RAD MTB CALCULATOR

How to Measure Your Body RAD (Rider Area Distance)

The RAD (Rider Area Distance) is a measure of your functional cockpit length, and getting it right is one of the most important factors for proper mountain bike fit, especially for dynamic riding like pumping and jumping.

Since the most accurate Body RAD measurement is physical, here is a step-by-step guide on how to measure your own Body RAD.

The measurement is the hypotenuse distance from the center of your bottom bracket (BB) to the center of your grips when you are in your optimal riding position. Since you can't measure this on the bike easily, you measure your body's required dimensions using a simple substitute.

You Will Need:

• A "Bike": Your actual mountain bike.
• A Stick: A long, straight object (like a broomstick, a long bubble level, or a piece of dowel rod) that can rest across your hands.
• A Tape Measure: Must be able to measure diagonally.
• Riding Gear: The shoes, pedals, and grips you typically use.

Step-by-Step Measurement Guide

Set Up the Body Position

The goal is to replicate your strong, dynamic riding posture.

1. Place the Bike: Stand your bike upright and put your usual riding shoes on.
2. Mount Up: Mount your bike and place your feet on the pedals. Ensure your pedals are level (3 and 9 o'clock position).
3. Find Your Stance: Stand on the pedals with your feet at your normal riding width. Stand slightly bent at the knees and hips, mimicking the position you take when you are actively pumping or bracing for a hit. This is the "strength position."
4. Hands Ready: Hold your hands out in front of you exactly where the grips would normally be. Keep your elbows slightly bent.

Take the Measurement

1. Bottom Bracket (BB) Reference: Use the tape measure and anchor the end at the very center of your Bottom Bracket spindle (the crank axle).
2. Grip Reference: Have a friend or assistant lay the straight stick across the palms of your hands. This stick represents the handlebar.
3. Measure the Hypotenuse (The RAD): Pull the tape measure diagonally from the center of the BB (where you anchored it) to the exact center of the stick resting in your hands.
   • Ensure the tape measure forms a straight line to the center point between your hands.
   • Measure the distance in centimeters (cm) or millimeters (mm).
4. Record the Number: Repeat the process three times to ensure consistency. This final number is your Body RAD.

How to Use Your Body RAD

Once you have your accurate Body RAD, you can use the calculator to see if your current bike setup (Reach, Stack, Stem, Spacers, Bar Rise) matches you:

• Body RAD = Bike RAD: This is the ideal fit. Your bike setup is optimized for your body’s dynamic range.
• Body RAD is Shorter than Bike RAD: Your cockpit is too long. You will feel stretched out, cramped when squatting, and less able to pump or move dynamically over the bike.
  • Solution: Use a shorter stem, fewer spacers, or a bar with more backsweep.
• Body RAD is Longer than Bike RAD: Your cockpit is too short. You may feel hunched, and the front wheel may feel twitchy or unstable at speed.
  • Solution: Use a longer stem, more spacers, or a bar with less backsweep.

What is rad calculator?

A RAD calculator is a specialized tool used in mountain biking (MTB) to help riders determine their ideal bike fit, primarily by calculating the Rider Area Distance (RAD).

Key Concepts

The RAD calculator uses several inputs from both the rider and the bike's geometry to produce metrics crucial for a dynamic, performance-oriented fit.

What is Rider Area Distance? (RAD)

• What it is: RAD is the straight-line, hypotenuse distance from the center of the bike's Bottom Bracket (BB) to the center of the handlebar grips.

• Why it Matters: This distance dictates the rider's fore/aft balance and how much room they have to move their body—to crouch, pump, jump, or absorb impacts. If the RAD is too long, the rider feels stretched and their movement is restricted. If it's too short, they feel cramped and unstable.
• The Goal: The calculator compares the calculated Bike RAD (based on bike geometry) to the rider's desired Body RAD (based on height and physical measurements) to determine if the bike's cockpit is correctly sized.

What is Rider Area Angle? (RAAD)

• What it is: RAAD is the angle of the RAD line (the hypotenuse) relative to the horizontal plane.
• Why it Matters: This angle dictates how high or low the grips are relative to the bottom bracket.
  • A higher RAAD (steeper angle) means a more upright position, often feeling more stable on steep climbs and less aggressive.
  • A lower RAAD (slacker angle) means a more aggressive, forward-leaning position, favoring high-speed stability and downhill performance.

Inputs Used in the Calculator

A comprehensive RAD calculator requires inputs that define the frame's size and the specific cockpit components: