The Tests

1. Rolling Resistance

rolling resistance test machine with a road bike tire mounted

All bicycle tires are tested on a rolling resistance test machine with a 77 cm drum and a DC electric motor. The drum is covered with diamond plate to simulate an average road surface.

Measurements are taken with an Arduino microcontroller equipped with custom software and hardware. Our setup calculates the average power required to keep the drum at a set speed for a period of 30 seconds. Using our custom setup to measure input power results in a very accurate rolling resistance measurement.

After a warm-up period of 30 minutes, three measurements per air pressure are taken. We then calculate the average of these three runs. After a correction for the electric motor efficiency and subtraction of the power required to spin the drum and wheel to the set speed, the result is the rolling resistance of the tire.

To guarantee our setup delivers consistent results over an infinite time period, we've built a calibration tool that's used to calibrate our machine to known values. We do not use control tires as we feel control tires do not provide a stable baseline over a longer period than 1 year.

The calibrations tool also provides a motor efficiency mapping that we use to calculate the rolling resistance of the tires to real watts.

Some facts about our "standard" rolling resistance test:

  • 77 cm drum diameter.
  • Standard test drum speed of 200 RPM which translates to a speed of 18 mph / 28.8 km/h.
  • Diamond plate drum surface.
  • 42.5 kg load.
  • Computerized measurements.
  • Controlled temperature between 21.5-22.5 °C / 70-73 °F.

For a detailed explanation of rolling resistance check Wikipedia.

2. Puncture Resistance

Steel needle puncturing road bike tire to test puncture resistance

All our puncture resistance test results can be compared directly to each other as they are the same tests for road bike, mountain bike, gravel bike, fat bike, or touring bike tires.

2.1 Total Puncture Score

As of 2021, we've improved the puncture resistance tests and now provide 'Total Puncture Score' as the main puncture resistance indicator.

Total Puncture Score consists of Puncture Force Sharp Needle, Puncture Force Blunt Needle, and Total Tire Thickness. This value will give the best indication of real-life puncture resistance.

After testing a lot of tires, we found that casing material and anti-puncture strips take a lot of force to puncture. The rubber, on the other hand, doesn't take much force to puncture as it's a very soft material. We also found that a tire without an anti-puncture strip, that does have a thick layer of rubber doesn't take a very large force to puncture. In reality, it does offer a lot of puncture protection because the thick layer of rubber simply doesn't allow the object to reach the inner tube.

Furthermore, we found that the hardness of the rubber does make a difference to the required force and our force tests capture some of the differences in rubber compounds. We also found that the thickness of the tire is even more important on tubeless tires as re-sealing after a puncture works better when there is more material for the sealant to hold on to.

Total Puncture Score is calculated by adding the puncture force sharp and blunt needle scores and then adding 50% of that score for every mm of tire thickness. To calculate Total Puncture Score (TPS) the following formula is used:

TPS = sharp + blunt + ((sharp + blunt) * thickness * 0.5)

This website was started in 2014 and we haven't been able to re-test all tires with the blunt needle. We analyzed the data of 75 tires (tread + sidewall = 150 tests) that were retested with the blunt needle to be able to estimate the Total Puncture Score of tires that only have sharp needle and tire thickness measurements.

2.2 Puncture Force Tests

The puncture force tests are performed with steel needles to which weight can be added. The needles get positioned at the center of the tread for the tread puncture test and on the sidewall for the sidewall puncture tests. More weight gets added until it punctures the tire.

We use both a needle with a sharp tip and a needle with a blunt tip to simulate different punctures. We puncture the tires 5 times with both the sharp and blunt needle in both positions for a total of 20 punctures (inner tubes filled with sealant). The large amount of punctures results in a low margin of error as opposed to a big puncture that is done just once.

2.3 Puncture Factor

As of 2021, 'Puncture Factor' has been deprecated and is replaced by 'Total Puncture Score'.

3. Static Grip Test

Steel needle puncturing road bike tire to test puncture resistance

The static grip test was introduced in November 2021 and is our latest test.

The grip test tests the static wet grip of both the center and the edge of the tires. On our website you can also find "average grip" which is the average value of the center and edge grip combined:

Average Grip = (center grip + edge grip) / 2

The scoring system in "Points" is simply the coefficient of friction multiplied by 100:

Grip in Points = coefficient of friction * 100

We have a special article dedicated to the grip test which includes much more information about the test: Introducing Grip Testing

3.1 Static Grip Test and Off-Road Tires

It's critical to understand our static wet grip test works with a hard surface. This means the grip data is only directly useful for comparing tires on hard surfaces where the rubber compound creates the grip. Understanding the test results gets more difficult when grip is created by the knobs digging into the surface.

On soft surfaces (loose sand, grass, etc), almost all grip will be created by the knobs digging into the surface, and our test results will be of little use.

There will also be many surfaces where the total grip will be a combination of the tread compound grip and the grip provided by the knobs. Under these circumstances, the hard surface grip can still be a deciding factor.

Given these shortcomings, we feel our grip test, combined with the knob height measurements, will still be valuable information when comparing tires.

3.2 How a Knobby Tread Affects the Test Results

A knobby tread reduces the grip in our hard surface test as the knobs reduce the contact area when compared to a "slick" tire. The wider the spacing between the knobs, the bigger the reduction in contact area and the harder it gets to score well in the hard surface test.

We also see a reduction in grip when the knobs are too flexible. On average, the higher the knobs, the more flexible they become, and the flexing under pressure reduces the grip on hard surfaces. For a knobby tire to grip well on a hard surface, the knobs should have enough "structural integrity" to overcome the forces experienced during the grip test.

These outcomes also show the limitations of the grip test when it comes to softer surfaces, as big and widely spaced knobs are precisely what you need to provide grip on soft surfaces where the knobs dig into the surface to create grip.

We always have to consider the tread pattern when judging the grip of an off-road tire.