Drag vs speed curves available for modern cars
Drag vs speed curves available for modern cars
(OP)
Due to this gas thing i would like very much to see a curve of the total rolling resistance vs speed for my two cars. Rav4 and Sienna.
I originally set out to measure these myself by finding a lone flat stretch of highway on a windless day and run er up to 75 mph and record the coast down. Fit this to a curve and differentiate and get a rolling resistance proportionality.
I searched Google but had no luck locating this type of data. I don't want the values calculated using ideal formulas and drag coefficients, as the real thing is bound to be better. Does anyone know of a site with data like this.??
Thanks
I originally set out to measure these myself by finding a lone flat stretch of highway on a windless day and run er up to 75 mph and record the coast down. Fit this to a curve and differentiate and get a rolling resistance proportionality.
I searched Google but had no luck locating this type of data. I don't want the values calculated using ideal formulas and drag coefficients, as the real thing is bound to be better. Does anyone know of a site with data like this.??
Thanks





RE: Drag vs speed curves available for modern cars
So you may need to measure the drag by yourself by performing several measurements in both directions and taking the average.
One possibility could be to tow your vehicle with a very long rope, and measure the force by a suitable scale/force sensor (don't try this on public road, or on road with tight corners :).
btw; why topics related to fuel consumption mysteriously dissappear from the forum after short perioid of time?
RE: Drag vs speed curves available for modern cars
A) you have to be many car lengths behind a towing vehicle before you will get accurate figures.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Drag vs speed curves available for modern cars
J2263
ABCD
Buckley
- Steve
RE: Drag vs speed curves available for modern cars
Bob
RE: Drag vs speed curves available for modern cars
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Drag vs speed curves available for modern cars
Power consumption due to rolling resistance is linear at any legal speeds
Power consumption due to aerodynamic drag is a cubic function of speed at the majority of speeds cars travel (at VERY low speeds it is a squared function)
RE: Drag vs speed curves available for modern cars
In the late 90's just after I retired, I did a little test, just for my own amusement. I had been driving my Model A everyday as is my habit. On the way home I go down a long hill and I always used 'Oklahoma overdrive' with the A only reaching around 30 to 35 mph. One day I was in the wife's Lincoln and tried the same thing. Wow. Speed was in the 60's. This led to the one day I was bored to tears and decided on 'The Big Test' ;o)
Standing start at top of hill and coast to bottom, braking before stop sign. Certainly not scientific, it was never intended to be.
1930 stock Model A Ford Std. Coupe---35mph
1937 stock Buick Roadmaster---45mph
1948 Norton ES-2---25mph
2001 Lincoln LS---55+ not max because of need to brake early.
I ran out of interest at this point and did not do my Dodge truck or the motor home. Now I'm curious about them, but the hill, while it's still there, is in a housing tract.
Rod
RE: Drag vs speed curves available for modern cars
RE: Drag vs speed curves available for modern cars
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Drag vs speed curves available for modern cars
I will check the Car and Driver source
I think i might just do some testing of my own though. Maybe build a little setup to record the data automatically to a laptop.
RE: Drag vs speed curves available for modern cars
This will give you a good indicator of the all resistances not just the wind resistance.
Make sure trye pressure are to spec and brakes are not dragging.
RE: Drag vs speed curves available for modern cars
RE: Drag vs speed curves available for modern cars
http://www.landracing.com/formula/coastdown.htm
Cheers
I don't know anything but the people that do.
RE: Drag vs speed curves available for modern cars
A downhill coast comparison will work for vehicles of a similar size and type but won't work comparing a motorcycle and a Lincoln, for example.------"
The original posting was to compare 2 similar vehicles, hence the suggestion of a downhill comparison.
RE: Drag vs speed curves available for modern cars
RE: Drag vs speed curves available for modern cars
If not then you are right, they must be in the certification somewhere.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Drag vs speed curves available for modern cars
So this in both directions preferable from the same starting and end point.
I think it should be possible to calculate out the road terrain given a run in both directions.
cibachrome I also think so.
By the way i spent the last tank of gas in my sienna hyper-miling (driving for efficiency) and got 27 mpg for my efforts.
This compared to 23 normally.
RE: Drag vs speed curves available for modern cars
Rod
RE: Drag vs speed curves available for modern cars
Still, a coast-dwon test is pretty easily done with no more than a stopwatch if you have fairly good resolution on the speedometer. Coast from e.g. 45mph to 35 mph, use that as the data point for 30 mph, etc.
Don't forget to make an allowance for wheel inertias.
RE: Drag vs speed curves available for modern cars
http://www.epa.gov/otaq/crttst.htm
Included in the downloadable data files are target A, B and C coefficients generated by the auto companies from coast-down data that are used for setting up chassis dynamometer road-load. You will be looking for the "target coefficients", not the setpoints.
Road force can then be calculated from the following:
F_r = A + Bv + Cv^2
where the coefficients have units of lbf, lbf/mph and lbf/mph^2, respectively, and v is velocity in mph.
Also note that you can look up the manufacturers emissions test results over different drive cycles within the same data set. It's all public information.
RE: Drag vs speed curves available for modern cars
How is the best way to read the text file downloaded from the EPA web site? The text files look like they should be in a spread sheet so you can tell what header the number matches.
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: Drag vs speed curves available for modern cars
...it's probably a CSV-file (Comma-Separated-Variables).
RE: Drag vs speed curves available for modern cars
I downloaded one of the files, saved it with a .CSV file extension instead of .TXT (after looking at it with an editor), and just clicked on the file to start my spreadsheet program and load it.
The field seperator was actually TAB rather than COMMA.
RE: Drag vs speed curves available for modern cars
Can anyone explain to me the two sets of road load coefficients labeled 'Target' and 'Set'? What units are they in and which should I use in a simulation?
The links on the EPA site to the actual test procedures are broken or empty, although I can find the drive cycle data OK. Can someone please point me to a download (or purchase) of the test procedures?
Regards, Ian
RE: Drag vs speed curves available for modern cars
Ed Danzer
www.danzcoinc.com
www.dehyds.com