Natural Frequency: Different Tires, Wheels, and Rider Weight

Recently, we discussed how you can measure the natural frequency of a wheel and tire combination, and how we proved that our theory that you could measure an impedance break point by measuring vibration was correct. This week we’ll focus on testing the natural frequency of a wheel/tire combination when you change the type of wheel, tire, and rider weight, as well as comparing front and rear wheels. Our previous testing showed tire pressure had little impact on natural frequency so a single pressure was used during this testing. Let’s look at each test.

First, we examined different wheels. We controlled the tire, psi, rider weight and used the front wheels. See below for the details of the test.

1. Continental GP 5000 28mm tire.
2. 120psi
3. 160 lb rider
4. Front wheel
5. Wheel models tested: FLO 49 AS Disc, FLO 64 AS Disc, and FLO 77 AS Disc

The images below are the results of each wheel. As you can see, the wheel matters. The FLO 64 AS Disc and the FLO 77 AS Disc are similar but the FLO 49 AS Disc has a unique profile.

While each wheel has a unique frequency profile, the frequency is roughly in the same band.

Next, we tested different tires. We controlled the wheel, psi, rider weight, and used a front wheel. See below for details.

1. 120psi
2. 160 lb rider
3. Front wheel
4. FLO 64 AS Disc
5. Tire models tested: Continental GP 5000 28mm and Vittoria Corsa Speed G+ 2.0 25mm

As you can see from the results below, the two different tires were almost identical. This definitely surprised me. I thought it would be more like a fingerprint since each tire has its own unique construction.

For additional data, we tested the FLO G700 with a WTB Riddler 37c at 40psi, a FLO G650 with a WTB ByWay 47c at 31psi, and an OEM DT Swiss rim with a Maxxis Assegai 2.5 at 20psi. We know there were many changes in variables, but we were curious to see the results. The two gravel wheels and their respective tires and psi’s had nearly identical profiles. The Maxxis was different. Could this be related to the wheel material since the DT Swiss wheel is an aluminum rim vs. the FLO Gravel carbon rims? We will need more exploration here.

We altered the weight, or load, on the wheels in these tests and kept the tire, wheel, psi, and front wheel the same. The weight differences in this scenario were a combination of dumbbell and different rider weights. See below for testing details.

1. Continental GP 5000 28mm
2. 120psi
3. Front wheel
4. FLO 64 AS Disc
5. Weights tested: Bike, Bike + 30lbs, Bike + 160lbs, Bike + 190lbs

This is where things got interesting. You can see different profiles for each. While there is a general consistency of natural frequency within the same band, the shapes are unique. Why? I’m not sure yet, but we are going to find out.

Our final test was to look at the response from of a front wheel vs. a rear wheel. We controlled the tires, psi, rider weight, and wheel. The test conditions are detailed below.

1. Continental GP 5000 28mm tire.
2. 120psi
3. 160 lb rider
4. FLO 64 AS Disc
5. Wheel positions tested: Front and rear

The plots below show that the front and rear wheels yielded different results. There are a number of factors in play for each of these wheels.  One, the weight distribution is different for a front and rear wheel.  Additionally, the rear wheel has a different hub and cassette which is also attached to a different part of the frame. We are not sure what exactly is causing the differences. This will also call for further exploration.

While more testing is needed for many of these scenarios, at first glance, the data as a whole shows a trend. We see that the natural frequencies of the wheel/tire combinations generally stay in the same frequency band. We also see that there isn’t much that happens above 100Hz.

This is significant because it tells us where to look,  and will allow us to focus our attention within a specific frequency range as we’re working to provide more evidence that we can measure an impedance break point with vibration. We would love to hear your thoughts; comment below if you have any suggestions!

Stay tuned for next week – we will look at testing vibration in different locations with different sensors.