Yeah, some days tired legs. Some days feel like a tail wind. My average speed commuting doesn't change by more than .5 mph though.

I agree that weather plays a huge part on my commuting speed. Every day is a "slow" day for me...I am not a speedy rider. However on rainy, snowy or very windy days I am slow. When weather is good I am a little faster. Also my fatigue that day and energy levels effects my speed too.

I feel fast and slow days. Oddly my times dont differ much, though I dont know why, as sometimes I look down at the cycle computer and think, are you kidding me, Im only going that fast!?

Its not predictable which will be which, sometimes I feel exhausted as I get on the bike, only to find myself feeling great on the bike in a mile or so, sometimes the opposite.

My fast days are the days I see another commuter. Today I was riding pretty slow, then I noticed another rider up ahead and you can really tell the difference when you look at my splits. This guy had to be 15 or 20 years older than me. I pedaled hard to catch him at the next intersection. Then he left me in the dust and made it through a light that caught me. I chased him the rest of the way home, just catching glimpses on the long straights. I took a hit to my pride, but got a great workout and inspiration.

Fast Days - commute on the Cannondale Synapse Carbon (17 lbs.) Slow days - commute on the Rocky Mountain Sherpa 30 touring bike (30 lbs.)

Yeah. There are too many factors to count. Some days I intentionally take it easy.

Nope...they're ALL slow days.

My speed is inversely proportional to the day's ordinal number, where Monday=1.

Yup, same bike, computer and route. Both days the weather was pretty near identical. Only differnce I can think of is that I didn't sleep as well before the faster ride. (?)

Definitely, and those days where you look up and say "Wow I'm this far already !!!" or "Dang I've only gotten this far ???".

I have an occasional fast day, but mostly it's slow or slower. I find the amount of time it takes to get out of the house matters more, and leaving just a few minutes earlier makes more difference than a faster pace on the bike. More prep the night before seems to occur on those days with lighter traffic, and I tend to get stuck by trains when I'm running late.

I always have "perceived" fast and slow days. Those days when I feel I'm really dragging, I push harder out of spite. Whether I'm feeling fast or slow, my avg speed doesn't change much. I don't have a computer on my fixie, but based on the time it takes me, I figure I'm averaging around 17 for my commute. Today I rode my geared bike to work for the first time and skipped using the train - 31.8 miles to work, averaging about 18.5, but that's uphill. Gonna try to get my average up to 19 for the round trip on the way home; we'll see, it'll be my first 60+ mile day in a month or so.

My last few days were slow. Something about the weather, didn't sleep well, felt low on energy

Sure, some days it's "upwind and uphill both ways" but usually not much variance, UNTIL I READ THIS THREAD!

This morning, I felt like I was pulling a parachute for 7 miles. WTF?

Might have more to do with me reading the thread at midnight and getting up at 5 am though. ;-)

Depends where the wind blows.

I have slow days <10mph
I have fast days 13mph

Most of the time I'm Halfassed (around 11.5 - ish).

This is my experience too. Weather has a much larger effect on my overall time than fatigue.

No. They are all fast days. I can count on 25min door to door, but sometimes wind and luck with lights gets me there a minute or two faster.

Definitely a slow day today. I did a hard set of 10x2' intervals at lunch yesterday followed by a long detour home at tempo.

i used to find i'd be way quicker in the rain but maybe it was just subconsciousness trying to get me out of the wet

Winter commute is always faster for me. I live by the bay, which makes it's own weather. Often, the wind is in my face both ways. Faster times drove me for a while but now I don't even look at my odometer. It just is nice to be out riding.

HAHA me too. 16.5 avg? I'm lucky to get 12. What can I say, I like the smell of roses : P.

Now that it is warm out and no snow/ice to deal with, my slow days and fast days are only 5 minutes apart. Where as during winter time the difference could be as much as 20 minutes.

There are days I'm just not feeling it (or dreading the work day), so I really don't put the pedals down. Some mornings, I get pretty aggressive, but despite the stronger headwinds on my evening commute, I make better time going home. Must be my motivation waiting for me...wife and 2 year old.

I seem to go slow on the way to work and arrive late then absolutely burn home! Not sure if this is really a reflection of my cycling or my job...