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Thursday, June 21, 2012

How to Find a Bicycle that Fits You

By Smokey Dymny from the Quadra Bike School

Too many beginners jump on a bike without knowing exactly how to set it up for
comfort. The worst examples are the riders who are on a bike that is way too small
or large. Too small shows up as a rider who has their legs very bent. Not being able to extend their legs straight at the bottom of the pedal stroke means they never get to develop optimum power. At the other extreme is the rider whose saddle is pushed all the way down to the frame so they can reach the pedals but they are bent too far forward in order to reach the handlebars. In between are many lesser fitting mistakes.

DETERMINING YOUR IDEAL FRAME SIZE

Bicycles come in different frame sizes to accommodate different sizes of riders. We simply need to know how to pick the right one. One method is not very difficult and works for most folks unless you want extreme precision because you are going to ride competitively. In that case go to a pro fitting bike shop or measure your self with the free fitting service at wrenchscience.com and click on the Fit System tab. The rest is explained there.

For the simple method try this:

First measure your inseam, that is your leg length, with your riding shoes on. You might need a friend’s help. Pull the measuring tape up tight under your crotch while your friend tells you the measurement at the floor with your feet about a pedal width apart.

Next you need to decide which type of bike you are trying to fit.

For a road bike subtract 10 ½ inches.
For a cruiser or hybrid subtract 12 ½ inches.
For a mountain bike subtract 14 ½.


For a 32 inch inseam this would mean we would fit a 21 ½ inch road bike; a 19 ½ inch hybrid or an 17 ½ inch mountain bike.

In actual practice we would look for a 22inch road bike (or 56cm as road bikes
are often listed in metric sizes) because bicycle frames are generally sold in 2 inch increments. Most companies use even numbers but some companies use odd number
frame sizes.

MEASURING FRAME SIZE

Now what is the frame size of your current bicycle you may ask?

Since it’s not always marked on the bike here’s how to tell. Measure from the middle of the crank to the top of the frame under the seat. That’s called the seat tube. Don’t measure the seat post itself. That’s the most common way to tell the frame size.

The difference between your frame size and your leg extension is made up by
adjusting the seat post upwards until your leg is fully extended at the bottom of your pedal stroke but with just the slightest bend in your knee. You NEVER want to be so high as to let you knees lock on each pedal stroke – this will cause knee damage. But you want it to be high enough to get the full power of your leg muscles.

SADDLE FITTING

Once your seat height is set, check the seat position itself. Set the saddle angle so it’s more or less level. Then sit on the bike while holding onto something. Place your cranks horizontally with the widest part of your shoe directly over the pedal axle.

Make a plumb bob with a nut or a bolt on a string or thread. Have your friend drop
the string from the back of your knee bone (patella) on your forward leg and down to the side of your foot. If the string bisects the pedal axle you are well positioned. If not, the saddle has rails which can slide (after loosening the bolt) forward or backward until this is achieved.

If you can’t get this position properly go back and check the frame size again. Also check the saddle mounting clamp. On the old ones, which are NOT integrated into the seat post, this could be mounted backwards which makes this adjustment difficult to achieve. There is some leeway according to preference here. You can ride a while and decide your preference is to shift a bit fore or aft. But DO NOT adjust the saddle to change your reach to the handlebar. This is done next.

HANDLE BAR FITTING

On a road bike the handlebar needs to be purchased in the right width. Your hands
need to reach out to meet the bar in parallel. You can get your friend to measure the distance between your shoulder bones across your back . This will be your optimal handlebar width. Some people seem to pick narrower bars in the city but this tends to hamper good breathing. In rough mountain bike territory bars are extra wide for better control over the bumps, potholes, etc.

If your hands are too widely spaced on a mountain bike you can cut the bars
down. These bars all come very wide from the manufacturer. Your bike shop was
supposed to tell you they could be shortened. Many people are too lazy to do this. Just place your hands on the bar where you think you would like them (never closer together than parallel, remember your breathing) and then measure how much you’ll cut off.

It’s generally not more that 1 ½ inches at each end. Remove the grips, they come off easily if you squirt water under the rubber while holding it up with a screwdriver. Then wiggle them off.

Don’t cut the bars with a hacksaw, it makes a ragged mess. Get a pipe cutter used for cutting 1 inch copper pipe. Place it on your mark and rotate until it cuts through. Use the cut off piece to measure the same length to be cut off the other end of the bar. Before you slide the grips back on you may have to move the brakes and shifters inboard by the length of bar you cut before the grips fit back on. For smaller folks the space left may now be limited. This is normal. Cut some length off the grips to make them fit.

I often cut my grips shorter just to get the brakes into a more ergonomic position vis à vis my hands.

BRAKES AND SHIFTERS

Now adjust your brakes' angle on a flat bar so they are at approximately 45 degrees below level. A more precise setting would be to adjust them so that the back of your hand is in line with your forearm when squeezing the brakes. If the shifters are separate align them close to the brakes but check for easy thumb reach too. On a road bike the handlebar is tilted so that the slope of the top part (just above the brake) is equal to the slope of the drops (the part below the brake). Then the brakes are adjusted up or down this curve until the bottom tip of the brake is just about even ( + or – ½”) with a straight edge extending forward from the flat part of the drops.

On cruiser bikes adjust the brakes so they are in line with the back of the hand and forearm rule.

STEMS

The stem is the gooseneck piece between the steerer tube and handlebar.

Stems are where you can change your reach to the handlebar and the tilt of your
torso. Stems come in very many lengths. They also come in so many different heights
and upward angles that you can accommodate just about any riding preference. I
can’t describe all the permutations here. Just go to a shop. Show them where you
want your hands to be when you’re riding and they should be able to get you the
right stem.

Be prepared. If you are changing the riding position on a bike to be radically more
upright than it was you may also have to change the brake and shifter cables because they will have to be longer.

Now GO have a comfortable ride!

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