Chip Seal Buzz
Rick Proctor
Do you get an annoying amount of buzz through your handlebars and saddle when riding your bike on chip seal pavement? Some of the best bike rides anywhere are on chip seal roads. Here’s a bit of the what-and-why of the chip seal buzz, and what you can do about it to help you enjoy those chip seal rides.
Chip seal is a durable and cost effective method favored by some public works departments to treat the surface of aging pavement with a layer of liquid tar-like substance (seal) and then a layer of rock chips. The chips get glued by the seal onto the underlaying pavement assisted by the hammering effect from the rolling tires of regular motor vehicle traffic. The seal hardens and holds the chips in place while the excess chips get thrown by motor vehicle tires onto road shoulders and other vehicle windshields.
The rock chips used are a specific type and size to meet the appropriate road standard. The small bump of each rock chip is what is felt by the cyclist as the buzz when rolling along. The frequency of the buzz depends on the chip width and speed of the rolling tires. When riding along at a comfortable speed on a bike the buzz frequency will likely be in the hundreds of Hz, where the bump of each chip is a single Hz. If you want to ride your bike on chip seal pavement, the frequency is unavoidable, but the magnitude can be mitigated.
The magnitude of the buzz is determined by the height of each chip and the pressure in the tires. Ideally, a tire should deform to conform to the surface it rolls over to provide a smooth ride. This is the best place to absorb the buzz – at the source, and tires will do a better job of this within the buzz frequency range than mechanical shock absorbers that are designed to absorb bigger bumps at a much lower frequency. Some bike frames may also help by flexing a bit to help soften bumps and the buzz. If the tire pressure is too high, the tire will not deform enough, and that little bit of chip bump gets pushed up through the wheel and frame to vibrate various body parts of the rider. If the tire pressure is too low the ride may be smooth, but a pinch flat could occur when a bigger bump is encountered, or the tire could become unseated off the rim while riding in a curve leading to a crash – bummer!
A small amount of energy is taken to deform the tire as the tire rolls onto the ground, but most of that taken energy is returned as the tire pushes off the ground and returns to its normal shape due to the internal tire pressure. There is also energy lost to vibrate the bike and rider when bumps get past the tire, and if the ground is soft enough to deform as the tire rolls over it. The total amount of energy lost through the tires is called rolling resistance. Variations in tire characteristics due to tire construction and pressure effect rolling resistance. In general, tires with high levels of durability and puncture protection have high rolling resistance, and low rolling resistance tires come with reduced durability and puncture protection. There are also considerations for price, weight, availability, advertised performance, real performance, personal preference, etc.
Somewhere in the pressure spectrum between too high and too low is a sweet spot of the best tire pressure that balances buzz absorption, safety, and rolling resistance. There are lots of variables that effect the best pressure, including the tire cross-section size, tire construction, tube type or tubeless option, bike frame characteristics, temperature, bike and rider weight, rider preferences, etc. Rather than play around with all these variables to arrive at the best bike configuration and pressure for racing, most of us who ride for recreation just want to find the best – but comfortable – pressure for the bike we have where we are riding with the prime expectation of recreational enjoyment.
You and your bike probably do not weigh enough to warrant using the maximum pressure rating of the tire printed on the tire sidewall, so a lower pressure may be more comfortable and provide more traction too. I have found success in these steps:
- 1. Never exceed the maximum pressure indicated on the side of the tire.
- 2. I keep my front tire pressure 5 PSI lower than the rear tire because most of my weight is over the rear tire. Normally, this keeps the tire traction balanced at both ends for me, which is important to me in curves.
- 3. Tire pressure is too low if a tire looks flattened when riding, or the bike handles adversely when cornering, or if the tire bottoms out with the wheel making a hard contact felt by the rider on bigger bumps.
- 4. Incrementally adjust tire pressures and do test rides to find the best pressure to reduce or eliminate chip seal buzz. 5 PSI increments should be adequate. Accurate tire pressure indications are important for this procedure.
- 5. I’ve found the best tire pressures for me are just below the buzz threshold yet still high enough to last at least a couple of days. When you find your “perfect pressure”, be sure to remember it.
I use the mechanical pressure gauge on my pump as a ballpark indicator of pressure, then use a digital tire pressure gauge that is easy to use, reliably accurate, and easy to read with a digital display of pressure in the XX.X format to provide indications in whole and 1/10th units of PSI. I have tried many, but not found a suitably accurate mechanical pressure gauge.
Get to know your pressure gauge and how to use it consistently to gain confidence in knowing, instead of hoping, what the pressure is in your tires. I can get the pressure gauge onto the stem with a minimal audible hiss, check the pressure, then remove it with minimal hiss. This should be repeated for practice until a minimal pressure drop of only 0.1 or 0.2 PSI is consistently obtained with each pressure check. Notice the amount of hiss when applying and removing the pressure gauge directly correlates with pressure drop, and even a moderate hiss can release several PSI of pressure. Several PSI too high or too low can be felt in the quality of the ride.
There should be no hiss when opening or closing the presta valve on the valve stem. Other than the pressure gauge and its technique of use, problems with valve stems can also make pressure measurement and adjustment difficult.
If you have been avoiding riding on chip seal pavement due to the buzz, then you have been missing out on some of the best bike rides available anywhere, and all you need to do is solve the chip seal buzz problem. I hope this helps you discover the wonderful world of chip seal rides.
