How to Determine the Best Bike Size Before Buying?

You have to ensure that your bike is the right size regardless of the type of terrain, length of time, and weather conditions of your rides. You may want to have your bike professionally fitted or you can make DIY adjustments on your existing bike.


You should also give your fitted or adjusted bike a few trial rides to determine whether it’s suitable for your cycling needs. When your bike is in the right size, you will enjoy numerous benefits including:

  • Increased comfort when riding: Your body is in the optimum position for short- and long-distance riding. Your arms and legs aren’t overextended while your back, shoulders and neck are in proper alignment.
  • Decreased risks for body aches: You will experience decreased levels of genital numbness, saddle discomfort, and numbness in your hands, fingers, and feet. Your sense of rider fatigue, especially after long-distance rides, will be lessened, too.
  • Reduced risks for injuries: Your risks for repetitive stress injuries can be reduced since your muscles, bones and joints are in their proper positions when riding.

​Of course, getting your correct bike size will require time, energy and effort, even money, but the results are well worth it!

A Note About Professional Bike Fitting

According to a study conducted by the Biomechanics and Ergonomics Research Laboratory at the Massachusetts Institute of Technology (MIT), a new technique in performing a bike fit is nearly as accurate as the computer and camera motion analysis technique.


The bottom line: You can spend as much as $300 on getting the correct bike fit via computerized techniques but you may also spend zero on a DIY technique. You have to work with a cycling professional for best results but the costs will be significantly lower.

You must also understand the basic parameters of a great bike fit, namely, correct saddle-to-stem distance, saddle height, and fore and aft saddle position.

The Basic Considerations

You can start by understanding the entry-level fit factors that contribute to the correct bike fit. Keep in mind, too, that bike sizing can become complicated when you’re a serious rider with unique needs in your bike’s specific performance characteristics.

Let’s take a look at the general bike sizing considerations first.


Fit Your Riding Needs

Your bike should be suitable for your current riding needs and wants. You may want the long and low aerodynamic position adopted by the pros but it may not fit your current abilities.

You can work toward it by increasing your strength, endurance and flexibility so that your bike can be readjusted to fit later.



Fine Tune the Fit

You must first determine your best possible bike frame size. This is a crucial step since you’ll likely have difficulty in achieving the right fit regardless of the adjustments made later.

You can easily make adjustments to a bike’s existing parts, such as the height and angle of the seat. You may also have to swap a few components, such as a new stem changing the handlebars’ location for a more comfortable riding position.


You must also be aware of the impact of proper cleat fit on your riding style and comfort. When your cleats are set too far forward, you can suffer from numbness, hotspots, and pain in the knee and Achilles heel.

When these are set too far back, you’re wasting energy since there’s no optimal power transfer between your muscles and your bike.

What Size of Bike Is Best for You?

Your next steps are to take a few measurements, test ride your bike for proper fit, and make the necessary adjustments to it.


Measure Your Inseam

The inseam is important in getting the right bike size because it determines whether your bike has sufficient standover height for your needs.

The standover height is the measurement from the top tube to the ground, which is take at the top tube’s mid-point and halfway between the head tube and seat tube


Basically, you want to ensure that you can straddle your bike while your feet are flat on the ground. If your inseam clears your bike frame’s standover by 2-3 centimeters for a road bike, larger for a mountain bike, then you have a good standover. To measure your inseam:

  • Stand against a wall while wearing your bike shoes.
  • Straddle a book with its spine up (i.e., place the book between your legs).
  • Mark the spot where the book’s spine meets the wall.
  • Measure from the mark to the floor, which will be your inseam.

Repeat, if necessary, since it’s such an important measurement.


Assess Your Upper Body Position

Aside from the standover height, get the effective top tube (ETT) length since it’s just as important in ensuring a great bike fit.

ETT is the horizontal distance between the seat tube and head tube, a measurement that applies whether you have a sloped or straight top tube. You can make smaller adjustments for fine-tuning purposes later.

effective top tube

Your upper body position will be affected by the following factors:

Saddle-to-stem distance: Get on your bike and lean your elbow against the front of its saddle. This will determine the precise position of your bike’s saddle in relation to its stem. Your middle finger should touch the steer tube’s middle exactly for the best fit.

Stem height and length: This has a direct relationship with the fore and aft saddle position although your level of flexibility will also play a part.

Your best stem height and length can be determined by applying the 3-finger rule – there should only be three fingers of space from the head tube’s top to the steer tube’s top.

You can adjust it depending on your needs – two fingers for women with high water retention and four fingers for commuters, touring pros, and older adults.


Bike Saddle Height

With the right saddle height, you can enjoy efficient and powerful transfers of energy from your leg muscles to the bike so that optimum speed can be achieved.

  • Hop on your bike.
  • Place your foot at the bottom of a pedal stroke.
  • Ask a sales associate to check that your leg has a slight bend with 80 to 90% full leg extension.

This is applicable for mountain, hybrid, and road bikes.


Bike Seat Fore and Aft Position

To determine if the bike suits the optimum bike fore and aft position:

Hop on your bike. Check that when your right foot is at its 3 o-clock position in a pedal stroke, your knee is in alignment with your forefoot.

You can drop a plumb line from your kneecap’s bottom to the ground – it should fall straight through the pedal’s center and to the ball of your foot while your shin is slightly tilted forward


This is applicable for mountain, hybrid, and road bikes.

Final Words

Of course, there’s no substitute for taking your new bike for a spin around the block before declaring it the correct fit! You can make adjustments as the need arises.

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