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Enjoy The Ride
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It appears the tach. on my 2000 reads low. According to a gear ratio speed calculator chart with these spec's, FD gear 2.75, Tire dia. 25.625, 5th gear 1.511 & 3500 rpm my speed should be 64 mph. On my GPS I'm at 71 mph at 3500. At 71 mph the tach. should be at 3850 rpm. My rev limiter doesn't always work either. I've noticed a few times the tach past the red zone in third gear without the limiter kicking in. Other times the limiter works just fine.

On my 2004 with the 2.62 FD gear my speed should be 67 mph @ 3500 rpm & the GPS has it at 66 mph. That is only 50 rpm off and I would consider that normal.

I don't know of any way to correct the tach on my 2000. :think:
 

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Wrencher Extraordinaire
2005 K1200LT
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I don't know what you could do. I do know that one half of the coil driver from the ECU is fed to the cluster for the tach. But not sure if the ECU uses that signal or the hall effect sensor to determine RPM for the limiter.
 

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The speedometer on my 2000 has been corrected and is consistent with my GPS. At 80 I show about 4000 RPM, 70 is 3500, and so on. I've always been happy with that since it's an easy way to see when the clutch might be slipping, since the speed in fifth gear should always be twice the amount of the first two numbers of the RPM.
 

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I also have a 2000, how did you correct the speedo? Mine is off by 10%.
 

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I myself, prefer the incorrect speedometer reading, most times it makes me think I am going faster than I really am, and when I pass a state patrol and freak out a little, I do the mental calculation to determine what my speed really is, and figure out why I didn't get a speeding ticket....not going as fast as I thought. Kind of like setting your clock fast, thinking you're late, and finding out you were on time for your appointment afterall! I guess you could say I use it as a crutch...Ahhh, the things these Germans think up to help us speed thirsty american motorcycle fanatics!!
As far as the Tach goes, as many manual transmission cars as I have owned without a tach, I am more intune with the sound of the engine as it revs anyway, although I DO respect the red line. Yea, its late, and I'm rambling..:cool:
 

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Enjoy The Ride
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Discussion Starter #7
This has nothing to do with the incorrect reading speedometer.
 

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Did u do the speedo mod? If yes with the SMD pcbs its easy to melt the solder on near by devices or just get a strand of multi strand wire out of place. with that descrepency I assume that you would have noticed it early on.

Only other oddity was where the speedo cable was straped to the rear "swing arm", many speedos started bouncing as the cable cut into the line.

bob
 

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Enjoy The Ride
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Discussion Starter #9
This is a tachometer issue & not a speedometer issue what part of that don't you understand.
 

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Enjoy The Ride
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Discussion Starter #10
If you want to post about speedometers start your own damn thread.
 

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It appears the tach. on my 2000 reads low. According to a gear ratio speed calculator chart with these spec's, FD gear 2.75, Tire dia. 25.625, 5th gear 1.511 & 3500 rpm my speed should be 64 mph. On my GPS I'm at 71 mph at 3500. At 71 mph the tach. should be at 3850 rpm. My rev limiter doesn't always work either. I've noticed a few times the tach past the red zone in third gear without the limiter kicking in. Other times the limiter works just fine.

On my 2004 with the 2.62 FD gear my speed should be 67 mph @ 3500 rpm & the GPS has it at 66 mph. That is only 50 rpm off and I would consider that normal.

I don't know of any way to correct the tach on my 2000. :think:
Hmmm. The calculated value should be pretty close, but do you have an independent way to directly measure RPM such as a tach that will use a spark plug pulse?
 

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Dave, if you have an electrical schematic, I'd like to take a close look at it.

See where that signal is generated and what else it may be used for/by. If just the tachometer, be pretty simple but if used for other things and I suspect it is, it might be move involved.

If it were the pick up, would think it would either work of not work. A hall effect type pick up is either good or its not, very rare for them to work intermittently. Most often the problem with them is they are not adjusted correctly. If too close to the trigger, will give a higher voltage than the device it is signalling will be expecting and may cause problems, especially at higher readings (rpm). If too far away, lower voltage but would expect erractic operation at lower rpm.

Then there is the issue of how the signal from the trigger processed. Look at the signal from the trigger, it will be AC. I'd expect to see around 1.5 or so at cranking speed and 20 or so with the engine at a high rpm and steady. The frequency wil change with engine speed.

I have a Fluke 123 Scope meter (with the manual) I'd be happy to let you use.
 

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Has it occurred to you that your prose might not be as clear as it could be?

I won't be reading any reply you post to my question since you seem to be very angry. Associating with angry people is something I avoid
 

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Has it occurred to you that your prose might not be as clear as it could be?

I won't be reading any reply you post to my question since you seem to be very angry. Associating with angry people is something I avoid
I am curious as to what part of Saddlemans very first sentence was unclear? He wrote, "It appears the tach. on my 2000 reads low." I don't see how he could have been more clear than that. Well, I guess he could have written out tachometer... :)
 

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The original post says "tach".
Any Questions?
Technical FYI... A tachometer is NOT a speedometer.

:wtf:


later..Randy
 

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My point was the correlation between tach reading and speedometer with a corrected speedometer. Your mileage may vary. Yea, it got off topic. Dave did you double check your math? If you're certain of the figures, looks like BMW built some error into the tachs, only on the wrong end.
 

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Enjoy The Ride
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Discussion Starter #17
I'm going to put a 2.75 gear in my 2004 LT and see what the RPM reads.
 

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Enjoy The Ride
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Discussion Starter #18
My point was the correlation between tach reading and speedometer with a corrected speedometer. Your mileage may vary. Yea, it got off topic. Dave did you double check your math? If you're certain of the figures, looks like BMW built some error into the tachs, only on the wrong end.
No problem Dean. I'm not using math but a gear ratio & speed chart. I've been using them for over 30 years on race cars. You can google it and add the numbers. The only variable is the tire diameter. Some tires grow more diameter at speed than others. We use to do it with a slide scale but the internet has made it much easier now.
 

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Of course you know there's no mechanical connection between your driveline and the tachometer--it's electronic. So only problem is likely internal friction in the tach's gears, needle shaft, etc., as electronic failure is likely all or nothing. How does it perform at idle? Does it appear to respond correctly when blipping throttle in neutral? Can you hook up another tach (e.g. on a timing light) to compare the two? I'd call one of the usual instrument repair places, North Hollywood Speedometer, etc., and discuss.
 

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No problem Dean. I'm not using math but a gear ratio & speed chart. I've been using them for over 30 years on race cars. You can google it and add the numbers. The only variable is the tire diameter. Some tires grow more diameter at speed than others. We use to do it with a slide scale but the internet has made it much easier now.
No problem. Just letting you know that mine seems to be the same as yours. I do have a portable digital tach. Might have to hook it up and check it out later this week to see what it says.
 
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