rsbob 

Tell me if extreme heat or cold is more detrimental to your average speed compared to a nice Spring day. I am not talking about moving to a fat tire snow bike in the winter, but riding the same route on your regular bike when it is blisteringly hot or super cold. If you keep stats, you can cheat and look back.

Mr Robot says, “Cold weather can pose challenges to athletes but also burns more calories. The body needs to work harder to perform in a harsher climate and generate adequate heat to keep warm . Cold stress can have a potent effect on performance, and the minimum temperature value is more important for cold weather sports due to the impact of cold stress.Exercising in hot weather can also have both positive and negative effects on sports performance. Heat acclimatization can improve athletic performance in warm-hot environments, especially for aerobically trained athletes . However, hot and humid environments can have deleterious effects on athletic performance. Increased temperature has been correlated with decreased athletic performance due to excessive fluid loss, impaired thermoregulation, and other factors.”

CrimsonEclipse

Hot weather, not even close
Once you hit thermal limits, you have to slow down or cause damage.
Over 35c I'm probably down to 25-33% of normal output

Cold weather DOES have a performance penalty physically but it's only about 25% for me, then at a certain temp, your penalty is the clothing and equipment needed.

Garthr

Pick a poison ! Neither ! Hahahahahaaha ! Ohio doesn't get extreme heat though, like say 100 degrees plus a high dewpoint. Even during the hottest days, say afternoon highs in the 90's, I'm riding just after dawn anyways and the sun's effects are much lesser than later in the day. I'm a summer lover for sure. In winter my legs and feet are always cold unless I overdress and then it's different kind of misery, not only from perspiration but the restricted feeling from wearing all that stuff. Even under 40 degrees I'm cold unless the sun is fully out. I have yet to find any magical bib tights either, that block the wind as needed, yet breathe well, offer the same compression fit as shorts can, and are supple enough not to notice them, basically make it feel like summer ! Leg length is another matter ! I have worn leg warmers with my compression shorts under some unpadded thermal bibs, but man, do the legs feel like they're wrapped in bandages.

The bottom line though is I'm slower in the cold than hot. Not that I'm exactly screamin' fast in summer either. you know, relatively speaking.

Jughed

Cold.

My legs feel like bricks in the cold. And I don’t want to be out in the col, the cold sucks. Winter sucks. Snow is stupid. Cold is stupid. Short days are stupid. Winter is stupid.

delbiker1 

Definitely extreme heat. I ride mostly early morning, very rarely after 11 am. Cold is much affected by the wind. I will ride when it is in the mid 20's f., but only if the wind is fairly light, maybe up to 10 mph.

cegerer

I've been living in Florida for 7-8 years. Originally from Michigan and could not tolerate heat whatsoever. Now? I ride all summer long down here, usually in the 90s, 90+ RH, and just baking under the sun. I love it. Although I have taken to wearing a sweat band under my helmet. Cold? No. It was a very chilly 61 yesterday and I was seriously thinking about not riding

PeteHski

I don’t ride in extreme temperatures, but I find cold weather slows me down more than hot weather in general. Breathing in cold air when riding at high intensity really limits my performance and feels very unpleasant. I much prefer riding in warmer conditions.

chaadster

The density of cold air and the higher aero drag of bulkier, warm clothing has serious and necessarily negative impact on speed.

Hot weather does not necessarily have a negative impact on speed.

Whatever hot weather’s impact on the limits of one’s physical performance, whatever work you do in hot weather will generate more speed in those conditions than that same amount of work in cold weather, simply because of aerodynamic effects.

Chuck M 

This is difficult for me to ponder. Living in Oklahoma with the heat and humidity I certainly need to plan better and slow down. But we also can get quite cold and the breathing in of cold air does a number on me no matter how much I slow down and cold in my feet and fingers is harder for me to deal with than it used to be.

BobbyG

The older I get the less well I do in the heat, and the better I do in the cold, although snow slows me down a little since I have to ride my heavy, treaded, studded snow bike.

ofajen

The same bike is slower in winter due to the tire rubber being stiffer and trails being sticky vs dry. I say sticky but below freezing is worse because then the trails are both deformed from ruts when it was sticky and then frozen into slippery ice mud, hence, me running on an indoor track three times a week and doing circuit and strength training most days.

Oh yeah, cold air is denser too. Optimal TT temp is pretty high. You can go until your body temp gets somewhere around 40C or so. I think the one hour record rides are done at about 30C.

Otto

wolfchild

I don't track speed but I definitely feel more drag in extreme cold. It just takes more effort to keep moving when the temps are in the negative double digits. Add a few inches of snow and slush and ice and studded tires and the ride becomes even slower.

WaveyGravey

Cold is worse for me. Riding or running.

wheelreason

Both, at the extremes, above freezing, and below 95, I'm good.

prairiepedaler

We get both extremes here, it can be +40c or -40c.

Either way, I don't want to be riding in it.

As far as winter riding goes, Winnipeg is tough going. I prefer it sunny, dry and colder though with no wind. Sloppy, windy and overcast aren't all that wonderful. Wreaks havoc on the bike.

Summerwise, I remember talking to a black dude who was visiting from Phoenix AZ and couldn't wait to get back there. I asked him about that and he said the humidity here was killing him. I asked that he preferred +42c and dry vs. +27c and humid??? He said, any day! Winnipeg has gotten progessively more humid over the last 15 years in it's summers. I pour with sweat as a result.

skidder

Yes

Iride01 

85° to just over 90°F is the temperature I enjoy riding the most. And we aren't going to have what others call ideal temps for more than a brief period. It's a given here in the south that you will get sweaty doing anything outside in the spring and summer. Riding hard and keeping the speed over 16 - 18 mph or better can keep one comfortably cool at even higher temperatures. My legs seem to gripe more and take longer to loosen up even at 70°F temperature ranges.

Carbonfiberboy 

I'm not interested in speed on short rides. Not my thing. Cold around here is like 40°, easy to dress for, not a problem. But pass climbs at >100° are tough and definitely slow me down.

Desert Ryder

Here in the southern NV desert we don't get the extreme cold. The heat though...it just sucks the energy and motivation to ride right out of me.

Maelochs

Cold doesn't slow me much if I dress for it ... but I am loathe to ride in cold weather.

Heat ... when I was really fit heat was not a huge issue but it was an issue ... I felt the precursors of heat stroke after too hard an effort in high heat. But that took years of daily riding in 90+ weather. Lately I find extreme heat slows me considerably ... and again, being old, fat, and lazy, I loathe riding in extreme heat.

greysquirrel

Cold slows me down. I normally ride in 60-65F weather. 90F+ is no problem but below 50F even with correct layers makes me lethargic/stiff.

Pratt

Heat definitely, I don't ride in the cold.

Alan K

If we aren’t talking about switching bicycles for winter, in my case, it wouldn’t be possible to bicycle in extreme cold on a regular road bicycle - too dangerous on random icy patches!
Having stated that, extreme heat (95F or above) is difficult but with minimal effect on my speed/time - just need to drink much more than normal amounts. Fortunately, we have relatively few days in the summer when the temp goes that high.

dedhed

IMO it kind of depends on where you live to define extreme. Where I live we rarely see 100F but often see below zero cold.
My experience here is that the cold is slower. Wearing more layers of less than aero clothing, as well as the mentioned breathing cold air, and riding an upright style bike more often. Below zero I'm not riding a bike I'm walking.

Lambkin55

Cold air is more dense, therefore harder to move through.