3

Bicycle Rolling Resistance is one of the most reputed sources online for rating tires, but some results are still a bit counter-intuitive, especially when tires have knobs.

I understand that the rolling resistance test is done on a hard surface (a steel metal plate with some safety), but how representative is this surface from surface in the real world? My impression is that the presence of knobs tend to underestimate the rolling resistance on hard surfaces on BRR. But are there other observations/measurement in their dataset that would allow to differentiate/nuance the rolling resistance number tires with very different tread patterns?

To give some context, I've seen that they added recently a semi-slick tire, that I'm using on a gravel bike for road rides (Michelin Power Adventure 48mm, but I'm using the 42mm). However, this tire has more rolling resistance than the "pure gravel tire" from Michelin in 40mm (Power Gravel). So if I accept the compromise of the lesser grip due to the little knobs, I may in fact be better off keeping the Power Gravel for road rides and gravel, and avoid having to swap wheels/tires. But other combinations can be found where the knobby tire performs similarly in BRR than a semi-slick tire, but probably not in real situation (for example: Specialized Pathfinder Pro vs Schwalbe Hans Dampf Pacestar).

EDIT: clarified the question to be closer to the original intent

7
  • 2
    Is the actual question "can I trust that the results are consistent between knobby and smooth tires"? Also, the difference is around 1 watt so it's going to be difficult to notice without controlled test setup.
    – ojs
    Commented May 2 at 19:21
  • 1
    @ojs The actual question is a generalization of that, yes. It's not only smooth versus knobby, but also between the different flavours of knobby. The Hans Dampf has for example a similar wattage as the Power Gravel, but it's the not impression it gives when riding on tarmac - another hard surface, but different from the steel used by BRR.
    – Rеnаud
    Commented May 2 at 21:39
  • 2
    You will wear down the knobs on the Power Gravel more by running them on asphalt, especially given you have 1) very small round knobs and 2) mediocre tires. Whether that is a problem depends on whether you actually need the knobs for your gravel riding.
    – oscu0
    Commented May 3 at 0:10
  • 1
    The BRR steel wheel/road is more about consistency between tests that may be years or decades apart in time. Its not trying to replicate any real-world condition, so it is slightly less-relevant to an off-road / mud / gravel rider. Maybe they need a dirt wheel and a pea-gravel wheel and a loose gravel wheel etc to test different classes of tyre ?
    – Criggie
    Commented May 3 at 0:50
  • 1
    @Criggie indeed, I understand the point of the steel plate, but the point of the question is mostly to know if there's some real-life value for these tests, especially when comparing tires with the different tread profiles, or if it's more of a "theoretical exercise" that only makes some sense if comparing two similar tires — without dismissing the amount of work behind the site.
    – Rеnаud
    Commented May 3 at 7:21

4 Answers 4

3

For the effect of knobs on otherwise identical tires, see this comparison on BRR. Less than 10% RR and no grip penalty for 1.3mm knobs vs a slick tire on the exact same casing. Lower-end tires might show a bigger discrepancy, but not by much. I'm not surprised by these results.

  1. I wouldn't expect ultimate grip to differ much on gravel-type knobbies. Although the knobby in the linked comparison, the Challenge Getaway, is particularly well-behaved on asphalt for an all-condition tire, since its lateral profile is essentially round. It feels pretty much like a slick to corner hard on asphalt.
  2. When talking about gravel-type tires, the knobs are under 2mm and just don't flex that much, so they don't have a very large contribution to rolling resistance.

The knobs are just one factor, in the end. We often think they make the biggest difference because we are used to comparing cheap 26x2.1 MTBs with expensive road bikes flying past us from back before we seriously got into bikes, I think. I also fervently follow BRR, and my impression has been that the factors that affect RR are, in order:

  1. Casing construction and thickness
  2. Then tread thickness and compound
  3. Then knobs

And if you can't or won't run tubeless, get latex tubes. It's the cheapest way to improve your rolling resistance and in fact the most speed per dollar you can buy short of a gym membership.

2
  • Just a curiosity, but if Michelin Power Gravel/Adventure tires are "lower-end" and "mediocre", what would you consider even a mid-range tire? These are tires with a €60 RRP, on par on many metrics with "Pro" tires of Specialized, SpeedGrip G-One's, Pirelli Cinturato's,... - sure, they are not top performers in all metrics, but it is to be expected for generalist products with good puncture resistance scores.
    – Rеnаud
    Commented May 3 at 12:14
  • 1
    €60 is not mid range, it’s high end price-wise. By mediocre I mean their speed to grip ratio is in my opinion unfavorable. I think Continental makes better, and cheaper, mid range tires (the Terras), although I can’t speak to their puncture protection. Puncture protection is inherently at odds with rolling resistance.
    – oscu0
    Commented May 3 at 14:12
0

Rolling resistance is about measuring how many joules are lost per each revolution. In real conditions, if your tyre slides (as a road tyre would slide on loose terrain), your apparent resistance is 0, but you lost many joules to the air instead of putting them at use to propel the bicycle forward. So it is a bit useless to define rolling resistance without having full contact, and it is difficult to translate rolling resistance results outside of time-trial and race conditions.

As every physicist will tell you, you compare oranges with oranges. The first check is "Do the things under comparison have the same measurment units?"

And then you compare a ship with a rocket, because they carry some weight over similar distances ;) .

Regarding the tyres you mentioned: first, do not be fooled by the "sound". A tyre with knobs produce more sounds, that your brain identifies with drag (whether it is true or not, this is exactly your question).

The best way is to apply some coefficient on the results. You are trying to translate the laboratory measurment into real-life variable conditions. In atmospheric science, this would be equal to translanting wind speed to the perceived cold (i.e. wind chill effect).

Get the worst possible slick tyre, one that roll so heavy that it looks like it has knobs (dutch-bike tyres that never wear out come to my mind), then try a tyre with knobs that give you a similar feeling, compare their rolling resistance, do the proportion, patent it and sell it as proprietary technology to the next greater gravel fool.

0

The question in the title:

How to interpret rolling resistance results on BBR?

The two tires mentioned are:
Michelin Power Adventure 48mm, RR Low = 21.9 watts, Rating = 4.0
Power Gravel (I'm assuming you mean the Power Gravel (v2) 40), RR Low = 22.9 watts, Rating = 4.0

Therefore: Power Adventure - given the testing conditions - comes in at 1 watt higher than the Power Gravel

Looking at the rest of the post the real question is:
What should I do with rolling resistance results in BRR?

Use the information as one factor in a list of requirements you have for your tires.

What do you want from your tires?
Based on the post:

  1. Low rolling resistance
  2. Good traction on the dirt when riding off road
  3. Good traction on the street when riding on road
  4. All requirements met in one tire so tires or wheels don't have to be swapped out for different riding conditions.

Sometimes people care about comfort or durability or flat resistance or looks.

It's a values question - what are my requirements and which ones are more important?

So if I accept the compromise of the lesser grip due to the little knobs, I may in fact be better off keeping the Power Gravel for road rides and gravel, and avoid having to swap wheels/tires.

Renaud is looking for confirmation that rather than swap wheels it might be better to just stay on the Power Gravel tires and not swap wheels/tires.

Grip=accepted reduction
Rolling resistance=small benefit
Swap wheels/tires=a hassle
Therefore: Don't swap wheels

Given the parameters this conclusion is logical

It might be good to make a complete list of requirements, rank them and see if the conclusion changes.

7
  • Thanks for the answer, but the question was probably not clear enough so I allowed myself to clarify it: it was not that I was looking for a confirmation (in that case, I have both Michelin's, wear is the main reason to keep stuff separate), but rather if there information in BRR's dataset that would allow to nuance that CRR number when comparing tires with different tread patterns, purely based on BRR's number, I can find very knobby MTB tires that perform even better than reputed gravel semi-slicks, and it's somehow inconsistent to me.
    – Rеnаud
    Commented May 6 at 19:27
  • @renaud - Is the goal still to have just one set of wheels/tires and ignore grip reduction?
    – David D
    Commented May 6 at 20:13
  • The goal of the question is more to understand what seems at first a discrepancy between a real life perception and a lab result. I have the impression that the presence of knobs in real life is a source of drag, while BRR's data doesn't always show that (especially on a hard surface, such as a steel plate). It's just hard for me to trust a source when results seem inconsistent with experience. But maybe there's nothing in BRR's dataset that can help to understand this kind of differences, or that a 10W difference is not that significant in non-competitive situations.
    – Rеnаud
    Commented May 6 at 20:54
  • @Renaud This wouldn't be the first time when real life perception doesn't match with reality. But you if you want to switch to different tires on road, you can do it without any lab results. Just say that you don't like the knob buzz or don't want to wear out the off road tires.
    – ojs
    Commented May 7 at 15:35
  • 2
    @Renaud I think your understanding of what seems like a discrepancy is related to your idea of what causes resistance losses: it's not because of deformation of the tire. Unless you run steel tires, there's going to be deformation: what matters is whether the energy used to deform the tire is returned or if it's lost. Knobs per se don't cause loss unless they're so deep and separated that they compress and deform beyond their ability to return energy.
    – R. Chung
    Commented May 7 at 17:59
0

Rolling Resistant site does good work... I question real world value. I ran tubeless for several yrs and had enough of the hassle which is the commodity being hawked mostly now. I ran extensive roll out tests off a hill under same non wind conditions. Any variance is essentially minor noise.. of no quantitative value.

Quality tubed vs tubeless ran down to 10mph off hill were within a few feet... often my tests showed results same within 1/2 foot. In short... RR can be scientifically diced varying ways... the out comes are negligible comparing same Q tire... translating to precious little distance traveled.

RR might well be a predictor of casing quality per roll out. Yet I prefer online real world reviews.. per wear, mounting fit, grip, ride Q etc.

Low RR figures = HIGH psi's. Rolling on 25mm's at 120 psi... might as well be running no rubber given the harsh ride Q.

2
  • 1
    Hi, welcome to bicycles. When you say the tests came out almost the same, are you comparing two tyres that BRR said had a greater difference than that? Without comparing like-to-like it's hard to say whether or not your results are comparable to theirs.
    – DavidW
    Commented May 7 at 22:02
  • My pt... most of what RR is graphing is minor noise between similar tires. Real world distance is minor/insignificant. In one case I ran C Ultra 11 vs Schwalbe Pro Ones both tubeless... much difference tires the end results per distance rolled not insignificant. TESTS 'same' meant the repeatabity of my runs very uniform. Commented May 7 at 23:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.