Tool for visualizing aero vs rolling resistance - Fuelly Forums

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Old 03-18-2006, 07:33 AM   #1
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Tool for visualizing aero vs rolling resistance

I have developed a spreadsheet that shows the contribution of aero drag and tire rolling resistance versus speed. I used the formula in the last post to this thread:

http://www.gassavers.org/forum_topic...reduction.html

Just enter your values (numbers in blue) and it will calculate aero and RR and also will calculate a theoretical MPG. Of course there may be an error in the calcs, but the MPG numbers seem to make sense. One caveat is the ICE efficiency. I set it up to show the same efficiency at all speeds which is not an accurate representation of reality. you can enter a separate efficiency for each speed to be more accurate, although it is really just a guess.

Anyway the point is not to calculate MPG, but rather to see how your CD and tire RR contribute to total drag at a given speed. You can simulate weight reduction, change in frontal area, CD and tire RR. Maybe it can help figure out the best place to spend your time/money.

Now if only I could figure out how to host a spreadsheet. Here is a jpg anyway...
http://img99.imageshack.us/img99/398...adsheet3ls.jpg
http://img206.imageshack.us/img206/4598/aerovsrr6yp.jpg
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Old 03-18-2006, 10:00 AM   #2
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Email it to me and I'll host

Email it to me and I'll host it or talk to Matt and he can prolly host it also. Looks very much on the cool side, can't wait to play with it, thanks a bunch,
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Old 03-18-2006, 10:45 AM   #3
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What I like about this is

What I like about this is that it shows target areas based on what you want to accomplish. For example, if you primarily drive around town, (under 35mph) you are better off getting LRR tires. If you drive over 35mph on a regular basis, aerodynamic modifications will yield the best results.
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Old 03-18-2006, 11:27 AM   #4
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SVOBoy is hosting it here.

SVOBoy is hosting it here. I'm sure that it can be improved upon.

http://www.geocities.com/frontsidesk8er/delsolaero.xls

A few more bits of info.

The CRR number is tire RR plus other mechanical losses. The 0.008 value is a good guess for LRR tires at 40 PSI based on the thread I referred to earlier. The CD and FA should be available on google for your car. The default fuel value is for summer fuel, 114,500 BTU converted to Watt hours. Winter fuel is 112,500 BTU and E85 is 80,000 BTU. Just google the BTU to kWh conversion to get the appropriate number to plug in.

The MPG figures are just based on the fuel energy content times the efficiency of the engine. The fuel value is well known but the engine efficiency changes based on RPM I would guess. The engine efficiency should be the highest and fairly flat between the torque and HP peaks. Based on my 55 MPH testing last week, a 26% efficiency with winter fuel gives me 57 MPG at 55 MPH, which is about what I got in my testing. The efficiency number sounds high, which might be an indication that the CD is lower than .378 or that the highway hypermiling technique, 50 - 60 MPH, accel down hill, bleed off up hill, effectively increases the engine efficiency.

As a comparison, I plugged in the weight, CD and FA for SVOBoy's Torino Rex and got 70 MPG at 55 MPH, 13 MPG better than with the Del Sol.

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Old 03-18-2006, 11:48 AM   #5
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awesome spreadsheet -

awesome spreadsheet - thanks. this is crying out to be made into a web page form. javascript anyone?

too bad it doesn't include a temperature variable which would show its effect on drag numbers (both aero and tire/mechanical).
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Old 03-18-2006, 11:57 AM   #6
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Quote:awesome spreadsheet -

Quote:
awesome spreadsheet - thanks. this is crying out to be made into a web page form. javascript anyone?
I'll try my hand with some java later.

And dan, sorry about the whole my car being a more efficient base thing, I'm sure I'll find a way to make it get bad gas mileage still.
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Old 03-18-2006, 12:00 PM   #7
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i'll make this up into a

i'll fire this into a coldfusion page later on today too. but right now i'm going outside to play with my forklift while it's still light out.

(no motorectomies today - we broke the jack handle! but there's other stuff i can still take apart...)
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Old 03-18-2006, 12:26 PM   #8
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Re: awesome spreadsheet -

Quote:
Originally Posted by MetroMPG
awesome spreadsheet - thanks. this is crying out to be made into a web page form. javascript anyone?

too bad it doesn't include a temperature variable which would show its effect on drag numbers (both aero and tire/mechanical).
Well actually with a little work we can. The RHO value has to do with the density of air at sealevel. Some googling should give us different numbers to plug in as they relate to temp and altitude. No time right now, maybe I will try later.
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Old 03-18-2006, 01:39 PM   #9
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If you make this into a web

If you make this into a web based spreadsheet I'll happily host it here. I've been thinking of adding a section of the site for "online tools." This would be perfect for such an area.
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Old 03-18-2006, 07:33 PM   #10
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http://metrompg.com/tool-aero-rr.htm

i left out (in the output) some of the fields that are constants. still need to add some form field / table column descriptions, credits & links.

feedback ?
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