who enjoys math...gotta good one for ya

HazMat404 · May 8, 2004

ok. well i have a stock t-5. got a 4.10 out back with that white lil speedo gear for the 3.73's. now i know for a fact im rackin up more miles than im going but im just tryiin to figure out how miles im going to each actual mile. im sure i could figure it out sooner but id rather have a smart person figure it out. thanx

1slow95 · May 8, 2004

Can't really help with the 4.10's, but with my 3.73's and the 3.55 speedo gear my odometer reads 2.1 miles after 2 miles, according to the mile markers on the interstate.

HazMat404 · May 8, 2004

if my tripometer was workin id be in good shape but that gave out a lil while ago. just the regular odometer

94GTLaserRC · May 8, 2004

There is no GOOD "math" way to do that.

BEST WAY: Get on a hwy with mile markers. Keep a note of the "tenths" your odo moves for 1 mile on the marker....THAT's just an estimate. Now mark how much your odo moves when you have travelled 5 miles on the hwy....see how those numbers compare. Do the same with 10 miles....The more miles you travel according to the hwy markers, the more accurate your reading will be.. If you have travelled EXACTLY 11 miles on the odo but 10 by the markers, you are 10% over.... OR you are putting 10% less miles on the car than the odo reads..

ANOTHER test: find someone with as new and reliable a car as possible, preferrably with a digital speedo. Have them drive EXACTLY at 60 MPH and see what your speedo says.

Conversely, YOU DRIVE at 60MPH and see what THEIR speed o says. That % is also a good amount of error correction..

I tried it..it works...saved me a speeding ticket once (My speedo is off by about 10%,)

GOOD LUCK
RC

maypo59 · May 8, 2004

The VERY best way is to get your GPS out, (or your friends), and just go cruise steady speed and see what you have. Worked for me...

HazMat404 · May 8, 2004

im an idiot....ive known for awhile that my car is about 10% off because im 1mph for ever 1mph i go. that means its chaulking up .1 miles more for every mile i go. thanx for bringing me into the light

BlackVert · May 8, 2004

the odometer works by counting the number of times the driveshaft rotates and multiplying that what it thinks is the circumference of the rear wheels.

ok. the stock gear ratio is 3.27 right? that means that every time the rear wheels make 1 rotation, the driveshaft goes around 3.27 times. also lets assume your wheels are 245/45/17, which is about 25.5" circumference, so to make the math easy, lets round it to 26".

so if you have 3.27 gears and your wheel circumference is 26", then: 26" / 3.27 = 7.95" traveled each time the driveshaft makes one rotation. now one mile is 5280' * 12" = 63360", so 63360 / 7.95 = 7969.81 rotations of the driveshaft is one mile.

so every 7970 rotations of the drive shaft gets you one mile on the odometer.

if you change gears to 4.10 and leave the wheels the same, you get:

26" / 4.10 = 6.34" per rotation, 63360" / 6.34" = 9993.69 rotations per mile.

so every 9993 DS rotations you go a mile in real life, but the odometer thinks you went 1.25 miles. (9993 / 7970 = 1.25)

if you make the wheels bigger, then the odometer is closer to correct because the rotations per mile is closer to 7970.

i hope this helps.

hey hazmat: are those ported stock heads thumpers? are you happy with them?

95snoozer · May 8, 2004

actually its easy math....

(miles you have on the car - mileage when the gears went in)/ 1.0992 + the milage when the gears went in. = actual milage

95snoozer · May 8, 2004

also to find what MPH you are at divide what your odometr says by .91

your reading ~ actual
70 ~ 64
77 ~ 70
61 ~ 55

BlackVert · May 9, 2004

95snoozer said:
actually its easy math....

(miles you have on the car - mileage when the gears went in)/ 1.0992 + the milage when the gears went in. = actual milage

95snoozer said:
also to find what MPH you are at divide what your odometr says by .91

your reading ~ actual
70 ~ 64
77 ~ 70
61 ~ 55

just curious, where do the numbers 1.0992 and .91 come from?

jmuva44 · May 9, 2004

I'm curious too...and how does the MPH you are going depend on the odometer reading???

94GTLaserRC · May 9, 2004

jmuva44 said:
I'm curious too...and how does the MPH you are going depend on the odometer reading???

MPH does not "depend" on the odometer, but both are affected by the gear calibration.

EG: when they put my 3.73's in I had to go back the next week b/c they didnt have the gear. SO for 1 week I drove without it. The speedometer showed I was doing 60 when I was going like 40.

I did 0-60 in 3.5 seconds

My gear now has slighly "over corrected" , so not IM going faster than what my gauge says, not slower.

RC

jmuva44 · May 9, 2004

I know they are both derived from the same factors and both are effected by a gear swap, but you cannot look at what your odometer reads at any ONE point in time and divide it by anything to find out what your MPH is. Now obviously you can count how many times the odometer rolls over per unit time. This will eventually give you Miles/Hr after a few calculations but even this would only be an average speed and not an instantaeous speed.

But simply dividing the odometer reading by .91 isnt going to give you anything as far as I can see. In his defense however, I think he meant the speedometer and not the odometer. And the .91 is a number he probably got from finding out that his speedo was off by 9%

I have an Abbott box now sitting on my tv that I need to install for my car. My last car after i had the 4.10s installed the speedo was off by like 35 MPH and the Odometer was rolling through crazy fast. So yeah, I know the bad effects of not accurately fixing the computer readings.

95snoozer · May 9, 2004

my numbers are correct

BlackVert · May 9, 2004

95snoozer said:
my numbers are correct

95snoozer said:
actually its easy math....

(miles you have on the car - mileage when the gears went in)/ 1.0992 + the milage when the gears went in. = actual milage

95snoozer said:
also to find what MPH you are at divide what your odometr says by .91

your reading ~ actual
70 ~ 64
77 ~ 70
61 ~ 55

i'm not accusing you of anything, i'm just just curious where the numbers 1.0992 and .91 come from.

95snoozer · May 9, 2004

his car is calibrated for 3.73s

its the ratio between 4.10s and 3.73s

.91 is actually, .9095.....

BlackVert · May 9, 2004

95snoozer said:
his car is calibrated for 3.73s

its the ratio between 4.10s and 3.73s

of course!

95snoozer · May 9, 2004

sorry I was studying and didnt want to make a long drawn out post. just gave the formula and didnt want to argue with that guy who was arguing because he doesnt understand the simple math.

of course I could be drunk and totally incorrect

who enjoys math...gotta good one for ya

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