Daily commute is short but brutal: roughly five traffic-filled miles with temps anywhere from 99-106 riding in, 90-100 riding home.
Longer rides have to start early enough that it seems like a good idea on departure. By the time things start getting ugly I'm already committed, so it's just a question of keeping the pedals moving.

Not long ago a car did something stupid during my commute, and I realized I'm less concerned about any potential impact than I am about whether I can get up off the 160+ degree asphalt afterward.

Short answer: Yes, it's too hot to cycle. I cycle anyway.

I still pedal in excessive heat but I just slow way down. Pedaling slow in the hot sun feels way better than standing around in the hot sun.

But since you ARE Nachoman I suspect you do sense when your queso is melting.

Living in the upper Midwest, I never say never since summer usually lasts a couple months and many years of late they are cool and cloudy. This year has been hot, sunny and glorious. Have been out in 90-95* with two polar bottles frozen prior to departure. I try to run a route close to lake Michigan which typically is 8-10* cooler than inland. I must say that I came close to an overdo in July on a 40 miler mid-day despite religious hydrating before and a few cliff bars and the aforementioned polar 20 ozers mid ride. Needless to say, that I am the exception to the rule here since most folks stop venturing outside by August in a hot summer. The majority population in Wisconsin consider 60* ideal and are looking forward to fall by Labor Day. Probably should mention that I was a serious runner before turning to the road and mountain bikes and loved a sweaty 5 miler in FL spring heat.

Another Wisconsinite here. My son and I took a 50 mile ride on Saturday. He kept up with me, which really means: I kept up with him. This is a "long" ride for me, but I'm gradually getting myself into the habit of taking longer rides. Like [MENTION=486746]jbbr[/MENTION] says, it's hard for it to be too hot in Wisconsin. The main adaptation for me is figuring out how much water I need. I don't really sweat a lot, and have not bothered with water for being out less than an hour, but I also see no good reason to skimp on water during longer rides. Figuring out where I can fill up my bottles en route is a complication that I don't want to bother with right now, so I just strap a big bottle to my rear rack, along with the two bottle cages on my frame. There's space for a 3rd cage, but it interferes with my cabling.

I once rode 240km at 40 celsius with humid air through sunny mid day in a hilly route, lightest gear was 39x25 then and there were hills going over 10%. Took 9 liters of liquid as I remember, and still I left home with some 63.5kg and got back with 59.5. I felt like flesh as falling from my bones. Not recommended.

​​​​​Still I commute year round to orchestra rehearsals that end 12:00 and I have a 30min ride with a backpack and a CELLO on my back, including very hot days, and a few times arrived home dizzy, a couple about to black out. I try to get my head under a tap with cold water as soon as I get off the bike in very hot days to avoid that. And thats how much I hate (not) driving in a traffic jam.

I live in Florianopolis, south Brazil, and guys in the north face waaay higher temps, still they ride. Rio is hot year round, and is still far from north.

I think the problem isn't really riding, it's stopping suddenly. Also climbing steep hills is a bad idea as theres no wind. Still I do it, I love climbing!

The heat disappeared in Tokyo. Summer was a few weeks late this year, people were still in sweaters in early July. Last week and a little before were hotter than hell. Today it's raining, and cool enough to wear a sweater again.

It depends where i have to cycle. We had around 35 degrees the last 2 weeks and since the cycle path i usually take after work that leads through the woods over a hill is closed down for reconstruction i'd have to take the one parallel to the main road. Tried it on the first day and after going over a hill in plain sun and all the car exhaust because of the evening traffic jam i got so dizzy that i allmost got run over by a tram. Now waiting for lower temp.

Living in the desert can be a lot of fun but you need to use common sense... I bike 5.3 miles Everytime I go to work (one way) so I've been out in 115 degree ...... you just have to drink about 2LTs of water before you start and take it easy..and keep drinking water on the ride....
I guess I'll know my limit when I find it..

I live in Tucson. I've ridden in 100+, but I really prefer to be done riding by the time it hits 95.

80-82 is when I start to question whether I really want to go. I prefer to ride at night since the temps are cooler and less traffic. I got some decent lights and, for the most part, I have the roads to myself.

After the beginning of summer, I only rode in the morning

When I lived in Indiana with the humidity, above 95 I'd start finding other things to do.

When I lived in dry west Texas, that went up to 110 or so, but at some point it seems like hot is just hot. I did a 10k TT at 115, and that was just too damned hot.

I guess I'd say both these were above my desirable limit, so I moved to Portland, OR. Where, by the way, it's 99 this week

Even though most of us are referring solely to the heat, its actually the humidity (beyond a certain temperature) that is much more relevant: 100/40 < 85/85.

I ride for exercise and pleasure, so temp/humidity aren't really important. I've ridden through snowstorms in Michigan, and hot humid days in Houston. Here in Central CA you pretty much accept its going to be over 100 all summer.

Cold was never a problem if you were dressed for it. Humid days well over 100 were no problem as long as you kept moving, you had a breeze. The only trouble I have over 100 is sweating all over the inside of my sunglasses and not being able to see.

Now if keeping a certain pace is critical to you, temp matters. I never worried about it.

If I were commuting,weather matters much more. I have never commuted on a regular basis. My job makes it difficult.

I do know there is nothing like riding at dusk after a hard ride as the temp starts to drop and a breeze comes up. Best time of day to be outside. Then a cold beer on the patio looking at the mountains. Awesome.

You're not going to sweat in Fresno. It can be 110 and you'd be as dry as a raisin in the sun. And yes, the sun will drain you (and age you). Even if you don't feel it immediately, you will in time.