# Histograms and Suspension Velocity Analysis

A theoretically ideal histogram for suspension velocities, showing a bell-shaped distribution of velocity over time. Positive values represent compression, while negative values represent rebound.

One very useful technique for suspension setup is to use histograms and suspension velocity analysis to evaluate spring and damping settings. Histograms put values to how much time the suspension is active in each damping range (high-speed and low-speed compression and rebound damping), and by using some basic statistical analysis techniques, that information can be used to make spring and/or damping adjustments to the motorcycle and improve its performance.

# Spring Rate Conversion

Use this spring rate conversion calculator to convert between units of kg/mm, N/mm and lb./in. for motorcycle spring rates. Input a value in the first field, select “from” and “to” units in the second, and the new value will be output.

Factors used for spring rate conversion:

1 kg/mm = 56.0 lb./in. = 9.81 N/mm

# Suspension Analysis – Position Data

Suspension data for a lap at Atlantic Motorsport Park in Shubenacadie, NS. Speed is shown in black, front fork travel in red, and rear wheel travel in blue. A zero value for suspension travel indicates the fork or shock is topped out, while a greater value indicates more travel.

In a previous post, we discussed the importance of using high-quality suspension potentiometers and properly calibrating them to accurately measure front and rear wheel travel. Here we will talk about basic position data and how it can be used to pinpoint handling problems.

However you have installed your potentiometers and related their position data to actual wheel travel, always ensure that your data stream reads zero for fully topped out, and positive numbers for more suspension travel. After any suspension work or removal and installation of the pots, be sure to re-zero them so you have consistent data that can be compared from day to day or track to track. It’s also worthwhile to know at what point the suspension bottoms or encounters a bump-stop. At the rear end, you can measure the shock’s overall travel and the thickness of the bump-stop, and calculate from there the available suspension travel. Another option is to remove the spring and monitor your data in real time while you fully compress the suspension.

# Suspension Potentiometers

The fork potentiometer on this Ducati superbike is mounted in front of the fork tube with the exposed portion nicely protected by the front fender.

For accurate, usable data it’s important to use good-quality suspension potentiometers intended specifically for data acquisition. These suspension potentiometers live a hard life exposed to the elements, and are subject to extremely high shaft speeds; look for units that have good specifications for resolution, repeatability and operating speed. We have had good success with the units offered from AiM, but there are others available.

Another important consideration for good suspension data is the sample rate of your base unit. While it’s possible to obtain useful suspension travel data logged at 100 Hz or even 10 Hz, if you wish to perform frequency or velocity analysis you will need to log potentiometer data at 200 Hz or higher. Wheel travel often exceeds velocities of 300mm/s, and a slow sampling rate can cause plenty of information to be lost.