I took my bike out the other day, it was about 40 degrees out, and it really seemed to respond well to the cold air. It was very easy to loft the front wheel, no clutch play or bouncing needed. :D
Does anyone else notice power gains when the weather is cool compared to warm humid days?-- or is it just my imagination.
I know cold air is more dense, and that = more power, the only problem is cold air also = numb fingers. :(

I haven't noticed it explicitly, but your physics is sound. Doesn't surprise me a bit if that's the case.

I, too, have noticed she's a little "zippier" when the air is cold and dense. Matter of fact, the first time I lofted the front end, it was about 40 degrees and relatively humid. Steady 6K in first + whack the throttle = VERTICAL! :shock:

What is "cold"?


:lol:

I've noticed it, too. I took it out for a ride a few days ago, mostly just a medium-paced ride, enjoying a few twisties around a lake and feeling cool downtown... but I stopped at a traffic light just before I got to my house and decided to nail it... much to my surprise, no popping the clutch, the front end just came up around 8k and kept going. I didn't think my bike could do it...

there is definetly a difference in power due to cooler less humid air. Mine stood right up in second the other day with minimal effort (except for revving it out to 13k and dumping the clutch.) :wink:

there is definetly a difference in power due to cooler less humid air. Mine stood right up in second the other day with minimal effort (except for revving it out to 13k and dumping the clutch.) :wink:
I'm too scared to wheelie my bike. I'm afraid of looking like one of those squids you see on YouTube flipping backwards trying to wheelie. I've never done it, so I wouldn't know where the "stopping" point is. Hell, with my history, it's probably best I just don't figure it out.

Sorry, back to cold air and power.

I'm only scared to do it because I don't want to hurt my beautiful bike... if I had a little beater, I'd suit up, hit a huge parking lot, and learn to stunt... looks like a lot of fun to me, but crashes are definitely a part of it.

I had not ridden in a couple of weeks due to 2 deaths in my family. I went for a ride to run errands when it was 50 degrees out. I was concerned it might be hard to start but it was actually easier than when it is high 90's and humid. I think it feels quicker in cold weather too.

....basically, without a dyno or a 1/4 mile time, the only way I can "measure" power is by the ease in which the front end comes up. (although I'm no wheelie master).
[quote="drew"] Matter of fact, the first time I lofted the front end, it was about 40 degrees and relatively humid.
Drew, was that a 40 degree temperature, or a 40 degree wheelie? :lol:
....and as far as "what is cold", well, I'll let Sachi define that. :bow

I'm not so sure about the physics. Denser air ought to affect the mixture, but would it make things a little leaner? Might have to look that one up.

Anyway, if Sachi will allow, "cold" is defined by Webster's New England Dictionary of Winter as: "Temperatures generally between 0 and 20 degrees (Fahrenheit), with frozen precipitation optional. Light northerly breezes of 10 - 30mph may also contribute to psychological affect..." :wink:

Steady 6K in first + whack the throttle = VERTICAL! :shock:

How high does the front wheel get? Does "whack the throttle" mean give it all the gas you can and hold it? I guess when you let off the throttle the front end comes back down. I want to do that, but I don't want to flip over. Ah, forget it! I know I'll flip over.

The best way to do a predictable wheelie is to start off in first and accelerate to just over 6k rpm, then let off the throttle to let the front end dive and compress the suspension a little, and then give it full throttle. The front wheel will float up nice and smooth, and continue to slowly rise as the rpm's climb. Just let off the throttle or hit the back brake a little to drop it back down, but not both at the same time.

If you do this...

KEEP YOUR FOOT ON THE REAR BRAKE.

You SO should not have told me that.

There's easily more power when the temps drop. Lower humidity increases power also but not as much as temps but both contribute to denser air. Denser air means more fuel can burn for a set volume of air, therefore more HP.

It's really easy to see in light airplanes of the 150-180 horsepower range. Take a Cessna 172 (typical high-wing 4-seater) that may struggle to climb at 500 feet per minute with a full load down here in the hot, humid Texas summer. But, with temps in the 40's it's easy to get an extra 200-250 feet per minute climb from the extra power. Just a 10-degree drop is enough to notice if you're paying attention.

We have charts and graphs in the airplane manuals that show the effect of temp on takeoff distance, climb peformance, and fuel consumption. A hot-humid day can decrease performance significantly. Of course the prop and wings provide more thrust and lift in the denser air, but that's a whole 'nuther discussion.

That's interesting. I'd be intrigued to know more about the differentials in effect from increased lift versus fuel mix density. But if I understand you correctly, you're saying that denser air allows for more complete combustion, probably due to how the fuel disperses in the charge? That would make perfect sense.

It makes me now wonder more about the effect of cold on efficiency. I don't have data tracked, but IIRC, last winter I had lower mpg. Wouldn't more complete combustion equate roughly to higher efficiency? Seems like there ought to be some more complex relationship in the effects of density and temperature.

Guess it's time to go back to school! :)

In actuality, your economy should drop. Cool air is nature's way of enriching your mix, giving you more power but lower fuel economy.

I think cool air, in effect increases your displacement. For the carbs... more air atomizes more gas... Rich or lean shouldn't be affected (effected?) much, especially so for you FI guys.

And oddly, yes, whenever one increases their displacement, economy will suffer...as we usually don't take it more easy...

Found some place:
Air temperature directly effects power. Cool air is denser so a more air (oxygen) actually enters the engine. A 7.2 degree change in air temperature causes a 1% horsepower change.
I think this is very optimistic, maybe he means 7.2 degree "C"? That would be more believable as I don't think I have an extra 5.5hp when temps go from 90 to 40...but who knows... I don't ride when it's 40 degree F outside :lol:

In Florida, "cold" = anything below 70

Cold air is, in fact, more dense. You should see gain. Taking in cooler, denser air is the whole idea behind cold air intakes, which do increase horsepower in cars.

I think the Cessna can probably better take advantage. It's been a long time since I did my few hours in flight school, but I'm pretty sure you could adjust the A/F ratio with a knob in the cockpit, allowing you to keep it at an optimal ratio.

Taking in cooler, denser air is the whole idea behind cold air intakes, which do increase horsepower in cars.
By how much and under what conditions?

You SO should not have told me that.
Dude, we're gonna die! You thinking what I'm thinking? You do it first and tell me how it went. :D

Taking in cooler, denser air is the whole idea behind cold air intakes, which do increase horsepower in cars.
By how much and under what conditions?

Well, of course, that varies depending on the application and conditions just like anything, but in most cases, 1-5 HP is generally accepted just by moving the intake from the engine bay to, say, the front bumper.

I'd say it's a bit more than just the butt dyno, though, if I can tuck in and still lift the front tire several inches off of the ground in cold weather as opposed to sitting straight up, even pulling a little on the bars in warmer weather and still in not lifting it. I'd suggest someone with access try to dyno it, but there are too many other factors that affect dyno numbers...

I think that since cold air is more dense, this means more oxygen into the same displacement, more oxygen to burn (maybe more fuel needed too?) bigger explosion forcing piston down, more power.
Cold air intakes and intercoolers achieve this, nitrous oxide systems do this in a different way by increasing oxygen, more fuel can be used, and the nitrous keeps temps in check.

Taking in cooler, denser air is the whole idea behind cold air intakes, which do increase horsepower in cars.
By how much and under what conditions?
Very little, if at all. The theory is solid but I have yet to see a kit on a dyno that amounts to anything more than jack squat. Companies will post sheets, but they are measured under the most ideal of circumstances, trying to get your money. I have a CAI in my 5.4L V8 F-150 from a small shop in Michigan and although it is well made it mostly just gives the engine a little more growl. We've had pretty heated debates at FordF150.net about it. Here's the jist:

The idea is that the kit isolates incoming air, separating it from the engine bay and keeping it separated until it meets the throttle body and the upper intake manifold, right? In that case, almost all stock intakes are technically "cold air" intakes anyway. So why are you spending more money?

When you think about a vehicle, how beneficial is that really going to be? When you're sitting in traffic, it would help some since the engine heat will overwhelm the engine bay and heat the surrounding air, but who needs cool air and extra power when you're idling? When your moving - when you really need the extra kick - the entire engine bay is flooded with outside air at velocity. How much different can the temperature be under the hood versus the ambient temperature outside? 5 degrees... maybe? I just don't see the benefit.

The kit looks nice, but I would say if there are any performance gains, they are neglegible.

http://www.fordf150.net/photos/data/3304/20395intake3.jpg

At the end of the day, if you are looking for power, $400 can go a lot farther with something else than the 3-5hp you'll get on a good day with a CAI.

You SO should not have told me that.
Dude, we're gonna die! You thinking what I'm thinking? You do it first and tell me how it went. :D
I half-heartedly tried it tonight but didn't get the wheel up. I chickened out. I'm a wimp. It's my first year on a bike so maybe I better wait until next season.

For real! Too many people flip over in those crash videos. Man, I don't want to screw ME or my bike up.

I think the Cessna can probably better take advantage. It's been a long time since I did my few hours in flight school, but I'm pretty sure you could adjust the A/F ratio with a knob in the cockpit, allowing you to keep it at an optimal ratio.
In all but a few of the new engines with complete computer control, there is the Mixture knob that adjusts the A/F mixture. Except in very high heat, the mixture is typically left at full rich for takeoff and while climbing at altitudes under around 3000 feet so you're pretty much running maximum fuel flow. As the airplane climbs, the air temp decrease on an average of about 2 degrees C per 1000 feet BUT this cooling is more than offset by the density of the air dropping faster. The mixture now is then leaned as you climb to decrease the fuel flow as the air pressure decreases.