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Discussion Starter #1
It's pretty common knowledge that the speedos are off by around 10%.

I've been running an LCD display that lets me monitor several engine functions, one of them is engine speed RPMs). I noticed the other day that it was off, way off - by up to 500 RPMs. However, it wasn't a constant, but a sliding scale.

I hooked up another tach the other day that ran off of the spark plug wire - basically like an old inductive timiing light. Low and behold, the test tach and the LCD display (which is wired in to the negative cable of the coil) are very, very close in their readings.

So, you say, what's the big deal with the tach being off, especially if we're not shifting?

In a broad sense, nothing (unless you want to run at redline a lot). However, since I'm mapping how I normally drive, it makes a big difference, especially at higher speeds.
 

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So it reads higher than it is?
 

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I found the same thing on my MZ 660 Skorpion. OEM tach was off about 500 rpm's. It would read 6,000 but the actual rpm's were 5,500. Base line to "real" rpm's was a Dyno Jet dyno pickup and a Autometer replacement tach.

Dyno operator said OEM manufacturers typically have the tach read about 10% higher than actual. His theory was less revs, less engine stress, less warrenty claims.
 

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Discussion Starter #4
Good - so I'm not the only one.

It's about 10% on mine too. I wonder how they do that? :confused:
 

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I have been riding 2-wheel thingys since I was 8 (that makes it 61 years in April) and one thing I have observed consistently is that the instruments are often inaccurate as heck, and not of particularly high quality to boot.

The speedometers in most automobiles are better, typically within +/-2% of actual speed--but dash tachs are not, +/- 7 to 10% is not unusual.

Even my $101,275 (when new in August of '97) '98 Mercedes SL500 has problems with the speedometer; at an indicated 155 my GPS said I was only going 153.8 mph...
 

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I believe they make them to read higher to avoid federal fines. Someone posted long ago that government regulations place large fines on manufacturers if speedometers read under so they play it safe by having them read over.
 

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Funny this thread is here I was going to start one about speedometers today. I'm 1700+ miles into my trip and noticed that the odometer is about 1%off but the speedometer is at least 10% off. If you can buy a device that fixes this how come the manufacture is not being held accountable to make their equiptment work right. BTW that 1% is costing us something when we go to sell the scooter.
Has anyone ever gotten an explanation from a manufactur about this?
Allen
 

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Allen see my post above.
 

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I drive by what the speedometer says with the posted speed limit. You would think that I would be getting passed all the time, but it is not so. Every ones speedometers must be wrong too then. When I pass one of those speed reader things out side a work zone, I am slow by 1or2 mph. I don't really care about the accuracy of the speedometer as much as the gas gage and odometer.
 
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