speedometer ques.

[Joe'sSHO]

I was recently reading a post and noticed a couple people say that @ 4k in fourth you should be going 80. Now I've always suspected my spedometer was off, but this confirms it. At 4k the spedo was only reading 70mph. Sometimes it would go up to 73 but no higher. It's even worse under heavy acceleration (If I redline it though 3rd and a quarter of the way into 4th it will only register 65) I took it to 6k in fourth and only got about 93. I know it sould be more like 115-120 right? How can I calibrate my spedometer to work correctly? Anyone else have this problem and was able to resolve it w/o buying a new cable? Could it be a loose connection w/ the cable somwhere. Any imput as always is greatly appreciated. thumb

 

[NotSoSlowSHO]

Its not the cable thats the problem.

And I would suspect the tachometer as reading incorrectly before suspecting the speedo. wink

 

[Joe'sSHO]

I'm pretty sure it's not the tach b/c I can hear the secondaries open right before it hits 4k. Also, that wouldn't explain why the speedo said I was only going 93@6k in foruth. Unless 6k is 93mph. shrug Felt a lot faster thats for sure.BTW did you get my PM about the gauges?

<small>[ November 18, 2003, 11:08 PM: Message edited by: Joe'sSHO ]</small>

 

[Joe'sSHO]

Just realized how stupid that last part of my post was. If the tach was reading incorrectly it wouldn't have been 6k. headbang Oh well. Is there anyway I can check the accuracy of the tach. That's gonna mess with my shift points too if that is indeed the case.

 

[SHOYourYama]

Doesn't atmospheric pressure rule in the equation? Living about a mile higher than sealevel, I experience a decrease in MPH per RPM.
Here is the specs from shotimes.com...

RPM Max Speed (@ 7000 RPM):
1st 44
2nd 67
3rd 101
4th 137
5th 143 @ 5350

Tire size also alter the gear to MPH ratio. These specs are for the OEM 215/60-16 tire/rim size, non modified n/a SHO.

Note: The stock tach is not very acurate..

 

[AutoSHO]

SHOYourYama:
Doesn't atmospheric pressure rule in the equation?

No, it doesnt. Just because there is less atmospheric pressure, it does not change the fact that your engine is spinning at a certain speed. It decreases power but not speed in gears.

Additionally, tire size will affect actual speed, but not indicated speed. Unless you change something between the engine and transmission (or the speedometer gear) the engine will be at about 4k rpms in 4th gear at about 80 mph indicated speed. First gear will end at 44 mph (indicated) on the rev limiter.

<small>[ November 19, 2003, 01:26 AM: Message edited by: AutoSHO ]</small>

 

[sdpatt]

If you look closely at the OEM speedmeter, you will notice several pairs of small white dots near the speed gradations. Those define the allowed range of indicated speed for a set road speed and define the requirements for the accuracy of the speedometer. Those markings are for stock wheels and tires. They will not necessarily be accurate for different size tires. See the Tire Calculator to determine the effect on speedometer accuracy with different size tires.

On the other hand, the tachometer is just a big voltmeter. It can be affected by extremes of temperature and under the hood, those can be found. My speedometer can read quite high in very cold temperatures (below 20F).

<small>[ November 19, 2003, 04:45 PM: Message edited by: sdpatt ]</small>

 

[Joe'sSHO]

101 @ redline in 3rd!!!!!!!I'm only registering about 75!! Something is seriously F***** up with this thing. And I am running the stock basket weaves with stock tires. And the weather up here is about 45 degrees (neither extreme heat nor cold) On an unrelated note, my car seems to run extremely cold regardless of how much it is driven or the outside temp. The highest I've seen it go is just touching the L in normal. Could this gauge be messed up too? Does it have anying to do with how the other gauges are working? Just a question. Thanks.

 

[rangerj]

Joe'sSHO,

Here are a couple of thoughts for you.

If you are racing you should be driving by the tachometer, not the speedometer. You can have your tach checked against a tach in professional diagnostic equiptment at a garage or dealership, or get a tach from a speed shop like Summit Racing.

On most State and Interstate highways there are white marks in quarter mile increments for a mile. These are used to time your speed from the air. At sixty miles per hour it will take one minute to go one mile. Distance = Rate X Time or Distance divided by the time = the rate. (Is that right Scott?)

Take a lovely assistant for a ride and have her time your elapsed time for one mile with a stop watch. Hold a steady speed of 60 for the mile, and compare your speedometer speed to the time it takes, that is the calculated speed. This will tell you approximately how far off your spedometer is.

Look in your yellow pages for a shop that does spedometer calibrations. The service is usually about a $100.

Check at a Ford dealership and see if a calibrated speedometer was made for your model year for the "Police Package" Taurus. With the advent of accurate and dependable radar, and lasar, speed detectors I do not think police bother with spedometer calibration any more, but you could look into it. Ask a friendly Highway Patrolman (is that an oxymoron)!

Lastly, if you modified your SHO with larger diameter wheels and larger tires you will have changed the speedometer calibration, but it should not be more than 5 or 6 mph different.

You could check at a Ford dealer's parts department to see if ford made different Speedometer gears to adjust for different sized wheels. Say for example a Taurus could be ordered with 14 inch, 15 inch, or 16 inch wheels. The gear should be different if everything else is the same.

Your speedometer cable may need lubricated or the speedometer head may need to be changed. If you have a speed "sensor" for an electronic speedometer, not mechanical, the sensor may be faulty or have a poor connection.
Just some thoughts! rangerj

 

[Joe'sSHO]

Thanks a lot rangerj. I always do drive by the tach (I'm used to it b/c my mustang didn't have a speedometer only a tach) but I have to drive 7 hrs on the highway back to CT and don't want to get pulled over doing 100 when my speedo is only registering 80. That was the whole reason I originally posted this. The ideas are great though. Hopefully I'll get this resolved soon. But on the other hand it's always a good excuse when getting pulled over "Do you know how fast you were going son? 80mph officer. I clocked you at 100mph. But my speedometer said..."

 

[SHOYourYama]

AutoSHO:

SHOYourYama:
Doesn't atmospheric pressure rule in the equation?

No, it doesnt. Just because there is less atmospheric pressure, it does not change the fact that your engine is spinning at a certain speed. It decreases power but not speed in gears.

I'm speaking for the spedo reading not the tach. Less power = less mph per selected gear's RPM.

 

[rangerj]

JoesSHO,

Try telling that to the judge! rangerj

 

[NotSoSlowSHO]

SHOYourYama:

AutoSHO:

SHOYourYama:
Doesn't atmospheric pressure rule in the equation?

No, it doesnt. Just because there is less atmospheric pressure, it does not change the fact that your engine is spinning at a certain speed. It decreases power but not speed in gears.

I'm speaking for the spedo reading not the tach. Less power = less mph per selected gear's RPM.

wrong, wrong, wrong.

Neither POWER nor Atmospheric pressure have ANYTHING to do with it.

No matter how much 'POWER' you have, if the gearing and tire size are consistant, the speedo : rpm readings will remain consistant.

simple ratios determine Speedo : rpm readings (per selected gear)

yourself

do the math.

 

[MOSHO92]

wrong, wrong, wrong.

Neither POWER nor Atmospheric pressure have ANYTHING to do with it.

No matter how much 'POWER' you have, if the gearing and tire size are consistant, the speedo : rpm readings will remain consistant.

simple ratios determine Speedo : rpm readings (per selected gear)

yourself

do the math. [/QB]

Agreed. Gear ratios do not change with temp or power, they are made of metal. If you supercharged your car, would your speedometer read different?....NO.

 

[AutoSHO]

<small>[ November 21, 2003, 07:34 PM: Message edited by: AutoSHO ]</small>

 

[NotSoSlowSHO]

My post wast directed at you Chris

It was at the "get out of a ticket based upon a flywheel tooth count" guy lol