The guys from NSMB were on their way from Canada to Sea Otter and wanted to ride some singletrack in Ashland. So, via our friends at Santa Cruz bikes, they hooked up with UBI instructor Nathan Riddle, who served as tour guide. Oh, the humanity!
More over at NSMB’s web site.
We are happy to announce the first two winners of the QBP/SRAM/UBI Female Mechanic scholarship. The winners will attend UBI’s Professional Repair and Shop Operation class at our Ashland location.
Elizabeth Jose: Elizabeth works at a shop in NYC, and is starting a non-profit focused on supporting women riders. She teaches a mechanic class in Spanish to women in Queens. These women earn a bike at the end of the class.
Vanessa Buccella: Vanessa is in the process of starting a women-focused bike shop in Chicago. She serves on the board of the Illinois Cycling Association.
We had over 300 applicants for these scholarships, which is an amazing response. We want to thank our partners, QBP and SRAM, as well as the many women who applied for this scholarship. You can read more about it in Bicycle Retailer.
Watch our blog for news about next year’s scholarship process!
Bicycle Tire Treads
An example of a smooth tread tire. Image courtesy of Bontrager.
The tread is where the rubber meets the road (or trail, if dirt is your preferred medium). This article will discuss what constitutes an ideal tread pattern for your intended usage.
Contrary to popular belief, tread on a road racing tire is not needed. In fact, the addition of a tread pattern onto a road racing tire takes away material that would otherwise be in contact with the road. At any given point, no more than about a dime-sized portion of the tire is in contact with the pavement. This is called the contact patch. Since such a small amount of rubber is in contact with the pavement, the removal of rubber in the form of tread pattern actually decreases grip.
Have a look at the tires on cars used for racing such as stock-cars or dragsters.
“But they don’t race in the rain”, you say?
Look at the smooth tread and rounded profile of motorcycle or aircraft tires. The rounded profile of these tires displaces water very efficiently, like the hull of a boat or ship. Mechanical engineer and bicycle wheel expert Jobst Brandt explains it like this:
Tread patterns have no effect on surfaces in which they leave no impression. That is to say, if the road is harder than the tire, a tread pattern does not improve traction. That smooth tires have better dry traction is probably accepted by most bicyclists, but wet pavement still appears to raise doubts even though motorcycles have shown that tread patterns do not improve wet traction.
A window-cleaning squeegee demonstrates this effect well. Even with a new sharp edge, it glides effortlessly over wet glass leaving a microscopic layer of water behind to evaporate. On a second swipe, the squeegee sticks to the dry glass. This example should make apparent that the lubricating water layer cannot be removed by tire tread, and that only the micro-grit of the road surface can penetrate this layer to give traction. For this reason, metal plates, paint stripes, and railway tracks are incorrigibly slippery.
An example of tire with negative tread. – Image courtesy of Continental.
It is important to understand though, that not every bicycle that is ridden on the pavement will benefit from an entirely slick tread. Touring, cyclocross, and hybrid bikes are often ridden on a variety of surfaces, including less than perfect pavement and dirt. In these instances, a perfectly smooth tread pattern may not be ideal; it may be detrimental to maintaining grip. Instead, a tire with a “negative tread” can be beneficial. Negative tread patterns may best be described as patterns where the relieved portion of the tread is smaller than the raised portion.
Off-road, or mountain bike tires require an entirely different set of considerations. It is first important to understand that unlike road or pavement oriented tires, the surfaces being ridden on can be both much softer, and highly variable. A tread pattern that performs very well in soft, loamy dirt, may not perform as well on hardpack, let alone mud.
Braking grip vs. traction –
The forces that a tire is tasked with handling off road are more pronounced than they are on the pavement. Grip is not the sole consideration. For example, when riding off-road a tire’s tread is tasked with providing forward momentum (traction), control under deceleration (braking), and maintaining traction while turning (side grip).
An example of an aggressive off-road tire with a positive tread pattern. Image courtesy of Schwalbe.
Picture a short section of trail consisting of a descent into a hard turn, and exiting into a short steep climb. Within the section of trail the tires of the bicycle are required to handle braking, turning, and acceleration. If a tread breaks free under hard braking (skidding) grip, and consequently control, is lost. Imagine losing grip while trying to slow down to enter the turn. Steep inclines and hard cornering are common occurrences when riding off road.
Unlike pavement, which whether wet or dry is still pavement, conditions found off road can pose a much larger question. While the dirt underneath the tire may still be dirt, the degree of moisture in it, as well as its composition, can have a drastic effect on the type of tread pattern that is needed. Dry conditions can warrant anything from small, tightly-spaced knobs, to large, widely-spaced chevrons depending on how hard or soft the ground is. Wet or muddy conditions might warrant a tire that does not “pack-up” with mud or debris, but still has pronounced enough knobs to bite through to firmer ground; while at the same time being narrower in order to cut through the mud.
There is no “perfect” tread pattern for any specific tire usage. Certainly there are many similarities that can be found between different manufacturers, but every tire maker puts their own spin on a given type of tire. If you are unsure about what will work best for the type of riding you do, consult with your local bike shop for what works best in your area!
Bicycle Tire Casings
The characteristics of a bike’s tires — profile, tread pattern, and running pressure, for example — can have a dramatic effect on the ride quality of the bicycle. At the heart of the bicycle tire, though, is its casing. The casing gives the tire its structural integrity, shape, and in large part is responsible for how well the tire will ride.
How it is measured
Bicycle tire casings are usually measured in Threads per Inch (TPI). Just like bed sheets, tires with a higher thread count are usually considered desirable. Higher thread counts generally translate to a thinner, more supple sidewall that allows for decreased rolling resistance and increased grip. An example of this would be if we were to drape a piece of burlap cloth over a bowl of fruit on a table. We would not be able to discern the individual pieces of fruit in the bowl; we would just see a lump under the cloth. If we were in turn, to cover the same fruit bowl with a piece of high TPI cotton or silk, we would be able to see the contours of the fruits in much higher detail. The higher thread count cloth conforms to the surface it is draped over much better. In tires, this translates to better grip through greater contact between the tire and riding surface as well as a more comfortable ride.
Modern bicycle tire casings are most often made from nylon. Nylon lends itself well to this application because it is light, strong, and inexpensive. Some high performance tires still use cotton or silk in their casings; however, these tires are often quite expensive and are designed for performance over longevity.
Density and plies
Any bicycle tire is at least two plies thick. Two plies equal one layer of casing. This is necessitated by the fact that the fibers used in tires are unidirectional, they are not woven. In order for the tire to have structural integrity, the plies must be laid on a bias (45 degree angle), perpendicular to each other.
Some tire casings are made of multiple layers. Multi-layered casings can be found in tires for almost any discipline of riding. They are found in downhill racing tires all the way to road racing tires. Multiple layers of casing increase the tire’s sidewall strength and overall durability. It is important to realize though, that the flexibility of a multi-layer tire is still dependent of the thread count of the base plies. For example, a two ply 60 TPI tire does not equate to 120TPI. Some companies will call out a number such as 3/330 TPI, this is referring to a 110 TPI casing multiplied by 3 layers, it does not equate to a 330 TPI casing.
Punctures resulting in a flat tire have been the bane of cyclists since the advent of the pneumatic tire. As such, many methods are available to aid in preventing punctures. One is the addition of some sort of material to the laminate of the tire, sandwiching it between the casing and the cap, or tread; this layer is called the “breaker”.
Image courtesy Continental.
Breaker materials are varied – synthetic woven materials such as Kevlar® or Vectran® are used, though some tires use some sort of solid plastic belt or solid layer.
What is the right tire?
The right tire for you is the tire that most closely suits your needs: the intended use, performance, puncture resistance, and price point are all factors that need to be considered in choosing the tire that is best for you. The casing is just one factor in choosing what best meets your needs. If you’re unsure, talk to your local bike shop!
Tony Pereira , no stranger to NAHBS awards, will teach UBI’s June brazing class in Portland.
UBI Portland brazing instructor and all-around framebuilding wizard Tony Pereira and his partner Ira Ryan, who together are Breadwinner Cycles, took top honors at last week’s NAHBS for Bad Otis, their 27.5 hardtail.
Breadwinner’s Bad Otis, getting down with its own bad self.
Congrats, Tony and Ira, from the UBI crew!
Tony moves from the NAHBS award podium to the UBI teaching podium in June, when he will teach a session of our Steel Brazing Frame Building class. Class dates are June 2 – 13, and we still have two spots in the class. One of them is yours! You can register on line.
Editor’s note: Craig DeAmbrose, an instructor at UBI-Portland, is the newest member of our staff. We posted the following picture of one of Craig’s bikes to our Facebook page last week and it caused quite a flutter in the hearts and minds of bike geeks. So we asked Craig to expound on his bike for the benefit of bike nerds everywhere.
Craig DeAmbrose’s retro-direct geekmobile. Need two speeds? You got ‘em! The smaller cog is hidden from view.
What you’re looking at is my home-made version of a retro-direct, 2 speed drivetrain. I built it after reading about the idea in The Dancing Chain, Frank Berto’s excellent book chronicling the history and development of the derailleur. I enjoy reading about the history of bicycle technology and thought it would be fun to build up a retro-direct bike to get in touch with my cycling roots. Yep, I’m that much of a bike nerd.
Before rear derailleurs had been refined to the point that they became ubiquitous on bikes, there were many different contraptions that allowed a rider multiple gears. Many of them came and went rather quickly due to their clunkiness and poor design. The retro-direct drivetrain in the late 19th and early 20th century was one of the more elegant and robust solutions to equipping a bike with multiple gears. The idea was first patented in in 1869 by Barberon & Meunier and was made popular by companies like Hirondelle and Magnat et Debon. Once derailleurs (and Internal Gear Hubs) started to be reliable and affordable in the 20′s and 30′s, the retro-direct drivetrain quickly faded into obscurity.
The concept behind the retro-direct is pretty simple. A rider pedals forward for one gear ratio and then pedals “backward” for a different gear ratio while still moving the bike forwards. This feat is typically achieved by having the bottom span of chain, which exits a chainring and normally returns to the freewheel from which it came, goes instead to a second, independent freewheel right next to the other one. Instead of the chain being routed to the “bottom” of the second freewheel it gets routed to the “top” where it can drive the freewheel forward as you pedal backwards. This is how mine is set up, but there are a couple of other variations on this idea — it only takes a quick search on Google to see a few other iterations. Most historic examples have the “backwards” gear as the low gear, but you can customize this depending on preference. You’ll notice on my example I have the “backwards” gear as the high gear.
One of the nice things about the retro-direct direct drivetrain is the lack of a shifter. The two gears are achieved simply by changing pedaling direction. No shifter also means no cable and housing to wear out which makes for a very robust (if somewhat limited) system. When the retro-direct was still something found on production bikes one of the purported benefits was that the backwards pedaling motion worked different, opposing muscles in the legs. Having ridden mine regularly I’d say the jury is still out on this aspect, as pedaling backwards seems comparatively awkward. This is especially so if you try to pedal backwards while out of the saddle. You’ll look as graceful as a hippo in ice skates. One of the drawbacks to the retro-direct was the tendency for the pedals to un-thread themselves while pedaling backwards. The problem was such an issue on production bikes of the era that if you look at some historical examples you’ll find that the pedal spindle was actually welded to the crank!
If you’re interested in making your own, it’s surprisingly easy with some basic bike knowledge. You can usually convert an existing bike with commonly available parts. There are a number of easy to follow “how-to’s” on the internet to get you started down the path to bicycle drivetrain nerd-dom. Just make sure to to tighten your pedals every now and then! For more information on the retro-direct drivetrain you can read Frank Berto’s aforementioned book or check out the brief but informative article on Wikipedia: http://en.wikipedia.org/wiki/Retro-direct.
The deadline is approaching to apply for the SRAM/QBP/UBI women’s mechanics scholarship. This scholarship will pay for two women to attend either the Professional repair and Shop Operation class or the Advanced Certification Seminar Week at UBI-Ashland. The deadline is March 22. Winners will be announced on April 4.
There’s more information available on QBP’s website.
You can apply here.
Have a piece!
It’s Pi day, celebrated on Albert Einstein’s birthday. No, we’re not going to give you an essay on gear inches, development, or gain ratios. Not that we couldn’t. We just don’t feel like it. For that, head on over to Sheldon Brown.
Rich Bernoulli, the Pi man.
We just wanted to roll along a little UBI trivia, which would be this. Our instructor, Rich Bernoulli, had a job before coming here that was, well, kind of boring. So to amuse himself, Mr. Bernoulli memorized the value of Pi to 200 decimal places. That’s 200. “My goal was 500,” he says.
The right fluid for the right bleed!
Hydraulic disc brakes are now everywhere. Knowing your hydraulic fluids is a key to proper maintenance and safe, predictable braking performance. UBI’s Jake Sawyer has this primer:
In the realm of bicycle hydraulic disc brakes, there are two common categories of fluid: DOT fluid and “Mineral Oil”. DOT fluid is a hydraulic fluid designed to meet specific criteria put forth by the United States Department of Transportation and organizations such as the Society of Automotive Engineers (SAE). There are numerous ratings available for DOT fluids, with DOT 3, 4, and 5.1 being used regularly in the bicycle industry. Mineral oil is a bit of a misnomer, as it is easily confused with the clear, colorless oil sold over-the-counter at pharmacies. The mineral oil used in bicycle disc brake systems is an engineered hydraulic fluid designed for this specific application, and is in no way compatible or interchangeable with other brake fluids. Or the pharmacy’s mineral oil, for that matter!
DOT 3, 4, and 5.1 are polyethylene-glycol based fluids, a group of chemical solvents that have high boiling points and have very low compressibility. DOT 5 fluid is silicone based, and is not compatible with any bicycle disc brake. Because of the high temperatures generated during braking, and the relatively miniscule volumes of fluid contained in a bicycle’s hydraulic system, a hydraulic fluid with a very high boiling point is considered quite desirable. If a brake fluid reaches its boiling point, transforming from a liquid to a gaseous state, its ability to stop the bike is greatly reduced.
The various grades of DOT fluids refer to the boiling points of the fluid. DOT fluid is considered to have two boiling points: a dry boiling point and a wet boiling point. Polyethylene-glycol based fluids are hygroscopic, or water absorbing. Given the conditions that disc brake-equipped bicycles are often ridden in, this can increase fluid replacement intervals. As DOT fluid absorbs moisture from the environment, its boiling point is significantly lowered. DOT fluid is considered “wet” when it has absorbed as little as 3 percent of water by volume. “Wet” fluid can have a boiling point over 30 percent lower than “dry” fluid. Once a container of DOT fluid is unsealed, it immediately begins to degrade; this is why DOT fluid for bicycle brakes is generally sold in small volumes.
Conversely, the other type of fluid used in bicycle disc brakes, mineral oil, is hydrophobic, meaning it does not absorb water. Because of this, mineral oil is able to maintain its non-compressible properties for longer periods. This is not to say that mineral oil systems are immune to water contamination and performance degradation due to heat, only that the fluid itself does not mix with water. Because mineral oils are proprietary, they are not categorized like DOT fluids into grades. That said, mineral oils can have boiling points as high, or higher, than “dry” DOT fluids.
Dry boiling point Wet boiling point
DOT 3 205 °C (401 °F) 140 °C (284 °F)
DOT 4 230 °C (446 °F) 155 °C (311 °F)
DOT 5.1 260 °C (500 °F) 180 °C (356 °F)
None of this is to say that one type of brake fluid is better than another. But it is important to understand that the fluid a manufacturer specifies in a given system is the only fluid that should be used. DOT systems will often state that they can be used with more than one grade of fluid, but those fluids should never be mixed. If you’re changing from DOT 4 to say, DOT 5.1, the system should be completely flushed of one grade before being bled with another grade. In mineral oil systems, it is important to use only the manufacturer’s fluid. While not as readily available as DOT fluid, mineral oil is generally not difficult to acquire through your local bike shop.
A well-maintained brake system is extremely important. Hydraulic brakes should be bled at regular intervals, even if they feel fine. Murphy’s Law predicts that when you most need the control that hydraulic brakes can offer, a poorly-maintained system will show its weaknesses. A good rule of thumb might be to bleed brakes every six months, or whenever your pads are changed.
Want to know more about disc brakes? Check out UBI’s one-day Disc Brake Seminar. The next session is Saturday, April 19 in Portland.
We’re excited to announce that SRAM, Quality Bicycle Products (QBP) and UBI have teamed to offer two scholarships for women mechanics to attend either the Professional Repair and Shop Operation class or the Advanced Certification Seminar Week at UBI Ashland. QBP is hosting the application form.
You can read more about the scholarship here.
Chelsey Reeves starts a suspension service at UBI Ashland. She works as a bike mechanic in the Sacramento, CA area.