OFFICIAL: 2021 Weather and Road Conditions MEGA THREAD

[90_Shelby]

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This is what I use. Their app gives you instant readings for your location based off Weather Underground data. (don’t need to select a track). -6531 right now, but also -38°C. A 13.0 second 1/4 mile time gets corrected to 14.2 under standard conditions, obviously not factoring for zero traction.

I wonder why the drag times app has such massively different DA’s compared to the airports? Slightly different location but not 5000 feet of difference. Weird.

[Sentry]

If you use dragtimes with Race City (rip) selected I get similar numbers to what you're getting.

[rage2]

@90_Shelby it's all up to you to get us some data. Do some runs where you're not traction limited (60-100mph?) and repeat when it's warmer haha.

[Sentry]

Well I'll tell you right now, wind resistance be damned, my shit feels a lot faster when it's cold out. The horsepower gained far outweighs any added drag, especially on a boosted car.

Source: precision calibrated butt dyno

[90_Shelby]

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The colder denser air is a lot higher in resistance. Not sure how much though. I remember testing my SLK32 back in the day, doing 100-200kmh runs at -40C temps, and it wasn't that much faster than summer. I expected a lot more. And of course watching how much hp it needs to maintain speed on the highway this week in -30C weather, it's like 15% more. So I figure air resistance is much worse as temps plummet.

Was wondering if anyone has done that side of the calculations.

I don’t think your taking into consideration that density altitude is calculated from temperature, humidity, and barometric pressure, to create an equivalent altitude number. Of course colder air would create more dense, higher resistant air, since we’re observing equivalent air density below sea level. High elevation and cold temperature or low elevation and higher temperature, you can end up with the same density altitude.

From Wikipedia, “ In aviation, the density altitude is used to assess an aircraft's aerodynamic performance under certain weather conditions. The lift generated by the aircraft's airfoils, and the relation between its indicated airspeed (IAS) and its true airspeed (TAS), are also subject to air-density changes. Furthermore, the power delivered by the aircraft's engine is affected by the density and composition of the atmosphere.”

Without measuring the actual 100-200km/hr time of your SLK and without knowing what the actual DA’s were when testing, we don’t really have any useful data. In the middle of summer I’ve seen DA’s swing 4000’ in 24 hours which has a massive effect on horsepower.

Similar to your example of how much power it takes to push through cold air while cruising, agreed, denser air has more resistance. At a steady cruising speed, you’d need slightly more power to push through the denser air.

On that note, we also know that cars are simply faster when the DA’s are lower because they make more hp regardless of greater air resistance. Any 100% stock vehicle, 1/4 mile record, is set when DA’s are at or below sea level.

TLDR:

Density altitude effects air resistance and hp, positive effects of hp are greater then negative effects of air resistance. Density altitude considers temp, pressure and humidity to create an equivalent density at a specific elevation.

[90_Shelby]

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@90_Shelby it's all up to you to get us some data. Do some runs where you're not traction limited (60-100mph?) and repeat when it's warmer haha.

My fastest times with my cars have all been around 0*C in the fall with DA’s around 3000’ when the roads were still warm. You’re correct I could do some 60-130mph hits (no 60-100 option) but that’s pretty damn fast for winter driving….. I don’t think I have many 60-130 hits from the summer to compare, I’d have to check.

[Darell_n]

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I wonder why the drag times app has such massively different DA’s compared to the airports? Slightly different location but not 5000 feet of difference. Weird.

I’m 6 hrs north of Calgary right now at 650’ elevation.

Edit: DragTimes is reading elevation in meters but displaying it as feet. I’m at 650m right now, big difference. (App now deleted, again)

[rage2]

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Density altitude effects air resistance and hp, positive effects of hp are greater then negative effects of air resistance. Density altitude considers temp, pressure and humidity to create an equivalent density at a specific elevation.

Yea, I was just curious how much. I wish I had a fast car to be able to test. Can't do much with a Sienna right now.

[mr2mike]

Can we have this moved to a 2021-22 air density mega thread?

[ExtraSlow]

My kid is at camp in the mountains all week. Bet that's a different experience than the camp organizers were hoping for!

[Buster]

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My kid is at camp in the mountains all week. Bet that's a different experience than the camp organizers were hoping for!

[88CRX]

Fucking hell it’s cold and generally terrible out there.

RDX popped a CEL (and every other sensor) and went into limp mode mid return from Manitoba. Car fully loaded with wife, dog and newborn is about as bad as it gets for a winter breakdown. Fuck me, finally home. Going to melt my face with edibles BRB.

[Buster]

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Fucking hell it’s cold and generally terrible out there.

RDX popped a CEL (and every other sensor) and went into limp mode mid return from Manitoba. Car fully loaded with wife, dog and newborn is about as bad as it gets for a winter breakdown. Fuck me, finally home. Going to melt my face with edibles BRB.

There's a lot to unpack here.

traveling in -80: bad decision
leaving Manitoba: good decision
going to Manitoba: bad decision
dog: bad decision
newborn: expensive decision
wife: need pics first

[ExtraSlow]

Face-melting dosage of edibles: neutral.

[tonytiger55]

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Fucking hell it’s cold and generally terrible out there.

RDX popped a CEL (and every other sensor) and went into limp mode mid return from Manitoba. Car fully loaded with wife, dog and newborn is about as bad as it gets for a winter breakdown. Fuck me, finally home. Going to melt my face with edibles BRB.

How did you get back the vehicle being in limp mode..?

[eglove]

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How did you get back the vehicle being in limp mode..?

You just drive it, you'll have shit mileage though

[ExtraSlow]

Depends on the vehicle. Some limit themselves to like 30 km'h in that mode.

[Darell_n]

And this is why I’ve been holed up at my Ma’s place for the last 48 hrs. Not risking a 600km drive with the wife and kidlets at -40

[jutes]

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Fucking hell it’s cold and generally terrible out there.

RDX popped a CEL (and every other sensor) and went into limp mode mid return from Manitoba. Car fully loaded with wife, dog and newborn is about as bad as it gets for a winter breakdown. Fuck me, finally home. Going to melt my face with edibles BRB.

This happened to me once in the X1, ended up being the gas cap needed a reseat.

[vengie]

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Fucking hell it’s cold and generally terrible out there.

RDX popped a CEL (and every other sensor) and went into limp mode mid return from Manitoba. Car fully loaded with wife, dog and newborn is about as bad as it gets for a winter breakdown. Fuck me, finally home. Going to melt my face with edibles BRB.

Intercooler up pipe freeze?

Happened once on our 1.6t Tuscon in a -35 drive from Regina.