More Wobble Diagnoses

Here are some responses to my previous post on wobble:

1. I'd mention how non-parallel drops will bow a hub axle & 'cone' out the bearing seat(s). I went through a couple hubs before I realized this. -WeedBMX

2. Some bearings just simply have play in them too. I've cured some wobbly hubs with new, higher quality bearings. I've also cured some hubs that are way too tight with once wobbly bearings. Although very very tight, bearing manufacturers also have a tolerance to work with. - Couch of Zodiac Engineering

3. It is very important to distinguish between bearing arrangements that may LOOK similar, but behave in different ways.

With a crank:-

The load acts in a relatively constant direction relative to the OUTER race, so the INNER race "sees" a load which acts radially but at a varying direction.

ie. if you mark a white dot on the inner race of the BB bearing, then when the dot is at the bottom, the load acts to push the axle INTO the dot.
But when the dot is at the top the load acts to pull the axle away from the dot.

So it is important that a crank axle is a fairly close fit inside the bearing to prevent the axle "rolling around" inside the race and causing wear.


With a hub:-

The load acts in a relatively constant direction relative to the INNER race, so the OUTER race "sees" a load which acts radially but at a varying direction.

So with a hub, it is more important that the OUTER race is a good fit in the hub shell and the inner race can be a looser fit on the axle (which helps allow the bearings to align with each other).


There are a number of standard bearing "arrangements" based upon whether load is radially oscillating or constant; and that "fully retain" different races. For the record it is "incorrect" to fully retain all the races. Bearing mountings should allow for differential thermal expansion of different components. - G of G-sport

Warranty Claims

I've had a number of cats come through the bike shop lately with various warranty claims. Some are legitimate (such as a new KHE tire's blown sidewall), while others are completely rider error. In this post I intend to discuss the purpose, scope, and effects of the warranty process...

A Little History

There was once a day when a manufacturing failure would lead to the rider swear off that particular company for life... or until they came out with some far too cool new part. At the same time, the quality of complementary that made its way into the BMX market was marginal. Tolerances were wide open, if specified at all; and materials were often very poor. What this did was leave an opening in the market for some quality.

Enter the high(er) quality manufacturers. Profile Racing began offering tight tolerance machined hubs; Primo introduced their cold forged Powerbite cranks (cold forging offers greater tolerance control than casting or hot forging along with good grain orientation in the outer limits of the structure). These components earned a reputation for being less likely to bend, break, or snap. But how could companies compete with high end, and high dollar, components?

In the late 1990's Odyssey took a turn from mediocre quality, fair variety components, toward a different business model. The idea was to introduce two concurrent and complimentary ideas to their product line: post weld heat treatment for their forks, and a no-questions-asked warranty.

41 Thermal, as they call their heat treatment regimen is designed not only to reduce the heat affected zone inherent in welded components, but also to make the component bend noticeably before breaking. From this, Odyssey forks developed a reputation for being extremely strong, while staying cost, and weight competitive. Even though there have been quite a number of bent components over the years, the easy, and fairly quick warranty process has reduced the amount of negative feedback on their components.

Today, it is quite common for riders to suggest purchasing Odyssey components because of their amazingly lenient warranty process (Nuno even offered to warranty my cracked Polycarbonate Twisted pedals!) Picking up on this, many other manufacturers have eased and streamlined their warranty systems. They have learned that supporting the rider, even to some immediate detriment, can have long term beneficial effects.

Purpose of the Warranty Process

You can ask around and I am sure you will get various responses to this question. My response is from the perspective of a shop manager, rider, and prospective manufacturer. The warranty process should be designed to induce a positive company image in the mind of the rider. What this means is that a component should not fail without due cause (i.e. riding hard will inevitably damage parts, especially when we get into lighter weight components). If a component fails due to manufacturing errors, it should most definitely be covered under warranty. A common example of this is a crack directly on a weld, which indicates contamination in the melt pool, and subsequent weld.

There is another purpose, as the Odyssey example shows: to increase customer base simply because of the streamlined warranty process. Although I do not list this as a primary reason for purchasing a particular component, it is certainly beneficial to the rider; even more so if they are on a budget.

When a claim goes too far

I had a cat come into the shop with corroded nipples on a machine built (pre-built) wheel. He claimed it was a warranty issue because he had never see that happen before. Perhaps unfortunately for him, I had. The corrosion was due to excessive sweating seeping onto the aluminum nipples. The electrolytes in sweat increase the rate of oxidation (and on some materials nitrogenation) of materials. Often these oxides are much more brittle than their parent materials, leading to sudden failure or cracking. The point is manufacturers have no way of knowing, nor a reasonable way of preventing all of the outlying conditions that may lead to failure.

So the next time a part fails on you, ask yourself a few questions:

* How did the component fail (break? bend? where? how much?)?

* What lead to the failure?

* Could it have been a manufacturing issue?

Of course you could send in the product in any case, but if they deny your claim, don't give them a bad wrap if they conclude that it is not a manufacturing issue. If they do deny and you feel it is unjust, post it up on line with the question of whether it is a manufacturing fault.

Bottom Bracket and Crank Standards

Browsing around the Cozy Behive, I found and article on the evolution of bottom brackets and interfaces in road and MTN bikes. Unfortunately, no mention of BMX bottom brackets. Here is the BMX-U page on BB's.

BMX has gone through the same evolution (loose ball, cartridge, press fit); the only difference being that BMX adopted the cupped, press fit US bottom bracket. Since then, we have moved independent, albeit parallel to the development of road/mtn bottom brackets. We have arrived at something very similar to the BB30 standard:

BB30: 42mm ID 68mm width

MID: 41.275mm (1 5/8") ID, 68mm width

Advantages of BB30

BB30 uses a standard metric ID, which makes off-the shelf bearings available for up to a 30mm spindle. Though it should be noted that to fit a fair sized bearing to take the extra side loads our bikes encounter, it may be best to limit spindle size to 25 mm. Even so, 25mm is larger than our existing 22, and 19mm spindles. With this increase comes the prospect of high strength 7068 or 7075 Aluminum.

Using an existing standard accepted by the rest of the cycling industry opens up the BMX market to larger manufacturers, higher technologies, and respectively, BMX companies' customer base. Hopefully, expanding their market will help smaller operations survive. Profile has a similar situation with their 48 spline cranks and dirt jumpers.

Fair Wheel Bikes Road Hubs Review

Wow, what a massively comprehensive review. Thanks to the guys at Fairwheels for their continued contributions to the cycling community! Although it is all road stuff, There is quite a bit we can take from this. I'll write a post sometime soon discussing the various designs available for cassettes. And here is an interesting quote about bracing angle. I am sure the square rule works well as an approximation for road wheels, but I wonder if it is accurate as we get down to smaller rim diameters:

Notes on Bracing angle: Bracing angle (or flange offset) is the most important factor effecting the lateral stiffness and stability of the wheel. The lateral stiffness imparted by the spokes goes up with the *square* of the bracing angles, while using more or heavier spokes only results in a linear increase in stiffness... and an increase in weight.


And now for some hub porn

C-4 Flangeless



Alchemy with super wide bearing and flange spacing


Tune carbon-wrapped flangeless:

Alchemy rear with bearings inside and outside driver to maintain concentricity




Tune with Carbon-fiber axle. Who wants to be the first to test this with pegs ;)

Chain Tensioners

... Or wheel positioners. It really depends on your purpose for putting them on. You may want them to maintain a consistent chain tension, like my tail-whip fiending friend, so the pedals will stay in position when your feet leave them. Or perhaps your wheel moves on you when you don't have it slammed in the dropouts, but slammed, the chain is too loose. A positioner will allow you to give extra support to prevent the wheel from moving. This post will analyze the various types of possitioners available and weigh their pros and cons against one another.


Pull-Type
The original tensioner design consists of a washer around the axle, with either a stud and nut, or bolt. The bolt/nut tightens against a plate on the end of the dropout
Some pull-type tensioners have issues with shorter dropouts. But as of late, slimmed down designs (such as the Poverty Short Stop shown above) have almost done away with that problem.

A variation on the design is the Premium SS Tesnioner, which uses the bolt to push directly against the dropout. With the proper bolt size, this tensioner can work with any size dropout. Unfortunately with only a bolt in contact with the curved end of the dropout, it can move around pretty easily.


Push-type
These tensioners have appeared in recent years in two variations:

1. Integrated tensioners into the dropout use a set screw or bolt through the dropout to push the wheel back and into possition. The pressure on the axle threads may compact them slightly. This may cause some issues on hubs with threaded collars, and may allow the wheel to slip forward slightly as the threads compact. (ex: Sunday wave dropouts)



2. Bolt-on tensioners use a bolt-on tab similar to gyro tabs and cable guides. They push on the hub collar rather than the axle itself. In some cases there can be interference with the chain and/or driver. (ex: Fly Tierra)



Spacer type
In the past, riders have jammed various items between their axle and dropout to allow their wheel to be "slammed". I used aluminum cable ends crushed down and carefully inserted, but they would continue to compact, and were difficult to work with. Simple BMX has come out with specially cut spacers in 0.1mm variations. With the availability of half-links (albeit current designs are rather flawed in that they stretch easily), a wheel only needs up to 13mm of adjustment as the chain is 12.7mm pin-to-pin. Unfortunately there are reports of these compacting down (or more likely compacting into the threads of the axle)





Drive vs. Non-drive
With the chain on the drive side, tensioners only need to work in one direction (the chain works in the other). As such, tensioners have been designed to work only moving the wheel out of the dropouts. The problem arises when working with the non-drive side, especially with pegs. When a load is taken pushing the drive side axle out of the dropouts (such as an ice pick or tail tap), the tensioner does not support the wheel, and thus it can move out of position. To fix this problem, we may want to start looking into a hybrid push-pull tensioner. I have done some work integrating this into a hub collar and/or guard. I'll post up more info when I get some prototypes done...

Book Recommendations

I've been doing some reading as of late. Here are two of the books I found most useful:


Industrial Design by Jim Lesko

I picked this book up at the local library expecting the usual design crap: Furnature, cars, and hubless wheels. To my surprise, I found a well organized overview of manufacturing methods for a variety of materials. The book doesn't go too in depth into any particular subject, but it provides a nice introduction and reference for the aspiring product designer. More than just an easy read, Lesko includes many informative diagrams. These pictures are worth a thousand words; I highly recommend this to anyone getting into the field/hobby/whatever.




The Ice Cream Maker by Subir Chowdhury

I know what you are thinking, "what the hell does this have to do with BMX?" This short (115 pg.) book is the tale of an ice cream factory manager who develops his company into a more efficient, competitive, and quality-focused organization. The book focuses on how supporting your customers and community (that includes everyone from the employees, to the people who live around you), in order to create a healthier, more self-sufficient organization. For any of you in management, or looking to get into business for yourself, this is a required read :)

How are the Director dropouts held together

I did a post a few days ago listing the Director patent. It was chalk full of interesting stuff. But the question quickly came up: How is the dropout insert held in place. The drawings show a seam weld, but those don't appear on production models. Eggit helped clear it up with some rawing and bluing of his:

Dropout insert from patent


Eggit's photos show spot welds holding it together


Edit: Comment from G

No spot welds.

Read the patent, look at fig 5 and item 67 in particular...

G.

An open attempt to improve axial free coasters

A few members on BikeGuide have started discussing how to improve axial coasters. The idea is to come up with a design that can be easily made and will at least improve the issues faced with axial freecoasters. Here are some requirements (see the thread for more details):

• Low cost (i.e. using as many existing components as possible)
• Low(er) weight; sub 20 oz
• Suitable for peg use, not necessarily abuse.
• Better bearing system, especially in the driver
• Easy, and safe maintenance (i.e. no little pieces to damage)

If you have suggestions, or would just like to participate in the process, please post your comments in the BG thread, or here and I will forward to the thread. Once we come up with something suitable, I will post the dimensions, CAD files, and any other info on BMX-U.

Director Patent and Construction

I was pleasantly surprised to find this in my Google Reader list this morning. If you don't know about Reader, it is a web based application for aggregating RSS feeds, updated search results, and other periodicals. The recommendation and searching functions are pretty good, but some of the BMX RSS feeds are surrounded by noise (i.e. one good feed with a bunch of dead ones).


Director Forks have interested me since they were first unveiled. Integrating the dropouts with the fork legs is a logical step that was taken by road and some mountain quite a while ago. Eliminating the weld at the dropout avoids cracks there as well. And using a simple insert gives good compression support, while maintaining a hollow dropout for weight. Overall a nice design. Unfortunately, since this is included in the patent, any other company who wishes to go the integrated dropout route will have to find a manufacturing method that does not violate George's patent.

The crown junction is another unique feature of the directors (unless you look at sunday's chainstay wishbone that G had a hand in as well). The claim is that it reduces localized stress and extra material found in conventional open ended steerers.

I'll dig into this deeper after some discussion, but I really have to head off to class, so this simple post is all that is going up for now :)



Some random feeds I subscribe to (post yours up!):

- Bicycle Design is not updated all that often, but can be interesting.

- Sweeter Skins for those of you with Android phones, this is really the future in UI.

- Roues Artisanales mostly posts in French about the road bike weight weenie scene.

- Cool Tools updates often with some neat little productivity tools.

- Scheier on Security is one of my favorite blogs. Written by a security expert who is often contacted to comment on security issues by media, government, and private agencies. He takes a very logical approach to dissecting issues. His post "Fear and Over-reaction" really struck a chord in me.

- Google Patent "Bicycle" Search feed updates every so often with new results (usually patent applications or updates). You can use Google patents to get customized results.

- Endless Innovation has some good posts, but can be a bit repetitive at times.

- Physics World has some neat, informative updates about research findings in classical, relativistic, and quantum physics.

- The Big Picture has great photography, and is updated very regularly. Each post contains a link to 40 high-def photos about a certain topic.

- F-Secure has regular, detailed computer security reports.

- Cycling Tech hasn't been updated in 2 months, but it has some cool stuff when they do.

- Industrial Design has a lot of design *cough* Crap *cough*, but you can find some real gems in there. Be weary of hub-less bicycles, there is a reason they haven't gone to production.

- Ted Talks are a great way to look at a situation from a particular (speaker's) perspective. They are all free videos on a very wide range of topics.

The History of the Lathe

Here is a very in-depth look at the history of the lathe. He does a good job of explaining what advancements were made, and how those affected the materials used and the quality of finished turnings.

Book Recommendation: The Noblest Invention

The first picture made me smile :)

300+ pages, but with short naration, packed full of side stories, short biographies, and historical perspective. It is a great, easy read (i.e. to be left out for guests or customers) that explained my love affair with bicycles better than I could. In a word, my bicycle represents Freedom. There is nothing I have felt better than the silence of a bicycle focused mind, hard-worked muscles, and a smile that just wont fade. This book kept me in the right state of mind.

p.s. I got my copy at the local library.

Sprocket/Crank Interface

In recent years we have seen a shift in sprocket/crank interface paradigm... Ok, that may be a bit exaggerated... At least there has been a change in design.

Traditional, Perpendicular Bolt

My first introduction to crank torque transfer was with the integrated stud on one piece cranks. Although effective, tolorances were often poor, and low-end sprockets were usually thin steel, further compounding any issues.

As BMX progressed, we moved to a bolt to secure the sprocket to the crankset (usually 3/8" or 10mm). Today, virtually all cranks use the bolt-on design. This helped solve some of the tolerance issues and has served as the standard for bmx. From a structural perspective, this design requires either a larger spindle boss or a separate hole cut in the crank arm for a sprocket boss.

A slight hybrid of one and three piece mounting systems, that has resurfaced recently is the use of a headless bolt. Mechanik makes a bolt called the Pin Head. The purpose of this design is not to hold the sprocket to the crank, but only to transfer torque. Using this design allows small spacers to be inserted between the arm and the sprocket to dial in the chainline.

Nano-drive

As Sprockets reduced in size (with flatland at the forefront), a need for less offset in the mounting position. Enter the nano-drive. Most nano-drive bosses use smaller bolts than the standard bosses.

Spline Drive

When faced with the challenge of small sprockets, Tree Bicycle Co. decided to redesign the mounting design. What they came up with was transfering torque through the spindle, rather than the crank arm. With most cranks now using 19mm, 48 spline, Tree's spline drive has a large potential market. Recently Profile decided to release their own version of spline drive (releasing a spline drive sprocket was logical for Profile as they are known for their 48 spline cranks). Unfortunately, Profile decided it was best to use 8 large splines on the adapter, rather than the 9 available on the Tree. I don't know why this happened, but it may be just to avoid any patent issues.

There is one big problem with spline drive: it is limited to 19mm, 48 spline cranks.

Socket Drive/ Nonogram

Flatware's (Odyssey) response to shrinking sprockets was to standardize. Well, sort of. They are the only company making a crank that works with the 9-sided mating surface, but do provide the specs and drawings(PDF) on their site. If this design is adopted, adapters can be made to adapt socket drive to a 48-spline crank, in effect making it another spline drive. The big advantage to this over standard spline drive is it does not limit the spindle design.

BMX-U Sprocket Page

KHE Clone Hubs: Calculating Slack

I recently posted this on BMX-U

Ok, this should apply to all KHE Clone coasters, as well as Odyssey and other "butterfly spring" coasters (though they may have different room in the hubshell. However, if you have an externally adjustable hub, you will just have to measure by backpedalling 1 revolution to 0* (or 90, whatever works for you), then pedaling forward and guestimating. Note: You cannot get 90* slack on these hubs, even with a relatively low 2.5 gearing and min spacers!

Driver/clutch thread pitch: 15mm per rotation (23mm/1.53 total)

KHE Spacer thickness: 1mm

Tophat Spacer: 5/7.5mm depending on orientation.

X= Total spacer stack (i.e. tophat set regular 7.5mm + 1mm spacer = 8.5)

G= Gear Ratio or Chainwheel (sprocket) size / Driver size (i.e. 25/9= 2.78)

( 12.7 - X ) / 15 * 360 / G = Degrees slack at pedals*

*assuming good chain tension, etc.

Bearing Specifications

Another great link. This one about the different designations given to bearings. It has helped me with bearing selection in some components.

EDIT: Wow, a long time later, I finally realize that I never posted the link. Sorry about that. The info its up at BMX-U now

Interesting Chain site

It's not BMX, or even bicycle specific, but a great link I picked up:

http://chain-guide.com/toc.html

BMX Wiki!

It's been a while since I posted, I have been working on getting a bmx wiki up. Thanks to a few cats over at http://www.bikeguide.org/forums it is getting filled up. Take a look, and please contribute what you can. Even the smallest stuff helps. http://www.bmx-u.com