​Storing mountain bikes in a hot car: These parts will be damaged – but these won’t!

Conclusion: The bike survives – but some parts don’t

A modern bicycle can withstand heat much better than many people realise. Frames made of aluminium or carbon fibre are not usually damaged by a hot interior. The real concern lies with components made of rubber, plastics and adhesives, as well as tubeless systems and, above all, e-bike batteries and electronic circuits. What’s particularly tricky is that it’s not the air temperature that causes the most damage. Surfaces in direct sunlight reach significantly higher temperatures than the air inside the vehicle. Anyone who regularly leaves their bike or individual components in a hot car for hours on end risks unnecessary wear and tear – and, in extreme cases, even damage.

Key points at a glance

• In the sun, the temperature inside a car can easily reach 70 °C within an hour. The dashboard and seats can get even hotter.
• Aluminium and carbon frames can usually cope with these temperatures without any problems.
• Tyres, tubeless sealant and plastics age much more quickly when exposed to heat.
• Rechargeable batteries really don’t like heat – storing them for long periods at temperatures above 40 °C shortens their lifespan.
• Wheels with tyres fitted may become distorted or build up high air pressure in extreme temperatures.
• Direct sunlight is often more harmful than the hot air inside the car.

How hot does a car really get in summer?

Many people underestimate the greenhouse effect inside a car. Even when the outside temperature is around 30 degrees, the temperature inside the car can rise to over 50 degrees within a short space of time. On hot days with outside temperatures of 35 to 40 degrees, the temperature inside the car can easily climb to around 70 degrees. Black dashboards or seats often even exceed 90 degrees. The greatest rise in temperature occurs within the first 20 to 30 minutes.

Carbon or aluminium frames: all clear

First, the good news: modern bicycle frames can cope with such temperatures without any problems. Aluminium only loses its strength at significantly higher temperatures. Carbon frames are also unaffected. The epoxy resins used in high-quality frames have an enormous temperature margin and are well above the temperatures reached by a parked car.

Tyres: This is where the greatest risk lies

The situation is quite different when it comes to tyres. Rubber loses its stability in high heat and ages more quickly. At the same time, the air pressure inside the tyre rises. If there is additional weight on the tyre or if an unfavourable load is exerted on the carcass over a prolonged period, this can lead to deformation.

That’s exactly what BIKE editor Max Fuchs experienced on a hot summer’s day: A spare set of wheels had been lying in the boot for hours, with a heavy bag resting on one part of the tyre – by the time the wheels were next due to be used, the tyre was completely deformed and wobbled wildly.

Tubeless sealant is also affected. Many sealants dry out much more quickly at high temperatures and lose their effectiveness.

Batteries and electronics don’t like saunas

The biggest casualty of the summer heat is tucked away in the down tube. Lithium-ion batteries age considerably faster at high temperatures. This applies to e-MTB batteries as well as to batteries for electronic gear systems or GPS devices. Manufacturers therefore recommend storing batteries in a cool place wherever possible and not leaving them in a hot car for hours on end. Have a look here if you want to find out more about heat and batteries.

Plastic parts age more quickly

Handlebar grips, saddles, bottle cages and protective films are often made from plastics or rubber compounds. Heat and UV radiation cause these materials to become brittle or fade more quickly. This doesn’t happen after just one summer’s day – but it certainly does after many weeks of regular exposure to sunlight. Even adhesives lose their bonding strength over time when exposed to very high temperatures.

How to protect your bike

The simplest solution costs nothing: park in the shade. If there’s a risk of direct sunlight, cover the sensitive parts. Batteries don’t belong in a hot car and should be stored somewhere cool. Ideally, you should transport bikes in an upright position or without placing any constant weight on the tyres.

Editorial commentary

Summers are getting hotter – and that’s precisely why heat is now just as much a part of everyday mountain biking as rain or mud. There’s no need to panic: a high-quality bike won’t fall apart after an afternoon in a hot car. However, if you regularly store your kit as if it were in an oven, you’ll unnecessarily shorten the lifespan of many wear-and-tear parts. Batteries, tyres and plastic components in particular will thank you for letting them sit out the heatwave in the shade.