Online tool: shows aerodynamic drag, rolling resistance, power required & est. MPG
 

Aerodynamic & rolling resistance calculator - EcoModder.com

Back in the day, krousdb made a spreadsheet to calculate aero & rolling resistance forces against his del Sol, their respective power requirements, and effect on fuel consumption at various speeds.

I've ported/expanded the spreadsheet into an online tool which asks you to enter or accept default values for...

- vehicle weight
- Crr (coefficient of rolling resistance - .008 represents a low rolling resistance tire on a smooth surface - see Wikipedia for other sample values)
- Cd
- Frontal Area
- Fuel energy density (in Watt hours / US gallon)
- Engine efficiency
- Air density (rho)

... and it spits out a table showing resistance force values, estimated power requirements and fuel consumption across a range of speeds.

It's online at EM here: Aerodynamic & rolling resistance calculator - EcoModder.com

It's not perfect (e.g. engine efficiency changes with load in real life, but remains fixed at the value you supply for all speeds in the calculations for fuel consumption).

Discussion, questions, suggestions welcome.

Thought of another flaw in the calculator: CRR entered is supposed to be for the tires' resistance, but rolling resistance involves some drivetrain resistance as well (bearings, possible brake drag, CV/U joints, differential).

Determining your actual Crr experimentally and entering it would be best. See:

http://ecomodder.com/forum/showthrea...stance-62.html

and/or http://ecomodder.com/forum/showthrea...mula-3737.html

Oh boy... I'm gonna be playing with this quite a bit!

Added km/h and L/100 km to the output.

I plan to make the inputs more flexible as well (SI/Metric & old units).

Ah! Found one. Point of reference:

IWillTry did just that with his '92 Metro with 145/r12 (I think) tires inflated to 45 psi: Crr = .0106

See his instructable: Measure the drag coefficient of your car

bearings and such
 

Darin,the SAE considers bearing losses to be so low,they are basically ignored with respect to RR.-------------------------------

Power-train efficiency is a consideration,once road-load power is determined,to calculate engine power required to overcome loads.-----------------------

I've been using 95 % efficiency for manual-transmission vehicles,as this is a value ascertained by the SAE in early research on pickups and big trucks.Basically,once you've arrived at aero and RR horsepower necessary at the drive wheels,you divide that value by 0.95,and it spits-out Bhp at the flywheel.Multiplying that value by BSFC yields pounds of fuel,and dividing that figure by 6.1626 pounds/gallon( for gasoline ),it spits out gallons,then divided by distance for mpg.Sorry for the US Standards!--------------

Sorry,I do not have any data for automatic transmission vehicles.-----------------------

Thanks for creating the calculation tool as I'm sure it will pay dividends to anyone who uses it. Way cool!!!!!!!!!!!

A suggestion for version 2.0 ...

- Tie in all the data values needed for the calculator in our vehicle entries in the Garage - Provide a link from one's vehicles to their own power-at-speed charts.

I'd imagine that gas/diesel vehicles will be somewhat easy to integrate ... you may have to work a little to figure out the same for HPV's and Electrics and Electric-Petro Hybrids.

The only big issue I could see would be the metric / imperial units confusion ... Some of the values already stored for cars are imperial (e.g. Frontal area), and the chart-script asks for the same in metric units.

And of course, thank you both, krousdb and MetroMPG for doing the legwork to get this up on the site! Takes me back to my highschool days, reading Korff's book borrowed from the library, and making these same charts on quad-paper for cars I wanted to design and build. :)

Do you know if the same thinking applies to losses in the CV/universal joints, potential brake drag, and differential/transaxle resistance - strictly for the purposes of calculating RR?

Good idea. Currently you can lump that into the "engine efficiency" figure in the calculator, if you're working backward from a known MPG at a certain speed.

Still some refinement to be done, for sure. Thanks for the feedback Phil.

ChrstphrR - we're on the same wavelength! Those garage fields were put there from the beginning specifically thinking of this tool and integrating the two.

The conversions shouldn't be too hard to do.

Good point abot the hybrids/EVs, etc. For now, we'll focus on ICE vehicles since they're in the majority, and most in need of this kind of info to help people improve their efficiency.

Diesel energy density figures for the drop-down.
 

Some energy-density figures for diesel fuel (since I'm an oil-burner... and want a nice simple drop down menu option too!)

http://www.biodiesel.org/pdf_files/f...al_Oct2005.pdf
HTML-ized version of:
Energy Content

Cites that:

• No. 2 Diesel has an average energy density of: 129,500 Btu/gallon
• B100 (100% Biodiesel) has an energy density of 118 296 Btu/gallon
• B20 (20% Bio blend) has an average energy density of 127 259 Btu/gallon
• Diesel stocks can vary in energy density by 15% between different suppliers.
• Winter blends of Diesel fuel from a single supplier tend to be 15% lower than summer diesel blends.
• This latter figure would mean the average energy density of Winter No. 2 Diesel is 110 075 Btu/gallon

Diesel values added to the select list.

In searching around, I've noticed there are varying values posted in various places for both diesel and gasoline energy content. Not sure how to decide which to rely on.

same thinking
 

Darin,the SAE likes to limit RR to the tires only,as an independent variable. When official testing is done,brake drag is checked for,and eliminated before the testing cycle(so it isn't included in the methodology,although we definitely need to be aware of it). With respect to bearings,ring and pinion,C-V joints,split-driveshaft center support bearing perch,pin-bearings in U-joints,dust seals,transmission/transaxle/transfer-case,oil,grease hydrodynamic losses,these are all contained within Mu,the mechanical -efficiency value of the driveline.

Hoerner uses 90%(1950),CAR and DRIVER have used as low as 80% when discussing their Maxda RX-7 at Bonneville.SAE says 95% for 1/2-ton pickup.

We could use some current good numbers for these values.CVTs are supposed to have horrible efficiencies which cancel out much of their benefit.

Perhaps GOOGLE can provide some up-to-date and accurate quanta for us to use.Anyone lurking could jump on this one and help out.

I'll check back should I have any revelations.Thanks for all you do,Phil.

Great tool!

does it make since to add a parasitic load input?
alternator, A/C and other loads would be relatively flat compared to speed

That's an interesting idea. Most people probably don't know how much power watts their power steering pump, for example, requires from the engine though. But for people who experimentally determine their electrical overhead, it could prove useful...

Anyway, I've added the drivetrain efficiency field.

And I prettied up the entry form a little bit and have started adding notes/explanations for the various fields/values.

determining ball park parasitic loads is not too hard with instrumentation

I just pulled the serpentine and watched the scan gauge
(I really love that thing)

~.1 GPH difference without any belt (from 900-3000 RPM pretty flat)
~.1 GPH difference A/C on and off (idle)
~.12 GPH difference steering wheel still to loaded against the stops (idle)
~.01 GPH difference head lights on and off (maybe)

I think the power steering pump should watch it's back
it is not worth .12 gph to me :)

for the hyper-miler with manual everything & EOC this may be insignificant
for my truck (and probably the average vehicle) this is significant
during the test my unloaded consumption was ~.46 GPH
parasitic load can be 70% of my idle load and 10-20% of my cruise load :eek:

a parasitic input might help folks determine what their "conveniences" cost

just a thought

Any suggestions on specifically how you'd like to see that variable worked in to the existing tool? What units?

I'm up for anything as long as there is a field for a flat load fudge factor :)
GPH, like I used is probably not appropriate

watts or Horsepower is probably more acceptable
- what do you think?

misc. data for spreadsheet
 

Darin,I know you'd probably like to finalize your estimator so I'll throw this last stuff at you,then leave you alone.When concrete brought up the mention of accessories,I thought I'd posted some things for that on the general ecomodding sticky,but I didn't,and was probably thinking of maxmpg. Anyway,I have a few things from SAE,they are dated now,however they may be considered a worst-case scenario.Also,they're for a "medium-size" car,about 3,500-lbs:

- Air conditioning 1.5mpg loss urban,1.0 mpg loss at constant 70 mph.
- Alternator 0.9 mpg loss urban, 0.5 mpg loss at 70 mph.
- Fan (cooling) 0.1 mpg loss urban,0.5 mpg loss at 70.
- Power steering 0.1 mpg urban, 0.4 loss at 70.
- Automatic transmission 5-15.5% loss urban.

++++++++++++++++++++++++++++

From a CAR and DRIVER experiment at 60-mph with a Ford Escort:

- 3rd instead of 4th-gear cruising 9.0 mpg loss.
- Rooftop carrier 6.0 mpg loss.
- Air conditioning 3.0 mpg loss.
- Windows down 1.0 mpg loss.
- Heavy load 1.0 mpg.
- Underinflated tires 0.5 mpg loss.
- Overinflated tires (no change).

***************************

From Road and Track: Geo Metro:

- calm wind 56.6 mpg
- 25-mph headwind 44 mpg
- 20 mph in 3rd gear 84.1 mpg
- Burn/glide/bumpstart-repeat,from 20 mph down to 8 mph = 116.6 mpg.
- Honda VX doing hyper-miling= 104.8mpg.(tests were conducted at U.C.Davis,with Professor Dr.Andrew Frank).
- The little university research car with 3.8-ft-sq frontal area and Cd 0.14 got 3,300-mpg doing hyper-mileing.

Last thought,and this is about Diesels.A diesel Rabbit had a 35mpg advantage over a gasoline Chevette at 30-mph.At 80-mph,that advantage had shrunk to 9mpg.At 80 mph(legal in West Texas and elsewhere now) my T-100 gets 3-mpg better than the Rabbit diesel.It looks like the high inertia loads of the early diesels really cost them at elevated velocities.Like to think modern TDis are much more efficient!

What is your base idle gph BTW?

about .46 GPH during testing
fully warm it would be a little less
but I did not want a hot engine while I was removing the belt on the water pump

the test was just rough order of magnitude work
I was discussing steering losses with a friend at work and he suggested a quick test
it was actually one of the easier and most fun tests I have run

Off topic end.
 

Thanks. That's about what I get with my Previa 2.4L when warmed up. I would have loved to do those load tests before and after but I only got my mpguino lately.

Thanks for the input, guys. I imagine this is going to be a work in progress for a while.

I chipped away at the basics a little more this evening: you can now enter weight & A in either Metric or Imperial units. Added a few more explanations & links to the notes as well.

I've made a new page "EcoModder tools". The aero/rr/power/mpg calculator is now linked there as well as a units conversion tool (for mpg --> L/100 km etc.)

You can access it via the "Tools" link in the navigation at the top of every page.

Expect the toolbox to grow & evolve to include more stuff.

I likey. Now they just need icons/pics.

Functionality first, then fancyness.

If this spreadsheet is valid, I must be doing a bang-up job of improving my aerodynamics and improving engine efficiency by slowing down engine RPM.

Last summer I went to Nashville, TN and back. Slightly cool weather - roughly 70 degrees F. Out and back to same fuel pump so delta y = 0.

I had the full aero treatment: "fastback" bed fairing, air dam, and side skirts.

The trip was entirely an Interstate run and set the cruise on 1700 RPM (70 MPH).

Thev truck weighs 7000 lb. Figure Crr of 0.011 for worn 235-85x16 E-Rated tires pumped up to 100 psi Estimate frontal area at 41 sq. ft. 95% drivetrain efficiency for an overdrive manual. Summer No. 2 diesel.

I got a documented 28.1 MPG over that trip of 600 miles. Playing the variables to duplicate that performance says my Cd is 0.30 and my engine efficiency is 35%.

Am I that good? I figure a open-bed pickup to have a Cd of 0.45 and a diesel engine to have 33% efficency.

Got your PM - haven't forgotten about this.

I'll work it in this weekend, probably as watts to start. (Can always do conversions to other units, if people want.)

Darin,
Thanks
looking forward to it!


Big Dave,
from what you describe and some of Aeroheads data
I bet you are really doing that well

those are great results & it seems you are in the ball park on your numbers
of course it is hard to argue the particulars without a test facility
but even matching +/- a few percent in each entry is good work

Perhaps you could also utilize this online tool for gear calculations and adjustments. That is for those of us who are interested in swapping transmissions and gears.

Gear Calculation Tool

I am so excited with all these numbers! God, I am such a nerd!

I thought I should point you towards an existing spreadsheet that is the culmination of years of research (I believe it is someones PhD thesis) that is availible on the web.

Just search for Pamvec on google, it should turn up an excel file. It is extremely customizeable for many things that you have already included but also for things like: various drivetrains (hybrids, electric etc), driving models, can specify design goals, or just input known variants. When I used it to model my current car it nailed its MPG rating and I used it to model hypothetical cars.

FWIW here are links to:

the actual spread sheet in xls format
an html view of the spread sheet.
a pdf of the actual thesis (281 pages)

That's coming too.

Blue Bomber: that's the mother of all spreadsheets!

online tool
 

When things slow down,and I can "camp-out" on the computer,I'd like to take a long look at this program.It looks like a terrific prediction tool and could save countless man-lives of computational time.An advanced thank you,and big thumbs-up for sharing this!

It does look very impressive.

Blue Bomber Man :thumbup::thumbup: is the one to be thanked, hadn't heard of it until I read his post. Simply googling Pamvec (as he suggested) produces the first two links on the very first hit.

The thesis was harder to find.

point you
 

Blue Bomber Man,TestDrive straightened me out on the "source" of the spreadsheet post and I wanted to throw a two-fisted thumbs-up your way.I'll have to park my regular life and spend some time with it.'looks like a awesome prediction tool.Thank you big-time!

concrete,
I have a '98 s10 4cyl manual (without factory A/C), and the power steering and the mechanical fan were not watching their backs. Not sure if this has been discussed here yet, It is pretty simple to use a short belt to run just the alternator and waterpump. Not sure how this would work with A/C, you'd probably have to quit that bad habit at the same time too...

Remove the fan, but put the fan pulley back on for use as an idler pulley. grind away a little bit under the thermostat housing for clearance to the belt. In the direction of belt travel: Belt comes off the crank, around the idler and alternator as before. then over the top of the fan pulley (this is where you needed the clearance), originally went under the fan pulley. And back down to the crank, the water pump is driven from the back side of the belt between the fan pulley and the crank. The water pump is still driven in the normal rotation, the fan pulley turns opposite so you probably want the mech fan removed.

What's it worth, I don't know, it's directionally correct, I've moved on...

I did put an electric fan on, but have never used it because I didn't finish wiring in a thermostatic switch, and it is not required the way I drive. With normal practices discussed here, (turn off engine while coasting or stopped). I should have not bothered putting in the fan. Anyone want an elec fan from a v6 camaro, with a couple aluminum angle pieces to fit in a 4cyl s10? 20$ ?

The steering is obviously not great for parking lots, but really it's much better otherwise, the steering does not change assist as you start & stop the engine.
Dale

Thanks for finding the links, interestingly enough I tried that day and for some reason was getting blocked by the host website and could not access them to verify that I had the right links. When I started to design a car a few months I came across that and it allowed me to start specing out what I thought I would need for batteries and motor. It is very useful if you want to estimate the effects of like removing mirrors, low rr tires, etc .

Excellent calculator that returns values close to my own:
http://home.hiwaay.net/~bzwilson/pri..._MPG_Rev_B.jpgThe blue line is what the calculator appears to be generating. My gray line includes the fixed vehicle overhead, the 'heart beat' cost of having the vehicle on. Thus at 0 mph the vehicle achieves 0 MPG.

The only element missing from the calculator is vehicle overhead, what it costs if the vehicle is turned on and not moving (aka., idling overhead.) What this does is identify the maximum range speed and expected MPG. The calculator is fairly accurate at speed ranges where the vehicle overhead is much less than the rolling and aerodynamic drag.

Performance models are great because they give an idea of what the vehicle should achieve. To a greater or lessor extent, I can evaluate changes with the model and verify them on the road. But it is very important to go on the road and plot the mph vs MPG. The gaps between the model and field measurements can identify "sweet spots" as well as 'black holes' and leads to insights about our vehicle systems.

Bob Wilson

Thanks for reminding me, Bob. Concrete had asked for this a while back and I just added a field for "Parasitic overhead" which you can optionally fill in with a value in Watts.

Oh, and another drawback to the tool (maybe obvious, but worth saying) is that it doesn't account for gearing changes affecting engine load/efficiency.

Obviously it was meant more for looking at the "top gear" speed range.