10% = 5%

[freebeard]

I think you are the number one source of misinformation on this subforum.

And I try so hard.

[JulianEdgar]

Originally Posted by freebeard

And I try so hard.

Nah. Quite honestly, in over 35 years of engaging with car enthusiasts - and over 20 years on web discussion groups, including moderating them - I have never seen a poster of so much misinformation as Aerohead.

Here in Australia - with our apparently much more blunt approach - he would have been sent on his way many years ago. But perhaps the information he used to post was more accurate?

All I know is that now is it much safer to assume his posted information is wrong (or misleading) than it is right.

I am sure he is a really nice guy, and it's genuinely great to see someone so enthusiastic about modifying car aero for so long, but boy, does he ever post a lot of rubbish here.

[ME_Andy]

The info he posted this time seems 100% reliable. Perhaps you've developed a strong aversion to Aerohead, and it is hard for you to believe it?

Got to suppress that knee jerk reaction.

[deluxx]

This bickering is killing me and this website, can you two just **** and get it over with already?

[freebeard]

Kills the signal/noise ratio, but the website gets (an estimated) half it's traffic from these two individuals.

[JulianEdgar]

Originally Posted by deluxx

This bickering is killing me and this website, can you two just **** and get it over with already?

At least we're talking about aerodynamics. What contribution have you made?

(Oh yes, except for sending an abusive PM?)

[JulianEdgar]

Originally Posted by ME_Andy

The info he posted this time seems 100% reliable. Perhaps you've developed a strong aversion to Aerohead, and it is hard for you to believe it?

Got to suppress that knee jerk reaction.

I am happy to discuss the relationship between aerodynamic drag changes and fuel economy changes - and they don't appear to match either Aerohead's rule of thumb or the ARC one (for which we don't know what 'highway' speed is).

Before you can even start to describe such a relationship accurately, you need to know:

1. The starting Cd (a car with a Cd of 0.35 will have a higher aerodynamic contribution to overall resistance than a car with a Cd of 0.25).

2. If at a constant speed, what that speed is (aero drag goes up at the square of the speed; rolling resistance does not), so if the term 'highway' is used, we need to know what highway speed is.

3. If it's in a drive cycle test, what is that drive cycle?

The nearest I can find to a rule of thumb for modern cars is this, from the Bosch Automotive Handbook (8th ed):

On an average production vehicle, 10 per cent reductions in weight, drag and rolling resistance result in fuel consumption reductions of roughly 6 per cent, 3 per cent and 2 per cent, respectively.

Note the 'roughly'.

Motor Vehicle Fuel Economy (Stone) describes a drag coefficient reduction from 0.45 to 0.35 (22 per cent) giving the following constant speed changes:

50 km/h - 6.7 per cent
80 km/h - 15.2 per cent
120 km/h - 20 per cent
160 km/h - 22.5 per cent

Aerodynamic of Road Vehicles (5th edition) does not even try to use any rule of thumb, suggesting it is too closely tied to speed and vehicle type (ie it depends on what percentage contribution to overall resistance is made up of aero drag - my points (1) and (2) above.

Road Vehicle Aerodynamic Drag (Barnard) gives no rule of thumb.

People love simplistic rules of thumb, but the real world of car engineering is nothing like that - in any area: suspension, engine management... or aerodynamics.

Without extensive qualifications and caveats, the title of the thread (10% = 5%) is misleading rubbish.

[freebeard]

....if the term 'highway' is used, we need to know what highway speed is.

Road Surface Influence on Tire Rolling Resistance
https://www.astm.org/DIGITAL_LIBRARY.../STP23377S.htm
On a wide variety of surface types and conditions on dry paved roads, the coefficient of rolling resistance ranges between 0.013 and 0.021. In terms of fuel consumption, this can be converted into 9% relative influence of the road surface.

I presume this is 9% of the 2%.

[JulianEdgar]

Originally Posted by freebeard

I presume this is 9% of the 2%.

Obviously different road surfaces have different rolling resistances, but in all cases on paved roads, the rolling resistance variation with different surfaces is a very small proportional change of a small proportion - ie pretty well irrelevant to this discussion.

So a different thread perhaps? "The impact of various types of paved surfaces on rolling resistance."

[freebeard]

It's all yours. It's all I can do today to shuffle three parked cars. The air compressor is running right now.

I was just trying to support your thesis. There's also curved vs straight, Van Duzer Corridor vs Kansas in the Spring.

H. B. Van Duzer Forest State Scenic Corridor
H. B. Van Duzer Forest State Scenic Corridor is a scenic driving route along Route 18 in Lincoln, Tillamook, and Polk counties in the U.S. state of Oregon that passes through a forested corridor. The Van Duzer Corridor stretches from northwestern Polk County to Lincoln City, passing through the Northern Oregon Coast Range.

Scenic? You can't see the forest for all the trees!