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Discussion Starter · #1 ·
So I know this has been covered in general but I want to know what you guys think about my specific case.

So I jacked my rear end up and spun the tire watching the driveshaft (used the yellow mark that was already there).

In one revolution of the tire the driveshaft turned 3 full revolutions and was only 6 inches of tire from 4 full revolutions. to clarify I went 6 inches past my mark on the tire to get 4 revolutions of the driveshaft.

Ummm I have 20inch rims and the tire I was spinning is a 245/35

I'm not too good with math anymore but what I'm thinking is that if the circumference of the tire is about 70" and the circumference of the driveshaft is about 15" that somehow means that I have 3.73's damn it I hate this thinking ****!!! lol! I was totally trying to work it out while typing but didn't work. leavin it for laughs.

so anyways 70"/3.73 is 18.76" and 76"/4 is 19" (thats my wheel circumference + the extra 6inches) then they are 3.73's right???

God Im confusing the hell out of myself! someone please tell me if I'm going about this the wrong way or just confirm whether or not I have 3.73's...
 

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it doesn't matter how big your tires/rim are - you just need to make one full revolution of the rear tires. Any/all points along the radius of the wheel will end at one full rev. at the exact same time.

might wanna grab something to make your own marks nice and clear, and try again. Mark the starting point, and ending point of the driveshaft (and obviously making sure to completely rotate the wheel 1 full turn.)

..at that point you can probably 'eye ball' it close enough to get a good guess,,or get fancy and bust out some simple geometry,,,circumference,,,distance between marks,,a little division,,etc etc etc.. :)
 

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Discussion Starter · #4 ·
Well the marks were plenty clear. I even rigged a pointer that actually touched the sidewall as to be more precise. So I know my measurements are correct it's just how to use those measurements that is confusing me. But upon further mental investigation while I may not be able to specify 3.73 vs 3.60 vs 3.90 I know they aren't 3.27 and damn it that's good enough for me!! Lol. My dad is an engineer so I'll ask him he'll be able to narrow it down.
 

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you have 3.73s
 

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your shaft spins 3 turns and 73% of another turn.
 

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Discussion Starter · #7 ·
it doesn't matter how big your tires/rim are - you just need to make one full revolution of the rear tires. Any/all points along the radius of the wheel will end at one full rev. at the exact same time.

might wanna grab something to make your own marks nice and clear, and try again. Mark the starting point, and ending point of the driveshaft (and obviously making sure to completely rotate the wheel 1 full turn.)

..at that point you can probably 'eye ball' it close enough to get a good guess,,or get fancy and bust out some simple geometry,,,circumference,,,distance between marks,,a little division,,etc etc etc.. :)

Not to be a dick but did you read my whole post or just the title?
 

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If you have 3.73 gears and you turn you rear tire over 1 full revolution your driveshaft should turn approximately 3 and 3/4 revolutions.

3.50's 3 and 1/2 revolutions...

4.10's 4 and 1/10 revolution...

3.90's 3 and 9/10 revolutions...

etc...

hope this helps.
 

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Discussion Starter · #9 ·
your shaft spins 3 turns and 73% of another turn.

Well like I said before I'm not positive on the percentage of the 4th revolution. While it's most likely that I have 3.73's I may have 3.90's that's what I can't figure out. I talked to my dad though and he gave me a super easy way to calculate it. While I was going on about converting measurements and all that fancy **** all we need to do is measure the circumference of the driveshaft and divide that into the final rotation distance. Yay for engineers!
 

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Well like I said before I'm not positive on the percentage of the 4th revolution. While it's most likely that I have 3.73's I may have 3.90's that's what I can't figure out. I talked to my dad though and he gave me a super easy way to calculate it. While I was going on about converting measurements and all that fancy **** all we need to do is measure the circumference of the driveshaft and divide that into the final rotation distance. Yay for engineers!
ya, no ****! lol. there isnt anything complicated involved. measure, divide.
 

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glad u figured it out
 

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,,or get fancy and bust out some simple geometry,,,circumference,,,distance between marks,,a little division,,etc etc etc.. :)
I read your whole post, and I was not being a dick,,,,just trying to help you out,,, i kinda gave away the secret formula there if you didn't notice......
 

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Discussion Starter · #13 ·
I read your whole post, and I was not being a dick,,,,just trying to help you out,,, i kinda gave away the secret formula there if you didn't notice......
Appreciated. just read as if you saw that I included the wheel size, and disregarded the rest.

but ofcourse with the wonder of the internet and no ability to convey tone or body language leaves my pessimistic mind to put its own "attitude" on other people's posts. so my apologies.
 

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it's all good - i didn't mean to sound like a dick if i did.

,,,'they' say communication is 20% verbal, 80% body language,,,,or I heard that somewhere.

I am jealous of your better gearing :) - pretty sure I gots da 3.27 out back :(
 

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Discussion Starter · #16 ·
Zen- its all good, **** happens and then you either put toilet paper in your underwear or go commando.

GT- couldn't tell you, I'm not driving it.

I will be getting it back on blocks tomorrow hopefully so I'll know then. I've decided I will take 2 pieces of string, measure the D/S, and then tape one end of string to the D/S and do one full wheel revolution and measure the string.

Thanks for all the ASSistance in the matter!
 

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Discussion Starter · #17 ·
Oh and now I'm on the hunt for a 3.27 geared GT so I can feel the difference. The only other GT I've ever driven was my friends Gutted S/C'd 98 so I have nothing to compare my cars performance too in the tush department.
 

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Discussion Starter · #20 ·
I'm manual, and I will let you know some rpm's by speed as soon as the COPS that BOB practically gifted to me come in.

I was thinking about it though and wouldn't my speedo need to be calibrated for the gears and wheels to have any kind of good info?
 
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