Fitting the bike to your body!
Every rider is different. Your goal is to adjust the bike so it fits your body and your riding style. You're trying to maximize pedaling efficiency. You want to go easily from sitting to standing and back again. You want to feel comfortable. You want to eliminate stress on your back, arms, and knees. You want the bike to feel stable yet responsive. A bike that fits puts you closer to all these goals.
As I talk about the "rules" for fitting a bike, remember that these are typical settings for the average rider. Your body probably isn't perfectly average, and your riding style isn't exactly the same as your buddies. So consider these recommendations as "starting points" -- they give you a place to begin. Then you can tweak to find your own sweet spots.
In this article, I discuss both road bikes and mountain bikes. The concepts are easier to understand on a road bike, and this helps you apply those concepts to your mountain bike. I also have a page for "automated Fit and Function" checkup for groups of riders -- such as scout troops who are preparing for a cycling activity.
First: Is your bike the right size for you?
It's very difficult to adjust a bike to your body if the bike (or any part of it) is the wrong size. For example, on a bike frame that's too small for you, the seat may not adjust back far enough to put you into the best pedaling position. Or you may discover that the long cranks on your little road bike are better suited to a tall guy. Installing a shorter crankset would let you pedal faster without knee pain.
The frame size is the distance from the middle of the bottom
bracket to the top of the seat tube (for a standard frame). We'll
work through bike fitting with my sister-in-law Julie.
|Bicycle frame sizes are based on the length of the seat tube (the piece that
goes from the saddle down to the pedals). Road bike frames are sized in centimeters,
while mountain bikes are sized in inches.
For a road bike, it's fairly clear cut. You can determine the frame size by sticking a tape measure along the seat tube. Middle of bottom bracket to where the seatpost sticks out. But this may not work on smaller bikes where the top tube slopes downward toward the seat. You'll need to measure a "virtual frame size" as below.
On mountain bikes, there may not even be a seat tube. Or the seat tube is shortened as the top tube bends downward.
Measuring a "virtual frame size". With a level on a board, we
find the spot that's level with the spot where the steerer emerges
from the frame and measure to a "pretend top" of the seat tube.
|For odd-shaped frames or down-sloping frames, we pretend there's a normal road-bike style frame,
spiritually superimposed over the weirdly misshapen mountain bike frame, and you
measure that "pretend" frame to get your frame size in inches. So for
mountain bikes, frame size in inches is more of a philosophy than an actual
Are you confused yet? That's why the store says "medium" instead of "sixteen inch frame". But not all "mediums" are the same either. For one bike manufacturer, their "medium" may be a 15-inch, while another brand of bike has a 17-inch frame as their "medium" size.
Some fine print: To further confuse things, there are two ways of measuring the seat tube length. If the frame size is reported as "CT", that's the distance from the Center of the bottom bracket (the big round hole in the bottom of the frame where the cranks connect to each other) to the Top of the seat tube where the seat post enters the frame. "CC" means Center of bottom bracket to Center of the joint where the horizontal top tube connects to the seat tube. This measurement is based on the standard road-bike triangle frame. The first mountain bikes looked like that, but nowadays when the mountain bike frame size is given in inches, it's a pretend measurement. The top tube of almost all mountain bikes slopes downward toward the rear of the bike. The top of the seat tube (if there's a seat tube at all) is a couple of inches lower than it would be on a true triangle frame.
Measuring yourself to get your ideal frame size: To select the correct frame size, you need to know your inseam length. That's the distance from the floor to the underside of your crotch.
Here's a formula for finding the right road bike frame size, measured in
Roadie frame size = inseam (pants length in inches) x 2.54 (cm per inch) x 0.67.
Manufacturers typically make frames in two-centimeter increments. For example, they may offer a 54 and a 56 frame, but no 55.
Road bike example: I'm tall. I buy pants with a 36 inch inseam. 36 x 2.54 x 0.67 = size 61. Let's round downward to 60, because for the brand I want, that's the closest frame size. Yeah, I could try a 62, but when it comes to stand-over height, it's better not to risk banging your junk on a frame that sticks too high into your crotch. Pick the first size below your calculated number.
For mountain bikes, the manufacturer will usually offer general frame sizes -- small, medium, large, extra large. We'll determine the ideal frame size in inches, then compare that size to the manufacturer's "sizing guide." For example, the guide may say that bikers who measure up for a 17 to 18 inch frame should select their "medium" frame. So let's calculate the ideal frame size.
For a mountain bike, we leave out the 2.54 conversion and report the frame size
Mountain bike frame size = inseam x 0.67.
Again I'll use myself as an example. Inseam of 36 inches x 0.67 = size 24 frame. For the model of bike I want to buy, the bike shop tells me to get the XL frame which is listed as a 22.5-inch. Again we round downward to get the appropriate frame size.
This crank is 170 mm. We're setting this bike up for a 5'4"
female. Julie is a "pedal-masher," so 170 is a good length
for her. If she were a "spinner" we'd go with 165.
Crank length: are you a masher or a spinner?
Crank arms come in different lengths. 165, 170, and 175 mm are common size breaks. An off-the-shelf bike has crank arms that are proportional to the size of the bike.
Of course, taller riders can use longer crank arms. But the decision about crank length is based mostly on riding style. What do you do when you need to go faster? Do you spin the pedals more quickly? If so, a shorter crank fits your style. Do you like to mash hard on the pedals? Then a longer crankarm lets you get more leverage.
If you decide to change crank size, you should adjust your front-to-back seat position. See below.
Handlebar width: often overlooked!For a road bike, start with a handlebar that's as wide as your armpits. The drops of the handlebar line up with the crease where your arms meet your upper chest. Now adjust for riding style and comfort. Wider handlebars give you more comfort and control, especially for beginners. A narrower handlebar makes a racer more aerodynamic.
Mountain bike handlebars should be wide enough to give good control, but not so wide that you have to move the shoulders or twist the body in a tight turn. Unlike road bike handlebars, you can cut a mountain bike handlebar to the appropriate size, and you can move grips and levers to adjust the hand position.
Rule of thumb for mountain bike handlebar width: Position the grips so the inside edge of each hand (where the index finger and thumb encircle the grip) lines up just outside the crease of the armpits. While holding the grips in a position where you can comfortably work both the shifters and the brakes, with shoulders and upper arms relaxed, the forearms should aim straight forward. Before getting out the hacksaw, ride some trail and fine-tune the position of the grips on the handlebar. Once you're sure you've got the right position for the grips and controls, cut off the handlebar ends.
And about the bike seat: Riding comfortably requires a nice-fitting bike seat. A seat with slimmer butt-supports lets you move around more easily when mountain biking on rough terrain, but you'll be more likely to get groin numbness when you're cranking on the pavement. Ladies have wider pelvic bones and need a slightly wider bike seat to get support onto the skeleton. The ideal seat depends on where you ride, how you ride, and how your body is put together. If you're unhappy with your saddle, sit on a few bike seats at the local bike shop. See if they'll let you take your favorite for a test-ride.
Starting the Fitting Process... Put it in a trainer!
Once it's installed in the trainer, make sure the bike is level by
measuring the distance from the hub to the floor.
|To do these adjustments, you'll need to put the bike in a trainer. You should
also have a wheel-cup or block to raise the front wheel to the same level as the
back. If you don't have a trainer, borrow one. To get things right, you need to
pedal the bike as you make adjustments.
Do the adjustments in the order they're written here. Why in specific order? Some adjustments depend on other things being done correctly first -- for example, on a dual-suspension mountain bike, you can't adjust the bike's seat and handlebar position correctly if the shock absorber preloads are mismatched.
And as you make each adjustment, recheck previous adjustments to see if you need to tweak them again. Once you're done, write down the settings that work for you.
1. Adjust the "sag" (mountain bikes)
You need: Trainer and wheel cup, shock pump, manufacturer's specifications. Helps to have: goniometer to measure head angle.
Unlike road bikes, most mountain bikes have shock absorbers. The bike designers plan for the bike frame to "sag" down as the shock absorber compresses under the rider's weight. The force that resists the compression of the shock absorber is called "preload." The key is to adjust the preload of each shock absorber for two things: (1) The bike frame should settle into the correct angle relative to the ground. For example, if the front shock doesn't have enough air pressure, the nose of the bike will aim more downward and you're more likely to endo. (2) Each shock should be set so it will function well. Too little preload, and the shocks will bottom out when you hit a bump. Too much, and every little pebble bounces the bike. Most bike manufacturers instruct you to adjust the shock's preload by measuring the amount of "sag" of the shock under the rider's weight. Some may give a suggested air pressure based on the rider's weight.
We'll assume you have air shocks, but the same principles apply to coil-spring shocks. First, go on the internet and get the specific recommendations for the shocks on your bike concerning preload and sag. (No, I can't tell you how much air to put in your shock. Don't bother emailing me. Go to your bike store or the manufacturer's web site!) Also check the bike manufacturer's specs for "head angle" -- the angle of the front fork relative to the ground.
Put the bike in the trainer and set the front tire in the wheel cup. Measure to insure that front and rear axles are exactly the same distance from the floor. Set an initial preload in front and rear shocks (using your "best guess" or the manufacturer's recommendation), then sit on the bike. Measure the sag of the bike under your weight (or measure the shortening of the shock, whichever the manufacturer recommends). Now adjust the front and/or rear shock air pressure until the sag meets the manufacturer's recommendation. If you have a goniometer, fine-tune the shock preload so the head angle meets the specs for your bike.
2. Set the cleat position on your shoes
You need: Trainer and wheel cup, shoes, cleats, clipless pedals, plumb line, tools to adjust cleat.
With the ankle in your "sprinting position," the middle of the
MTPJ should fall directly over the pedal axle. Most riders
put the cleat too far back. Julie's cleats will move 1 cm forward.
|For efficient pedaling, the bony bump on the inner side of the foot -- the
metatarsophalangeal joint (MTPJ) of the large toe -- should lie directly over
the middle of the pedal axle. (Many riders make the mistake of adjusting the
cleat to the upside-down shoe, without any reference to where the foot actually
sits within the shoe, or to where the shoe sits on the pedal.) Use your plumb
line to check the cleat position while you're locked onto the pedals.
Pedal a minute, then stand with the ankle in your usual pedaling position. Feel through the shoe to find the bony bump of the MTPJ. Drop a line down to the pedal axle for a "true vertical" reference. Note how far the cleat must be moved forward or back to bring the first MTPJ directly over the pedal axle. Unclip and adjust the cleat position, then recheck the position of the foot over the pedal.
Racing roadies usually like the cleat pretty far forward, because it increases sprinting power. Mountain bikers who jump their bikes may want to sneak the cleat back a little, for more stable landings. But the recommended position is: set your cleat so the bony bump at the base of the big toe is directly over the axle of the pedal.
3. Set the seat tilt
You need: Trainer and wheel cup, large book, a level, and tools to loosen the seat.
Level the seat using a book and a level. If the nose of the seat
tilts up, you'll climb better. If the nose tilts down, it puts more of
your weight on the handlebars. Julie likes the nose slightly down.
Lock the bike into the trainer. Check to be sure the wheel cup has raised the front wheel so that each wheel axle is exactly the same distance off the floor. Put the book on the bike seat. It should hit in three points: the saddle's nose plus the two butt-supports. Put the level on top of the book, parallel to the bike frame.
To set an "average" starting position from which to further adjust saddle tilt, adjust the tilt of the seat so the bubble in the level just begins to move toward the handlebars of the bike. Most riders like the seat angled very slightly up at the nose -- so the level tips about 1/2 bubble toward the handlebars.
You'll want to revisit "seat tilt" after adjusting the seat position and handlebar height.
If you tend to ride more upright, the nose of the saddle can be tipped up higher. If you tend to ride with your body forward (like a roadie in the drops), you'll want to drop the nose down a little to decrease pressure on your crotch.
4. Set the saddle height
You need: Trainer, bike shoes, tools to adjust the seat. Optional: measuring tape, goniometer.
Do the seat height measurements with the crankarm in line
with the seat tube, not straight up-and-down.
The saddle height is the distance from the lowest spot on the saddle (where your butt will rest), and the middle of the bottom bracket (which is the "average" position of your feet). We're measuring this distance straight up along the seat tube.
Correct saddle height lets the rider pedal efficiently with the pelvis perfectly still on the seat (no side-to-side rocking motion). A higher seat lets you climb better, and takes stress off your knees. Mountain bikers often set their saddle height for efficient climbing, then switch to a lower seat height for better control on rough descents. Let's find a good "roadie" or XC trail seat height.
Here's a formula for where to start:
Low spot of saddle to center of bottom bracket distance = inseam x 0.883
The seat will usually need to be moved up a tiny bit for clipless pedals, especially if the rider tends to pedal with the foot bent downward.
|Put the bike into the trainer and put the wheel-cup under the front tire. Pedal. There should be no rocking or side-to-side motion. Lower the seat if necessary.|
Landmarks for measuring knee and hip angle when adjusting
the height of the saddle. Julie's seat height is perfect.
| Have the rider stop pedaling with one pedal as far away as possible.
By "far away" I mean pushing the pedal to its fullest extent so the
crank arm lines up with the seat tube, not so the pedal is closest to the floor.
The knee should have a slight bend. If you're into measuring, find the trochanter of the femur (the lowermost bump of bone at the hip), the head of the fibula (the bony lump on the outside of the knee), and the lateral maleolus (the bone on the outer side of the ankle). Draw a line connecting these three spots. The angle at the knee should be about 155 degrees -- 25 to 30 degrees off straight.
There should be no tipping of the pelvis as you pedal. The
ankles should feel comfortable in their neutral position, not
"stretching" to meet the pedals. No wobbling here.
Some riders will keep raising the seat until they begin to wobble as they pedal, then drop the seat until they reach the highest comfortable and stable pedaling position.
Beginning riders may feel uneasy with the seat raised to the most efficient pedaling position. They feel too high off the ground, and are nervous they won't be able to get a foot down as the bike stops. Compromise for security, then gradually raise the seat height as the rider becomes more confident.
Bottom line is: comfortable and efficient pedaling while preserving good control. Mountain bikers, use a file to mark your seatpost at three spots: (1) your climbing spot (seat the highest), (2) slightly-lower compromise spot for rough up-and-down terrain, and (3) lowest downhiller seat height that still allows you to pedal uphill without knee strain.
5. Set saddle front-to-back position
You need: Trainer, wheel cup, plumb line (a string with a weight attached), bike shoes, and tools to adjust the seat.
Before starting, make sure the cleats on your biking shoes are in the correct spot. Adjust the seat height. See above.
At the top end, press your plumb line against the bony bump
below the patellar tendon.
|Start with the saddle rails in the "average" middle position. Clip
into the pedals. If you're riding with platform pedals, position the foot in
your usual "riding gently uphill" position. Pedal a minute or so, then
stop with the cranks exactly horizontal (one foot fully to the front, the other
foot all the way back).
Put the top of your plumb line on the tibial tubercle (the bump on the bone about two inches below the kneecap). Drop the plumb line past your foot, insuring that it isn't tangled up on clothing or shoes. The line should hit in the middle of the pedal axle.
Pedal a minute to get the ankle into its usual position.
The line should fall directly through the middle of the pedal axle.
|Note how far the string falls from the middle of the pedal axle. If the
string is in front of the axle, the seat should be moved back about the same
distance as between the string and the middle of the pedal. If the string falls
behind the pedal axle, the seat must move forward.
Have the rider get off the bike. Reset the seat position. Now pedal again, recheck the position of the knee above the pedal with the cranks horizontal, and adjust the front-to-back position of the seat again if necessary.
Now recheck the seat height. If the saddle was moved a significant amount, you may need to readjust the seat height. And if you change the seat height, you must again recheck the saddle's front-to-back position.
6. Adjust the position of the handlebars
You need: Trainer and wheel cup, stem spacers, stem-tightening tool.
If you haven't done it already, adjust the bike's shock absorbers to give the correct sag and head angle. Adjust the saddle height and front-to-back position. Get on the bike, grasp the handlebars and start pedaling. Does your back feel comfortable? Do your knees have enough room as they pump up and down? Can you breathe easily? Can you let go of the handlebars and maintain the same body position, or are you leaning on your hands as you pedal?
|There are no absolute rules for adjusting the handlebar position. You're looking for the right combination of aerodynamics, steering control, upper body comfort, and power transfer. Let's start with:|
A good starting height for the handlebar is two inches lower
than the top of the seat. We'll drop out one of Julie's spacers.
Rule of thumb #1: The handlebar should be about two inches lower than the saddle. If you want to check it, throw a board between seat and handlebar. Put a level on the board, and measure how much you have to raise the board off the handlebar to center the bubble. There should be two inches of space. (If you're measuring riser handlebars on a mountain bike, tie a string between the grips. The string is where you measure your "height.")
While pedaling, you should NOT be able to see the front axle.
In this case the axle appears in front of the handlebar. This suggests that the rider either has a longer body than average, or is riding a bike that's too small. Assuming the bike is the correct size, and the saddle is in the correct position, we need to raise the handlebar or swap for a longer stem.
|Rule of thumb #2: The handlebar should block your view of the front axle. That's
a good starting point for making your tweaks.
If you see the axle in front of the handlebar, such as in the photo, you may need either a longer stem, or a higher handlebar. (Spacer rings are used to raise the handlebar.) If you see the axle behind the handlebar, you should lower the handlebar.
Check to see if you have spacers (rings) between the bike frame and the stem. A new bike usually has a couple of them, so an off-the-shelf bike often comes with handlebars that are a little bit too high. (Most beginners like a more upright riding position, which is another reason that bike-builders raise the handlebars.)
Julie's wrist is bent sharply upward as she extends for the brake.
Suggestions: (1) Rotate the handlebars down a little. Or, (2) move
the brake/shifter attachment down "around the corner" so the
lever is closer to her preferred hand position. Or both.
|Rule of thumb #3: If the cockpit is comfortable, you've
got it right. If you're fitting a road bike, get down in the drops. Check
the angle of the handlebars, and the position of the brake levers relative
to your hands. The wrists should be neutral (comfortably straight, not
tipped side-to-side), and you should be able to get a finger or two on the
brake without moving the wrist.
You need to start your adjustments with the hands in the position you'll be riding in. Adjust the tilt of the handlebar (and if necessary, the position of the brake levers on the handlebar) before going on.
If you're fitting a mountain bike with riser handlebars, your riding will be affected by the tilt (amount of rotation) of the handlebars. While adjusting handlebar height and stem length, start with the handlebar in the neutral position. Most riser handlebars have a rotation and centering guide marked on the front.
Use spacers to adjust the tilt of your body and "reach" of your
shoulders. Many brands are put together with an extra spacer.
We're removing a spacer to drop Julie's handlebars.
|Rule of thumb #4: The stem length and the handlebar height can be changed together to keep your upper body in balance. Either higher handlebars or a shorter stem will put you more upright. Lower handlebars or a longer stem will both stretch you out more over the bike. The difference is how they change the angle of your shoulders. If you make a big change in handlebar height, changing the stem length can keep your upper body in balance.|
|For example, if you raised the handlebars by an inch, you may want to switch to the next-longer stem to keep your arms and upper body in an efficient forward position. Or if you lowered the handlebars dramatically, substituting a shorter stem raises your body and moves your shoulders to a less-extended position.|
Hint: If you prefer a very low riding position but don't want to cut the steerer and eliminate all the spacers, you can flip the stem (turn it over so it angles downward). Depending on the angle of your stem, this can make a big difference in the handlebar height.
And here are two concepts: If your arms or shoulders feel uncomfortable as you ride and steer, but you like your hip and chest position, adjust the stem length. If anything else (neck, back, breathing, hips) is uncomfortable, adjust the height of the handlebars or change to a stem with a different amount of "rise."
Note: I suggest you make major adjustments of riding position by changing handlebar height. Then, if necessary, make very small changes in stem length only if the new stem length fits your riding style. Changing the stem length changes the way the bike steers.
On a mountain bike with riser handlebars, you can now fine-tune the rotation of the handlebar. On most handlebars, there's a cross-hair in the middle of the bar. Center this cross-hair in the front of the stem as your starting position. Rotating the handlebar forward gives you a more aggressive climbing position and flattens your body for less wind resistance. But it makes you more likely to endo, and makes it harder to get behind the seat on steep descents. Rotating the handlebar back gives you a more upright riding position, and easier downhill steering. You may want to revisit riser-handlebar rotation (tilt) during your trail test-ride.
|Test the riding position. While riding in the drops, you should be able to
comfortably raise your head to look a little uphill. If your neck feels strained
while looking straight down the road, you need to raise your handlebars.
Your knees should not touch your elbows as you pedal. In fact, you should have a couple of inches of clearance.
The hips should not feel compressed, and breathing should be easy. If you feel at all "squished", raise the stem with spacers or switch to a "riser stem" (one that angles upward from its attachment to the front fork) for a more upright riding position.
If you have a big upper body, you may find yourself leaning uncomfortably on your hands as you ride. Raising the handlebars puts more of your weight on the butt, and less on your hands.
As you adjust handlebar height, you may feel a change in how the saddle feels. Adjust the seat tilt to your comfort. In general, adjust the nose of the saddle in the same direction as you're adjusting the handlebar: if you raise the handlebar, tilt the seat so the nose of the saddle is slightly higher. If you lower the handlebars, tilt the nose of the saddle downward.
7. Adjusting brake lever and shifter position
You need: tools to loosen brake levers and shifters.
With the wrist neutral, a straight line passes from the middle
of the elbow through the middle of the wrist and middle of
the grip. Move the brake lever so the finger falls over it while
the wrist stays in this position.
If you have a riser handlebar, you should have adjusted the handlebar rotation while you were setting the handlebar height.
Loosen the brake levers and shifters. Get on the trainer. While pedaling on the bike in a sitting position, put your hands into a natural-feeling spot on the grips. It should be your "climbing and aggressive riding" hand position, not a "looking around at the scenery" position. Adjust your wrist alignment to neutral. Imagine a straight line going from the middle of your elbow directly through the middle of the wrist and out through the space between thumb and index finger. This line should continue through the middle of the handlebar.
While lightly holding the grip, raise your index finger and middle fingers in a slightly-curved position. Now, without moving your hand or fingers, move the brake lever so the "sweet spot" of the lever falls under the outer knuckles of the fingers. The lever should feel secure within the groove in the knuckle as you pull it.
If you usually ride with thick padded gloves, adjust the lever position while wearing those gloves!
Adjust the starting position of the lever so you don't have to stretch to get hold of it. The best start position depends on your finger length, the thickness of the tissue in your palm, and the thickness of your grips. If the lever seems too far away and can't be adjusted inward, install thinner grips. A smaller-diameter grip lets you extend your finger further toward the lever.
Sweet spot for brake and shifters. The fingers and thumb
can engage any control without moving the hand and wrist. You should NOT have to move the outside of your palm or the little finger as index finger and thumb move from brake to shifter and back again.
|Once you've got the brake lever positioned, relax your fingers off the brake,
while keeping the hand in the same spot on the grips. Slide the shifters into
the position that lets you make upshifts and downshifts with the least amount of
hand and finger motion.
The most common fitting mistake here? Many riders assume the mounting rings for brake and shifter HAVE to touch each other. Just like it came from the factory. Nonsense. Slide it, twist it, until the shift paddles naturally fall under your thumb. And index finger, depending on what type of shifters you have.
If you're fitting a road bike, you should already have adjusted the rotational position of the handlebars and the brake/shifter lever position, because this was a necessary step before setting handlebar height. Recheck your settings. The wrists should be neutral (comfortably straight, not tipped side-to-side), and you should be able to get a finger or two on the brake without moving the wrist.
8. Test ride. Tweak your settings
Review all the settings you've made. Because one new setting may affect something you did earlier, recheck and readjust until riding on the trainer feels perfect. Shift. Stand up. Sit back down. Pedal fast. Pedal slow in a big gear. Find any settings that need tweaking while the bike is still on the trainer.
What feels good on a trainer may not work as well once you start bouncing over rocks. Take a long ride with a tool kit, and make tiny tweaks to your setup until it feels comfortable and natural. Be sure your ride includes stiff climbs, steep downhills, and tight corners.