In this research project, the variation in ice grip of different bicycle tyres has been studied. Results show that studded tyres improve the grip on ice and the braking stability compared to regular bicycle tyres. There can be a great difference in grip on ice between different types of studded tyres. The main purpose with the project was to define a useful methodology for comparing the ice grip of different bicycle tyres and to perform initial measurements. The long term objective is to set up recommendations to winter cyclists regarding bicycle tyres based on measurements performed according to the defined methodology. The friction forces between a tyre and an ice surface is highly dependent on the characteristics of the ice. Therefore, an ice surface condition that is as well specified and repeatable as possible is needed to be able to compare different tyres. Here are some examples of what can be concluded based on the results from the study: • Studded tyres improve the grip on ice compared to regular bicycle tyres. • The braking stability of studded tyres is a lot better than that of regular, non-studded tyres – which positively influence the overall stability of the bicycle when braking on ice. • There can be a great difference in grip on ice between different types of studded tyres, but all the tested tyres performed better than non-studded tyres. • When braking with locked wheel the frictional forces measured, were up to 2.5 times higher with a studded tyre compared to the non-studded reference tyre. The braking distance will then be less than half and it will be possible to apply a braking force that is 2.5 times greater before the wheel starts slipping sideways. • A larger number of studs is not necessarily related to a better grip on ice. Other tyre characteristics such as the rubber mixture, the tyre pattern and the placement of the studs also seems to have a great influence on the ice grip. The defined test method has proved to be suitable for comparing studies, but so far only a limited number of measurements have been performed. In order to produce more general conclusions, further studies are needed including additional types of studded tyres and also with varying tyre pressure. Based on the results so far, cyclists should be recommended to use studded tyres when cycling during winter conditions. The measurements were done on smooth slippery ice using two regular (non-studded) bicycle tyres and four studded tyres of different brands and models. The tests were carried out in the VTI tyre test facility (TTF). The TTF is a unique indoor flat track machine for tyre tests on ice or asphalt pavement. This construction enables measurement of frictional forces under controlled conditions both when braking and steering. The project was financially supported by the research fund of Länsförsäkringar Alliance. (Author/publisher)
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