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Old 08-27-2013, 10:44 PM   #1
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Default What to use to tune my NB's speedometer?

Found some threads on m.net that were years old, not sure what the solution is these days (lots of those products were no longer sold/websites down).

So what does anyone here use to calibrate their speedometers? (for people who do, anyway)
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Old 08-28-2013, 03:27 AM   #2
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Have you changed differential? If so you are meant to grab the sender from the gearbox in the car it came from (or one with the same ratio).
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Old 08-28-2013, 03:36 AM   #3
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No, I have not.

I have a 4.3 rear end.

The speedo would read properly if I had a 4.72 rear end.

It's way off. It needs calibration.
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Old 08-28-2013, 03:39 AM   #4
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I have no idea what your question is. Or what you're even talking about.

What have you changed from stock that requires a whole recalibration? Usually any significant changes in trans/rear are paired with the appropriate speed sensor resulting in proper reading
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Old 08-28-2013, 03:49 AM   #5
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Okay, I'll break this down for you.

My speedometer reads a different speed than I'm going, as verified by the GPS.

Many cars are not very accurate with that setting. Most read high.

Mine is reading high enough to cause issues, that I wish to resolve.

To bring the displayed speed in line with reality, is called calibration. This means that the speedometer and the GPS should say about the same speed.

In order to do this, there are signal modifiers that plug into the electric signal of the speedometer and alter it so that the displayed speed can be accuratized.

That's what calibration means.

I'm asking for the thing that plugs in. Which would be the best, where to get it. It's something you buy. Plug in. Program. Problem fixed.
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Old 08-28-2013, 08:57 AM   #6
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Just saw a post about this and there is a plug in module available for 100 bucks...I just forget who sells it now... Trackspeed maybe?
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Old 08-28-2013, 11:05 AM   #7
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Is your speedometer consistently incorrect at all speeds, meaning it's always off by 5mph for instance? Or is it correct at lower speeds and progressively gets further off as you go faster?

Last edited by RotorNutFD3S; 08-28-2013 at 11:16 AM.
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Old 08-28-2013, 01:12 PM   #8
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Needs YellowBox.
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Old 08-28-2013, 02:28 PM   #9
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Quote:
Originally Posted by Preluding View Post
Just saw a post about this and there is a plug in module available for 100 bucks...I just forget who sells it now... Trackspeed maybe?
Nope
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Old 08-28-2013, 02:48 PM   #10
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Quote:
Originally Posted by Nagase View Post
No, I have not.

I have a 4.3 rear end.

The speedo would read properly if I had a 4.72 rear end.

It's way off. It needs calibration.
Miata speedometers are not generally off by 10%, so why not focus on trying to find the broken part in your system rather than band-aiding it by modifying the electrical signal?

What size are your tires? A different tire diameter will affect the speedo.

Which rear end ratio sender is physically installed? You may not have changed it, but did you buy the car new? Maybe the PO changed the sender and put in the wrong one? It's one bolt to pop it out and count the teeth on the gear.

Is your odometer correct, or is it also off? Usually those are calibrated a lot more accurately than the speedometers. So if your odometer is right, but your speedometer is high, then you probably just have a speedo that's not displaying the input signal correctly. If that's the case, then modifying the input signal will make the odometer update incorrectly.

--Ian
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Old 08-28-2013, 05:18 PM   #11
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Thank you Cordus.

Exactly what I was trying to comprehend/ask.
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Old 08-28-2013, 05:22 PM   #12
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This is the first I've heard of calibration. I thought everyone just swapped in various tooth count gears. I have one or two around the garage.

If you find out how many teeth you need to get it spot on and I happen to have one I'll trade you.
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Old 08-28-2013, 05:22 PM   #13
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Quote:
Originally Posted by RotorNutFD3S View Post
Is your speedometer consistently incorrect at all speeds, meaning it's always off by 5mph for instance? Or is it correct at lower speeds and progressively gets further off as you go faster?
As I said above, it would read correctly at 4.72. That compared to 4.3 is a percentage.

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Needs YellowBox.
What's that?

Quote:
Originally Posted by codrus View Post
Miata speedometers are not generally off by 10%, so why not focus on trying to find the broken part in your system rather than band-aiding it by modifying the electrical signal?

What size are your tires? A different tire diameter will affect the speedo.

Which rear end ratio sender is physically installed? You may not have changed it, but did you buy the car new? Maybe the PO changed the sender and put in the wrong one? It's one bolt to pop it out and count the teeth on the gear.

Is your odometer correct, or is it also off? Usually those are calibrated a lot more accurately than the speedometers. So if your odometer is right, but your speedometer is high, then you probably just have a speedo that's not displaying the input signal correctly. If that's the case, then modifying the input signal will make the odometer update incorrectly.

--Ian
I've installed two senders. Haven't tested the odo. Tires are smaller than stock. This will not be changed.
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Old 08-28-2013, 05:23 PM   #14
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Quote:
Originally Posted by FRT_Fun View Post
This is the first I've heard of calibration. I thought everyone just swapped in various tooth count gears. I have one or two around the garage.

If you find out how many teeth you need to get it spot on and I happen to have one I'll trade you.
That's exactly right... for the NA.

For the NB, it's digital. For my 3.63 rear end for the NA, I got TSE to set me up with the correct tooth count gears, IIRC.

For the NB, it's about modifying a current instead of a mechanical sender, from everywhere I've looked.
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Old 08-28-2013, 05:33 PM   #15
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Old 08-28-2013, 06:13 PM   #16
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Quote:
Originally Posted by Nagase View Post
For the NB, it's about modifying a current instead of a mechanical sender, from everywhere I've looked.
Why would you modify the current instead of the mechanical sender? I can't believe that buying or building a circuit to do that is easier than swapping out a gear on the sender.
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Old 08-28-2013, 06:23 PM   #17
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Quote:
Originally Posted by thenuge26 View Post
Why would you modify the current instead of the mechanical sender? I can't believe that buying or building a circuit to do that is easier than swapping out a gear on the sender.
Who says there is a gear that will be accurate for her diff/tire/transmission setup? Figuring out that is step 1 I guess. But to be extremely accurate signal modification may be the only way. If "in the ball park" is good enough a gear swap may work.
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Old 08-28-2013, 06:29 PM   #18
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Well, a 4.77 would be close enough, if it's made.

Have some part numbers for me, thenudge?
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Old 08-28-2013, 06:33 PM   #19
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So you have a 4.3 rear, 6 speed, and wheel/tire size? Is this how you are getting your 4.77?
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Old 08-28-2013, 06:38 PM   #20
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My tire size is listed in my signature.

185/55/15.

Got my numbers with math.

Displayed speed x final gear = GPS verified speed x unknown correct final gear

(DS X FG) / GPSS = UCFG
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