Calculate the Cd of your car - Instructable

[Nerds laugh at me]

Imagine a nerd that is interested in 'nerdy' things but lacks entellagents.

That's me.

I look at all of those things that you have to calculate and just give up.

I don't know the newtonian resistance, the rolling resistance, or any of the other variables that you need.
What I would be able to furnish would be the weight of the vehicle with me in it, the frontal area, the approximate barometric pressure around the area, the altittude above sea level and a video giving exact time to speed data after shifting into neutral using my automatic.......... but that's about it.

What can I do with this data since I lack the other data ?

[usedgeo]

This is not the answer to your question but it is almost relevant. Marks Standard Handbook stated that the rule of thumb for trains was that a 100 lb force could accelerate 1 ton of train 1 mph/sec. This figure was including the angular acceleration of the wheels.

You can do a coast down test of your car and figure the force acting on the car. Then again I have not read the whole thread. Maybe you are already that far along.

[trebuchet03]

Originally Posted by usedgeo

This is not the answer to your question but it is almost relevant. Marks Standard Handbook stated that the rule of thumb for trains was that a 100 lb force could accelerate 1 ton of train 1 mph/sec. This figure was including the angular acceleration of the wheels.

That's a really goofy unit... At least, something I'm very not used to and required an extra thought step to comprehend (and now can see how it's useful) So I checked the number (assuming no wheel slip and no wheel-mass losses) just for fun...

1 ton ~ 62slug
100/62= 1.61 ft/s*s --> 5806 ft/hr*s --> 1.0968 mile/hr*s --> 1.0968 mph/s

Something tells me the momentum in a train bogie is greater than the momentum in car wheels Angular momentum for a wheel will be the wheel's moment of inertia * angular velocity. This will vary quite a bit depending on wheel size, material and shape. So, if you want to include angular momentum -- first find it - then add to 100 in that poorly described equation above (the easy way to do unit conversion is to type 1.61 ft/s^2 to mph/s into google ).

[MetroMPG]

Originally Posted by Nerds laugh at me

Imagine a nerd that is interested in 'nerdy' I don't know the newtonian resistance, the rolling resistance, or any of the other variables that you need.

What I would be able to furnish would be the weight of the vehicle with me in it, the frontal area, the approximate barometric pressure around the area, the altittude above sea level and a video giving exact time to speed data after shifting into neutral using my automatic.......... but that's about it.

What can I do with this data since I lack the other data ?

Have you looked at the Excel file available in the Instructable?

You already have all the info you need to supply:

- best estimate of your vehicle's frontal area in m^2.
- your vehicle's mass including occupants in kg.

You don't have to provide rolling resistance; it's one of the figures that the test & spreadsheet help you to determine.

[Nerds laugh at me]

Originally Posted by MetroMPG

Have you looked at the Excel file available in the Instructable?

You already have all the info you need to supply:

- best estimate of your vehicle's frontal area in m^2.
- your vehicle's mass including occupants in kg.

You don't have to provide rolling resistance; it's one of the figures that the test & spreadsheet help you to determine.

I'll have to get Excel to read it. ( I deleted it from my computer thinking I'd never use it. )
This weekend I plan to go to my folks and do a few aeo mods.
You know how vacations go though ( "the best laid plans ..." )

[iwilltry]

... to everyone. I'm glad you liked my instructable. Thanks, MetroMPG for posting the link here. Sorry I didn't notice earlier. I had just signed up to gassavers and then got distracted by other projects.
-iwilltry

[Gearshredder]

wow, yes very belated, by 2 months
welcome to the site

[GasSavers_Bruce]

Originally Posted by trebuchet03

Something tells me the momentum in a train bogie is greater than the momentum in car wheels

True, but 1 ton of train isn't very much -- probably a small fraction of a boxcar. The percentage of gross mass that is rotating mass is probably comparable.