8

It's a no brainer, right? Yet a comment links to a blog post claiming to have scientifically proven there is no significant effect. It looks solid but is not a paper in a peer-reviewed journal.

What is the current understanding of rolling resistance of a slick tire on pavement?

Vorac
  • 13,698
  • 19
  • 82
  • 153
  • 4
    As anyone who has been foolish (or unfortunate) enough to ride underinflated (or straight up flat) tires would attest, tire pressure does affect rolling resistance. At the lower end, the functional dependency is clearly inverse: lower pressure → more resistance. Whether or not there is an extremum point (i.e. optimal pressure) is up to debate. – Grigory Rechistov Sep 10 '20 at 08:53
  • Note that the post assumes you stay within reasonable limits. Maybe implicitly so, but it does. The debate is, whether the savings from high pressures you can measure using ideal instruments where you mount your wheel exist on real roads when you ride the wheels on an actual bicycle with an actual rider. – Vladimir F Героям слава Sep 10 '20 at 08:54
  • Also, both the quoted answer and the quoted blog post explicitly state that there is a dependency between the two parameters. – Grigory Rechistov Sep 10 '20 at 08:56
  • The stuff in the Jan Heine post kind of makes sense, but there are three problems with it: First, he's using some secret / undocumented testing protocol and data analysis to get his results. Second, it just happens that the exotic tires he's selling get the best results. Third, professional racing teams put significant effort to optimizing their equipment, and they don't seem to agree. – ojs Sep 10 '20 at 08:57
  • This paper https://www.tandfonline.com/doi/abs/10.1080/001401399185009?casa_token=HrY6GJEJ0x0AAAAA%3AWVVk3_y3zJhLoDFXJiEKz8gwWk4eRQdzOzDjA92-I1HdwWMQOcrRn3E0ByiDS8VxjbUkBmTRndQm& shows a similar curve as those seen at the so-often linked https://www.bicyclerollingresistance.com/ They used an actual cyclist on a smooth floor. – Vladimir F Героям слава Sep 10 '20 at 09:01
  • @ojs They don't seem to agree with what exactly? How exactly seem? There are many subtle points here. But they use wider tyres now than they used to. An interesting point is that the pro riders themselves do not really know well which pressure their mechanics use https://www.youtube.com/watch?v=FI7cniRBsNc – Vladimir F Героям слава Sep 10 '20 at 09:06
  • @VladimirF they use wider tires than before, but well below the 30 to 40 mm range Heine is selling. It's also not like this is new information for tire manufacturers. I remember that Michelin tires years ago came with pressure recommendation chart that gave similar pressures Heine's chart for 25mm tires has. – ojs Sep 10 '20 at 09:07
  • 1
    I don't have access to the paper at tandfonline, but I think the debate here is about the effect of rough pavement, and how rough real riding surfaces are compared to smooth floor, the diamond pattern at bicyclerollingresistance or the worst crumbled asphalt you can find. – ojs Sep 10 '20 at 09:10
  • @ojs Exactly, as I commented at https://bicycles.stackexchange.com/a/71790/21133 You do not really need to read that paper, the curve is in the abstract and pretty much conforms to the other ones you have seen. – Vladimir F Героям слава Sep 10 '20 at 09:12
  • @VladimirF I don't see any curve at the link, so I assumed it's part of the paper behind paywall. – ojs Sep 10 '20 at 09:24
  • @ojs Really, you do not need to see it, but it is the equation available in the abstract Cr = 0.1071 Pr^−0.477 . I am at home but it seems I have the access to the paper through some cookies or something. – Vladimir F Героям слава Sep 10 '20 at 09:36
  • @VladimirF well, the interesting questions are how well measurements match the curve and are there controls for different road surfaces – ojs Sep 10 '20 at 10:54
  • @ojs No, I am not aware of any such public data. Surely the industry has a lot of data, but it is not public. – Vladimir F Героям слава Sep 10 '20 at 11:00

1 Answers1

17

This study: William M. Bertucci, Simon Rogier & Raoul F. Reiser II (2013) Evaluation of aerodynamic and rolling resistances in mountain-bike field conditions, Journal of Sports Sciences, 31:14, 1606-1613, DOI: 10.1080/02640414.2013.792945

is very far from comprehensive, but it reports rolling resistances for two pressures (2 and 4 bar - 200 and 400 kPa) for wider tyres. Of them, Vittoria Radonneur could be considered reasonably slick. They report slightly higher speed and slightly lower rolling resistance, but with a large uncertainty, with 2 bar on 5.9% road slope. The uncertainty is larger than the difference 12.6 ± 3.4 N at 2 bar vs. 13.5 ± 2.2 N at 4 bar. Be aware that this is the force, not the power required to overcome it at the given speed! The study did not really concentrate on the effect of inflation pressure and they conclude that the difference is not statistically significant. Interestingly, the idealized measurement in the link I already gave say "When using these tires, you should monitor air pressures very closely. Don't let these drop under 60 psi EVER.". (60 PSI is 4.1 bar)

Another study used a smooth treadmill: Yves Henchoz, Giacomo Crivelli, Fabio Borrani & Grégoire P. Millet (2010) A new method to measure rolling resistance in treadmill cycling, Journal of Sports Sciences, 28:10, 1043-1046, DOI: 10.1080/02640414.2010.498483

It found that for two tyres (23 and 28 mm) the rolling resistance decreased uniformly with the inflation pressure. For the third tyre (22 mm) the lowest inflation pressure was achieved at 6 bar (600 kPa) and then it rose slightly. I stress again that this was not on the tarmac but on a smooth treadmill.

Very comprehensive measurements of various tyres with several different inflation pressures are regularly published by https://www.bicyclerollingresistance.com . They test a single wheel in a dedicated machine on a rather idealized surface. The rolling resistance mostly uniformly decreases with the inflation pressure in these conditions although the curve is often quite flat at higher pressures.

example resistance An example of the dependence of the rolling resistance (as a power required) to the inflation pressure on the idealized test bed of https://www.bicyclerollingresistance.com for four road tyres.

However, a study by SILCA indirectly mentioned in the comment by R. Chung considers real asphalt concrete surfaces and found that the suspension losses/transmitted losses/impedance are quite substantial at higher pressures and cause turning of the resistance curve upwards. It isargued that a tyre that is "too hard" suffers from high resistance when overcoming and jumping over the small bumps that create the tarmac surface.

A schematic explanation by SILCA, more in the study: enter image description here

Vladimir F Героям слава
  • 16,203
  • 1
  • 32
  • 76
  • 2
    I think the contradiction between field and laboratory measurements supports the idea that there are significant losses from vibration transmitted through tires and absorbed by the rider. The similar rolling resistance at different pressures could be explained by assigning the losses for tire hysteresis at low pressures and vibration at high pressures, but one set of measurements with one type of tires is not enough data for any conclusions. – ojs Sep 10 '20 at 11:04
  • Randonneur has really thick and stiff tread, so the rolling resistance is really sensitive to small changes in pressure, and they are horrible to ride at all pressures. The only redeeming qualities in those tires are that they don't puncture easily and they wear really fast so you have an excuse to throw them away. – ojs Sep 10 '20 at 11:05
  • 1
    I think even an amateur with a good powermeter could try to do a nice experiment. Hold some lowish speed in zero wind and measure the power. Repeat several times with different pressures. Repeat several times the whole cycle. Without a powermeter one could still try how far one gets from a fixed point on a small hill, but it would be less reliable. – Vladimir F Героям слава Sep 10 '20 at 11:10
  • 1
    @VladimirF the problem is that aerodynamic effects will probably dominate, as the effect we're looking for is so small. Tiny changes in wind, clothing, or riding position, even at low speed, will be noticeable. If you could take a velomobile on an indoor track you might be able to measure something. – Chris H Sep 10 '20 at 11:20
  • 4
    Well, someone with a good power meter and good test protocol could measure both aero drag and rolling resistance at various pressures and speeds. That's been done, and that's how tire "impedance" came to light. – R. Chung Sep 10 '20 at 12:33
  • 3
    @R.Chung Thanks for the pointer, I knew I read the study https://blog.silca.cc/part-4b-rolling-resistance-and-impedance before, but I could not find it. It is also just a blogpost, but it appears quite trustworthy. – Vladimir F Героям слава Sep 10 '20 at 12:42
  • I like that the Silca post uses data from mainstream tires and shows their test conditions. – ojs Sep 10 '20 at 13:26