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Auto Talk => General Automotive => Topic started by: giant_mtb on May 20, 2009, 12:28:36 PM

Title: % grade. What does it really mean?
Post by: giant_mtb on May 20, 2009, 12:28:36 PM
(http://www.worldofstock.com/slides/MES2737.jpg)

Nothing major, just wondering why they decided to use a percentage system instead of, well, angles for the denotation of hill angles.  I may be wrong, but it is my understanding that they took some maximum angle and divided it into 100 pieces, giving the percentile system.  For example, the "max" angle may be vertical, 90 degrees (100%).  A 7 degree decline would be a ~7.8% grade.

Is that how it works?  If it is, what angle are they dividing into pieces?  Why didn't they just use degrees?
:huh: :nutty: :huh:
Title: Re: % grade. What does it really mean?
Post by: sportyaccordy on May 20, 2009, 12:39:20 PM
I thought it was just amount of height per unit length of width traveled in percentage form. Meaning a 45 degree angle would be 100% grade, etc... it's probably not that though.
Title: Re: % grade. What does it really mean?
Post by: giant_mtb on May 20, 2009, 12:40:57 PM
Perhaps. :huh: Makes more sense than what I thought it was. :mask:
Title: Re: % grade. What does it really mean?
Post by: SVT_Power on May 20, 2009, 12:48:04 PM
Quote from: sportyaccordy on May 20, 2009, 12:39:20 PM
I thought it was just amount of height per unit length of width traveled in percentage form. Meaning a 45 degree angle would be 100% grade, etc... it's probably not that though.

that's what i thought it was  :mask:
Title: Re: % grade. What does it really mean?
Post by: Tave on May 20, 2009, 01:00:39 PM
C'mon peoples. This is easy.

Grade is Slope. Slope is rise over run. Percent Grade = Slope * 100

Quote from: sportyaccordy on May 20, 2009, 12:39:20 PM
I thought it was just amount of height per unit length of width traveled in percentage form. Meaning a 45 degree angle would be 100% grade, etc... it's probably not that though.

Exactly.
Title: Re: % grade. What does it really mean?
Post by: GoCougs on May 20, 2009, 01:04:15 PM
Yes - Sporty has it correct - 8% grade = 8 ft vertical change for 100 ft of horizontal travel.

To really impress the girls, divide % grade by 100 to get the tangent of the angle, and then take arc tangent to get the angle itself; arc tan (.08) = 5.08 degrees.
Title: Re: % grade. What does it really mean?
Post by: sportyaccordy on May 20, 2009, 01:55:53 PM
Quote from: GoCougs on May 20, 2009, 01:04:15 PM
Yes - Sporty has it correct - 8% grade = 8 ft vertical change for 100 ft of horizontal travel.

To really impress the girls, divide % grade by 100 to get the tangent of the angle, and then take arc tangent to get the angle itself; arc tan (.08) = 5.08 degrees.
Totally unnecessary
Title: Re: % grade. What does it really mean?
Post by: S204STi on May 20, 2009, 01:59:03 PM
Quote from: GoCougs on May 20, 2009, 01:04:15 PM
Yes - Sporty has it correct - 8% grade = 8 ft vertical change for 100 ft of horizontal travel.

To really impress the girls, divide % grade by 100 to get the tangent of the angle, and then take arc tangent to get the angle itself; arc tan (.08) = 5.08 degrees.

Do you carry a scientific calculator to impress the gals? :lol:
Title: Re: % grade. What does it really mean?
Post by: bing_oh on May 20, 2009, 02:55:36 PM
Quote from: R-inge on May 20, 2009, 01:59:03 PM
Do you carry a scientific calculator to impress the gals? :lol:

They do so love to fondle his pocket protector.
Title: Re: % grade. What does it really mean?
Post by: S204STi on May 20, 2009, 04:29:54 PM
Quote from: bing_oh on May 20, 2009, 02:55:36 PM
They do so love to fondle his pocket protector.

:lol:

Seriously though, I'm just jealous of his math skills.  I am worthless with math any more complex than the basics like adding, subtracting, multiplying and dividing.  Geometry got be bad back then, and it still gets me now.
Title: Re: % grade. What does it really mean?
Post by: MX793 on May 20, 2009, 04:31:50 PM
Quote from: R-inge on May 20, 2009, 01:59:03 PM
Do you carry a scientific calculator to impress the gals? :lol:

Scientific calculator?  You're not going to impress anybody with one of those trinkets.  Now a graphing calculator, that'll get you some respect.
Title: Re: % grade. What does it really mean?
Post by: Laconian on May 20, 2009, 04:36:04 PM
The honeys are all up ons over my RPN.
Title: Re: % grade. What does it really mean?
Post by: S204STi on May 20, 2009, 04:41:44 PM
Quote from: MX793 on May 20, 2009, 04:31:50 PM
Scientific calculator?  You're not going to impress anybody with one of those trinkets.  Now a graphing calculator, that'll get you some respect.

:lol:
Title: Re: % grade. What does it really mean?
Post by: GoCougs on May 20, 2009, 05:02:35 PM
Quote from: bing_oh on May 20, 2009, 02:55:36 PM
They do so love to fondle his pocket protector.

You mean, fondle The Canon:

(http://img36.imageshack.us/img36/5308/dscf0645y.jpg) (http://img36.imageshack.us/my.php?image=dscf0645y.jpg)

And no, Sporty, it wasn't unnecessary; "grade" is the tangent of the angle, a function without which one cannot find the angle, which is exactly what the OP was trying to do.
Title: Re: % grade. What does it really mean?
Post by: 93JC on May 20, 2009, 06:18:24 PM
Not just 'a Canon'? The Canon?

Oooooh...
Title: Re: % grade. What does it really mean?
Post by: AutobahnSHO on May 20, 2009, 07:11:28 PM
lawl

I sold my TI-85 years ago-

(http://www.datamath.org/Graphing/Images/TI-85_ZOOM.jpg)
Title: Re: % grade. What does it really mean?
Post by: sportyaccordy on May 20, 2009, 07:12:52 PM
Cougs I was just joking.
Title: Re: % grade. What does it really mean?
Post by: GoCougs on May 20, 2009, 08:59:33 PM
Quote from: sportyaccordy on May 20, 2009, 07:12:52 PM
Cougs I was just joking.

Okay, I just thought maybe you were still hating me...
Title: Re: % grade. What does it really mean?
Post by: VTEC_Inside on May 21, 2009, 11:47:02 AM
Quote from: AutobahnSHO on May 20, 2009, 07:11:28 PM
lawl

I sold my TI-85 years ago-

(http://www.datamath.org/Graphing/Images/TI-85_ZOOM.jpg)

Still have mine... I put Tetris on mine back in College. :)
Title: Re: % grade. What does it really mean?
Post by: sportyaccordy on May 21, 2009, 11:57:14 AM
Quote from: GoCougs on May 20, 2009, 08:59:33 PM
Okay, I just thought maybe you were still hating me...
That hasn't changed.
Title: Re: % grade. What does it really mean?
Post by: BimmerM3 on May 21, 2009, 03:28:19 PM
I'm still rockin' the TI-83 Plus.
Title: Re: % grade. What does it really mean?
Post by: Eye of the Tiger on May 21, 2009, 03:31:22 PM
I have The Pirate's TI-89. :praise:
But I don't know how to use half of the shit :frown:
Title: Re: % grade. What does it really mean?
Post by: 93JC on May 21, 2009, 03:58:26 PM
Quote from: BimmerM3 on May 21, 2009, 03:28:19 PM
I'm still rockin' the TI-83 Plus.

Mine's kicking around somewhere.
Title: Re: % grade. What does it really mean?
Post by: SVT_Power on May 21, 2009, 04:18:58 PM
Quote from: NACar on May 21, 2009, 03:31:22 PM
I have The Pirate's TI-89. :praise:
But I don't know how to use half of the shit :frown:

damn you
Title: Re: % grade. What does it really mean?
Post by: Eye of the Tiger on May 21, 2009, 04:23:00 PM
Quote from: M_power on May 21, 2009, 04:18:58 PM
damn you

I'll sell it to you for $199.99.99.
Title: Re: % grade. What does it really mean?
Post by: MX793 on May 21, 2009, 04:31:35 PM
Quote from: BimmerM3 on May 21, 2009, 03:28:19 PM
I'm still rockin' the TI-83 Plus.

I've got an original TI-83 from before the "plus" model ever came out.  I remember when the Plus version came out and everybody was like "ooh, look, it's the Plus version so it's better" only to find out that all of the games for the regular TI-83 like pong and tetris didn't work on it.
Title: Re: % grade. What does it really mean?
Post by: r0tor on May 22, 2009, 06:19:04 AM
Quote from: R-inge on May 20, 2009, 01:59:03 PM
Do you carry a scientific calculator to impress the gals? :lol:

To really impress the girls, you tell them the tangent or slope of the incline is equal to the coefficient of friction needed to stay on the incline  :winkguy:
Title: Re: % grade. What does it really mean?
Post by: bing_oh on May 22, 2009, 07:29:42 AM
Quote from: R-inge on May 20, 2009, 04:29:54 PM
:lol:

Seriously though, I'm just jealous of his math skills.  I am worthless with math any more complex than the basics like adding, subtracting, multiplying and dividing.  Geometry got be bad back then, and it still gets me now.

I'm right there with ya. My sister's a high school math tecaher, teaching things like advanced algebra and trig. Me, I can't figure out the tip at a restaurant without the tip calculator on my cell phone. :huh:
Title: Re: % grade. What does it really mean?
Post by: 93JC on May 22, 2009, 07:56:58 AM
Quote from: r0tor on May 22, 2009, 06:19:04 AM
To really impress the girls, you tell them the tangent or slope of the incline is equal to the coefficient of friction needed to stay on the incline  :winkguy:

Have you tried the old "I wish I were a derivative so I could lie tangent to your curves" pickup line?
Title: Re: % grade. What does it really mean?
Post by: hotrodalex on May 22, 2009, 01:16:30 PM
Quote from: bing_oh on May 22, 2009, 07:29:42 AM
I'm right there with ya. My sister's a high school math tecaher, teaching things like advanced algebra and trig. Me, I can't figure out the tip at a restaurant without the tip calculator on my cell phone. :huh:

I just take 10% and add a bit to it.
Title: Re: % grade. What does it really mean?
Post by: MX793 on May 22, 2009, 01:18:52 PM
Quote from: 93JC on May 22, 2009, 07:56:58 AM
Have you tried the old "I wish I were a derivative so I could lie tangent to your curves" pickup line?

Shouldn't it be "I wish I were your derivative..."?

You could also say "I wish you were my integral so I could lie tangent to your curves." 
Title: Re: % grade. What does it really mean?
Post by: 93JC on May 22, 2009, 06:36:33 PM
The fact that you're nitpicking this shit speaks volumes, you know.
Title: Re: % grade. What does it really mean?
Post by: SVT_Power on May 22, 2009, 08:35:17 PM
:lol: