Tech Corner

Article by Pedro P. Bonilla, Tech Editor

As part of PCA’s Tech Committee I get to field a lot of questions regarding our cars.

Many have to do with performance but just about as many have to do with comfort.

Manufacturers do an incredible job of developing better and better-quality components that aim to obtain better performance and better comfort at the same time, but I must say, if you have a sportscar, performance should trump comfort at some level.

Let’s talk tires and tire noise.

All tires generate noise as the tire rolls in contact with the road and as air rushes through its tread pattern (grooves). So keeping this in mind, tire designers have to balance the tire’s performance (traction) with tread noise.

I’m sure you’ve had a “monster” truck go by you on the highway with it’s wild-pattern-off-road tires growling loudly, while the opposite happens with extremely quiet tires that sacrifice foul weather (wet and wintry) traction for their low noise.

Tire noise is dependent on the relationship between the tread pattern and the surface it’s rolling on.

The different types of roads and road surfaces influence the loudness and pitch of the sound generated by tires rolling on them. You can clearly hear the difference when the road you’re driving on changes from asphalt to concrete or vice-versa.

Many drivers tend to blame their tires as being noisy, when they should actually blame the roads they’re driving on. If you’d like to determine how noisy your tires are, find a stretch of brand-new asphalt or spacer-less concrete road, as these prove to be the least noisy surfaces to drive on, then use that sound as your tire’s base sound.

The term “pitch” is used in the tire industry to describe the number of tread blocks around the tire’s entire tread. As a general rule, summer performance tires have larger tread blocks and fewer pitches to enhance steering response and handling, while winter tires feature smaller tread blocks and more pitches to increase the number of biting edges that enhance traction in snow and ice. All-season tires fall in the middle.

Tire manufacturers do not create all pitches equal because if every tread block was the same as the next, each one would generate the same exact sound tone and loudness as they rolled through contact on the road. This would result in all four tires producing a very unpleasant, monotonous tone.

To prevent that from happening, tire designers use computers to include multi-pitch tread designs that subtly change tread block size and shape to randomize the road contact and therefore the sound generated by such contact. They also offset block placement of neighboring ribs to reduce noise by aligning lateral grooves with adjacent tread blocks. The tire designers’ and engineers’ goal is to produce a pleasant “white” noise from the tire.

3 Pitch 6 Pitch

In the above images you can compare a 3-pitch tread with a 6-pitch tread.

Tread blocks are highlighted in different colors on each tire.

All of this work can be thrown out the window by the tire itself. Depending on its diameter, a tire will roll about 800 times per mile. On every revolution, the leading edge of each independent tread block collides into contact with the road, followed by the rest of the block until the trailing edge is released from contact a fraction of a second later.

Noisy?

This happens about 4,000,000 times in 5,000 miles. This constant on-off contact of each block with the road has been shown to produce irregular tread wear. If not prevented, this irregular wear is likely to change the size and shape of the tread block and undo the design and engineering that went into it.

To promote even wear, tire manufacturers recommend tire rotation as a preventive maintenance. And herein lies the issue of noisy tires in Porsches. Because of the staggered fitment (different size tires front-to-rear) and use of asymmetrical treads, our tires cannot be rotated in the normal sense, so they do tend to generate more noise with use.

I’ve always found that after a day at the Autocross (AX) Track, my street tires seem to be a bit quieter than when they arrived. I had always wondered why that was. I now realize that the AX is equivalent to a tire rotation because it promotes even wear!

Now you know too!

For more information on tires and more, please visit my website: www. PedrosGarage.com.

Happy Porsche’ing, Pedro

2021 Technolab / PedrosGarage.com