Bike seemed faster in cold? Coincidence? And More!

I got a new front tire today, and by the time I got it on the [strike]car [/strike] bike and finished cleaning the wheel, regreasing speedometer drive, and polishing stuff, it had been dark. I put away tools and such,

After a bit, I decided I wanted to test drive the new tire. (in case you are wondering, a front Bridgestone Spitfire 100/90-16). Tire was sweet (more later), T'was about 35 degrees F. chilly. I didn't want to wait, though lol. but the main thing was, i got carried away on my ride, ended up being out for like 2 hours, and during that time i got on the throttle multiple times, noticing the bike seemed to have noticeably more high end power then usual. I was very excited and repeatedly used the WOT button (haha).

weird thing is, it was running rough for the first 15 mins, then something must have happened and WAAAHHH *click WAAAAAHHHH *click WAAAAAHHHHHHHHHHH. seemed much faster lol. seemed like a 10-15 hp increase. i think. This is the coldest weather I've ever ridden this particular bike in.

HAve any of you ever experienced this? could it be the fabled higher air density theory? would it be this noticable? Do carburrators react differently to cold? I want some theory in this discussion if it happens.




I am also happy with the new tire. it has a "taller, steeper profile" then the old tire. The old tire was the original dunlop qualifier from 1981. was getting bald with 13k miles on the bike haha. The bike feels a bit heavier on the steering now, but leans in with much less effort required. It also tracks steadier during those harder turns when you're really leaning into it. I don't have to put effort into leaning anymore, i kind of nudge the bike to do it, and it leans itself. i like it now, I'll see how I feel after a couple hundred miles on it. Oh and I also got a traffic ticket during my "test ride" for weaving through the dotted lane markers haha . i enjoy turning. especially with this new tire. :silly:

I noticed this too, my old 550 I went everywhere on it night and day, summer and winter. When it was running best was during cold foggy nights, just the time I needed to slow down.

No coincidence, as the air temp drops so it becomes denser so you are getting more air mass per 'breath'. The volumetric efficiency of any piston engine increases inversely proportional to ambient air temperature: the colder the better.

Add some fog to the cold air and volumetric efficiency increases further: the minute suspended water droplets turn to steam in the combustion chamber - a simple water injection system.

(Water injection was experimented with in WW2, the later Merlin 2600 hp 27 litre V12 aero engine was supercharged running 150 octane fuel with water injection. Superchargers running at 36 psi; this air mass/volume becomes even more critical at 30 000 ft altitude, where air pressure is just 4.3 psi compared to sea level air at 14.7 psi ...)

Maple grove race way is right here and when they run this time of year they set world records because of the cool temps.

it was running rough for the first 15 mins, then something must have happened and WAAAHHH *click WAAAAAHHHH *click WAAAAAHHHHHHHHHHH. seemed much faster

When mine did that it was because a piece of crud that was blocking a jet in the carburetor washed it's way through and it started running right again.

Cold air is more dense, hence more power. Like Peter1958 said, the colder temps equal faster times.

Your warm weather jetting is just a tad rich.
The cooler denser air will make more power
IF there's added fuel.
Since your's picked up that say's you have the extra fuel all ready.

zukdave wrote: Your warm weather jetting is just a tad rich.
The cooler denser air will make more power
IF there's added fuel.
Since your's picked up that say's you have the extra fuel all ready.

+1

I suppose the same would happen if you rode from Denver down to sea level, and were jetted for sea level.

Normally, people in colder climates are better off slightly rich on hot days. This gives good rideability all year round, and then it will have a slight increase in power on cold days. It may take a while to notice the difference if the bike is new to you.

Sometimes I'll jet the bike a tad lean for cold weather, it sill runs good, but has to stay on choke longer. Then on a really hot day, it just screams. Not sure which way is better. It's probably safer to have more power when the tires grip better, ie on a hot day.

Also, setting the mixture a tad rich on a really hot day can help reduce the affect of the idle speed climbing as the bike warms up.

These are just very subtle changes, by the way.

I always liked the way my bike runs on cool days