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Trying to calculate my gear ratio

Discussion in 'Performance and Tuning' started by Stout890, Oct 11, 2011.

  1. Oct 11, 2011 at 4:20 PM
    #1
    Stout890

    Stout890 [OP] Well-Known Member

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    Let me first say im pretty sure i do not have stock gears. My spedo is off by +20

    Ok so I just jacked up my rear and did the wheel rotation trick now I'm getting confused on how to do the math

    For 10 tire rotations I got approx 26.45 I put shaft rotations..

    Now if I divide 26.45 into 10 I get 2.545..now that isn't right-so 10 divided In to 26.45 gets me..0.378...

    Am I doing something g wrong?

    Now I looked up another way of doing it that only requires 2 shaft rotations and that you take the percentage of the wheel rotation and divide by 1, getting it's reciprocal than times by 4

    So I do that and get prettymuch exactly .75 or 3/4 wheel rotation for exactly 1 shaft rotation. I do that math and get 3

    So do I have 2.54 gears or 3.0?
    Neither sounds right at all

    What are the symptoms of lower gearing?
     
  2. Oct 11, 2011 at 4:23 PM
    #2
    Highland Logan

    Highland Logan UBIQUE

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  3. Oct 11, 2011 at 4:24 PM
    #3
    whippersnapper02

    whippersnapper02 Well-Known Member

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    Turn wheels 360 degrees once and count the number of times the driveshaft turns. The best way to figure out what you have is to break down the diff.
     
  4. Oct 11, 2011 at 4:33 PM
    #4
    Stout890

    Stout890 [OP] Well-Known Member

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    yeah thats too much for what im doing...

    this is a good idea ill report back
     
  5. Oct 11, 2011 at 4:41 PM
    #5
    Stout890

    Stout890 [OP] Well-Known Member

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    Just got like 2.6 axle rotations for one wheel rotation.

    This is blowing me away who puts 2.6's In a Tacoma?

    No wonder the truck drives like shit
    Also I have 31" tires on here and it has a huge body lift with suspension lift and looks like it used to run 36"+ tires
     
  6. Oct 11, 2011 at 4:43 PM
    #6
    whippersnapper02

    whippersnapper02 Well-Known Member

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    Well if both wheels aren't turning equally then you will lose some driveshaft rotation through the spider gears. I suggest pulling the 3rd to see what the stamp on the ring gear says.

    Posted via :sandwich:
     
  7. Oct 11, 2011 at 5:10 PM
    #7
    Stout890

    Stout890 [OP] Well-Known Member

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    What exactly is the 3rd? I see people referencing the whole axle as the third.
    I honestly don't want to take this thing apart. I'm about to pick up a whole other axle tomorrow morning with a e-locker. I was just basically wondering what the difference is going to be between the two by finding out the gears in what I'm driving with now.

    Anyone know what gears came in a 03 v6 taco prerunner with an e-locker? That what this new axle came from
     
  8. Oct 11, 2011 at 5:11 PM
    #8
    Stout890

    Stout890 [OP] Well-Known Member

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    Would it help if I only jack up 1 weel?
     
  9. Oct 11, 2011 at 5:23 PM
    #9
    luk8272

    luk8272 Poodoo

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    My 02 prerunner tacoma came with 3.91 gears and 31" tall tires, stock.

    Your best bet is lift both rear tires off the ground. Mark the tire and driveshaft, spin the tires 1 rotation, count the turns the driveshaft makes and that is it. No math involved. You'll have to guestimate the decimal, meaning half a turn is .5, or 3/4 turn is .75 you get the picture.

    Your tire size won't make a difference here because you are trying to figure out the actual ratio, your wheel size will play a role when you want to know what correction to make to your speedo. Then you'll need to know the stock gear and tire to multiply them to find out what your new ratio is.

    The third they are reffering to is when you remove your diff cover, its the chunk inside. You would need to count the teeth on the ring gear and the pinion and multiply them together to get the ratio. Or like said above it could be stamped on it somewhere.
     
  10. Oct 11, 2011 at 5:31 PM
    #10
    Stout890

    Stout890 [OP] Well-Known Member

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    Yeah just did it again with 1 wheel of the ground ad still got 2.6 rotations and 26.40 for 10 tire rotations.
     
  11. Oct 11, 2011 at 5:41 PM
    #11
    luk8272

    luk8272 Poodoo

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    That seems like an odd Gearing to me but so did my 3.91 gears in a 2wd. Now you just have to multiply your stock tire height to your stock ratio then divide that by your new tire height and that will be your actual driving ratio.
     
  12. Oct 11, 2011 at 6:26 PM
    #12
    Stout890

    Stout890 [OP] Well-Known Member

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    yes vary odd gearing...iv never even heard of 2.54 but how can it be wrong?? i mean i did it 2 ways and am getting the same...

    26.45 divided into 10 tire rotations=2.54

    and 1 wheel rotation gave me about 2.6 input shaft rotations

    im mean i knew it wasnt normal gearing, i have threads going about how my truck drives funny, feels bogged down and has no power. could this be the reason? my spedo is off +20mph

    what are the symptoms of low gearing, does it cause the spedo to read high or low? and why would someone wanna do that?
     
  13. Oct 11, 2011 at 6:39 PM
    #13
    luk8272

    luk8272 Poodoo

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    The ratio you have is considered high (numerically low) a low ratio is a numerically higher number. 4.10 gears are low.

    Your gears would indeed make your truck feel under powered. Harder and slower to accelerate but give you lower RPM's at higher speeds.

    I don't know why anyone would want to do that to your truck.

    Being off by 20mph is incredible!
    Here is a sight that will give you what your tire is off by and your mph
    http://www.miata.net/garage/tirecalc.html
    You can check that with a GPS. I'm not doubting you but I can't help but think something is off, or your truck is just strange.

    Try this site out http://www.eldemoniorojo.com/calculator.htm
    Go to the race calculator then scroll down it will give you your ratio based off of your tire diameter and RPMs. This will allow you to double check our answers, which I am sure are right but just hard to believe.
     
  14. Oct 11, 2011 at 8:16 PM
    #14
    Stout890

    Stout890 [OP] Well-Known Member

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    nice great find, thanks for the el demon rojo site im gonna go on a drive tonight and check my rpms at speed

    and yes the reason i know my speed is off +20 is because i used gps...when im doing 70 im at 90 and i also feel like my tranny has bad shift points..it doesn't hold gears long at all it always shifts making me stomp the pedal more to keep accelerating
     
  15. Oct 11, 2011 at 8:25 PM
    #15
    bjmoose

    bjmoose Bullwinkle J. Moose

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    Guys! He's only spinning one wheel! The other one remains stationary.

    So you have roughly 2.6 x 2 or a 5.29 diff. :)
     
  16. Oct 11, 2011 at 10:20 PM
    #16
    luk8272

    luk8272 Poodoo

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    Pretty sure he doesn't have 5.29 gears becase he would not be complaining about being under powered, nor would he be able to do 70+mph without his engine screaming for more gears.
     
  17. Oct 11, 2011 at 10:24 PM
    #17
    whippersnapper02

    whippersnapper02 Well-Known Member

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    Time to bust out the tools and break it down.:D
     
  18. Oct 11, 2011 at 10:27 PM
    #18
    luk8272

    luk8272 Poodoo

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    I wouldn't waste my time with the tools until I was ready to change the guts.
     
  19. Oct 12, 2011 at 12:24 AM
    #19
    Stout890

    Stout890 [OP] Well-Known Member

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    no i did it both ways, i did it with both off the ground first than thought to try doing it with only one off the ground and got the exact same results

    this is what im sayin...from what i know doing it this way is close enough and i cant imagine it being wrong when so many other people do it this way and get almost exactly the correct gear ratio..plus im picking up an entire new axle tomorrow morning with an e locker off of an 03 prerunner v6 so im just gonna swap the whole axle...hope it has 4:30's in it lol the guy doesnt know whats in it either ha ha:eek:
     
  20. Oct 12, 2011 at 6:44 AM
    #20
    bjmoose

    bjmoose Bullwinkle J. Moose

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    Speedo reading 20mph FASTER than you are going....

    Automatic transmission shift points confused all to hell, shifting too early unless you stomp it...

    2.6 rotations of the driveshaft for one turn of ONE wheel...

    History of huge body lift and huge oversize tires...

    No man, what you've got right now is 5.29 gears. I'd bet you a sammich on it.
     
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