Terry Peloton

Category: Cycling Savvy

This is where we cover more technical and practical cycling topics – bikes, gear, clothing, particularly of interest to female cyclists.

  • Hey Mister, your tires need air!

    I make rubbings of tire sidewalls and I like to doodle — hence this very stylized tracing of the Schwalbe Durano tire used on my Valkyrie Tour. You can see from this that the maximum recommended inflation pressure for this tire is 115 psi and the minimum is 85 psi.

    Do you think it’s always easiest to pedal your bicycle when the tires are pumped up to the maximum inflation pressure? That’s not necessarily correct. What?!? Well, unless you’re riding on a road as smooth as glass or you weigh quite a bit, a lower pressure might actually make you a faster rider.

    There’s a “magic land” somewhere between tires that are so hard that they jump all over the road and tires that are soft and deform too much, losing the ability to “push back” on the road, helping move the bicycle forward. The idea behind the perfect pressure is that the tire is allowed to become a shock absorber — sucking up the irregularities of the road before they get to the rider and tire her out. A recent article in Bicycle Quarterly estimated that even on smooth roads, you exert 10% of your power just overcoming these “suspension losses”.

    So what’s the optimum pressure? Well, some use the 15% “tire drop” formula. Very simply, the height of the tire is measured without the rider on the bike. With the rider on the bike, the tire pressure is reduced until the height drops by 15%. Voila! Uh, except for the fact that you really do want to stay within the recommended max and min pressures and this might not be possible… unless you want to play around with tires of varying widths.

    Vittoria Tires has another method that relies on rider “feel”. Using a chart, the rider starts with the recommended inflation pressure and then reduces it by 5 psi at a time until the tire “wallows”. This is the least amount of pressure for this rider. Next, the rider increases the pressure by 5psi until the bike bounces. This is the maximum pressure for this rider. Back down we go, 5 psi at a time until things feel just right.

    The long and short of it is that rarely does the maximum tire pressure provide the best ride. It may sound really fast, as you go humming down the road, but the power meter will show that it’s usually not as efficient as a lower tire pressure.

    “Hey Mister. Your tires need some air.” That’s what someone standing by the side of the road might have said to cyclist Jan Heine. Indeed, Jan was running low pressures in these 41mm tires during a tour of gravel roads in the Cascades. The result was an efficient but comfortable ride. Looks can be deceiving.

    So — go forth and let some air out of your tires!

    Tailwinds,

    Georgena

    Sources:

    http://www.vittoria.com/tech/recom-tyre-pressure/

    PSI RX by Jan Heine, Adventure Cyclist, March 2009, pp 34 – 35.

    Comfort Equals Speed by Jan Heine and Mark Vande Kamp, Bicycle Quarterly, Autumn 2009

  • Bikes for Women: Looks can be deceiving

    When I first started building bicycles for women some 25 years ago, it took only a quick glance at a man and a woman of the same height to see that her legs were longer than his.  Her shorter torso was clearly the reason why she felt “stretched out” on a bike and had to endure discomfort in her shoulders and back. So Terry bikes were built with shorter top tubes on all sizes to address this concern.

    Around 1990, I decided to get a more analytical and less anecdotal about the root causes of some women’s discomfort while riding.  There’s a lot of information about men’s and women’s anatomy and I was looking forward to finding out just how much shorter a woman’s upper body was proportionate to a man’s.  Guess what?  Women have proportionately longer arms and trunks than men.  Looks can be very deceptive, thanks to women’s higher waist lines.

    Yet, women’s discomfort on bikes was very real. But what was the underlying cause?  We were doing the right thing but for the wrong reason.  We needed to know the right reason.

    Enter Laura Lund, then working on her Masters in Mechanical Engineering-Bioengineering at Carnegie Mellon University.  She did some research and came up with some possible causes for women’s discomfort.  In doing so, she confirmed why our designs were working.

    So what was going on? It has to do with the distribution of body mass and the location of the center of those masses. They differ between men and women. More of a woman’s body mass is in her trunk than a man’s. And, speaking in simple terms, it’s higher on her trunk than on a man’s.  Think of it like this: if you put a five pound weight on your lower back and then bend over, it will be a lot easier than if you bend over with the same weight on your shoulders.  Your total weight is the same in both cases, but in the latter case, you’ve moved the center of that weight up and away from the muscles that are doing the work.  This higher “center of mass” means more effort is required by the lower back muscles.  A similar situation exists in the arms with regard to the forces exerted on the rider’s shoulders.

    Add to this the fact that women tend to have smaller muscles than men to support these forces. Not a good scenario!

    But the story doesn’t end there.  Stay tuned….

    Tailwinds,

    Georgena

     

  • Where Have All the Women’s Bikes Gone?

    Based on a quick review of bike manufacturers’ websites, women’s bikes don’t seem to have gone anywhere, but a little probing shows the industry might to be in retrograde mode. Having made so much progress in the last 25 years, it would be a shame to lose sight of the goal: bountiful offerings for all riders.  Although there are more choices than ever for female cyclists, the true distinctions between those bikes and unisex bikes are disappearing quickly.

     

     

    Last month, Bicycling magazine’s annual Buyer’s Guide hit the news stands and for the first time in years, there was no mention of women’s bikes.  Poof! Gone with the wind! I haven’t been able to find the reason for this — so far, all Bicycling will say is women’s bikes will be covered in their Editor’s Choice and in individual bike reviews.  Gone, but not forgotten.

    Now, add to this the fact that, with the notable exception of Specialized, in the past most smaller women’s bikes have offered 650c wheel sizes to fit the rider properly. (At Terry, we go a step further with not only 650c and 700c, but 24” wheels as well.)  But recently, 650c has been disappearing from the lineup faster than real sugar in soft drinks.  No more 650c for Cannondale, Trek, Orbea or Fuji to name just a few.

    So what’s going on??? I spoke to some manufacturers — those who continue to carry 650c and those who have dropped them.  They all told me the same thing. 650c wheels are a must-have for a properly built small bicycle. But there is mounting pressure to build small bikes with 700c wheels.

    Some told me the consumer herself is driving this change. Apparently there are quite a few women who would prefer to ride an ill-fitting bike with 700c wheels than a properly-fitting 650c bicycle. This may be driven by hesitancy about the availability of 650c or the need to conform.

    Others think the “push back” is from those dealers who don’t really understand how a 650c wheel makes a difference in bike fit and choose to stay in the 700c comfort zone rather than educate the consumer.

    Once a manufacturer has decided to embrace 700c wheels exclusively, just how will women’s bikes be differentiated from “unisex” bikes?  Expect to see a lot more of this: “…a shorter crank and stem length, along with narrower handlebars, give it a women-specific fit”.  Gee, that’s just what we did in the good old days of unisex! I can guarantee you that women on the tail of the bell curve, i.e. those very petite women are in for a rough time of it.  As 700c returns, stand over heights are rising.

    Are manufacturers really reading the market correctly? Is there indeed a trade-off between the desire for a properly fitting bicycle and wheel size? What say you, dear reader?

     

  • The Wheel Debate Continues

    A recent posting on FaceBook reminded me yet again of what a poor job our industry does of educating the consumer. My small effort to right this wrong is this eLetter, which I hope will clear up the continuing miasma surrounding yet again…wheel sizes!

    Here’s the gist of the post:

    “I have a 650 Brand X. I also have a 650 Brand Y. I now ride a 700 Brand Z. What a HUGE difference when I went from the 650 tire to the 700. I never realized how much more work you do on the 650. One revolution of the 700 tire goes 15 inches further than the 650. Over the course of 50 miles, that is a lot of ground to make up.”

    Now, while I’m thrilled to hear this person is thoroughly enjoying her new ride and is a faster cyclist for it, I sincerely doubt the wheel size has anything to do with it.

    For the record, the difference in circumference between a 650c and a 700c wheel is about 5.2 inches, not 15. But that’s not really the point. No matter what size your wheel is, it has to “push off” the road to in order to turn. And that push can be traced back to you, when you ”push off” on the pedals. Through the magic of gearing, the 650c rider won’t work any harder to make this push happen than the 700c rider.

    Let’s dig a little deeper into the wheel issue. From this point on, I’m using information from the 2nd Edition of Bicycling Science, by Frank Rowland Whitt and David Gordon Wilson, Chapters 5 and 7.

    Not to upset the math-phobic, but take a look at this equation, which calculates how much power a cyclist exerts on the pedals. I’ve highlighted all the instances of “m” in red. It stands for “mass”, or weight, loosely speaking. If we can make “m” smaller, then power will be smaller as well. In the general scheme of things, the weight of the wheels may only represent 1 or 2% of the total weight of rider and bike, but it still accounts for something. Lighter wheels: less power needed.

    Have you ever heard the expression that saving a pound on the wheels is like saving two pounds on the frame? That’s because not only do you have to move the mass of the wheels down the road, they’re turning at the same time, so you also have to rotate their mass. A wheel with less mass is easier to work with on both counts. Again, it’s not much work, since the rotation of the wheels accounts for only about 3% of the total kinetic energy (think of that as mass in motion) of the bike, but it’s work nonetheless. Score another one for the 650c wheel.

    So why all the hard feelings about the 650c wheel? Well, it does have a bit more rolling resistance than a larger wheel. The smaller the wheel, the more the tire deforms under load. And when it deforms, it creates more rolling resistance. For similar tire models, widths, materials and inflation pressures, you’d see your speed decline from about 12.5 mph to 12.3 mph with a 650c tire. For faster speeds, the decline is less because air resistance becomes much more of a hindrance than rolling resistance. Following through with this idea, a 50 mile ride would take you 4.2 minutes longer on 650c wheels.

    So, there’s a tradeoff going on here — less mass, less power required; more rolling resistance, more power required. But then there’s another factor: your mind. If you think you’re fast and cool, you are! Attitude will trump wheel size any day of the week.

    But the question has to be asked: why are so many manufacturers jumping ship on the 650c size? Because it’s a lot cheaper to build a bike line around one tire size than two or three. That’s another whole topic to be addressed in another Cycling Savvy eLetter.

    Tailwinds!

  • The Good, the Bad and the Ugly

    This eLetter is about challenging our perception of the definition of a “good” bike. I thought a visual presentation of how we regard bicycles would be cool way to put things in perspective. So I’ve come up with a grid to illustrate my point. Even if you shun math, I think you’ll find this very palatable. We tend to evaluate bikes based on their weight and stiffness. So one axis on the graph is for weight, the other is for stiffness. Simple.

    Let’s begin with “ugly” bikes. Most riders would agree that a bike that weighs too much isn’t a good thing. There are pros and cons to that argument, but for now, let’s just assume that we’re talking about a tank, not about a bike that weighs 16 pounds or even one that weighs 23 pounds. The bike we’re concerned with is a boat anchor! And not only does it weigh a lot, it’s really stiff. Every piece of grit on the road feels like a boulder. The constant chattering from the road wears the rider down. Here’s where that ugly bike would fit on my grid:

    I think we’d all agree that even if we gave this ponderous bike a little more flexibility, it would improve slightly since the it wouldn’t rattle our bodies as much as its stiffer counterpart, but it still wouldn’t have that “lively” feel we’d like. So, I’ll call this bike “Bad” since it still doesn’t achieve the ride I’d like.

    Now that I’ve eliminated bikes in the lower half of the grid, it’s time to take a look at the upper half. This is the world the bike media tells us is biking nirvana. In particular, every bike aspires to land in that upper right quadrant: the world of stiff and light. Read any review of a bicycle and you’ll find that references to stiffness (more is better) and weight (less is better) abound. This combination is indeed the essence of speed. Well….it’s perceived to be…..

    Still vacant is the upper left quadrant, where light weight bikes that aren’t super-stiff reside. In our quest for ever stiffer bikes, we’ve neglected this quadrant, but it turns out that it’s home to something we crave as much as speed: comfort. Are the two mutually exclusive???

    Not only is the frame’s ability to absorb some road shock enhanced when it can flex, but it can also spring back and return energy to the drivetrain (i.e., help you turn the pedals).

    Think about it. When you feel comfortable on your bike, you can usually keep riding strong for a longer time than when you’re not comfortable. The bike works with you. When I feel this way on my bike, I think of it as a harmony in which the bike “plays” the road like a musician might play an instrument. The road, the bike and the cyclist all contribute to the ride rather than working against each other. Yep, we’re all bouncing around, but the whole is greater than the sum of our parts, so to speak.

    Recently, there’s been a revival of interest in this interplay of frame stiffness, rider comfort, speed and (ultimately) rider efficiency. While no one has yet to subject these anecdotal sensations to truly rigorous testing done across a broad sampling of riders, power meter testing with a small sample has verified that efficiency (I want to go fast, but be comfortable, too) is indeed rampant in the upper left quadrangle. So give it the respect it deserves!

    Tailwinds,

     

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  • Make Me Ride Faster

    One of my favorite cycling publications is Bicycle Quarterly. Now in its eighth year, it began life as Vintage Bicycle Quarterly, but has evolved to cover modern bicycles as well as vintage bikes. It was created by Jan Heine, a German emigrant, avid randonneur and former road racer. He brings his education in mathematics and geology to the party and mixes in a wonderful devotion to bicycles.

    The most recent issue (Vol. 8, No. 4) focusses quite a bit on modern bikes. Jan’s never afraid to take on a question whose answer, on the surface, seems obvious. For instance, “are modern bikes faster?” Sure, given all the technological improvements in cycling, of course we’re all riding faster as a result. Isn’t that why we all aspire to the latest and greatest technology?

    Jan wasn’t convinced one way or the other, so he looked at long-term speeds of Tour de France cyclists from 1910 to the present and compared these to the speeds of distance runners, whose speed is a reflection purely of human performance, not changes in technology. His hypothesis was that if the average speed over time of the runners kept up with the trend for cyclists, then improvements in human performance were responsible for increased speeds, not technological changes.

    And sure enough, he found that 88% (a correlation of 0.94) of the faster speed of Tour de France cyclists over time was explained by improvements in human performance — training, nutrition, etc. The other 12%? Well, it included increases in speed as well as decreases.

    Here’s an excerpt from his conclusions: “Increases in racing speeds show no systematic correlation with the introduction of new technology.” But wait, Jan, bikes are a lot lighter now than they were then. Surely that’s a big deal? Uh, no. Jan’s data reveal that weight “is too small to be discerned among other factors that caused speed to increase.” Even changes in components haven’t been enough to move the needle significantly.

    This kind of analysis also finds its way into bike tests. Jan and other testers ride with open eyes (figuratively speaking, that is). As cyclists with experience in road racing, randonneuring and club riding, they tend to speak to a broader audience than most do most reviewers. Such was the case in this same issue with a review of the Trek Madone 5.2. This bike is designed for road racing, allowing the rider to “Climb faster, ride further and stay up front” according to Trek’s website. Jan’s take on the bike was that it performed best under a very strong rider capable of exerting a lot of power. Lance Armstrong, anyone? When testing the Trek’s aerodynamics, Jan felt the advantages were easily negated by changes in the rider’s position on the bike. Comparing the Madone to other road bikes, he concluded that it “does not offer improved performance uphill, nor superior aerodynamics.”

    So, while the goal of riding faster is something that appeals to every cyclist, keep in mind your own abilities and how you intend to use your bike. All that glitters is not necessarily gold. But then again, that “wow” factor is really appealing!

    Tailwinds,

  • It’s Not About the Wheels

    Recently I read a forum posting in which the writer stated she preferred 700c wheels to 650c wheels because she sat higher on the bike and felt more on a par with riders around her. She may have felt this way, but it had nothing to do with wheel size. Something else was going on.

    On first take, you might think the larger the wheel, the higher the bike. Seems logical, but it’s not. Whether a bike is being designed around 700c, 650c, 650b, 24″ or 20″ wheels, there’s one dimension that usually doesn’t change much — the bottom bracket height. It’s the distance from the ground to the center of the bottom bracket, the “central movement” according to the Italians. It’s where the crank arms meet the bicycle.

    So why is the bottom bracket height important? Well, if it’s too low, you’ll scrape your downside pedal when you’re cornering. Not a safe situation. If you have really short crank arms on your bike, the bottom bracket height can be lower than it would be on a bike with long crank arms. If the bottom bracket height is too high, your center of gravity will be high and the bike won’t feel stable in turns. Mountain bikes used to be built with very high bottom bracket heights to clear debris on the trail.

    Back to our rider. Assuming she had the same fit on both bikes, then she was using the same crank arm length on both bikes and therefore, the distance from the pedal to the top of her saddle was the same. If the seat angle was the same, then the distance from the ground to the top of the saddle was identical on both bikes. So her hips were in the same place on both bikes.

    How about her upper body? Again, if the “cockpit” fit identically on both bikes, her reach to the handlebars was the same and the vertical distance between the seat and the handlebars was the same. So her upper body was in the same position. In other words, she was exactly the same rider in exactly the same height/position on both bikes.

    Here are two drawings showing our hypothetical rider on bikes with 650c and 700c wheels. The distance to the saddle from the pedals is identical as are the “cockpit” dimensions. Two drawings are worth six words: “it’s not about the wheel size.”

    So why does this rider feel taller on the 700c bike? Well, one reason might have to do with the seat angle on the bike. If the 700c bike has a steeper seat angle than the 650c bike, she will ride higher in the saddle. Imagine a 90 degree seat angle: she would be sitting really high! There are a lot of 700c bikes for women built with steep seat angles in order to make the top tubes shorter, so that might be one of these bikes. (Not the right way to do it, by the way…)

    Or perhaps she’s riding with different “cockpit” dimensions. If the reach to the bars is shorter, the stem is shorter and/or the stem is taller, she will sit more upright. Taller in the saddle. And back to the bottom bracket height — it may indeed be higher on the 700c bike.

    Lots to think about here. One of the most important is that wheel size is one of many tools available to bike designers so we can give our riders the best fit possible. The bike is a wonderful work of engineering and art whose pieces are remarkably intertwined — as much with each other as they are with you, the cyclist.

    Tailwinds,

  • Saga of the Stuck Seatpost

    If you followed my recent tweets, you know I was obsessed for a while trying to remove a stuck seatpost from one of my favorite rides, “Moo”, a 22 year old hybrid. Last summer, I designated this winter as the time when Moo would shed her tired 7-speed components for something a little more up-to-date. Everything was going according to plan as I tore her down — until I got to the seatpost — which wouldnt budge. What followed was an excursion into part stubborn, part “Im not going to give up on this bike after 22 years”. In the end, everything worked out. The seatpost, in pieces, came out and I experienced a moment of euphoria not unlike Lindsey Vonn’s when she won the gold.

    Googling “stuck seatpost” directed me to several good posts, in particular, Sheldon Brown‘s and Lennard Zinn‘s. I exhausted the “easy” solutions first and quickly found myself with hacksaw in hand. My blog, complete with color glossy photos, will tell you how I finally extricated the seatpost. And you should read it before you read the rest of this so things will make sense.

    Sometimes you learn as much after an experience like this as you do when you’re in the thick of it. I continued to snoop around the web and talk to some bike mechanic friends about it. Was hacksawing the only way to remove the seatpost? And how did that little 2 mm ribbon of aluminum corrosion around the base of the seatpost lock it in so tightly given that the steel seat tube was very clean, only showing some slight oxidation on its surface?

    Some of the best information I found came from Jobst Brandt. I learned that aluminum oxide (corrosion) has more volume than aluminum that has not corroded. So it was as though a larger seatpost had taken over my bike. Like cramming a slightly oversize round peg into a round hole. This explained why the CO2 cartridges didn’t have much effect. The cold temperatures caused the seatpost to contract, but it just wasn’t enough to overcome the effect of the corrosion.

    Brandt also mentioned that some shops will Dremel out the seatpost. I think that would require the same kind of finesse with the Dremel tool as it does with the hacksaw. I also wonder how this would work with a long seatpost, like the 300 mm variety so commonly found on bikes with sloping top tubes? In retrospect, that was one thing I did right with my seatpost. When it was new, it was 300 mm long, but I cut it down to 220 mm since I couldn’t see why I should carry around all that extra seatpost when I wasn’t using it.

    One of the more interesting concepts on removal came from a friend who spends a lot of time at Kraynick’s Bike Shop in Pittsburgh. He prefers to pull the seatpost straight out of the seat tube. To do this, he’s designed a tool that “hooks” the bottom of the seatpost. Using the top of the seat lug as a platform, he slowly winches the seatpost up:

    “I used a length of threaded rod. At one end I put two nuts and tightened them against each other. I took a deep 3/8″ drive socket and cut slits through the socket wall from the nut-engaging end and down about two-thirds of its length. Then I heated and bent the tangs slightly outward. The tangs catch the bottom rim of the seat post but don’t scar the inner surface of the seat tube when the rod is installed. I bored out the square drive hole to a loose fit over the threaded rod and slid it on. I put a pin in a hole drilled through the socket base and the threaded rod. I cut the seatpost off beneath the seatpost clamp and tapped the threaded rod and s ocket assembly into the seatpost. The tangs were bent enough so that they could spring out and get purchase on the underneath of the post. A piece of tubing was put over the the threaded rod and cushioned and rested on the seat tube lug area and a washer was added to create a platform against this tube. Screw on a coupling nut about 1″ long and begin tightening it…”

    Photos to follow, I hope!

    Okay, if you’ve read this far, you’re probably thinking to yourself, “I hope this never happens to me!” Just make sure your seatpost is greased and check it a couple of times a year to make sure it moves freely. That’s all it takes.

    Tailwinds,

  • The Tale of the Beater Bike

    Recently, I received an email from a customer inquiring about “step through” frames. Often the need arises from a physical disability, a lack of flexibility or the need to achieve that certain comfort and confidence level that only a step through provides. As we exchanged emails, I learned a lot about bike design, thanks to this customer’s curiosity and engineering nous. I thought it would be helpful to share this wealth of information.

    The Problem:

    A small rider (4’11” – 5′ tall with a 25″ inseam) wants a bike with a step through height no higher than 16.5″. Since she’s returning to cycling after a 30 year hiatus, she has to re-learn the sport. The goal is to participate in a 50k race at least once a year. But for now, she needs a bike on which she can reintroduce herself to riding.

    Unraveling The Problem:

    We could build a custom bicycle for this customer, but as she investigated her options, it seemed to her to make more sense in the short term to try to find a beater bike she could use as an intermediate step to a bespoke solution. The beauty of taking this path is that it allowed her to determine what the geometry of her ultimate bike would look like. What better place to start than the local pawn shop?! I’m sure this little Gary Fisher bike thought it had died and gone to heaven when it was rescued from a life of curb jumping.

    One of the first issues to deal with was the seat tube length and the crank arm length. She reasoned that given her 25″ inseam, a custom bicycle with a 43 cm seat tube didn’t leave much left over for the seat height and the reach to the pedals. Worst case, if she couldn’t lower the saddle enough, her hips would rock as she pedaled — not only uncomfortable, but inefficient as well. At this size, there is clearly a relationship going on between choosing the right seat tube length and the right crank arm length.

    The Fisher came with 162.5 mm cranks, but they felt too long when it came to getting re-acquainted with balancing and starting up the bike. After all, skills need to be refreshed after 30 years! The solution was crank shorteners. These aren’t hard to find and are often used on tandems to accommodate a child’s shorter legs.

    By trying different crank arm lengths, she was able to find the one that let her gradually acclimate to the feel of starting up on the bike. As she became more comfortable with this, she was able to lengthen the crank arm. Because of some physical limitations she has, the final crank arm length may end up being more a function of what works best for her rather than what the rules say about crank arm length.

    For that matter, the rules seem to be perpetually in flux, depending on whose study you’re reading at the time. One study has indicated that the optimal crank length is 20% of leg length and that most adults are fine with the ubiquitous 170 mm crank. In response to the concern that what applies to “average” adults may not apply to those with smaller legs, the same study done with 8 – 11 year old boys also supported the use of the 170 mm length.

    A July, 1982 Bicycling article by a former research engineer at Schwinn Bicycle Company matched up leg length and riding style to determine optimal crank arm length through use of a nomograph. The author focused on “pedal feel”, which depends on crank length and crank rpm. Much like wheel size, crank arm length is not hallowed on its own, but part of an integrated system.

    Dig deeper into the research and you’ll learn about pedal speed (the velocity of the pedal and your foot) and pedaling rate (the revolutions made in a certain period of time) and how these tie into muscle excitation states.

    Also of interest is the bottom bracket height on the beater bike — at about 10.8″, it’s on the high side when compared to sports bicycles, which are typically around 10.2″ or 10.3″. (The bb height is the distance from the ground to the center of the bottom bracket — the “central movement”, where the crank arms are attached to the bicycle.) That additional 1/2″ or so that she will gain in a reduced step through height will be very beneficial on her custom bike.

    Now that the lower body was squared away, it was time to address the upper body. As it came equipped from the pawn shop, the Fisher felt very cramped, causing the rider to push back on the saddle in search of a more natural position. Without knowing this rider’s “geometry”, I would guess that this is a result of trying to get the knee in the correct position over the pedal. A lot of women find themselves doing this! Her solution was to put a very set-back seat post on the bike. Other adjustments involved raising the handlebars to get them in the right position relative to the saddle. Here’s the “new” bike:

    You may be looking at this and thinking it still looks like a pawn shop bike. Yes, but, to turn the phrase, beauty is only skin deep. What this is becoming is a blueprint to a bike that fits and does what its owner wants it to do. Once the crucial measurements are dialed in, like the reach, the crank arm length, the effective seat angle, etc., the blueprint is complete.

    Wow! Have we learned a lot, or what?! As this rider renews her cycling skills, she will undoubtedly tweak the bike even more. The search for the proper riding position is always ongoing. I think the term “evergreen” applies perfectly to this situation.

    Many thanks to her for sharing the journey so I could share it with you!

    Tailwinds,



    Resources:

    • Crank Shorteners
    • Adjustable length cranks
    • Customizing crank length
    • Studies on crank arm length:
    • Adults
    • Children
    • Buttars, Kent R. “Crank Length and Gearing.” Bicycling July 1982: 26-37.
    • Make your own bike “blueprint”

  • Will my tires explode?

    The fodder for this eLetter came from this blog post:

    “I won a new bike at my company picnic and I’d love to ride it, but I’m extremely afraid of popping all the tires at my weight!!!”

    Here’s the quick answer — the tires will be fine. Food for thought: a 4000 pound car is supported by four tires, each with typical inflation pressures of 30 -35 psi.

    But getting to this answer led me through a neat maze, full of twists and turns. Logically, I started with the sidewall markings on tires. Auto tires have a plethora of information and, in North America, are required to state the maximum load the tire can handle. But I have yet to see a bicycle tire with a load marking on it. Tire pressure range, size, yes — but no maximum load.

    That doesn’t mean it hasn’t been calculated for bike tires, though. Many manufacturers have done this, but only publish it in their literature or on their website. Since we spec Schwalbe tires on most of our bikes, they seemed to be the logical company to contact for more information. Schwalbe calculates loads, but the data is currently only published for off-road tires. In the future, it may be published for road tires as well, but Schwalbe has no plans to mark the load data on the tire itself. Here’s a look at the data for one of Schawlbe’s off-road tires.

    This [b]single[/b] tire can withstand a load of 140 kg (308 lbs). Pretty amazing, huh? I asked Carsten Zahn from Schwalbe for a little more information about how this was calculated. A load is applied to the wheel. The maximum load is the load that will cause the tire to deflect by 20% (that is, when the tire “drops” by 20% from its unloaded height). The test is always done with the tire at the maximum recommended inflation pressure. Remember, this is a static load. Things are very different when jumping off cliffs….

    The choice of 20% as the maximum allowable deflection begged for more explanation. Schwalbe says this comes about from their experience and from a standard in the ETRTO (European Tyre and Rim Technical Organization) norm. If the tires are ridden for a long period of time at a higher defection, the sidewalls will eventually collapse.

    Interesting. I wondered what the Consumer Product Safety Commission had to say about load requirements for bicycle tires. Not a lot. The only reference to loads refers to “side loads” — the wheel is turned on its side and supported around the circumference of the tire sidewall while a 450 pound force is applied to the axle for 30 seconds. During this time, the tire must stay on the rim when the tire is inflated to 110% of the recommended pressure.

    But that wasn’t the end of it. The deflection issue would come back in a different context. I’m the kind of person who runs my tires at the maximum recommended pressure. I figure they’re going to lose pressure as I ride them, even if it’s only a tiny amount, so I might as well start at the top and work my way down until I re-air in seven days. (Schwalbe says to check your tire pressure monthly, which is way too long for my taste.) Besides, there’s something nice about the swish and hum of hard tires on the road. Or is there…..???

    “Inflating your tires to achieve 15% tire drop will optimize your bicycle’s performance, comfort and handling.” This is the first sentence in an article by Jan Heine (see full citation below). The logic here is that even though rolling resistance is lower at higher pressures, comfort is lessened because of vibration and bouncing of the bike. By lowering the pressure, comfort improves. The trick is to find the “sweet spot” where the most comfort is achieved at the least performance cost. Download the full article here.

    As you’ll see, the article contains a chart which tells the reader what inflation pressure to use given the width of the tire and the weight it bears. I tired this using my own weight and tire size, but I was off the chart! Extrapolating, I shouldn’t be riding a bike at all. (The perils of the rider with a slight build…the same thing happens to me with those BMI charts.)

    Nonetheless, I lowered my tire pressure about 10% just to see what the ride was like. Hardly scientific, but the bike just didn’t seem to have its usual zing. Which made me start thinking about the “comfort” aspect of this and how dependent it is on a variety of things, like frame material, frame geometry, road surfaces, wheel construction, ambient temperatures, to name just a few. Tire resistance can be measured with a lot more accuracy than comfort. There’s nothing better than a fine ride on a fall day spent mulling over things like this.

    But, coming back to our cyclist who won the bike — even though this chart was designed around a 15% deflection, she can see that she’ll be better off with a wider tire she can inflate within the recommended inflation range. A very narrow tire will have to be quite a bit overinflated to do the job. The widest tire on this chart is 37 mm (about 1.5″). Think back to the Schwalbe tire, 2.1″ wide, with a maximum inflation pressure of 55 psi and able to sustain a load of about 300 pounds. Ride yer bike and enjoy it!

    Tailwinds,