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Tubeless sealant and rolling resistance

15 June 2020
In previous tests we have shown the importance of rolling resistance on cycling performance. A tyre with a high rolling resistance will require more power to travel at the same speed, whilst a low rolling resistance tyre requires less power.

In this experiment we explored how varying the amount of sealant in a tubeless compatible tyre affects the rolling resistance.

The goal of this test was to evaluate the rolling resistance performance of varying amounts of tubeless sealant.

For this test we used the popular Continental GP5000 TL (tubeless) tyre in 25mm. This tyre has both good rolling resistance & aerodynamic properties as we have previously found.


It was mounted on a shallow section aluminium rim with an internal width of 19.6mm and external width of 24.7mm.


SEALANT

We used Zefal sealant, two layers of standard tubeless rim tape and a standard tubeless valve. During the development of our AEOX tubeless wheel range we found Zefal sealant to perform well and seal effectively.


WHICH IS FASTER - TUBELESS OR CLINCHER?

Tubeless tyres use sealant to create an airtight seal and allow inflation, whereas clincher tyres use inner tubes. The speed of a tyre depends on its construction, not just on whether it is tubeless or clincher. This means that a slow tubeless tyre will have a higher rolling resistance than a fast clincher tyre, so each must be taken on their own merit. There is also overall no difference in rolling resistance between the same tyre set up tubeless with ~30ml of sealant, and using a latex tube.

In order to test rolling resistance a rider rode a bike on rollers, measuring power output and speed, as well as atmospheric conditions and bike/rider weight, repeated over a number of days testing. This allows us to calculate what is known as the Coefficient of Rolling Resistance (or "Crr"), which can be used to model the power output required to travel on a normal road. A lower Crr is better - in that it requires less power to travel at the same speed.

The results can be seen below for rolling resistance vs sealant. 


There was an increase in rolling resistance as more sealant was added - no sealant at all was fastest, and 100ml was slower by 5.5w for a pair of wheels at 45kph.


10ml, 20ml and 30ml all resulted in very similar rolling resistance, and then over 40ml there was a steady increase in Crr up to 80ml.

In this test we found that increasing amounts of Zefal sealant also increased the rolling resistance of a Continental GP5000 TL.


It is much more sensible to use sealant because of the improved ability to seal punctures (and some tubeless tyres specifically require the use of sealant), and so in this test up to around 30ml of sealant for one wheel with a 25mm tyre resulted in a good tradeoff between good Crr and higher puncture resistance.


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