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Today the weather was 36°C (97°F) and sunny.

What should I know about riding when it's a bit hot like that?

I'm a kind of casual rider now (no longer commuting by bike) -- when the weather is above freezing I'm like:

  • 20 to 80 km rides at an average 20-25 kph.
  • Don't stop en route (except for gulps of water).
  • Drink a bottle or two of water, and eat a banana or two on the way home.
  • Cotton shorts and T-shirt.
  • Over 50 and a bit overweight.
  • Roads are slightly hilly and unshaded.

I went out today wanting a longer ride but returned home half-way because of the heat (so I managed only 20 km each way, 40 km round-trip).

I've heard that occasionally people can get heat stroke (and brain damage) from their e.g. running in the heat. What should I know about how to cycle?

  • Is it just like, "Don't: stay home and drink plenty of fluids"?
  • Is there a temperature above which you don't ride (or ride less, or more slowly)?
  • Do I have to be cleverer than my usual (water), about electrolytes or something?
  • Do you stop for rests (to cool down)? Do you know/recognize symptoms of overheating?
  • Is it necessary to stick to shadier routes?
  • Is pouring water on yourself necessary, or a luxury? Any other precautions?
  • Do you ride without a helmet (I did, because with a helmet my eyes flood with stinging sweat)?
  • Do you live in a humid or dry area? And do you have a lot of body hair? – Batman Jul 19 '16 at 19:05
  • The humidity was 30% today. I'm dark-haired and tend to tan rather than sun-burn, male but not especially hairy for a man (nor shaven). Does that make a difference? – ChrisW Jul 19 '16 at 19:09
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    Even if you tan, you should still use Sunblock - more important in some parts of the world than others, but ultimately melanoma is a horrible way to die. – mattnz Jul 19 '16 at 20:07
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    What time of day do you ride? Consider going at dawn to avoid the heat (and the traffic is far better that that time too!) – Criggie Jul 19 '16 at 23:34
  • Lycra and coolmax are fantastic fabrics, much better than cotton and polyprop in the heat - try a white longsleeved shirt that is snug around your torso and with arms that go right down to your wrists. Often available from the local discount place for ~$20 (The Warehouse in New Zealand) there's no need to spend silly money on cycling branded gear. – Criggie Jul 20 '16 at 3:32

11 Answers 11

40

Several questions, several answers:

  • Is there a temperature above which you don't ride

Yes, for me that's about 45°C. At that temperature where I live (Australia) the air is usually so hot that even wearing glasses it's hard to blink often enough to keep my eyeballs from drying out. Wrap-around glasses, complete skin coverage, and riding slowly is the only way to go. Or it's just before the rainy season and sweat is pouring off me just standing in the shade, so I don't go outside if I can avoid it.

  • Do I have to be cleverer than my usual (water)

Ideally, yes, regardless of whether you're riding. But 35°C is not especially hot, it's more that it is useful to pre-hydrate and make sure you're drinking to replace sweat. My usual is to buy cordial powder and add salt until it's undrinkable when I'm at home testing it. When I'm riding it starts to taste good, so I drink it. "electrolyte drinks" that work taste foul when you don't need them, if they taste like soft drink they're purely there to replace the sugar and are thus a waste of money. You should also be drinking 2-3 times as much water as electrolyte drink. But again, at 35°C you should be able to ride an hour or more without issues (I ride 45 minutes home from work at that temperature in the summer, and drink before the ride and after, rarely during).

  • Do you know/recognize symptoms of overheating?

This is important. If you start to feel weak or have a headache you should stop, drink and cool down. If you stop sweating you're about to die, so you should immediately seek cool shelter and warn the people present (there must be people present) that you're suffering heatstroke and may pass out. Note that "sweat evaporates as fast as it appears" and "not sweating" are very different things. I find my back will generally stay wet up to about 40°C, and above that I try not to ride very hard because my body and especially my brain does not like getting above 40°C so I need to sweat just to stay alive, forget exercising.

  • Is it necessary to stick to shadier routes?

Anything you can do to stay cooler while riding is good. But note that riding close to building or on roads "in the shade" is often no better than being in the sun as they will reflect and absorb/re-radiate heat. Trees are good, riverside or on a path near a creek (even a dry creek) are better. Mostly, pay attention to how hot you feel.

I took photos last summer of heat blisters on my hands from resting on the brake hoods of my bike. That was at only about 38-40°C, but riding through a built up area with lots of shiny buildings and fingerless cycle gloves - you could see that the blisters were where bare skin had touched black plastic hoods. The blisters were really annoying to work around while they healed.

  • Is pouring water on yourself necessary, or a luxury?

It's a waste of water, unless you have lots. A sock around a waterbottle, wet, can help but if it's hot and dry it won't help much, or for long. Keep the water for when you need it.

  • Do you ride without a helmet?

Not in Australia, where the law requires a helmet. I would consider it, and sometimes do, but I much prefer a helmet cover with a wide brim, then a headsock under the helmet to stop the sweat running into my eyes. It's much easier to wash or swap a sweatband or head-covering than to clean a helmet, especially if you're riding in the heat every day.

Clothing

The hotter it is the more I cover up. I'm a white guy, so in theory my skin is more reflective than black skin, but forget it, if I don't cover up I get way too hot.

At moderate temperatures I don't bother, riding home from work I just accept that I'll get hot and since it's a known journey if I get home uncomfortably hot that's bearable. So I wear a white, long sleeve t short and white knee-length cargo shorts, plus helmet cover.

But when it's hot, usually I'm touring, so I wear the full kit. Head covering as above, then a long sleeve white t shift (cotton is fine, and SPF 50 or higher is better (in Australia we get SPF rated clothing)). I will attach that to white gloves, buying the lightest, baggiest gloves I can find. Strangely, dishwashing gloves are more available and work better than gardening gloves. I wear cycling glove under them, because the offer basically no road protection. Then I wear cycling kicks with long, baggy cotton pants over the top. Those tuck into my socks. Basically the only skin you see is my face, and not a lot of that.

Hydration

I prefer to drink enough that I have to stop and pee every couple of hours. If the pee burns I will drink right there until I can't drink any more without throwing up. This is when I will normally drop a film canister full of cordial powder+salt into my drink bottle, drink that, then straight water until I'm full. The goal is to get that water into my bloodstream as fast as possible.

You should never, ever get to that stage just riding at 35°C. That has only happened to me when I've been at the end of a long day touring after making a mistake and having to ride further, harder, than I expected.

Time of Day/ Avoid the darn heat

Finally, and most importantly, if you can avoid riding when it's uncomfortably hot, do that. I have flexitime at work, and in the hot part of the summer I will start later and finish later so I'm not riding home when it's hottest (normally I work 7am-3pm, but much over 35°C I'll start between 0830 and 1000, so I finish later). When cycle touring I'll either ride early or ride a split shift. I'll start at first light (30-60 minutes before dawn) then ride until I'm hungry, tired, or hot. Then I'll stop and spend the day trying to avoid the heat while being a tourist, and possibly ride again when it cools down.

If you're working and riding for exercise, do it before or after work/office hours. First light is a great time to be out, you'll see any local wildlife before people drive them out of sight, and it's a very calm time of the day in most places. Or follow the crowd and go out for a ride after work. There's more people, less wildlife, and it's usually hotter, but that is relative to dawn, not midday, it's still a lot better than riding at 3pm.

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    Snap again. It takes a while to write these things! – andy256 Jul 20 '16 at 2:43
  • But you have references! – Móż Jul 20 '16 at 2:48
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    I learned stuff when I checked them. Just when I thought I knew sumpin' too. – andy256 Jul 20 '16 at 2:50
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    @Criggie not even close - there's a list and a query to get it. My longest answer is the 78th longest on bicycles (and it's not this one!) Zenbike holds the record here – Móż Jul 20 '16 at 5:25
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    Worth mentioning that drinking too much pure water when already dehydrated can dilute the salt levels further, leading to dilutional hyponatremia which can come on quickly and be fatal. The salt that @Móż adds is very important. – jackohug Jul 22 '16 at 12:16
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Lets get this in perspective. 36˚C is one degree less than normal body temperature. When our body temperature rises above normal (37˚C) we are at risk of Heat Exhaustion. Since one of the symptoms of Heat Exhaustion is mental confusion, it can quickly become Heatstroke. Heat stroke is fatal in up to 80% of cases.

Factors that increase the risks (see the reading list at the end) are

  • ambient temperature above 32˚C (90˚F)
  • direct sun exposure
  • being overdressed (lack of ventilation)
  • humidity above 60% (reduces evaporation of sweat)
  • altitude (your body loses fluids faster)
  • body fat (keeps heat inside you)
  • low initial hydration level.

So physical exertion when the temperature is high should be taken seriously.

How to ride when the weather is hot?
If possible don't. In many places, the early morning or late evening are cooler. Even if the temperature is not lower, the solar heating effect is lower. Plan to ride then, if possible.

If you are not used to riding in the heat, then start with very short rides. You and your body will need to learn to cope with it.

Start by being well hydrated. This means several hours, or at least an hour before riding. If you're riding early, it means the previous day.

Plan your route to avoid as much direct sun as possible. Wear SPF 50 sunblock, and reapply if it's a long ride.

Dress appropriately. Avoid 100% cotton, because it can act as an insulator. For road riding wear light colored skin fitting cycling specific clothing: Lycra. It's designed for this job, and it does it well. In his answer Móż recommends full coverup for serious touring.

Ride at an appropriate pace. At speeds around 15-20 kph (10-12 mph) the cooling effect (caused by our body sweat evaporating) can be more comfortable than lower speeds. As we ride faster, our muscles produce more power, much of which becomes body heat. But the power we produce rises as the square of our speed and the cooling effect of sweating only rises linearly with airspeed, so riding fast can quickly cause overheating.

As mentioned in comments

Airflow can cause evaporative cooling even above body temperature so long as the humidity isn't stupidly high. This is why you go from slightly damp to sweating buckets when you stop. - Chris H

If you're only going a short distance or time (30 minutes or less), you can ride more quickly. You may spend an hour or more recovering (drinking cool fluids). It can be tempting to ride fast when it's hot, because the road seems fast.

If you're riding a longer distance (30 min to 2 hours), you've got to be more serious about hydration. As many people have said drink before you are thirsty. Drink as much as you physically can (caveat below). If the ambient temperature is above body temperature, then the water bottle will quickly get hot. It's better to be inside you.

How do you know how much you can drink? There is plenty of conflicting information about this. Hydration - What You Need to Know discusses the science, and on my reading suggests that the maximum is around 500-750 ml/hr (about 17-25 oz/hr). The article points out

As your muscles burn glycogen, water is released as a metabolic by-product and excreted as sweat. Researchers found that during a marathon (26.2 miles), runners released an average of two liters of sweat from muscle glycogen stores. This is in addition to sweat from other body liquids.

It's important to know that drinking too much can be just as dangerous as drinking too little (essentially, due to blood dilution).

Is there a temperature above which you don't ride (or ride less, or more slowly)?
For me that depends on the humidity and general health. As a kid we never cared, but only rode very short distances. In my 30's and 40's I would ride short distances (eg 15km commutes) in any temperature up to 43˚C. Now that I'm 60 I find I don't recover from such bouts of stupidity quite as quickly, and avoid starting a multi-hour ride when it's over ~32˚ish.

What about electrolytes?
Yep. There are actually two kinds of heat exhaustion

  • Water depletion. Signs include excessive thirst, weakness, headache, and loss of consciousness.
  • Salt depletion. Signs include nausea and vomiting, muscle cramps, and dizziness.

Using some kind of sport nutrition / electrolyte drink is the key to avoiding the second type. On any ride of an hour or more I recommend starting to drink it (read the label folks) after about an hour, and sooner when it's hot. At the kind of temperature you mention, I drink my preferred concoction after about 30 minutes, usually alternating with plain water. I figure my body is telling me that I need it when it tastes good.

Is pouring water on yourself necessary, or a luxury?
Depends on your symptoms. Head and thighs are the important bits to cool. Head to help you think clearly. Thighs because that where most of the heat is coming from.

Do you ride without a helmet?
No, I always wear a helmet. And wear a cycling cap under it too. The cap (mostly) stops the sweat running down, and seems to help with cooling. And it stops sunburn.

One important item is some kind of neck covering at the back. On a big ride (multiday etc) I add some sort of legionnaire neck cover at the back. On a short ride I sometimes just turn my cap backwards, so the peak shades the back of my neck.

Further reading

  • I thought bonking usually meant hypoglaecemia, not heat exhaustion. – David Richerby Jul 21 '16 at 9:11
  • Drat! I think you are correct! Thanks @David. – andy256 Jul 21 '16 at 11:16
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    Airflow can cause evaporative cooling even above body temperature so long as the humidity isn't stupidly high. This is why you go from slightly damp to sweating buckets when you stop. – Chris H Jul 21 '16 at 16:00
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    @Chris Ok. Cool. er. Pun intended :-) I've tried adding more of a response here three times, and then erased it. I think it means I'm still thinking about how to react to your feedback. – andy256 Jul 22 '16 at 6:40
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    It's only my opinion and is not unknown for me to over-explain and end up on a tangent. Maybe my comment can serve as a footnote. – Chris H Jul 22 '16 at 6:46
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I live in Southern California: if I didn't ride when it was hot I'd never ride.

My suggestion is to hydrate way more than you think you'll need to. And I like to wear long sleeves of white moisture-wicking technical fabric. It keeps the sun off you and therefore keeps you cooler. And take more frequent stops to drink and eat a banana to replenish electrolytes.

If you stop sweating while riding, pull over, drink water, and wait till you cool off.

And hydrate.

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    Can't stress enough how important hydration is, but also how important it is to drink more than just water. Add Skratch, Osmo, Hammer, whatever your preference; just don't dilute your system. – altomnr Jul 19 '16 at 19:40
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    @altomnr What essential ingredients do Skratch, Osmo, and Hammer have in common? I've never heard of them and doubt I can buy them here. You might repost your comment as an answer, if you like. – ChrisW Jul 19 '16 at 19:46
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    You can absolutely get those in Toronto. They're just brands of sports drink powder. – Stephen Touset Jul 19 '16 at 20:03
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    Make sure you get a real sports drinks, not lollie water sold as sport drink. A rough guide - if its beside the soda, or kids powdered drinks its not sports drink. – mattnz Jul 19 '16 at 20:06
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    Seriously, electrolyte drinks are just sugar, salt and flavour. Two of those things are very, very cheap. Paying $50/kg for sugar and salt is nuts. You're much better off buying powdered cordial sachets and adding salt to taste. If you must, send a donation to your sports drink provider to cover the difference. – Móż Jul 20 '16 at 2:03
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97˚F isn't really that hot for a bike ride.

Don't wear cotton; there's a reason cyclists wear lycra. It wicks away moisture and contributes significantly to evaporative cooling. Cotton gets damp and doesn't evaporate, which creates a heat-trapping barrier around you. Drink constantly; 2 bottles per hour is pretty common for long distance rides like centuries and double centuries. Use a sports drink (powder is convenient) or gels to ensure you replace lost electrolytes.

If you're doing the above, you're probably not going to have any ill effects whatsoever. That said, pay attention to your body and what it's telling you. Stop if you need to. Pour water on your head if you need to. Call it a day if you need to.

  • 2 bottles per hour is pretty common Wow! I thought less, that a number to aim for was like at least a gulp or three every 15 minutes or so. – ChrisW Jul 19 '16 at 20:22
  • 200 km takes at least 6 hours, right? Two bottles is 1.3 liters (per hour) ... so you were saying, at least 8 liters in total? Wow. – ChrisW Jul 19 '16 at 22:10
  • 5 if you're going fast, but 6 is reasonable. That's really not that much water if you think about how much you're sweating. In hot temperatures without considering exercise (for example, camping), recommendations range from 4-6L/day. For a hot 200 mile ride, I've easily gone through 18L of drink in 12 hours of cycling. – Stephen Touset Jul 19 '16 at 22:18
  • As someone who overheats more easily than most, I have to underscore packing enough water that pouring it over your head is viable-- this is a relatively quick fix for overheating and will keep you going a lot longer. – Michelle C. Funk Jul 20 '16 at 16:46
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Answering the sweat question

Going without a helmet is not recommended as a solution.

I suffered the same problems with sweat, (always in the left eye for some reason) and what helped me was to wear something inside the headband to absorb or direct the sweat elsewhere.

  1. scrap of cloth - worked okay but would often fall out and get lost.

  2. a woman's panty liner - This worked great, providing extra absorption around the forehead and lasted a whole-day ride easily. I kept forgetting to take them though.

  3. bandanna - worked well, but looked retarded. Also the extra folded fabric had to go somewhere which made the fit unomfortable

    enter image description here

  4. tube-hat - works excellent. About $3 US. On cold days I wear a second one around my neck.

    enter image description here

  5. skull cap - works great, except it was a bit small and I split the top pulling it over my ears once. I still use it like this.

    enter image description here

  6. classic cycling cap under helmet - I have never tried one, because it looks a bit posey. Probably not going to do a lot for sweat either.

    • If your helmet has a brim / peak / sunvisor, try unclipping it. Sometimes this creates a still zone of air, whereas a cooling breeze above your eyebrows can evaporate the sweat before it pools into your eyes. Glasses or sunglasses can contribute to this lack of airflow.
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    I sweat badly -- much more than the average person. I combine a thin sweat band (there are versions with a thin plastic strip to channel the sweat away from the eyes) and a women's "maxi-pad" which is about 3/8" thick when not compressed and much more absorbent than a panty liner. The pad has an adhesive strip and it fits nicely in my helmet, between the foam pads. (Unfortunately, the newer maxi-pads have gone all high-tech, with "wings" and the like which make then less suitable for this duty, but you can still sometimes find the old style.) – Daniel R Hicks Jul 21 '16 at 20:14
  • -1 for "looked retarded" – SeldomNeedy Oct 11 '16 at 4:56
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One of the most common mistakes is to simply hydrate with water. The body needs salts and electrolytes.

The Australian New Zealand Council on Resuscitation says,

ANZCOR Guideline 9.3.4 - Heat Induced Illness (Hyperthermia): First Aid Management

ANZCOR suggest a 3-8% carbohydrate electrolyte fluid [any commercially available “sports drink”] for the treatment of exertion related dehydration (CoSTR 2015, weak recommendation, very low quality evidence). If carbohydrate electrolyte fluid is unavailable, water is an acceptable alternative.

Their "CoSTR" citation is to:

Zideman, D. A., Singletary, E. M., De Buck, E.,et al. (2015). Part 9: First aid: 2015 International Consensus on First Aid Science with Treatment Recommendations. Resuscitation, 95, e225. http://www.cprguidelines.eu/assets/downloads/costr/S0300-9572(15)00368-8_main.pdf Accessed 19/11/2015

Its really important to have some type of formal first aid training before heading out also. You never know what you may come across.

1

The fitter and smaller you are the less water you need. I went out for a ride 20 mile ride a couple weeks ago when the temperature was about as hot as you describe with high humidity. I carried two bottles and still had to stop twice for water. I'm 51. I used to be a racer, but I'm kinda slow now about 16 mph. When I was a racer and about 15 lbs lighter. I generally wouldn't need but a bottle an hour, but in really hot conditions I would drink about two. Listen to your body. It's always better to drink too much than not enough. One thing I've noticed about when I'm starting to overheat is that I'll feel kind of a chill, sort of like hairs on the back of your neck standing up. I've ridden through this feeling in long centuries and road races, but I've always tried to increase my water intake when I start to feel it.

  • I think this says that, a couple of weeks ago, you had 6 bottles in an-hour-and-a-quarter ... and that one or two bottles an hour was when you were younger and racing. – ChrisW Jul 20 '16 at 10:23
  • Petty much. I I've think other people say that they got the chill - the hair standing on the back of your neck feeling when they were really hot, bordering on overheating. – Eric Jul 24 '16 at 12:24
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I think it depends a lot on what you're used to.

I doubt that everyone has the same upper or lower limit of temperature that they can cycle in. Acclimatisation is often overlooked.

I ride all year round in the UK, which means most of my riding is in the range of 5-15 degrees C.

Last year I attempted the international randoneé Paris-Brest-Paris and met cyclists from all over the world. It's arguable that those of us from temperate climates had an advantage as we were already used to the conditions. At the start of the ride it was about 18 deg C. I was wearing short trousers and short jersey and a thin gilet. I felt a little too warm, but was basically comfortable. I was shocked to see riders from India dressed in full-length tights and several layers including helmet covers and a "winter" jacket. One rider, from Malaysia I think, also covered his face apart from the eyes with a buff. When I spoke to them, they consistently mentioned how cold it was. I guess they must've found it really hard as temperatures dropped riding into the night.

On the other hand I guess they were used to riding in 40 degrees C, in which I'm sure I'd suffer badly. I can't believe this is down to some genetic difference between Northern Europeans and Asians, because those who live here seem to be comfortable in similar clothing to me.

So if you're willing to put up with an uncomfortably high or low temperature, whilst taking proper safety precautions, I'd guess you can acclimatise to a wide range of temperatures.

  • I was wondering what those "proper safety precautions" are, to be taken; but from your answer I guess I should add "be/become acclimatized" to that list. – ChrisW Jul 21 '16 at 13:18
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    @ChrisW. I admit my answer doesn't fully address your question, but I figured that other people have already done a good job of covering the proper safety precautions. – James Bradbury Jul 22 '16 at 7:18
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Is it necessary to stick to shadier routes?

It is advantageous to ride along shadier routes. I ride along a tree-covered route in the Central Plains (Topeka, Kansas, USA—a converted rail bed with 75% coverage which runs along a creek for the vast majority of the route). On 100°F+ (38°C+) days, it generally runs between 10°F and 25°F (6°C and 14°C) lower than the ambient temperature. That makes an uncomfortable ride downright bearable. One advantage of these higher temperatures is that flying insects stay home. As a beard-wearer, I really appreciate that.

Of course, you are far less likely to get heat injuries when you reduce your exposure to heat, but you will avoid a particular set of problems by avoiding direct exposure to sunlight, like burns, heat rash, and in the long term, melanoma, etc. You will also reduce your need for water, and increase your potential range. I am able to push myself on 15 - 25 mile rides even on these 100°F+/38°C+ days because of the shade, etc.

0

Spandex. Wear spandex.

When it is hot, I usually wear as little as possible, but on a bicycle spandex works great. Ride faster when possible so that you have wind for cooling.

Wearing cotton just gets wet and sweaty fast and cotton insulates, which is not good when it is hot.

0

The only solution for me has been to stop outdoor cycling completely in favor of indoor cycling in air conditioned home with fan.

I live in southwest Florida where weather is consistent - +90 degrees F, 90% humidity. For 15 years after retirement, I was cycling approximately 100 miles weekly. Increasingly severe physical and mental heat exhaustion symptoms occurred on almost every ride in recent years, despite use of full coverage lycra clothing, significant hydration (2 or 3 28 oz bottles of electrolyte solution over a a 3 hour ride), and experiments with various riding tempos and intensities. Following most rides, I would be 5 to 10 lbs lighter and not recover for many hours.

  • Thanks. Maybe it's that "90% humidity" impairs the cooling process which people rely on. – ChrisW Jul 27 '16 at 16:24
  • Sorry to hear that. Did you try riding earlier in the day, at dawn ? – Criggie Jul 27 '16 at 20:01

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