Saturday 28 October 2023

New cyclocross tyre rolling resistance testing using virtual elevation analysis

Cyclocross Challenge Grifo Baby Limus rolling resistance tyre testing with inserts
A few weeks ago I did some additional tyre rolling resistance testing using proper 33mm wide cyclocross tyres, with foam tyre inserts installed in them.

The aim of my testing was to check how tyre pressure affects rolling resistance and in particular to see whether the installation of tyre inserts would negatively affect rolling resistance at low pressures, when there is greater deformation of the tyre (and potentially deformation of the insert).  The results confirmed my previous testing, that lower pressures are faster, and also showed that the presence of tyre inserts doesn't affect that conclusion, that lower pressure is faster.

Previous testing

2020 CX tyre testing: I first performed off-road rolling resistance testing in 2020, during the first Covid-19 wave, and described previously in this post.  That testing used Schwalbe X-One tyres (the blue curve in the plot above).  The surprising results of that first test was that on grass, even with dry & hard underlying ground, lower pressures were always faster, producing lower CRR values.

2022 MTB tyre testing: In 2022 I repeated the test method but using my hardtail mountain bike.  The results are described in this post here (and shown above with the red curve).  That testing used Schwalbe Thunder Burt tyres and also showed that lower pressures were always faster, albeit with a more subtle effect of tyre pressure on CRR values.

New testing

In previous cyclocross seasons I have done only a handful of the races, often picking the early season races that had the best and driest weather.  For this coming cyclocross season, I intend to do most of the races throughout the season, including the muddy ones, therefore I have bought some good quality 33mm cyclocross tyres that will be suitable for the later races in the season.

The tyres I bought are Challenge Handmade Tubeless Ready (HTLR) tyres, which are 33mm wide.  I have a Baby Limus on the front, and a Grifo for the rear wheel.

In addition, I installed these tubeless tyres with tyre inserts because from what I have read (for example, here), the use of inserts allows the tyres to run at lower pressures.  I ordered some Tubolight tyre inserts, as described in the article, but I was disappointed to find that they are simply closed cell foam cylindrical rods with a diameter of about 25mm.  

Considering the price of ~£50 for the Tubolights, I decided to instead return them and instead go the DIY route. I bought some 25mm 'backer rod' from Ebay, for ~£10 for 10 metres, and made my own inserts.

Having installed the inserts, I was keen to measure the rolling resistance at different pressures.  I'll be aiming for pressures around 20-24 psi probably in the races, and with such low pressures there is a chance that the compressed contact patch will touch the insert and cause a higher rolling resistance.

I was pleased withe results (below), which showed the similar trends to my 2020 CX tyre testing, albeit with high CRR values due to the softer ground.  In conclusion, lower tyre pressures are still faster, and the tyre inserts don't seem to negatively affect the rolling resistance.  A reduction of 5 psi, from 25 psi to 20 psi saves around 6 Watts of rolling resistance at 15 mph.


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