RPMs running higher than usual. - Page 4 - Honda CBR250R Forum : Honda CBR 250 Forums
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post #31 of 36 Old 05-26-2016, 06:14 PM
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'actual or real speed' in context of the subject here
is velocity, or speed of the vehicle..
not rotational speed of a '17, 16 or 15" wheel'..

the reality is self evident, as is context..

observation; this is not a lesson in pure physics/mechanics
but a question as to apparent change in rpm at indicated speed..
various factors could contribute to this apparent change..
thus members mention speedo or tacho variability,
reliability of memory of numbers over time,
particular tyre pressure at different times [etc]..

its not a matter of exactly 500rpm at gps calibrated speed[s]
but what appears to be [to the op] together with factors
which may, contribute to that apparent observation
thus concern..

and some members esp novices may not be aware
of different tyre pressures effecting riding conditions..
or clutch lever adjustment influencing clutch friction
under load such as in 6th gear or uphill etc..

of potential for some oil additives to influence
clutch plate friction.. factors which could,,
result in the ops few hundred rpm variance..

and it would do no harm for op or novices etc
to check their tyre pressure and know what
pressures to use variously, or adjust their clutch,
or use motorcycle specific oil, and so on..

information exchange is the go here,
with possible motorcycling applications..
[as opposed to pedantics and so on]

note the fine ear of LTR...
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post #32 of 36 Old 06-02-2016, 11:47 AM
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I've been away from my computer the past couple weeks, so I missed out on joining in the previous couple pages of debate on the relationship between indicated speed, indicated RPM, and true road speed etc. Reading those posts could certainly leave the reader dazed and confused about how it all works, when in reality it's pretty simple to understand.

The Tachometer displays engine RPM's according to the crankshaft revolutions, which is calculated using ignition pulses. The transmission gear ratios (1st through 6th), rear tire size, or the size of the final drive sprockets have nothing to do with what the Tachometer readout is.

In other words, the Tachometer always displays the engine RPM's on a one to one basis, and that doesn't change. So the Tachometer is still reading the engine RPM the same as it did before any changes to the tire size or sprocket sizes... 6000 RPM shown on the Tachometer is still 6000 revolutions of the crankshaft.

Changing rear tire size (ie. diameter), final drive sprocket sizes changes the true road speed of the bike as it relates to the RPM displayed by the Tachometer, as well as the indicated speed displayed by the Speedometer. That the true road speed has changed, it causes the Speedometer to display a + or - error.

The ONLY way to change the Speedometer readout and make it accurate as it relates to the true road speed is by installing a speedo healer (aka Speedo DRD), which allows a correction factor to be programmed between the Speedo Sensor signal and the Speedometer display.
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Last edited by MotoMike; 06-02-2016 at 11:58 AM. Reason: correction
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post #33 of 36 Old 06-02-2016, 01:17 PM
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Talking

A lot of confusion, here!

Quote:
Originally Posted by MotoMike View Post
...
The transmission gear ratios (1st through 6th), rear tire size, or the size of the final drive sprockets have nothing to do with what the Tachometer readout is.
That is abolutely right.
The Tach readout is set by the ignition system.
Quote:
....
Changing rear tire size (ie. diameter), final drive sprocket sizes changes the true road speed of the bike as it relates to the RPM displayed by the Tachometer, as well as the indicated speed displayed by the Speedometer. That the true road speed has changed, it causes the Speedometer to display a + or - error.
.....
Mike I'm sorry, but you wrote "as well as the indicated speed displayed by the Speedometer", which is wrong:

Yes, it does change the true speed
But never the indicated speed.

it causes the Speedometer to display a + or - error.
But it still indicates the same speed at the same rpm of the engine!
b/c the sensor is only reading the driveshafts rpm
Which have not changed.
Which can not change.
Unless the clutch slips!

Transmission gear ratio
1-speed 3.333
2-speed 2.118
3-speed 1.571
4-speed 1.304
5-speed 1.115
6-speed 0.963

Nothing, that comes behind/outside the driveshaft, has anything to do with the indicated speed on any Speedometer.
"Only" with the real speed!
Not only on our bikes.
Not only on driveshaft sensors.

This (CBR250R) speedo is set to show always the same km/h at the same rpm of the driveshaft.

And the driveshaft is hard connected, thru the chosen gear, with the rpm of the crankshaft.
In our case, ~6000prm at the tach are ~6230 rpm at the driveshaft.
And always, without a Speedometer Corrector, the Speedo "read" this amount of rpm at the driveshaft as about 100km/h.
Like he did from the first day.


As long noone "tells" the Speedo this with a correction factor, it indicates a wrong speed.
Which would be right, with the right chainset ratio, the right tire pressure, the ....!

Or:
it's called indicated, because it is set by honda with several given factors:
xy,z rpm of driveshaft + chainset 14/38 + tiresize 140/17-70
= 1km/h
Change one thing behind the driveshaft, the setup is wrong.
But it still indicates the same numbers. It only reads the driveshaft rpm

Conclusion:
If rpm on Tach is 500 higher at the very same indicated speed and gear, there is only one mechanical thing, that will let the rpm rise but keeps the Speedometer readout unaffected: Clutch

I can't think of any electrical problem, that could affect the tachometer to read 500 rpm more, as the engine is turning, so....!

By the way: Has anyone "seen" Webster?

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Last edited by CBR-250-R; 06-02-2016 at 01:24 PM.
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post #34 of 36 Old 06-02-2016, 02:08 PM
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@CBR-250-R... your basically saying the same thing as what I wrote in my previous post. You just happen to use many more words than what I did. That English isn't your first language unfortunately often adds to unnecessary confusion.

Beyond that, there really is no further need to continue this discussion.

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post #35 of 36 Old 06-02-2016, 02:41 PM
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Quote:
Originally Posted by MotoMike View Post
@CBR-250-R... your basically saying the same thing as what I wrote in my previous post.....
You think so?

"Changing rear tire size (ie. diameter), final drive sprocket sizes changes ..... the indicated speed displayed by the Speedometer."

Wrong is wrong.
Even with english as sec. or third language!


And that may confuse people more, as some "more words"

But I assume, you must be right
And I have to be wrong, huu?
By definition.

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post #36 of 36 Old 06-02-2016, 03:34 PM
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Try reading what I wrote again, in it's entire context...


Quote:
Originally Posted by MotoMike View Post
... Changing rear tire size (ie. diameter), final drive sprocket sizes changes the true road speed of the bike as it relates to the RPM displayed by the Tachometer, as well as the indicated speed displayed by the Speedometer. That the true road speed has changed, causes the Speedometer to display a + or - error.

The ONLY way to change the Speedometer readout and make it accurate as it relates to the true road speed is by installing a speedo healer (aka Speedo DRD), which allows a correction factor to be programmed between the Speedo Sensor signal and the Speedometer display.
Obviously I could explain these same concepts in another way, using "other words", however it is still up to the reader (you) to supply reading comprehension in order to fully understand what is written. That you may not comprehend a concept in the way that it is written, doesn't then mean that the writer is wrong.
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Last edited by MotoMike; 06-02-2016 at 03:44 PM.
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