Road bikes are most often used by commuters, fitness, and racing fitness riding. The frames are usually large, isosceles (all sides the same length) triangles with a top bar, or top tube, that is parallel to the ground. Racing bikes usually have smaller frames, while touring or commuter bikes often have larger frames. Road bike frame sizes are measured in centimeters. Mountain bikes have a lower center of gravity to keep you on balance riding over roots, rocks, and mud on the trail. The center triangle is more compact, with the top tube sometimes angling down, away from the handlebars. Mountain bike frame sizes are measured in inches. Hybrid bikes combine features of road and mountain bikes. You can use these for both street riding and casual trail riding. These frames are usually measured in centimeters. Cruiser bikes have odd, sideways S-shaped or curved frames that allow you to sit nearly upright while riding. The handlebars are high above the seat and the pedals slightly in front of you so that you comfortably cruise around town. Sometimes called “city bikes” or “commuter bikes,” these are made for short distances. Fitting these bikes is less about measurements than pure comfort on a test ride. [1] X Research source Kids bikes have smaller frames similar to mountain bikes, helping them keep their balance with a lower center of gravity. They are very adjustable to compensate for quickly growing kids. They are usually measured by wheel size. [2] X Research source
The seat tube is usually, though not always, measured from the top of the tube to the center point of the crankshaft. [5] X Research source Know that this measurement is simply a starting point – you will likely need to make specific adjustments later on.
For example, if you have a 33 inch inseam, you would need a 17. 5" top tube (17. 75" tubes are hard to find):33" x . 67 = 21. 75" 21. 75" - 4" = 17. 75 Some mountain bikers prefer to measure by seat tube length, like road bikers. If your bike shop gives frame size by seat tube length, take your inseam and multiply it by . 185. The resulting number is the recommended distance between your seat and the middle of the crankshaft, which is the circular piece the pedal rotates on.
For a child’s inseam of 12-17 inches: 12-inch wheels For a child’s inseam of 18-22 inches: 16-inch wheels For a child’s inseam of 22-25 inches: 20-inch wheels[8] X Research source
It is very rare that the last person who tested the bike needed the same seat height as you, so you must adjust this before knowing if the frame is the wrong size. Make sure you are not shifting or dropping your hips with each pedal stroke, as this will make your foot drop lower than it should and result in an improper fit. [9] X Research source
You can touch every shifter and brakes comfortably. Your elbows are slightly bent. You can bend from the waist, not the back, to reach down. In general, casual riders will want closer, higher handlebars while racers want a longer reach. [10] X Research source
A road bike should only have 1–2 in (2. 5–5. 1 cm) of space between the wheels and ground. If not, then you need a bigger frame. A mountain bike should have 3–4 in (7. 6–10. 2 cm) of space beneath the tires. If it’s any more or less, change the frame size.
Smaller bikes are generally lighter and a bit more maneuverable. However, this difference is negligible, and you might not be able to adjust the bike a size if you find yourself uncomfortable later on. Many mountain bikers and racers opt for the smaller frame. Larger bikes can make you reach a bit too far, but you can often raise and lower the handlebars to a greater degree, allowing you better customization options if you decide you need a better fit further down the road. Many road bikers chose the larger bike for a more comfortable fit.
Rent a few bikes before buying so that you can get 2-3 days of riding in. Talk to you local bike staff, even if you might buy a bike online. Let them know about any specific issues you’ve had and possible reasons. [13] X Research source
If you feel pain in the back of your knee when riding, your seat is too high. Lower it 1-2cm. If you feel pain in the front of your knee when riding, your seat is too low. Raise it 1-2cm. [14] X Research source
If your seat is in the right position, you will be able to stand on the pedals without using the handlebars to pull you up. If you have trouble standing, reaching for the bars, or feel finger numbness, then your seat is too far back. Trouble riding down hills and/or shoulder pain usually means your seat is too far forward. [16] X Research source
Women typically tilt the seat down for comfort. Men typically tilt the seat up for comfort. [17] X Research source Loosen the bolt on the side of the seat to change the seat angle. You can easily loosen the bolt, change the angle, then tighten again. Some older seats have two small bolts underneath the seat, one in front of the seat post and one behind. You must tighten one side to push that side up while loosening the other, almost like a see-saw. [18] X Research source
Top Tube Length refers to the length of the bar between your handlebar stem and seat post. These are adjusted to fit the frame, and unless you have a very disproportionate body (torso much larger/smaller than legs) getting a properly sized frame will give you a properly sized top-tube. Stem length is the distance between your top tube and the handlebars. The longer the stem, the further away the bars will be from your seat. Stems run from $15-$150 and are the primary way to adjust your frame to make it fit your torso. Longer stems bend you into a more aerodynamic position while shorter stems lead to a more upright, calmer riding style. [19] X Research source Handlebar angle can be changed independently from your stem. To do so, loosen the 4 bolts where the stem meets the handlebars and angle it up or down to your comfort. This is a great way to get an extra 1-3 inches on your handlebar position, which can make a big difference in comfort. [20] X Research source Handlebar height may often be changed by adding or removing the metal spacers where your stem meets your frame. To do so, loosen the bolt on the top of the stem and the two that clamp the stem to your frame and remove the handlebars. Then add or remove the spacers accordingly. You can only make minor changes, however, as there is not a lot of room for new spacers. Some older road bikes with quill or threaded stems may allow you to adjust the handlebar height by raising or lowering the stem.
