Most cyclists like a bit of sun to top up the tan lines, but right now riders at the Tour de France are ploughing through temperatures in excess of 40ºc -and UK cyclists have up to 35ºc to contend with.
Earlier this year, stages of the Tour Down Under were slashed as riders battled extreme heat. But is there a defining temperature when it's just too hot to race?
Dave Colley, of specialist sports drink company Precision Hydration told us: "Everyone is different, so there isn't a point at which we'd say it's not safe to be racing - you have to find that point for yourself as an individual."
Precision Hydration provide tailored drinks with varying electrolyte levels to suit different riders' sweat rates, and are now working with Team Sunweb to optimise the squad's intake.
"Riders on pro teams will be racing all over the world in hot climates, and might have access to heat chambers, so they'll be acclimatised to the heat. However, being fitter, they'll have a higher sweat rate - and they'll still be losing the same amount of sodium."
"Potentially, if they are a salty sweater, there's more risk to them if they're not replacing salts adequately."
The pros have soigneurs and domestiques to make sure they get enough bottles - but some need special care.
"We sweat tested Sunweb rider Jan Bakelants two years ago. He's a very heavy sweater, so his net losses over a day were very high.
"He switched over to our 1500 drink, which contains about three times as many electrolytes than the average, and saw a massive difference - he just wasn't touching the sides with weaker electrolyte drinks. He has it before, during and after races now."
When temperatures are high, Colley explains, over-drinking plain water or carbohydrate energy drinks solutions can present issues.
Hyponatremia is a low concentration of sodium in the blood. Some symptoms such as headaches, fatigue and sickness can be mistaken for dehydration, which can be a problem if people then consume more water in response. At worst, the condition can result in brain swelling and death, though of course this is in extreme cases.
"The main thing to be careful with is keeping the ratio of electrolytes and water in balance," Colley says. "When you sweat, you lose water and electrolytes, including sodium. If you pile on a load of plain water, you dilute your blood sodium levels further - and that can lead to hyponatremia."
So plain water is out, but sports drinks are not created equally. Isotonic drinks, containing some carbs, are designed to mimic the concentration of the blood. Hypotonic drinks, with no carbs, are lower in concentration and hypertonic drinks which are high in carbs are higher in concentration.
Hypotonic drinks are best during long rides in the heat - when hydration is a priority - whereas isotonic drinks can be saved for shorter, high intensity efforts where you want energy delivered fast - assuming you start well hydrated.
"When hydration is important, it's best to get your calories from solid food, and then use a hypotonic electrolyte drink - which doesn't contain carbohydrate. This is because hypotonic drinks will absorb faster, so are more efficient as a hydrator.
"When you move to isotonic or hypertonic drinks – absorption will be slower. Sometimes people will ‘add an extra scoop’ in when mixing up an isotonic drink. That can make it hypertonic and just means the gut is trying to absorb the calories as well as the fluids and electrolytes, which slows everything down, and can actually even have dehydrating effect.”
Outside of drinking lots, there's always the good old fashioned bidon shower. Studies have suggested that pouring water over your head can have a positive effect.
"It's likely that it's providing some psychological relief from the feelings of heat stress, even if it’s unlikely that it's actually improving your performance by itself,” Colley says.
He also points out the importance of pacing.
"The guys at the Tour are not going to going off at the same pace as if it was five or six degrees cooler," he explains.
"If you're doing RideLondon and you're expecting it to be 19, 20 degrees and it turns out to be 30 degrees, you shouldn't be flying off at the same pace that you were expecting. It's about knowing your limits, and pacing yourself."
“It’s also worth checking the heat index in the forecast to get an idea of the expected humidity as well as the temperature. Riding in high temperature and humidity is harder than in just high temperatures.
"And bear in mind that when you’re climbing, you're producing more heat and you're riding slower, so there’s less airflow cooling you down – so, if possible, rides with considerable elevation are best avoided in the hottest, most humid conditions.”
Michelle Arthurs-Brennan is Cycling Weekly's Tech Editor, and is responsible for managing the tech news and reviews both on the website and in Cycling Weekly magazine.
A traditional journalist by trade, Arthurs-Brennan began her career working for a local newspaper, before spending a few years at Evans Cycles, then combining writing and her love of bicycles first at Total Women's Cycling and then Cycling Weekly.
When not typing up reviews, news, and interviews Arthurs-Brennan is a road racer who also enjoys track riding and the occasional time trial, though dabbles in off-road riding too (either on a mountain bike, or a 'gravel bike'). She is passionate about supporting grassroots women's racing and founded the women's road race team 190rt.
She rides bikes of all kinds, but favourites include a custom carbon Werking road bike as well as the Specialized Tarmac SL6.
Ethan Vernon to debut Hope TT bike at World Championship U23 time trial
First international appearance for the roadgoing version of the Great Britain Hope x Lotus track bike
By Simon Smythe •
Wout van Aert and Remco Evenepoel looking for extra one per cent at Worlds as task of beating Filippo Ganna looms
The Belgian duo hope for home advantage in order to defeat the Italian in the men's elite individual time trial
By Jonny Long •
The life of a Paralympics tandem pilot
Tandem pilot Helen Scott discusses her experiences on route to silver and bronze medal with Aileen McGlynn at the Paralympic Games in London.
By Richard Windsor •
Cycling knee pain: everything you need to know
Knee pain is common among cyclists - we explain some of the causes and how to address them with help from a coach, bike fitter and osteopath.
By Michelle Arthurs-Brennan •
Lower back pain: causes and prevention for cyclists
Correct bike geometry and set-up are both vital for a healthy back, but for some cyclists, fatigue produces undesirable changes in muscle movement which also affects spinal posture
By Michelle Arthurs-Brennan •
Train your body to beat the heat
How the pros train their bodies to cope with the heat, and why it's easier to do it than you might think.
By Cycling Weekly •
Climb like a Grand Tour stage winner
How to climb faster without losing weight? Chris Marshall-Bell asks all-star selection of WorldTour stage winners
By Chris Marshall-Bell •
How to be aero (without breaking UCI rules)
Cycling’s governing body has banned the forearms TT position on road bikes, so what is the next fastest position?
By Alex Ballinger •
How cross-training can help reach your cycling goals
Got a big challenge lined up for later in the summer?
By Paul Knott •
You ARE a real cyclist: Taking on impostor syndrome
In a sport hung up on rules and details, it’s easy to feel you’re falling short of the mark and failing to fit in. Dr Josephine Perry goes to work on impostor syndrome
By Josephine Perry •