Revs Vs Speed


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jcbrown630

New Member
Bone stock riders, What is your indicated speed @ 5k rpm?

I'm curious because i'm almost certain mine changed with my R6 headers and the D&D pipe. I'm not going to state mine just yet so as not to influence any answers.
 
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Diluted

Super *********
Elite Member
I'm thinking you should probably pick a gear you'd want the results from :p
 
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jcbrown630

New Member
If the bike is making more power it will absolutely change your revs @ specific speed. Also i'm asking re: 6th Gear.
 
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toddjcruz

New Member
Not sure how thats possible! LOL. It may be making more HP, but speed at a specific RPM is controlled by the gearbox and the final drive. you could have 1000 HP added, if the gearing doesnt change, the RPMs at a speed wouldnt change.

Just the way it works.
 
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jcbrown630

New Member
toddjcruz said:
Not sure how thats possible! LOL. It may be making more HP, but speed at a specific RPM is controlled by the gearbox and the final drive. you could have 1000 HP added, if the gearing doesnt change, the RPMs at a speed wouldnt change.

Just the way it works.
Click to expand...
Laugh away but ur not absolutely correct. When a car is mis firing it will turn more revs yet still not accelerate. So yes the gearbox does control speed to a certain extent. But the POWER PER REVOLUTION does have an effect on revs @ speed.

EDIT: To be fair.
Obviously you will not see a HUGE difference because yes the gearbox does determine the lion's share of the speed @ spec. RPM.
 
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toddjcruz

New Member
A car can do this with an automatic or a slipping cluch, but its not not physically possible. There is a direct relationship between the speed the engine is turning and the speed the wheels are turning. They are physically connected at a fixed ratio. That ratios cant change unless you change the gears, final drive or tire size. You just cant.

A slipping clutch or an car with a torque converter (that allows slippage between the engine and the transmission) would be the only way this would happen.

Sorry.
 
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Stephenfz6r

New Member
As stated above, speed is calculated via rpm vs final drive ratio. Power only determines how quickly you can get there vs the weight you are driving. As mentioned above you could add 1000 HP and it would not change your RPM/speed indication. If you could add 1000 RPM then you would add the corresponding increase of speed to the top speed to each gear used.

:rant:
 
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Spunky99

New Member
I have noticed that my speedo will show 70 mph and the tach will vary between 5800 and 6200 RPM on my +1 primary setup. It was also the same variance when stock but obviously higher RPM for the same speed.

The digital electronics seem to not always display correctly the exact RPM and or speed the bike is at...Maybe this is what he is seeing....

I do understand the absolute physics of RPM + gearbox + primary + secondary + outside rear wheel diameter = same speed no matter the HP and know it to be true.
 
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JonKerr

Senior Member
Elite Member
jcbrown630 said:
Laugh away but ur not absolutely correct. When a car is mis firing it will turn more revs yet still not accelerate. So yes the gearbox does control speed to a certain extent. But the POWER PER REVOLUTION does have an effect on revs @ speed.

EDIT: To be fair.
Obviously you will not see a HUGE difference because yes the gearbox does determine the lion's share of the speed @ spec. RPM.
Click to expand...
Yes he is. Gearing is gearing. No matter what horsepower you have behind it. When you have a 5:1 gear ratio coming out of the transmission, your engine will turn 5 times for every one time the transmission output shaft turns over. How much power is behind that spinning does nothing to change that. More Power usually will be accompanied by higher gearing to use that extra power to have a higher top end speed.

Like others have mentioned, it's different in a car with slipping automatic clutches and torque converters.
 
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toddjcruz

New Member
Interesting, I've never noticed my speed changing on me much, but then again, I only look at it for a moment at a time. He could be talking about that. I'll have to watch mine next time I ride and see if it moves any while maintaining a constant speed or changing speed just a little bit at a time.
 
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motomc2

New Member
I can tell ya....

at 80 mph I'm pulling 7000 rpms. I rode a 2006 gixxer 600 Wednesday and at 82 mph it was pulling 7000 rpm's. Of course the gixxer has a much higher redline.
 
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Stephenfz6r

New Member
I agree with spunky, it seems these bikes do not read out the speed and rpm with any accuracy.


:rockon: :rockon:
 
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dart1963

Super Moderator
Elite Member
cruising at 65ish, tach reads right around, or just under 6k.
 
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Spunky99

New Member
I'm at work and don't have time to investigate so I'll ask the question so we can rule out dumb questions and disparaging comments.

Where does the tach physically get the RPM from.......and
Where does the Speedo physically get the speed from?

I see no cables to either wheel for a mechanical speedo.
And there isn't a pitot tube mounted on my bike like an airplane has.....:rolleyes:
 
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JnT4Life

New Member
Spunky99 said:
I'm at work and don't have time to investigate so I'll ask the question so we can rule out dumb questions and disparaging comments.

Where does the tach physically get the RPM from.......and
Where does the Speedo physically get the speed from?

I see no cables to either wheel for a mechanical speedo.
And there isn't a pitot tube mounted on my bike like an airplane has.....:rolleyes:
Click to expand...
Ooo Ooo I know this one! (raises hand)
1. from the ignition or spark plug wire
2. sensor in the transmission
:cool:
 
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Spunky99

New Member
JnT4Life said:
Ooo Ooo I know this one! (raises hand)
1. from the ignition or spark plug wire
2. sensor in the transmission
:cool:
Click to expand...
OK....I can understand that the CDI or ignition system could give a very accurate RPM reading.

Then if the sensor in the transmission doesn't have a clue what you've done to the primary or secondary sprockets then it would not be able to tell how fast you are going. That way a +1 on the primary gets you close to true speed as indicated on the speedo.

OK...but it still does not explain the +- about 400 RPM I see with the same speed....Just a crappy system? Not a high enough sample rate to give an accurate reading?

Also I see the difference more going uphill or downhill than on the flat. Or accelerating to a steady speed and watching the RPM keep changing until it settles.
 

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dart1963

Super Moderator
Elite Member
Spunky99 said:
OK....I can understand that the CDI or ignition system could give a very accurate RPM reading.

Then if the sensor in the transmission doesn't have a clue what you've done to the primary or secondary sprockets then it would not be able to tell how fast you are going. That way a +1 on the primary gets you close to true speed as indicated on the speedo.

OK...but it still does not explain the +- about 400 RPM I see with the same speed....Just a crappy system? Not a high enough sample rate to give an accurate reading?

Also I see the difference more going uphill or downhill than on the flat. Or accelerating to a steady speed and watching the RPM keep changing until it settles.
Click to expand...

[ame=http://www.youtube.com/watch?v=TmrW9AoTkts]YouTube - Gravel Roads[/ame]

tach looks fine to me.... I know it jumps around a bit, but we have about 333rpm indicators, mine seems to be able to sit pretty stable, at least from the vid I've seen. Maybe if you can get vid, you can see how bad or good it's jumping around?
 
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