New tire rolling resistance test - 23mm, 25mm, 28mm & 32mm GP5000 tires

[Mark McM]

Just posted to the BicycleRollingResistance.com web site is a new special test on various sizes of the Continental GP5000 tire. Like many tests, the first part of these tests measures rolling resistance at several fixed pressures. But the 2nd part of the test is the more interesting, where the rolling resistance is measured with pressures selected to achieve a specific tire deflection/stiffness (i.e., a specific shock absorption/comfort). This 2nd part shows that in real world usage (real world pressures), there is not a big difference in tire rolling resistance between even the widest and narrowest version of the GP5000.

Here's the test.

[m_sasso]

Now they need to combine wind resistance in these tests to get a partial picture of real world performance!

[pjbaz]

Hmmmm, maybe I will try the 25c size ... I did buy a pair last year, just never used them lol. #23formeusually

[weisan]

.

[Mark McM]

Originally Posted by m_sasso

Now they need to combine wind resistance in these tests to get a partial picture of real world performance!

There can often be more variables in aerodynamic testing than rolling resistance testing, so when throw tires into the equation it becomes even more complicated. But that hasn't stopped some groups from trying.

For example, Flo Cycling, a maker of aero wheels, ran some tests on a variety of different tires to find the best tire for a combination of aerodynamics and tire rolling resistance. However, they only used one model of their wheels, and the results of their test may not be applicable to other wheels. Still, their test and results are interesting (the test and results can be found here).

One interesting thing from this test is that the highest aerodynamic drag power with any of the tires tested was only about half the lowest rolling resistance drag power of any of the tires tested - i.e., rolling resistance is a much bigger factor in wheel performance than aero drag. When Flo combined aero + rolling drag, the best combination was not the one with the lowest air resistance, it was the one with the lowest rolling resistance tire (in fact, that combination actually had the 11th best aero drag out of 20).

Also of note is that Flo used a speed of 21.75 mph for the test. While many companies report wind tunnel results at much higher speeds (30 mph is a typical speed), and therefore exaggerate aero benefits, the Flo results are reported for a speed that probably more closely matches most people's actual speeds. In at least one regard, Flo's results confirm my own personal experiences - I can barely detect speed differences between aero and non-aero wheels, but I can easily detect speed differences between high and low rolling resistance tires.

[cmg]

From the video,
Test conditions

•Speed of 29 km/h / 18 mph
•Total wheel load of 42.5 kg / 94 lbs
•700 x 17C wheel
•Temperature between 21.5-22.5 °C / 71-72 °F
•Diamond plate drum surface
•77 cm drum diameter
•Tires are run in for 30 minutes at 60 psi / 4.1 bar

If you're new to our site, below is a YouTube video that gives you an idea about our set up. This video shows the spin-up of a Continental Grand Prix 5000 25-622. When measuring rolling resistance, the tire is run at a constant speed.

Then how do they measure? Is the torque provided by the spinning drum the same for the different weights of the tires in order to get the wheel up to a constant speed? Do they cut the power to rolling device, measure the force the tire exerts on the spinning drum to it keep spinning? Measure the rotational force of the spinning wheel and compare to the force exerted by the spinning drum? What parts the moving bits are they measuring? just isolating the rolling resistance does tell all that is needed to spin a wheel.

[Mark McM]

Here's part of the web page where they describe the test:

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 measurement.

After a warm-up period of 30 minutes, three measurements 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.

The page also includes a listing that appears to be a read out of motor speed, voltage, and current.

From this, I surmise that they are measuring the (electrical) power going into the motor to maintain a constant drum speed. That should be sufficient, as long as they have calibrated the motor efficiency, and the zero load power.

[saab2000]

It’s interesting that the resistance increases as pressure decreases. This is contrary to what we’re always told, making me thing their testing drum should be updated to more realistically simulate real conditions. Or else we’re not always being told the truth...

[kppolich]

Decreased pressure to me means that more of the tire would be in contact with the ground at any given time, increasing resistance. Width and pressure are interesting.

Road surface is the kicker

[Mark McM]

Originally Posted by saab2000

It’s interesting that the resistance increases as pressure decreases. This is contrary to what we’re always told, making me thing their testing drum should be updated to more realistically simulate real conditions. Or else we’re not always being told the truth...

It's been known for a long time that the rolling losses internal to the tire itself increases with decreasing pressure. What has come into better appreciation in recent years is that vibrational losses external to the tire (some times called 'suspension losses' or 'impedance losses') decrease with decreasing pressure. Josh Poertner at Silca wrote up a series of blog posts about this:

https://silca.cc/blogs/journal/part-...previous-works

The BicycleRollngResistance.com tests measure the internal tire losses (Poertner refers to this as the 'casing losses'), so their data will show a decrease in resistance with increasing pressure. Other testing has shown that tires with lower casing losses also have lower suspension losses, so the BicycleRollingResistance should still be reliable for indicating the relative differences in total rolling resistance between tires, even for real world conditions.

[tylercheung]

What about grip and handling - does anyone test the G-force required to induce skid?

[ultraman6970]

Somebody told you the opposite?? interesting Remember a guy in university, he was not able to comprehend how is that the less the volume you have more pressure.

My main thing with all these tests is that some are way too biased, some guy put a new tire in the market and they made up stuff in the lab so the new tire is super fast compared with other ones eventhought defeat the logic of how physics works.

Originally Posted by saab2000

It’s interesting that the resistance increases as pressure decreases. This is contrary to what we’re always told, making me thing their testing drum should be updated to more realistically simulate real conditions. Or else we’re not always being told the truth...

[old_fat_and_slow]

Yea, skinny tires inflated to umpteen psi still rule !!!

[Hellgate]

Originally Posted by saab2000

It’s interesting that the resistance increases as pressure decreases. This is contrary to what we’re always told, making me thing their testing drum should be updated to more realistically simulate real conditions. Or else we’re not always being told the truth...

That data has been on the site for a while. People have become obsessed with lower pressure and LARGER tire for comfort. Mainly due to the gravel uprising... In other words, if you're not on terrible roads, use a higher pressure.

I still run 95 psi on 25mm and people think I'm nuts, but the roads I ride are relatively smooth as crank it up!

[bikinchris]

Originally Posted by saab2000

It’s interesting that the resistance increases as pressure decreases. This is contrary to what we’re always told, making me thing their testing drum should be updated to more realistically simulate real conditions. Or else we’re not always being told the truth...

I don't know who said that. I always understood that too much pressure and too little pressure were both going to increase rolling resistance.