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Wednesday, March 10, 2010

Passing Geometry

Understanding Bike Geometry When Choosing A Bike:

I know the word, but what does it mean?


ST (ct) Seat Tube.

The seat tube determines the height of the bike or your frame size. This is generally measured from the center of the bottom bracket to the top of the top tube.

TT (cc) Top Tube Center to Center.

This is also known as the “effective top tube”. This measurement ranges from the center of the seat post to the center of the steering tube. This measurement determines the rider’s cockpit size and reach. The TT (cc) measurement is important to understand so that the rider will not be too stretched out or scrunched up. Most riders can feel when they are too stretched, but often make the mistake of getting too scrunched and not allowing a good position for proper breathing. Good breathing technique is vital for climbing and hard rides.

TT (hz) Horizontal Top Tube.

This is the actual length of the top tube. On compact frames this measurement may be longer than the effective top tube.

ST angle: Seat Tube Angle.

The angle of the seat tube is measured in relation to the ground, and tends to fall somewhere between 68 and 75 degrees.

A frame's seat tube angle determines the position of a bike's saddle related to its bottom bracket. Since the bottom bracket is the axis around which the bike's cranks and pedal rotate, this affects the orientation of the rider's legs and body in relation to the bike. Seat tube angle also influences how the rider's weight is distributed between saddle and handlebar.

A steeper seat tube brings the bike's saddle more into a vertical line with the bottom bracket, thrusts the rider forward into a more aerodynamic position, situates more of the rider's weight on the handlebars, and so the rider employs more of the hamstring muscles. Triathlon bikes often have steep seat tubes, because they're built exclusively for speed and tend to be ridden by people who are strong runners (and therefore have well-developed hamstring muscles).

The shallower the seat tube, the further the bike's seat is pushed behind its bottom bracket. This is a less aerodynamic position, but it also puts more demand on the thighs and glutes (which tend to be well developed in cyclists), and places more of the rider's weight on the saddle, to increase rider comfort.

A steeper seat tube makes a shorter seat tube for a frame of a given size, and making for a stiffer, more responsive feel. A shallower seat tube requires longer chain stays which can allow for grater comfort over rough terrain.

The steeper seat tube enables a more direct transfer of power through the rider's legs, although a shallow seat tube angle puts the rider in a better position to exert power during low cadence riding, such as seated climbing.

HT Angle: Head Tube Angle

Most head tube angles vary from about 69 degrees (when 90 degrees is perpendicular to the ground) to 75 degrees. In general, the steeper your head angle (closer to 75 degrees) yields quicker and more responsive the steering. Responsiveness can be explained by the following:

a) - A steeper head angle allows for a more weight-forward riding position, placing the body and head closer to the front of the bike, allowing the rider to see the road ahead sooner.

b) - A more upright head angle allows the front wheel to be tucked down under the rider, thus easier to steer.

c) - With the rider's weight more aligned with the turning angle, the bike will turn with more subtle weight and shoulder shifts rather than large arm movements.

You Gotta Have An Angle:


Bikes with the steepest angles are the dedicated road racing bikes, which have angles averaging 74 degrees for both the head and seat tube. Racers want quick, agile and efficient machines, geared towards speed with comfort being a bonus if you get it. A steep head tube angle means that most of the rider's weight will be evenly distributed between legs and shoulders. A racer has to be in good shape to ride with more weight on the shoulders with eyes focused directly on the road in front rather than the trees and mountains.

Touring / Sportive/Recreational Road Bikes:

Steep angles allow for a very efficient ride. You can get racing angles to fit this category as well. In this category however, you get the luxury of having a slightly slacker HT angle for a more upright position, better for taking in the scenery, watching for cars ahead, and a little less interest in controlling the bike. In a more upright position, more weight gets transferred to the sit bones, which is usually more comfortable.

BB drop: Bottom Bracket Drop

If you were to draw a line horizontally between the front and rear dropouts and a perpendicular line through the center of the bottom bracket. The distance between the center of the bottom bracket and the first line, measured along the second is what is known as he "BB drop, which measures how far below the axles the bottom bracket sits.

Mountain, cyclocross, and track frames bottom brackets tend to be quite high (mine is 65mm). The reason is to keep stones, dips, roots or a severely sloping track from causing a pedal strike, hitting the chain rings or frame. The bottom bracket in these bikes is built up and way from these dangers which could end a ride or a season in a hurry. A higher bottom bracket also shortens the chain stays and down tube of a frame, which are put under the greatest stress under riding conditions, which translates into a stiffer, more responsive feel.

The advantage of stiffness and safety come at the cost of stability; the lower the bottom bracket, the lower the bike's center of gravity, for a more stable ride. Touring and commuter frames often have a lot of drop, to be more practical than concerned about winning a sprint. Many good road bikes tend to have medium BB drop for the best of both worlds.

CS: Chain Stays. The chain stays run from the bottom bracket to the rear dropouts. This can be measured as "actual" or "effective" length due to the fact that the bottom bracket drop will increase or decrease the length of a frame's chain stays without changing the position of the wheel.

Most models tend towards shorter chain stays. Short stays makes them stiffer and minimize the flex and therefore adds greater power transfer from the pedal stroke. This shortens the wheelbase for a snappier feel and low speed turning. It also puts more of the rider's weight over the rear wheel for optimized traction. Mountain bikes use short chain stays to better dig in to fight up loose climbs.

A longer wheelbase with longer chain stays makes a more stable bike at higher speed. The long chain stays add more flex. They push the rider forward off the rear wheel to add to the comfort of the ride. These bikes will often have a more shallow seat tube angle; great for seated climbs and women's bodies. The longer stays also allow greater tire clearance for larger tires to be used and making it easier to remove the wheel. Another added benefit of longer chain stays is that they will keep the rider's heels from hitting a rear pannier rack. This is generally why you see commuter and touring bikes with longer chain stays.

SO: Standover.

This is how high the top tube will be from the ground. This measurement may vary based on tire size. Some companies measure this differently, so it is good to double check before ordering.

HT Length: Head Tube Length

This may vary to allow for greater aero position.

WB: One fundamental measurement is wheelbase. The WB is calculated either by measuring the center of the hubs or the center of the spot where the wheels meet the ground; these distances must be equal (assuming the wheels are round!). A longer wheelbase should make a bike more stable in a straight line but less agile in turns. It may make a bike feel more comfortable or smoother due, in part, to the flexy stays.

Stem: Stem length is a completely adjustable parameter to adjust the feel of a bike. Most stem lengths are selected based on fit, but a rider can opt for a longer stem with a forward seat position to create slower, more stable steering, or the opposite effect with a shorter stem. Stems may vary from 130mm to under 90mm.

Taipei CYCLE 2010

Taipei CYCLE 2010 (The 2010 Taipei International Cycle Show) is warming up to present its biggest show in its two-decade-plus history. Taipei CYCLE, Asia's leading bicycle trade show hosts 2,900 booths at the TWTC NANGANG Exhibition Hall in Taipei from March 17 to 20, 2010.

Choosing Your Taiwan Bike

Which Bike To Buy For Taiwan Riding?

Sometimes when I am out riding or talking to friends and coworkers about my rides, I get a lot of questions from people who are interested in doing something similar. A lot of people want to explore the pretty pictures on a bicycle, have adventures with friends or just get into better shape when the creaks of creeping middle age start making a descent night’s sleep an impossibility.

A lot of folks just hop on down to the Giant shop and the sales clerk sticks them on any moderately priced mountain bike that is clogging the stock room and off they go (fitted or not). At some time in the 90’s someone decided that fat tired mountain bikes were the cure-all for the average. This is great for a weekend duffer and going around town, but for serious riding there is a lot to think about that can seriously affect whether the rider will ever reach their goals. Getting the right bike is like selecting the right tool for the job.

For Taiwan riding here are some common bikes and things to think about. I hope this post will help those of you on the fence thinking about biking Taiwan better understand your options and choose the best weapon.

The Mountain Bike:

Many people who first start riding in Taiwan often reach for a flat-bar mountain bike as their initial choice. Giant sells them by the truckload. They look sturdy, have fat tires for rough surfaces. They often come with an assortment of shock absorbers which many people feel will add to comfort, and the stable looking flat-bar looks simple and easy. Some have disc brakes and feel like a tank.

The Pros: Mountain bikes are rugged, sturdy and cheap. They often use 26” tires, which are easy to spin up to speed. They are great climbers and often have a wide range of gears designed to spin across loose dirt without torquing out and sliding. Mountain bike geometry is more upright for added visibility and the quick steering makes negotiating obstacles much easier. Mountain bikes can descend with confidence due to their center of gravity being shifted to the rear. They are great for slow speed balancing as well. The fast spinning crank and finesse can improve a rider's pedal stroke, making it smooth, fluid and even. There are many mountain bike trails in the hills above Taipei, Taoyuan and Miaoli where a mountain bike enthusiast can have a lot of fun.

The Cons: Unless you really have the opportunity to ride on singletrack and rough trails and have convenient transportation to those trails, a mountain bike is not the ideal choice. Mountain bikes are designed for off road where they excel, but on road they can be extremely uncomfortable over long periods. The geometry is not designed for long road rides and the tiny cranks mean that a lot of energy is wasted spinning a crank without as much forward motion. The gearing is not practical for the road. Mountain bikes are made to withstand abuse, but that means they are unnecessarily heavy for most road riding in Taiwan. The knobby tires take about 3-5 mph off road speed and the soft tires combined with the shock absorbers sap energy from the rider that could be better used for forward motion. This demand for effort can actually reduce comfort. The flat-bar is great for negotiating roots and stones, but it puts a lot of stress on the wrists and may be painful after a couple hours. Even with additional bullhorn bar-ends, the number of hand positions is greatly reduced when compared to a drop bar.

The Standard Road Bike:

There are all kinds of road bikes from race bikes to relaxed bikes. They all serve a different purpose. These bikes are usually rigid framed bikes with skinny tires and drop handlebars. In Taiwan, road bikes have taken off and have an air of exclusivity and sex appeal. Road bikes are designed for mainly road riding and Taiwan has some wonderful roads. I used to scoff at Taiwan's roadways, until I actually went out and discovered how much smooth pavement there actually is.

The Pros: Since road bikes are designed for road riding, they obviously are better for… the road. If you ride mainly on pavement then a road bike is truly worth a hard look. Although the novice may assume a road bike will naturally be unstable and uncomfortable, with the proper fitting the opposite may be true. A road bike better balances the rider for putting down distance on the roads and they are generally geared to achieve greater speeds. The standard 53/39 crank may be fine for flats, but for mixed conditions the compact 50/34 has replaced the road triple. Road bikes are usually between 9 and 11 cogs on the rear cassette (speeds) and so a 10 speed with two cranks has “20 speeds”, but it is called a 10-speed because of the number of cogs. The drop handlebars offer a wider range of hand positions to relieve stress on the wrists and avoid numbness. Road bikes come with many add-ons, including: rack mounts, fender eyelets, bottle mounts and other options. A road bike may weigh between 16 and 23lbs depending on the material and construction. I like to imagine one lb as a can of coke. There gets to be a point that it just doesn’t matter… especially when the rider is carrying 30 extra cokes around the middle. It is not uncommon for a road rider to log 8-12 hours in the saddle. The 700c wheels have a more gradual angle of attack, so the bumps don’t feel as rough. With so much of Taiwan accessible by paved roadway, a road bike is an excellent choice for exploring Taiwan.

The Cons: Road bikes are generally more expensive than mountain bikes. In my opinion, a “good” road bike should be between $1500 and $3000, but in Taiwan a descent Giant or Merida road bike can be found for half that. For a lot of beginners the road gearing may be difficult for a beginner, especially for hill climbing. A road triple may be a better choice or the SRAM Apex , which gives the rider a road double with a wider rage of gears. Some bumpy roads may be harsh and a road bike really shouldn’t be abused on harsh terrain like a mountain bike. The smaller frame limits the width of tires you can use. My wife, a novice, spent NT50,000 on a very good road bike that she should be happy with for a long time. In her case she chose the Shimano 105 group with a compact crank and 11-28 cog cassette. She has not needed a triple crank thus far to tackle the local hills.

The Cross Country Bike:

An XC (Cross Country) bike is generally a term used to describe a larger framed rigid mountain bike, often with larger 29” wheels. They often have a wide range of gearing between mountain and road bikes. An XC bike has flat bars and an upright position. They are often designed with rack and fender mounts. The term “Cross Country” refers to the type of long rides over dirt trails.

The Pros: XC bikes are often used by travelers and Mormon missionaries in Taiwan for their versatility and durability in a variety of conditions. They make a pretty good all rounder and they can be loaded for touring. XC bikes are often inexpensive and not a theft risk. They can use wider tires for mixed conditions and the 26” and 29” tires can be found all over the globe. The XC bike geometry favors climbing over a stable descent. XC bikes also boast longer chainstays which can allow for frame-mounted rear racks that sit far enough back to avoid heel-strike during the pedal stroke.

The Cons: XC bikes are not as fast as road bikes. They are heavier and are often geared with mountain triple cranks, which are not ideal for road use. The flat bars can lead to fatigue over long hours of touring and the upright position is less aerodynamic. With much of the rider's weight shifted to the rear, the sit bones must bear much of the weight rather than dividing the load between the front, rear and torso as with road geometry.

The Touring Bike:

A touring bike is a road bike that is specifically designed for long, loaded touring. When asking about touring bikes in some Taiwanese shops, I was routinely pointed toward the Cross Country bikes. While an XC bike can be a great light tourer, it is defiantly not a touring bike. Touring bikes should have drop-bars for the superior had positions for long riding. The geometry should be upright with longer chainstays and a longer wheelbase. A true touring bike should use 650c wheels for their versatility around the world, but many have switched to the more comfortable 700c wheels. Touring bikes use cantilever or V-brakes to better accommodate fenders and fatter road tires. The geometry of most touring bikes is optimized for riding loaded with gear and thus may actually perform better under load. They are extremely stable bikes and offer a wide range of gears for heavy pushing up mountain passes.

The Pros: For long, long distances day in and day out over all kinds of roads, a touring bike can’t be beat. Both front and read panniers can be loaded for months on the move and the tough frame can handle all kinds of abuse. The rider can pedal for hours at a time in total comfort. The components are durable and readily available in all parts of the world.

The Cons: These are hard to find in Taiwan, though I do know a few places. If you are not planning long trips involving plenty of camping, then a touring bike may be overkill and impractical for daily or weekly day-rides. Basically, if you are not planning to cross the Gobi desert, then there may be better options.

The Cyclocross Bike

A cyclocross bike is a special kind of drop-bar road bike designed for racing semi-off road races in often muddy conditions. Cyclocross was traditionally used as Fall training for road riders. A typical cyclocross bike has slightly more relaxed geometry than a road bike and greater tire clearance for knobby tires. They tend to have longer wheelbases for stability and comfort over rough courses and they are slightly more robust than a typical road bike. Cyclocross bikes primarily use cantilever or V- brakes like mountain bikes (though some use disc brakes). The forward geometry lends itself to climbing and they often have higher bottom brackets for greater clearance.

The Pros: Despite being designed around a particular racing discipline, cyclocross bikes have become a favorite as a do-all bike for the person who wants to have it all. They can be stripped down with skinny tires for speed or beefed up for dirt. Some can be loaded with panniers and racks. They use drop bars for better hand position and more upright geometry for better visibility in traffic. Their robustness and design makes them comfortable like a tourer, but nimble like a race bike: A good bike for Taiwan… if you can only have one bike.

The Cons: Cyclocross bikes have a higher center of gravity and may not feel as stable descending. The upright position catches wind and, depending on the geometry, they can be twitchy at times. The long chainstays reduce some of the bike's agility in comparison with a true road bike. Although cyclocross bikes can be loaded with racks, they are not as stable as a touring bike nor do they have the descending chops of a mountain bike. A jack of all trades… master of none.

The Folding Bike:

Folding bikes are small, lightweight bikes, designed with a hinge in the middle to carry in the trunks of cars or on train cars. They use unconventionally small wheels and standard cranks. Some use drop bars and others use flat bars.

The Pros: They are portable and great for getting from the train to the office.

The Cons: Folding bikes are less stable with smaller wheels and thus less able to roll through bumps and ruts. The hinge can act to absorb energy that could go into forward motion. Folding bikes sit lower and drivers are less able to spot them.

Summary: Taiwan has a variety of conditions to ride and it is up to the individual rider to determine which bike is right for their needs. Think about the rider you are and will likely become within the life of your bike. In general most road bikes would be the best option for the type of riding most people do. A cyclocross bike or XC bike would be a close second if there is a possibility of dirt and back road cycling. Heavy mountain bikes should only be considered if you are seriously considering the mountain trails. Forget folding bikes unless you don't intend to travel beyond the train and the office. Most importantly, for whichever bike you choose... be sure you get a proper fitting and don't buy unless you can ride for an hour.

Spend just a little bit more than you intended to keep the "shoulda' syndrome" in check. It is all too common to deny yourself the extras and then spend two years kicking yourself for being too cheap.

Happy riding!!!