Buying running kit is an investment. To get more out of their pair of trail shoes, many runners are tempted to use them on tarmac. While technically possible, it runs up against physical and physiological laws that are detrimental to both your kit and your health.
1. Premature wear: why tarmac destroys the soft rubber of a trail shoe
The sole of a trail shoe is made of soft rubber designed to "bite" into earth or rock. On the road, this rubber undergoes constant thermal build-up.
The consequence: You risk reducing the lifespan of your lugs by 50% in just a few urban outings.
Key fact: Tarmac acts like a grater. With every stride, friction tears away micro-particles of rubber.
2. Increased risk of falling: the lack of grip from lugs on asphalt
Contrary to popular belief, a large lug does not provide better grip on the road — quite the opposite. Traction on tarmac depends on the contact surface area with the ground.
- Key fact: Crampons reduce the contact surface area by nearly half compared to a flat sole.
- The consequence: On wet tarmac, water cannot drain away and creates a film between the lug and the road. This is the micro-aquaplaning phenomenon: your trail shoes become unsafe.
3. A threat to your joints: the rigidity of a trail shoe can cause shin splints
A trail shoe is a rigid structure designed to protect against rocks (toe cap). On the road, this rigidity blocks the natural movement of the foot.
- Key fact: Tarmac does not flex. The vibrations from impact are not filtered by the rigid sole and travel directly up into the shin.
- The consequence: Running on roads in trail shoes increases the risk of shin splints and knee pain due to a restricted foot roll.
4. Wasted energy: the unnecessary weight of reinforcements in the city
In sports physics, every gram on your feet counts double in terms of energy expenditure.
- Key fact: A trail shoe weighs on average 30 to 50 g more than a road shoe due to its lateral protection.
- The consequence: You tire more quickly. Over a 10 km outing, this represents a significant amount of unnecessary weight lifted, degrading your running economy.
When does mixed use become acceptable?
While it is inadvisable to rack up the kilometres on asphalt, your trail shoes handle link sections very well (the journey from your home to the start of the trail).
What's more, if road running is off the cards, you can perfectly well hike in your trail shoes. At walking pace, the impact speed and rubber heat build-up are minimal, which means you can use your pair on towpaths or tarmac roads without any major risk.
