Tachometer Inaccuracy??

[orenp]

I'm fairly new here and to Hayabusas. I saw a statement on a recent post referencing the inherent inaccuracy of Gen-I tachometers. I think it was in a thread polling shift RPM for drag racing. Someone said that actual engine speed is approximately 500 RPM less than indicated at 10-11,000 RPM.

Is this a 'given' that applies to all Gen-I bikes? If so, is it a percentage error (ie 500 RPMs at 10,000 = 5%; so 250 RPMs at 5,000) or a fixed error? What is the cause of the error and are there any fixes that will correct it?

 

[IG.]

Good question! Heard plenty of complaints about speedo error being anywhere 7%+ optimistic, but don't remember any complaints about RPM. Could be that very few measure the actual RPM.

 

[RedBusarider]

Yup speedo's are often off but not sure if tach's are.

At 55mph indicated I run about 2900 rpm, or just under 3000, in 6th gear.
I guess it's not a big deal unless you plan on running it to redline all the time
and want to get it to the Max output, but not blow it up, that it would be important to know
exactly what the rpm's were at. Better low, in that case as to NOT blow it up, right?

I doubt that it would be a fixed error as if it was it would be 500 low at idle.
meaning that at 1200rpm's it would only show 700rpm's.

On the flip side my speedo is high - meaning 80 indicated is only 76 actual according to my GPS.
So could it really be that the tach is low and the speedo is high? I don't know for sure but I doubt it.

Since very few people shift at the same rpm all the time and there appears to
be no set rule about when you have to shift I wouldn't worry if my tech was off just a little.

 

[orenp]

I have done lots of gearing calculations and used the Gearing Commander site to check my numbers. I thought I had a good handle on speedo error based on some GPS tests that I ran. As I (and Gearing Commander) figure it a stock geared (17/40) Busa with stock size rear tire (190/50 -17)should calculate at 18.6 MPH per 1000 RPM. The speedo seems to read about 19.5 MPH per 1000 RPM, or a little less than 5% off (optimistic).
Everything seemed right - then I saw the post referring to tachometer error....

 

[IG.]

The reason I am a bit suspicious about tachometer error is this... Every tuner reads RPM through their own feed. If there was a significant discrepancy between the actual RPM and the tachometer, we would've heard about it form every other tuner, and from quiet a few riders who tuned their bikes. And over the years, I don't recall a single mentioning of such discrepancy.

 

[orenp]

The tach reads around 500rpm high of actual.

This is the reference to tachometer inaccuracy that I'm talking about.

 

[StrtRac3r]

My only experience is this, on my old 1k I wanted to see if first gear would get to the speeds I read about. From what I found it seemed it did, but only a very gradual roll on. If I slammed first gear in a drag racing scenario it didn't seem to get the speed I expected out of 1st gear.

Sooo, I guess I'm saying revving slow it seemed to hit the rev limiter at the correct displayed rpm. But when hitting it quick it seemed to cut out early. So maybe the display has a bit of lag....

Don't know about my Busa, I just ride it.

 

[mjl3truck]

On my Gen II it reads about 8% high. My peak power is 11,000 and I shift at 12,000 on the tach. You can check it when your bike is dyno'd with the tach on the dyno or what it reads in ECU Editor.

 

[outlawbusa]

I agree. If I remember correctly your limiter reads about 500 RPMS off. It'll show different on your Tach vs a laptop or data logger.

 

[outlawbusa]

Here's some pretty good info...and it's not isolated to the Gen 1

https://www.hayabusa.org/forum/1-4-mile/129745-what-rpm-do-you-shift.html

 

[Pecan Pouch]

According to the guy that tuned my bike my tach is about 500 rpms low at the upper rpm's.

 

[outlawbusa]

Yes, I should have specified around the limiter

 

[Jaguarcat311]

On my Gen II it reads about 8% high. My peak power is 11,000 and I shift at 12,000 on the tach. You can check it when your bike is dyno'd with the tach on the dyno or what it reads in ECU Editor.

Just got my gen II dyno tuned last Friday, same result with the tach. Speedometer is also 8% over, reporting 100mph at 92mph. Speedo healer will fix this though...... Perhaps a tach healer is in order...

 

[Dopey]

Just got my gen II dyno tuned last Friday, same result with the tach. Speedometer is also 8% over, reporting 100mph at 92mph. Speedo healer will fix this though...... Perhaps a tach healer is in order...

I've wondered about this but never bothered looking into it, after my ecu flash I know my limiter was bumped up some but I noticed a few times while riding hard that my tach seemed to be reading above where the limiter is set. Guess this explains it

 

[smithabusa]

tach's read high just like speedos, 10800 actual at limiter looks about 11300 on a gen 1 busa. This causes people confusion at first with my shift lights as they read real RPM, and the tach reads high, making it seem like shift light comes on late.

 

[Dennis]

tach's read high just like speedos, 10800 actual at limiter looks about 11300 on a gen 1 busa. This causes people confusion at first with my shift lights as they read real RPM, and the tach reads high, making it seem like shift light comes on late.

Same for Gen2.