Feeling Fast.
Back in my university days, I owned a 2001 Kia Sephia that had less-than-showroom suspension. While on a road trip to Death Valley, I wondered what going 100mph felt like, and accelerated to 105mph. It felt like we were flying, but the vibration was unnerving, and I feared my life!
Shortly after this experience, I borrowed a friend’s new Acura TL for a road trip. I would glance down at the speedometer and saw that I was going about 100 mph in a 75 mph zone. This happened more times than I will admit here, but at the time, I couldn’t wrap my head around why I could carry on a conversation in comfort doing 100 mph in one car, while feeling like I was going to die in another.
Vibration & Speed Perception
There are several factors that account for speed perception but I want to focus on vibration.
In my old car, the vibration gave a sense of speed and impending doom that was not present in the new car. Vibration simulates a feeling of speed. When traveling the same speed, simply adding vibration to a system will make you feel faster.
Since those days, I’ve been in tuned race cars traveling 200 mph+ in complete comfort.
However, when the tuning is off, things get scary quickly.
Vibration & Cycling
Cars use shocks to absorb vibration. Mountain bikes and gravel bikes use large tires with lower pressure and sometimes shocks, to help absorb vibration. In these disciplines, it is somewhat common knowledge that lower tire pressure creates better grip, lowers vibration, and improves speed.
However in road cycling, we hear the importance of “feeling fast,” which is usually from overinflated tires causing vibration. Vibration causes a bounce, or an up and down motion, which affects your grip with the surface you’re riding on. On pavement, small amounts of vibration affects grip but still allows for corning, whereas when riding on dirt with overinflated tires, the up and down motion would cause you to slide out.
When you consider my experience in the two different cars, we learned that adding vibration will feel faster. And while it may “feel faster” to have a higher tire pressure, we know that this is not true.
Tire Pressure & Impedance
Previously, we’ve written about tire pressure and the impedance break point. Here is a quick recap:
The amount of rolling resistance impacts your speed. In a lab, as you increase tire pressure, your rolling resistance decreases. (Great!) However, on pavement, your rolling resistance decreases to a point and then drastically spikes, which makes you slower. (Oh.) The point where the rolling resistance stops decreasing and starts increasing is called the impedance break point. For more on rolling resistance and impedance, check out this article.
Once the impedance break point is reached, your tires start to bounce up and down over the small bumps in the pavement, which increases the vibration in the bike. You feel faster, but in reality your rolling resistance has spiked and you are losing speed. See where we are going with this?
Connecting Speed & Vibration
After researching human perception with reference to speed, I came across a study conducted in Italy that tested human perception of road surface smoothness at different speeds. Here is what they found:
For the same road (same smoothness), people reported that road surface quality was poorer the faster they were going. The graph below shows the number of people who reported the road was in very good, good, mediocre, or poor condition at speeds of 60km/h, 70km/h, 80km/h, and 90km/h.
In the study, they measured vertical motion to determine the vibration felt by the participants and determined that the vibration in the car increased as the speed increased.
In a recent FLO article, we discussed our findings on how velocity affects the impedance break point. The faster you go, the sooner you hit the impedance break point. This means that if you hit the impedance break point at 20mph and continue to pedal to 30mph, you passed the impedance break point and spiked your rolling resistance. Once you pass the impedance break point, the watts you’re putting into the pedals are no longer just moving your forward, but they are also moving you up and down (vibration), creating inefficiency.
What our work and this study prove is that as speed increases, vibration also increases. To create the most efficiency and go faster, the goal is to decrease vibration, even if you feel faster.
What Can We Do As Cyclists
We must move past our “feels faster” mentality when on a road bike. The reason it feels fast is because you are experiencing vibration. This vibration is not beneficial for a few reasons:
1. As a cyclist, we want the watts put into the pedals to move us forward, not up and down. The vibration creates and up and down motion, which wastes the watts we put into the pedals.
2. Our grip is reduced since the bouncing creates small amounts of time where our contact with the road is decreased. When you eliminate the bouncing, the tire stays in contact with the road surface and improves your grip.
3. Vibration that the bike experiences transfers to our bodies. The vibration in our bodies increases muscle fatigue and the friction caused by our bodies vibrating is an additional loss of watts.
In order to be faster on the road, lower your tire pressure to optimize rolling resistance. Rolling resistance accounts for a large number of watts and was the focus of our R&D efforts for the FLO All Sport and FLO Gravel wheel lines. If you are wondering what tire pressures are good for you, we recommend checking out the tire pressure recommendation charts on our wheel pages.
So, lower your pressures on the road and don’t worry about “feeling faster.” Ride smarter and ride faster. Plus, it will be more comfortable—your butt will thank you.
Co-founder at FLO Cycling. Jon manages the day to day operations and acts as the lead engineer for all FLO products.