Head wind vs tail wind-ET impact
 

Hi all,
In your experience, what is your experience dialing from a day with a tail wind to a day with a head wind....if DA was similar?

We're running ET finals this weekend at Topeka.
68 Camaro runs around 7.00/96mph 1/8 and 11.10/122mph 1/4 mile.
SBC, glide and 4.88s on a 29x10 tire.

Friday is a NNE 10 mph wind.
Weather forecast says Saturday will be a 7 mph SW wind, and Sunday will be around 12 mph S wind.

Thanks
Clark

Re: Head wind vs tail wind-ET impact
 

I ran a 68 Camaro for several years, mostly 10.90 stuff. Had the stock spoiler on front and rear. On the T-stop it ran 10.90 at about 125-127 and ran 10.40's off, with most of my motors.

Direct headwind was -.15 in quarter, and tail was about +.10... on my car. Everyone is a little different. Also, the JEGs log books used to have a guide on the first page... not sure if it still does or not. Don't have one handy.

Topeka track runs about due south...

Good luck.

Ken

Re: Head wind vs tail wind-ET impact
 

The Jegs log book said that 8 mph wind = .05 ET, using a 9.90 car as an example.
It doesn't address differences in frontal area.

My experience with a Camaro running a little slower than yours matched the Jegs formula pretty well for a head wind, but is affected a bit less by a tail wind.

Re: Head wind vs tail wind-ET impact
 

Thanks guys. I appreciate it!

Re: Head wind vs tail wind-ET impact
 

My Chevy II at topeka with a wind change you are talking about was anywhere from 15 20.That place is a dailing nitemare with the wind go luck. Tom

Re: Head wind vs tail wind-ET impact
 

Thursday looks like rain and Friday looks beautiful, so we'll get the gambler in.
We get 1 time trial Saturday and straight into Race of Champions, so at least we get 1 shot.

Re: Head wind vs tail wind-ET impact
 

X2, the layout of the track at topeka makes it like a wind tunnel if you got a headwind, lost 2 tenths when the wind picked up, the da only changed a couple hundred ft. gsa612

Re: Head wind vs tail wind-ET impact
 

http://www.altronicsinc.com/media/pr...maire-line.jpg



PerformAIRE systems offer wind sensors and wind prediction/correction. You can select between several car type and also features an adjustable "effect" (drag coefficient) to fine tune your wind correction.

Re: Head wind vs tail wind-ET impact
 

Clark, when you think about headwind vs tailwind they should be treated the same when predicting ET. Once the car has any reasonable speed it only "feels" a headwind. Example: if you were sitting on the hood of a car and there was a 20 mph tailwind you would "feel" zero wind when the car goes 20 mph. At 120 mph the the car only "feels" a 100 mph headwind (you would have already fallen off). Conversly with a 20 mph headwind the car "feels" a 140 mph headwind at 120 mph. The car can accelerate more at a 100 mph headwind than at a 140 mph headwind thereby changing the ET and mph .
Each car has its own amount of aero drag and is dependant on the trap speed. It is easy to get the change in ET vs wind speed over a reasonable range, just measure it (at the same DA). The number for my car is 0.0063 sec/ mph of wind and it works for BOTH head and tailwind.

The big problem is to know what the wind speed is where most of the drag occurs i.e. the last half of the race. Very seldom is the wind steady enough so it is the same at the starting line as at the finish AND very seldom is it directly in line with the track!

Good luck. Vic