September 5, 2023
One of the most commonly asked questions we receive at Heeluxe is, "How Long Do Running Shoes Last?" Since 2012 we've been running shoe research studies to answer this question with objective data. In this post we'll cover how we measure running shoe breakdown and what part of the shoe breaks down the fastest (the results will surprise you!).
There are 4 main areas of running shoe durability that we measure: Outsole (traction) breakdown, heel cushioning, ball cushioning, and fit. Most consumers focus on outsole durability, replacing their shoes when the tread is worn away. The average running shoe outsole in our database lasts 760 miles.
What runners often miss is how long the cushioning of their shoes will last. Heel cushioning lasts, on average, 550 miles before 15% cushioning loss (more on this later). Ball of foot cushioning only lasts 400 miles. Heel cushioning tends to last longer because it is thicker.
Upper fit does change as we put more miles on shoes. For example, knit shoes can sometimes transform from a slightly narrow fit to being extremely wide. In 2022-2023 upper technologies improved and we do not observe upper fit changes in many modern running shoes.
Our findings show that the least durable part of a shoe is the cushioning under the ball of the foot. Surprised? Let's go into more detail on how we got here.
Testing shoes with humans provides valuable insight into shoe performance. During this 2-year period we supplied testers with running shoes and asked them to return after every 50 miles of running to re-test the shoes in the lab. We analyzed their running performance for many measurements: deceleration sheer force, acceleration sheer force, and medial to lateral forces for stability (force plate), shoe flex (high speed video), and cushioning (in shoe pressure sensors).
For each 50-mile test, runners ran in the "used" shoe and a brand-new version of the same style. After being measured in each shoe we asked the tester if they could feel a difference in the new and used shoe. They also identified when they would want to replace the shoe.
In these studies, only 1 measurement would change when the testers identified that they chose to replace the used shoe: Ball of Foot Cushioning. On average testers reported the shoe needed replacement or was "dead" when the ball cushioning had 15% higher pressure. Force plate, video, and heel cushioning changes would be 5% or less relative to the new shoe at this time.
As Heeluxe grew more brands requested shoe durability testing. However, they did not want to wait 6-12 months to get the results from human testing. They needed the results in a week. Heeluxe set out to build a machine that replicates human running and walking called The Time Machine.
The goal of the Time Machine was to replicate a 170-pound person running 150 miles (8min/mile pace) or walking 100 miles (2.8 mph) on an asphalt surface. These distances were chosen because most footwear brands we worked with used these standards in fit and wear testing. Validation included joint angle and pressure sensor analysis to ensure the machine was as close to human movement as possible.
Early analysis of shoes included caliper measurements to analyze foam compression, weight to measure outsole loss due to abrasion, and visual inspection to identify any premature failures of the shoe.
The Time Machine experienced early success because of its repeatability, accuracy, and shortened time to get durability feedback during product development. But we couldn't tell someone how long their shoes would last.
In 2020 the Time Machine received dramatic upgrades. These upgrades included a more human-like foot and suspension upgrades. These changes allow us to have multiple Time Machines at Heeluxe that all produce the same results. And we could sell the machines to footwear brands that wanted a machine for their internal labs.
At Heeluxe, we've always been inspired by car tires. In particular, how car tires have a mileage rating on them. These mileage ratings allow you to compare how long 2 tires you are considering would last. A 100,000-mile tire is certainly more durable than a 50,000-mile tire and is worth a higher price tag. These mileage ratings are appropriate for "average" driving conditions; if you do a lot of burnouts, drive a heavier car, or drive on rough roads you may not see those expected miles. This is what inspired Heeluxe's Mileage Forecasting for shoes.
Mileage forecasting provides a benchmark to compare the durability of shoes. For this blog let's focus on running (but we do have databases for hiking, work, and casual shoes!).
The outsole durability Mileage Forecasting identifies when the tread is worn completely smooth. This is calculated by a combination of measuring outsole weight loss during a 150-mile test, knowing the abrasion properties of our belt surface, and then manually sanding the outsole lugs smooth.
The cushioning durability Mileage Forecasting identifies when the shoe loses 15% of its cushioning performance. To analyze cushioning, we use ASTM 1976F protocol for both the heel and ball areas of the shoe. New and used shoes (after 150mile run) are tested which create a foam breakdown curve. This is how we can calculate 15% breakdown without having to run every shoe to failure (saving brands time and money!).
Both of these methods have been validated on humans and long-term Time Machine testing, with both humans and Time Machine running shoes to failure.
To answer this question let's use the Time Machine road-running database (237 shoe results). All shoes were tested in identical conditions at Heeluxe's lab.
Ball of Foot Cushioning lasts, on average, 385 miles. The variation in ball cushioning is large! The least durable shoes last only 100 miles while the most durable shoes last over 1000 miles.
Heel Cushioning lasts longer than Ball Cushioning, 549 miles on average. The least durable heel cushioning is 125 miles and the most durable shoes last over 1000 miles.
The most durable part of the running shoe is the outsole with an average durability of 707 miles. The least durable outsole lasts 300 miles and the most durable outsoles last more than 1000 miles.
Another consideration for durability of a running shoe is the insole. Insoles lose 15% of their cushioning in 440 miles on average, but the least durable insoles last less than 100 miles.
Lastly, the midsoles of running shoes compress differently in the heel and the ball. On average the heels compress 3.8 mm while the ball only compresses 2.1mm. This 1.7mm difference changes the "drop" of the running shoe and may alter the runner's experience in the shoe.
There are many ways that your running shoe durability results will be different than the average data from Heeluxe's Time Machine.
Cushioning durability will be less if you run at faster speeds or have larger body mass. The ball of foot cushioning will break down faster if you run more on the ball of your foot.
Outsole durability will be less if you run on abrasive surfaces (such as brushed concrete, gravel or granite pathways), have a longer stride, or your foot has excessive pronation or supination.
Performance and sustainability are major factors influencing running shoe durability. The proliferation of "super shoes" resulted in many large and light weight shoes that tend to lose the cushioning faster than our database averages. These shoes make up the majority of styles that breakdown in under 200 miles.
Alternatively, one way to make a shoe more sustainable is to make it last longer. This focus on sustainability is why we've seen many shoes with durability over 1000 miles in the past 3 years.
For now, make sure you pay attention to the cushioning under the ball of your foot in your running shoes. You could be using your shoes for too long if you're waiting for the sole to wear out.
The only way to know how durable running shoes are is to test them. Thank you to all footwear brands that trust Heeluxe to test the durability of their shoes. If you'd like to test your shoe durability, please contact firstname.lastname@example.org.