FRStop Pickin’ Up Bad Vibrations
TSE Barriers to Speed Part IV: Vibration Loss
As he gained experience at Zipp and on the bike, Senior Advanced Development Engineer Dave Morse became obsessed with vibration loss and its deleterious effects on speed. He’s dug for data, called professors, and rode highway rumble stripes until he got blisters.
In this episode of the Zipp Speed Podcast, Dave reveals what he's learned about the fundamental importance of Vibration Loss as one of the four barriers to speed identified by Zipp’s Total System Efficiency (TSE). He summed it up this way: “10 PSI, plus or minus, is going to make a significant impact on your speed because the effects of vibration loss will change your watts."
But there's so much more to the story.
Vibration Loss is the last—and perhaps least understood—of the four TSE barriers to speed, with the others being aerodynamic efficiency, rolling resistance, and gravity (weight). This podcast is the final of our four-part podcast and blog series on the TSE barriers to speed and how Zipp wheels help you confront each one to make you faster. Listen to the entire Vibration Loss episode below. Links to the other three episodes are at the bottom of this page. Below also are edited excerpts of our conversation with Dave. However, we encourage you to listen to the full podcast since Dave goes into great depth on this most exciting cycling subject:
Most cyclists have seen slow-motion videos of pro riders bouncing and rattling over the cobblestones during Paris-Roubaix. Are those images a good illustration of the effects of vibration loss as a barrier to speed?
I love that imagery. It’s so brutal. It’s so extreme. It also highlights the more important points of vibration loss. Vibration loss is one of the least studied concepts and least rigorously understood forms of (speed and power) loss on the bike. Everyone knows on a rough road, it takes more power to go the same speed. But I don’t think many people have contemplated what is happening.
Vibration loss impacts speed even on smoother pavement. Why?
Whenever you’re riding, every bump, crack, or rock in the road is pushing you upwards— giving you a vertical displacement. When discussing vibration loss, one of the most rudimentary details to keep in mind is that any vertical displacement caused by those bumps will have a component of a force that’s pushing you upwards but also a component of force pushing you backward. The implication is that if you feel a bump in the road, you just were slowed down. If you’re on an asphalt road, any pothole, frost heave, or pebble you encounter will add to your vibration loss.
Vibration testing on RollingRoad
Is the key to reducing vibration loss reducing tire pressure? How important is the design of the wheel?
Yes. Many wheel designs don’t really allow you to drop your tire pressure to an optimal level. Some factors would make the wheel unsafe or unstable to ride. It might not be able to support lateral cornering forces at low pressures. The tire pressure is the key, but you must have a whole bike system to achieve that optimum tire pressure.
At what speed does vibration loss become a significant barrier to speed?
I feel like it’s a trick question! The answer is, it’s always a factor. It’s kind of like aerodynamics. Aero drag is always slowing you down; as you go faster, it becomes more and more critical. But I will throw this question on its head and say that vibration loss is a major factor that dictates the speed at which we can ride a bike. The entire bike design is driven by the surface roughness on the course (consider the difference between a track bike, road-racing bike, and gravel bike, for instance).
How should riders evaluate how to minimize the slowing effects of vibration loss?
We try to make it as easy as possible by baking the benefits of Total System Efficiency into the product. Our rim tirebed geometry helps make any tire faster, and we offer a tire guide and a tire pressure tool for wheel setup.
Zipp TSE smooths the ride
How do we test and research for vibration loss? Is the RollingRoad in the SRAM Indy Test Lab the primary method?
The RollingRoad is the best way to isolate the effects of vibration loss. Picture an oversized treadmill where you can install bumps or surface textures on the treadmill tread itself. There are no aero losses. You can tilt the treadmill up or down to negate any losses due to gravity. It lets us isolate and study vibration loss and rolling resistance from the tire hysteresis. We can study minor effects. We take our Power Spectral Density plots from outdoor riding and replicate that response on the rolling road. We also test outdoors, considering aero, rolling, and gravity losses. We’ve gone to downtown Indianapolis and tested on old brick streets and vacant stretches of highway to ride on rumble strips.