yep.... another gear thread..but a diff. Q

Discussion in 'SN95 4.6L Mustang Tech' started by Bill9000, Jun 5, 2005.

  1. Ive got a question, after doing some "paying attention" going by those "your speed is" signs the police have, and having someone witha brand new car clock me, I've discovered that my speedo is 10-12 mph slow. And further into that, I drove a 140 mile trip over the weekend, (according to road signs) and my trip odometer read 90 miles.

    the car has what I believe to be the stock size tires... 245/45/ZR17, so that shouldnt be throwing off the gears, Im wondering if someone before me had replaced the ring&pinion?

    Now, accurte speedby someone in a brand new car clocking me, when my stang's going exactly 80 MPH in 5th gear, it's right at 2,000 rpm... does anyone have any idea what gear ratio that sounds like? I know it seems really high! I tried those "calculators" andthat didnt really tell me anything.

    thanks in advance for the help
  2. There is a way to determine the gear ration by jacking up the rear wheels and noting how many times the driveshaft rotates when you rotate the rear wheel one time.
  3. if you are really doing 80mph @ 2000rpm, that sounds like 2.73's. dunno why the speedo is off.
  4. 2.73 sounds abut right, wouldnt the speedo be off, if say the car came with 3.55's and someone put 2.73's in and did'nt re-calibratethe speedo?????
  5. Yes. Since you have a 97 GT, your stock speedo gear might be burning out as well. Thats something else it could be. I'm also going to let you know that some of those Police speed scanners that say, "Your speed is _" aren't always totally accurate. They are off on mine sometimes and I know my speedo is accurate due to gear calculator turn out accoridngly to speed and rpms. Not to mention my car has a custom SCT tune for my gears and setup.
  6. I was concerned with my 3000GT that my speedo wasn't right, so my brother gave me a quick and easy way to check:

    1) Go on the highway
    2) Drive for exactly one minute at 60mph
    3) See if you have gone for less, more, or a mile.

    Obviously, if you have gone less than a mile your speedo is too high, etc. Just a thought to check.
  7. do remeber that most speedo's unless using GPS are going to be +- 10% and it will vary depending on what speed you are going.

    A survey a few years back found that most mechanical speedo's read to fast below 50mph (e.g. your speed would say 30mph but you would really being going 33-35mph)

    And over 50mph it would read under and progressivly getting worse the faster you go (e.g. 80mph on the speedo was in fact 72mph)

  8. Oh oh Mitsubishi. :rlaugh: At first I was like "your 3000 GT??? That must be a typo!"

    Yeah I'm a retard :owned: