to remove off paintwork, so sometimes it’s good to lay down a layer of decent electrical tape before you add the 3M tape. That makes it easier to remove further down the line for sale or for re-applying a new protection setup. The 3M tape also enables you to get wild with your protector design with ridges and bumps galore. In any case, it’s best to stick your stuff to a clean and degreased surface. If it’s warm, that also helps the adhesion between the glue and your frame. Other solutions have popped up, with the likes of the STFU offering their take on chain slap silencing which appears to receive praise. Otherwise, channel your inner Neko Mulally or Aaron Gwin and do away with the chain all together. |
Velcro and rubber tape are two of the most common protector solutions. After that you can go wild to get the coverage and silence you're after.
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what the heck
The printing definitely isn't useless, I get use out of it all the time by not needing a tape measure to check sag on my Pike.
And obviously the patent isn't useless since it's prevented anyone else from doing it, so it's a differentiator for RS products.
just a clever patent engineer who is handy with words so he could reinvent a ruler, or is it really a new technical process (laseredging the writing into metal/surface treatment etc.)?
can somebody please elaborate?
RS with a patent application on writing things down where you need to know them.
Spec with the FSR patent(finally expired) on the suspension system used in almost every car for the last 40 years.
VPP and all the other patents on multi link suspension(invented something like 100 years ago.
A lot of these are just "we patent a pivot location in space on a very common type of suspension".
I always joked about patenting even tooth chainrings as it seems like it would work in the cycling world.
I don't know. Santa Cruz went after Yeti over violating their patent on an axle path, even though it was done totally different with the switch infinity rear end. Bike patents seem to be the silliest patents out there.
I think VPP may be a bit more difficult to work with as it requires bearings that take higher loads, higher speeds and they need to have less play than what horst link allows.
Just wait until you come up with a concept you want to develop and then a big player with big development, prototyping and manufacturing capabilities releases it to the market in 2 seconds for half the price you could ever do.
I'm sure the concept of intellectual property would still be BS by then...
The reason I say that patents like FSR are silly is because it was a patent on McPherson strut suspension, the most common suspension layout for vehicles. In my head it is a very short hop from being able to patent the most common type of vehicle suspension system to being able to patent things like even number of teeth on a chainring and whole number sizes of Allen wrench bolts.
There are other silly patents like split pivot where it is just a simple swingarm with a linkage driven shock, but with a patent on moving the pivot for the linkage an inch away from where it typically goes.
The problem isn't when someone patents something which is innovative or pushes the boundaries somehow. It is when someone takes a completely common design which has been proved to be a good idea, works well and is adaptable to many different layouts and situations. They then add "but on a bike" and somehow are granted a patent on it. Those are the silly patents, it is not new processes in manufacturing or actual inovations that shouldn't be granted patents.
Another great example is the Shimano derailleur clutch patent. They somehow patented being able to have the ability to turn off or service the clutch. Then SRAM somehow got a patent on being able to have a little poppet that keeps the derailleur fully extended. These are all just silly, not a big innovation, just the bike companies poking each other in the eye.
I agree that some patent offices could be more competent and use better criteria, but the patent system, even if subject to potential improvement, is fundamental for the market and for entrepreneurship.
Also, is very easy to say from the couch that "they are patenting trivial applications of existing concepts" but in real life the line is not that easy to draw. Don't forget a good number of innovations are in fact improvements on existing designs or the use of concepts from a different area. But someone had to have the idea to do that nonetheless. Patents exist to protect innovation and intellectual property.
Using some aerospace technology in passenger cars is generally considered an innovation, why can't be using automotive suspension designs in a bicycle innovative as well? Lots of shades of grey here
I see the point you are talking about but just totally disagree. Taking an established design and just applying it in an obvious way is not an innovation. Helmets in many Motorsport are designed to limit buffeting at high speed, should I be able to patent this for cycling because it is an established design but not specifically for bicycles? If someone started making cored composite structures for bicycle parts should they be allowed to patent this very established form of manufacturing because it is for bikes?
In my opinion, no, they should not be allowed to do that. These things are not unique, they are not innovative, they would take almost no effort to patent or research, because it is a completely mature technology and would just be an effort to stop other people from using a very obvious technology.
Being obvious or not is not the criteria used to warrant a patent, nor it is to consider something an innovation or not. Someone still had to come with the idea of applying the concept to the different product or field. On the other hand, being the first to do so meet the general accepted criteria.
I understand that those are not a criteria for patents, but should be, which is where FuzzyL is coming from. To just be able to make vague patents on established designs or on something like an axle path no matter how you get there is a broken system. Shimano patenting being able to maintain a part of your bike??? Come on, that is ridiculous.
Straight out of the US Constitution, Article I, Section 8, clause 8:
“The Congress shall have Power To…promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries….”
And also, 35 USC 101
"Whoever invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent therefor, subject to the conditions and requirements of this title."
RS has a fabulous patent and they are differentiated in the market as a result. They have secured a limited monopoly as a reward for bringing innovation to the marketplace.
For instance, with a 50mm stroke shock, I'd mark 12mm, 13mm, 14mm, 15mm, 16mm, 17mm (for checking sag), 25mm (50% usage), 37mm (75% usage), 48mm/49mm/50mm (for the last few mm of stroke)
www.pinkbike.com/u/JBW450/album/Handy-tool
I heard Sick are looking for new recruits
This is a German bike company explaining the whole process of the frame development in a very transparent way. BUT, it’s in German.
www.mtb-news.de/news/forschungsprojekt-mountainbike-geometrie-teil-1
@bbqmike: it can be classy when it's well done with patience and precision ;-)
MTBR frame building forum is also a wealth of knowledge. I know I just read a report jdyer8989 (over on MTBR) just wrote for one of his engineering classes that has some good information in it. Plenty of threads with good info if you search.
BTW you may find 3D graphics on a remote Windows server to be to slow to use.
The simplest answer is "it varies". Fox and RockShox both sometimes use the same size damper body/shaft for a few different strokes per e2e length, adding internal spacers to limit travel. So some shocks might not go right to the end, but others will be much closer.
My own DPX2 210x50 is the same as the 210x52.5 and 210x55, just by removing 1 or both internal travel limiters. I'll be having one taken one out during next service, since I bought a Stumpy 29 shock for my Stumpy 27, and the 27 frame has room for the extra 2.5mm of stroke at 52.5mm (allegedly it'll fit the 55, but it looks too close for comfort to me).
Even the uneeded answers are overly complex. To find what the stroke length should be you either enter the 4 digit code on Fox's website (I think there is a place to lookup by the serial number also), or you check the bike's manufacturer's site (and hope their archives of past models are easy to navigate). Compare that measurement to what you see, give or take a few mm for tolerances and bottom-out bumper, and boom done.
(As a last resort to get the actual stroke measurement you remove the bottom out bumper and measure how far the shaft actually goes in and out.)
Take the air out of the shock/fork and push it down. Voila, bottom out point.
The original question isn't about finding the bottom out point. It was if the bottom out point not being right up to the end of the shaft/leg is expected. OP was not seeing the o-ring get to the "end", and wanted to know if that's normal: "Should bottom out always use the entire visible shaft?". Thus the simple answer of "It varies." Then I gave a little explanation, still pretty simple.
Most shocks and bikes are made such that if you set the recommended sag, you will achieve full travel at least some of the time.
Also, have most Clydesdales concluded that our mass sufficiently dampens the shock? I have these knobs set to zero damping. I don't notice a huge difference when I go to maximum damping.
(For example, lets say I want to machine a head tube. Where can you find what the internal dimensions need to be?)
Headtube was an example, but things like current bottom bracket widths / diameters, axle spacings, correct threads for thru axle dropouts, standard seatclamp diameters etc?
Each manufacturer has their own version of the 'standard'. Usually published somewhere obscure on their website. What's the point of worrying about .25mm when your first bikes won't be within 3mm? For those purposes, measure what you have and use that info. For things like BBs dropouts, headtubes etc - you'd just be buying those off the shelf, not making them, so it's not really an issue. What's the bearing seat dia of a PF92 BB shell? Who cares, you're buying it ready made and using a standardized reamer - that someone has made up from the specifications - to ream it post weld.
Read Peter Verdone's blog (yes him) for more info. Most useful compilation of information on bike design and the process of design and manufacturing. He is (IME) willing to share information when asked from the perspective of trying to learn something, not debate with him about whether he's right or wrong (he's right BTW). He actually digs down into the 'how' of the standard and is able to articulate on why it might be flawed - disc mount 'standards' for example.
I'd start here: www.peterverdone.com/actually-youre-not-a-bike-expert
And this is coming from someone who just upgraded from an RS to a Fox because the DPX2 is so much better than a Deluxe (I'm assuming the damping on a Super Deluxe would be closer, but the DPX2 3pos-adj damper is hard to beat. And looking at parts I think the air spring on the 2 RSes is quite similar, and the Fox spring is just so much better.) The sag and full travel indicators still aren't even close to enough to make up for the performance difference.
That's not innovation
But you derailleur in a box makes it real quiet!