Looking for drag effect vs mph chart

[mikeyjd]

I know I've seen one or more, but I've come up empty so far in my searches. I'm looking for a chart that shows % of aerodynamic drag effect at increasing speed. Thanks.

[JRMichler]

Right here on this site: Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com. Results are in a chart, every 5 MPH from 5 MPH to 200 MPH. If you want a graph, just cut and paste into a spreadsheet.

[aerohead]

Originally Posted by mikeyjd

I know I've seen one or more, but I've come up empty so far in my searches. I'm looking for a chart that shows % of aerodynamic drag effect at increasing speed. Thanks.

Hucho presents a Drag vs Top Speed table in his book.
It's for a particular range for frontal area and inertial class,but he makes a generalized relationship.
The most important criteria for us modders is that the unmodified vehicles top speed actually reflect full net power,just above the rated power rpm.
American cars are 'governed' with their gearing and won't actually achieve their actual power-limited/drag-limited top end.
European cars appear to be geared to actually take advantage of all available horsepower.
Once you're properly geared and have a bona-fide terminal velocity at rated power + 100-200 rpm,then any 30% drag reduction will net a 10% increase in top speed under standard conditions.
This ratio reflects standard passenger car radial tire technology performance
circa 1986.

[Diesel_Dave]

Not sure if this is what you're looking for, but I posted this a while ago. It's from Cummins and for a semi truck, but you get the idea as the same principles apply.

[gone-ot]

...industry "rule-of-thumb" is that HP(aero) = HP(road) at 55 mph...roughly.

...where (road) is tires & engine, etc.

[mikeyjd]

Originally Posted by Diesel_Dave

Not sure if this is what you're looking for, but I posted this a while ago. It's from Cummins and for a semi truck, but you get the idea as the same principles apply.

This is similar to what I was looking for. The one I was thinking of was posted by Darin I think, and it displayed mph on a grid with aero % increasing incrementally. Something like 20mph = 30% and 40mph = 50% . It was a nice looking graph and I just wanted to have it on hand for reference.

[Diesel_Dave]

Incidently the chart also highlights the stupidity of the diesel pickup "power wars" where pickup owners think they need 400+ hp. A 80,000 lb semi truck only needs 264 hp to cruise down a level highway at 65 mph.

[ChazInMT]

Originally Posted by Diesel_Dave

Incidently the chart also highlights the stupidity of the diesel pickup "power wars" where pickup owners think they need 400+ hp. A 80,000 lb semi truck only needs 264 hp to cruise down a level highway at 65 mph.

One thing to keep in mind here though is the 400+ HP is used for a very short time, 250+ hp output from most regular pick-up or car engines for any appreciable length of time would result in a melt down, speeding ticket, destroyed property, and/or death.

[aerohead]

Originally Posted by mikeyjd

This is similar to what I was looking for. The one I was thinking of was posted by Darin I think, and it displayed mph on a grid with aero % increasing incrementally. Something like 20mph = 30% and 40mph = 50% . It was a nice looking graph and I just wanted to have it on hand for reference.

*The drag FORCE varies as the square of the velocity:If you double your velocity,you're hitting twice as much air,twice as hard.
The Power required to overcome the drag force varies as the cube of the velocity:When you double your velocity,you're hitting twice as much air,twice as hard,twice as often.
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When you know the 'starting point' for your car you can throw in a new drag coefficient,holding everything else constant and see how it impacts the road load horsepower for any given velocity.
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Top speed is achieved when power-train losses,rolling resistance,and aero drag equal the brake horsepower of the engine at whatever conditions you're operating at.
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The mechanical efficiency of the power-train is essentially constant at full power so you can just discount the brake horsepower by that fractional multiplier,then any drag reduction allows a speed increase which balances the new aero load and new(higher) R-R value at the higher velocity at that discounted horsepower.