Repeating the Thunder Burt vs Race King CRR test

Yesterday (27th Dec '23) I repeated the rolling resistance test that I did last year, in which I compared two of the fastest mountain bike tyres that are available: The Schwalbe Thunder Burt Super Race tyre and the Continental Race King Protection.

Why repeat?

A couple of things have changed since I did that previous test in February 2022, which I think will improve the quality of my testing.

 

Firstly, last year I bought a Power2max spider-based power meter for my MTB.  A spider-based power meter has the benefit over my single-sided Stages power meter that I used last year because it measures total power.  Any single-sided power meter assumes that the total power is double the power that is measured on the left hand side, so has some inherent uncertainties coming from that assumption.

Secondly, I now have a second pair of wheels for my MTB.  This enables me to mount a 2nd tyre on the other rear wheel and perform a back-to-back test with less effort to swap the tyres over, and less delay between tests.

Testing protocol

I performed the testing in exactly the same manner as I did previously.  The process is briefly summarised below:

1)  Mount tyre/wheel on bike.  Measure how much weight is on the back wheel when I'm sitting on the bike (which in this case, was 54.9 kg).

2)  Warm up the tyre for five minutes at 80-85 rpm and ~150W / 24mph.

3)  Adjust tyre pressure (takes ~1-2 mins) to the desired value.  During this time, the Power2Max power meter will automatically calibrate its zero offset value.

4)  Pedal for 4 minutes in same gear, at a similar 80-85 rpm.  For the final 2 minutes, measure the average power and speed.

5) Results were recorded in the spreadsheet and the CRR was calculated using the standard Tom Anhalt method. 

For this test, I performed an ABABA style test (A=Thunder Burt, B=Race King), so with two repeats for the Thunder Burts and 1 repeat for the Race Kings.  The reason for repeating the Thunder Burt a second time was because I got a strange results for the first test at 16 psi.

Results and observations

As shown in the CRR plot below, the Thunder Burt is clearly the faster tyre of the two. During test, the power needed to keep the rear wheel spinning at ~23mph was noticeably higher by 15-20 Watts for the Race King.  The results from my 2022 test are shown in grey in the plot, for reference.  Note that those 2022 tests were performed with a butyl inner tube, instead of tubeless.  This difference, together with the single-sided power meter, might account for the difference in results.

Note also that the Bicycle Rolling Resistance test results in the plot below have been updated to show the tubeless BRR results instead.  In previous years, all of the BRR testing was performed with a butyl inner tube. It's only recently in 2023 that BRR changed it's protocol and updated their results to show data for a tubeless setup whenever appropriate.

What's also noticeable in the plot above is that the results are incredibly consistent and repeatable, which I am really pleased with.  This is probably due to my new power meter which avoids errors coming from inconsistent left/right leg balance.  

There is one outlier though, one of the low pressure results for the Thunder Burt (denoted by the red circle in the plot above).  As this is a clear anomaly in the otherwise consistent data, I ignored it when of creating the green Thunder Burt trendline.

What I'm not so pleased about though (and this is a massive "DOH!"), is that I have just realised that I mounted the Race King in the wrong direction.  This is really annoying and it might be the reason why the Race King has higher CRR values than the Thunder Burt and why the differences seem to be larger than I measured previously.

I need to think what to do next.  At the moment, I am not inclined to repeat the whole test!

Addendum 28/12/23 - Correcting my mistakes

I really couldn't leave this test as it was, with Race King results for the tyre mounted in the wrong orientation.  On the following day (28th Dec '23), I decided to repeat the Race King test with the tyre mounted the correct way round.

Before re-mounting the tyre, I first performed a repeat test with the tyre exactly as it was the previous day (i.e. the wrong way round), to ensure I could get get consistent results with the previous day.  The results from this repeat test are shown with the light blue triangles in the plot below.  It's pleasing to see that the repeatability of the test results with the previous day's testing is very good, so on this basis, I didn't feel that it was necessary to repeat any of the Thunder Burt tests too.

I then removed the tyre, flipped it around and remounted it so that it was now rotating in the correct direction.  The new results for the Race King tyre mounted in the correct direction are shown with dark blue circular symbols in the plot below:

It's interesting to see that when the Race King was mounted in the correct direction, the rolling resistance seems to be similar.  In fact, if anything the CRR values are slightly higher than when it was mounted backwards, which was a little surprising. The differences are very small though, and are the same order of magnitude as the repeatability.

Conclusion

After this additional testing, I think it's safe the conclude that the 2.35" Schwalbe Thunder Burt Super Race is a faster tyre than the 2.2" Continental Race King Protection.  The differences seem to be ~4-6 Watts of rolling resistance for a 85kg rider+bike cycling at 25kph (~15.5mph), depending on the tyre pressure.

It's worth noting that the 2.2" Race King measured slightly narrower by 0.11 inches (=2.8mm or 4.7%), which would penalise the rolling resistance for Race King relative to the wider 2.35" Thunder Burt at a given pressure.  The effect of the width difference should be quite small though I think, based of tyre width effects I've seen on BRR.com, like this test for example.

As with all roller or drum testing, it is worth remembering that testing of this nature only detects the tyre hysteresis effects of the tyres.  These tests cannot capture the other losses associated with riding off-road, such as the so-called suspension losses that that are created from the rider 'jiggling around', or the hysteresis losses that occur in the ground itself.  So for example, the CRR relationship versus tyre pressure seen in roller testing or drum testing goes in the opposite direction to what the tyre pressure effects I have seen when doing proper off-road tyre testing (see here, for example).

Nevertheless, I believe that the relative tyre hysteresis losses that are captured by roller testing of this nature are still relevant to off-road riding, and will be one element of the total rolling resistance that remains present when riding off-road.  Therefore I think this result and results from tests like it (on BRR.com for example) will still show which tyre is relatively faster.