Can RPM's fluctuate at a locked speed and gear? - Wrist Twisters
 
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post #1 of 32 Old 05-29-2010, 11:46 AM Thread Starter
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Can RPM's fluctuate at a locked speed and gear?

Simple example.
I have a 1 speed bicycle.

It takes me 100 RPM to maintain 20MPH.

If there is a tailwind, does it still take 100 RPM to maintain 20MPH?

If there is a headwind, does it still take 100 RPM to maintain 20 MPH?

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post #2 of 32 Old 05-29-2010, 12:22 PM
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yes, its fixed gearing, it takes less or more power to maintain the speed but the rpm is the same... you can notice on moto's that the rpm vs speed will change as you lean over however, but this is because you are changing the grear ratio b/c the tire's diameter is changing

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post #3 of 32 Old 05-29-2010, 12:27 PM Thread Starter
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I'm noticing on my Triumph Trophy that the RPM can vary 2-300 RPM when going 70mph and I can't figure it out; the clutch is not slipping.

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post #4 of 32 Old 05-29-2010, 01:15 PM
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Quote:
Originally Posted by Jeef View Post
yes, its fixed gearing, it takes less or more power to maintain the speed but the rpm is the same... you can notice on moto's that the rpm vs speed will change as you lean over however, but this is because you are changing the grear ratio b/c the tire's diameter is changing
im not the smartest dude in the world, and definitely not a math/science guy, but lets just say we are doing said 70mph and the bike weighs 400lbs. now if there is a tail wind behind us, doesnt that actually make the bike lighter? and if so, shouldnt a lighter bike take less power (like stated) and effectively lower rpm cause the engine isnt under the same stress to move the bike? i assume this is along the lines of going up/down hills. where down hill, you can get the same speed with less rpm, and uphill requires more rpm to maintain that speed

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post #5 of 32 Old 05-29-2010, 01:50 PM Thread Starter
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hornet,
Pretend you're on a single speed bicycle and ask yourself that same question.

To go uphill on that bike at 20mph will take you cranking those pedals a certain RPM.

Now go downhill and pretend you're going 20mph... how fast will your feet be pedalling... slower, the same, or faster?

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post #6 of 32 Old 05-29-2010, 02:07 PM
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.... uh ya guys unless your running a torque converter in your motorcycle (which you arnt) your rpms will be the exact same in the same gear at the same speed... ALWAYS. this is because there shouldnt be any spot along the drive line where slippage can occur.

That is unless you 1. change tire size... which will make a difference either one way or another... but with that combo your speed will be the same in the same gear at the same rpms. Or you are in a turn where the diameter of the tire is dynamicaly changing..

But in a straight line given the same bike with same tires and same gearing... rpms will be the same.

The whole headwind tail wind will just make you either use less or more throttle to go the same speed.

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post #7 of 32 Old 05-29-2010, 03:19 PM
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Quote:
Originally Posted by nd4spdbh View Post
.... uh ya guys unless your running a torque converter in your motorcycle (which you arnt) your rpms will be the exact same in the same gear at the same speed... ALWAYS. this is because there shouldnt be any spot along the drive line where slippage can occur.

........

The whole headwind tail wind will just make you either use less or more throttle to go the same speed.
I think this is a contadiction....Could you please explain how your throttle has nothing to do with your rpms and just your speed?

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post #8 of 32 Old 05-29-2010, 03:25 PM
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In perfect conditions RPM's will stay the same. However, if vehicle power supply is limited in horsepower the engine will rev up on hills or anything else that offers resistance. Once the engine is comfy again it will settle in to same RPM's.

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post #9 of 32 Old 05-29-2010, 03:40 PM
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Refer to Jeef and nd4 and dont argue, lol.

mtbkman: hes not discussin his ford taurus

07919Dave: of course it has todo with it, but your speed/rpm relationship are going to stay the same. if you stay at the same throttle position approaching a downhill your going to increase in speed AND rpm

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post #10 of 32 Old 05-29-2010, 03:42 PM
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Quote:
Originally Posted by mtbkrman View Post
In perfect conditions RPM's will stay the same. However, if vehicle power supply is limited in horsepower the engine will rev up on hills or anything else that offers resistance. Once the engine is comfy again it will settle in to same RPM's.
Throttle does affect speed, but it's not a direct effect...or maybe I should say it's not a direct ratio like the trans gearing and sprockets. Throttle simply adjusts the fuel input to the engine. Your RPM's will always be the same at a consistent speed, but you may need more or less throttle if you are going up a steep hill or downhill.

does that make any better sense to you?

Well, fire the engines! Spur this iron space-pony on!

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post #11 of 32 Old 05-29-2010, 08:15 PM
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post #12 of 32 Old 05-29-2010, 09:57 PM
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Are you always in top gear when going 70? If for some reason you were actually a gear lower the RPMs would obviously be higher. I believe this is the only explanation other than the lean angle which has been discussed

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post #13 of 32 Old 05-30-2010, 07:32 AM
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accept the obvious.......but agrue the theory

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post #14 of 32 Old 05-30-2010, 07:38 AM
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Engine rpms go up, speed of motorcycle go up. Rpms go down, speed goes down. That has nothing to do with load or throttle position.

If your tac is jumping around at a steady speed, and your clutch isn't slipping, it's a tac issue. (it wasn't made in china, was it?) You don't hear your engine revving and falling, do you?

I wouldn't worry about it, probably within spec. Tacs are about as accurate as speedometers, which isn't very.

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post #15 of 32 Old 05-30-2010, 08:08 AM
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rpms and speed

It never ceases to amaze me the number of people that report changing to XYZ expensive oil and report that their bike idles smoother, runs quieter, and takes less rpm to go a given mph. At least the last thing, rpms at a given mph, is totally imagined.

Unless the new oil corrected a slipping clutch issue, it's IMPOSSIBLE!

Gear-inches is the technical term that describes the distance the bike moves per X number of revolutions of the engine. The ONLY FACTORS that affect Gear-inches are: Wheel/tire diameter, Rear Sprocket teeth, Countersprocket teeth, total Transmission ratio.

We have seven transmission selections in our bikes. 1-6 and neutral. Since 1-6 are FIXED, the Rear Sprocket and Countersprocket teeth are FIXED, and the Wheel diameter is FIXED, the only thing that can change the relationship between rpm and speed is the TIRE or CLUTCH slippage.

IF you assume the clutch isn't slipping, the chain is intact, and the tire isn't more or less inflated or running off-center (leaning), and the tire isn't slipping on the road (which it CAN do under hard acceleration or deceleration) it matters not if there is a headwind, tailwind, wide-open throttle or zero throttle:

RPMS in a given gear will always be equal at any given speed.

An exception is NEUTRAL...because, the 6 transmission fixed gearsets are taken out of the equation, and speed is then independent from rpms.

Weight doesn't matter. Power doesn't matter. Head- or Tail-winds don't matter. Relative speed doesn't matter (whether it's one mph or 100 mph)...one rpm will move the bike a certain number of inches in a given gear, as long as the clutch or tires aren't slipping, or you aren't leaning off-center of the tire, and the tire inflation/deflection is unchanged, and the chain is intact.

So, if you divide your rpm by minutes to get rpms/minute, you do the same to your inches per minute to get inches/minute...which we conveniently change to miles/hour or km/hour.

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post #16 of 32 Old 05-30-2010, 10:05 AM
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Quote:
Originally Posted by Sniper View Post
Engine rpms go up, speed of motorcycle go up. Rpms go down, speed goes down. That has nothing to do with load or throttle position.

If your tac is jumping around at a steady speed, and your clutch isn't slipping, it's a tac issue. (it wasn't made in china, was it?) You don't hear your engine revving and falling, do you?

I wouldn't worry about it, probably within spec. Tacs are about as accurate as speedometers, which isn't very.
As this pertains to the OP I would have to agree. Try cleaning your electrical connections and see if this steadies your tach up a bit.

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post #17 of 32 Old 05-30-2010, 12:05 PM
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its all in the gas additive one uses

dont need a bike to ride the fast lane
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post #18 of 32 Old 05-30-2010, 12:15 PM
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Quote:
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its all in the gas additive one uses
that or how worn your muffler bearings are...

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post #19 of 32 Old 05-30-2010, 03:26 PM
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Quote:
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that or how worn your muffler bearings are...

...or the flux capacitor shim stack is askew....

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post #20 of 32 Old 05-30-2010, 04:30 PM
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If ya'll had little gremlin bells on yer bikes then none of this would be happening right now.

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post #21 of 32 Old 05-30-2010, 05:35 PM
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Stupidest fucking thread in history..........

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post #22 of 32 Old 05-30-2010, 06:30 PM
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IBTL!

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post #23 of 32 Old 05-30-2010, 08:05 PM
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Quote:
Originally Posted by catonsvilleguy View Post
Stupidest fucking thread in history..........
Agreed

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post #24 of 32 Old 05-31-2010, 07:40 PM Thread Starter
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Quote:
Originally Posted by catonsvilleguy View Post
Stupidest fucking thread in history..........
Quote:
Originally Posted by peoples1234 View Post
Agreed
Really? I'm seeing something on my (other) bike that doesn't make sense to me.

I try to simplify the question by creating my own example.

I then re-state my simplified question to clarify in my own melon.

That's "the stupidest fucking thread in history" ?

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post #25 of 32 Old 06-01-2010, 08:41 AM
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Agreed, what is stupid about this?

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post #26 of 32 Old 06-01-2010, 04:39 PM
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agreed w/ Catonsville: IS STUPID. i just lost 7 i.q. points reading this thread, and i didn't really have 7 to spare. as often in life, "if you have to ask "what's stupid?" ...the answer may be in the mirror."

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post #27 of 32 Old 06-01-2010, 05:06 PM Thread Starter
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Wow. That's pretty harsh. :/

At least you guys are open about it.

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post #28 of 32 Old 06-01-2010, 06:35 PM
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Sorry for any offense guys. None intended.

I'm not going to explain why I said what I said except I felt it was appropriate and I felt motivated by what I was reading..........

Peace..........

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post #29 of 32 Old 06-01-2010, 10:28 PM Thread Starter
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Quote:
Originally Posted by catonsvilleguy View Post
Stupidest fucking thread in history..........
Quote:
Originally Posted by catonsvilleguy View Post
Sorry for any offense guys. None intended.
I suppose to you, the question was beyond obvious, and the fact that doubt and naivety was seen just tipped it over for you.

I've been known to throw my ignorance out in the open in hopes of learning something... maybe even someone else learning from my caution in the wind.

I see that on this board that's not really the right thing to do.

I'll make sure to just talk about tires, oil and RC51 front end swaps.

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post #30 of 32 Old 06-01-2010, 10:36 PM
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Quote:
Originally Posted by curiousmike View Post

I see that on this board that's not really the right thing to do.

I'll make sure to just talk about tires, oil and RC51 front end swaps.


Jeez...lighten up buttwheat! no speaka ze sarcasm?

besides, the man did apologize!




.

Well, fire the engines! Spur this iron space-pony on!

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post #31 of 32 Old 06-01-2010, 10:42 PM Thread Starter
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The fact that three individual members echo'ed his *"stupidest fucking thread in history" should tell me something.

Do I win an award?

*BTW, No offense intended.

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post #32 of 32 Old 06-02-2010, 08:37 AM
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I think the problem is the way you phrased your original question vs. the actual situation. The first is almost a laboratory style setup and the reality is very different.

I know that all motorcycles I have ridden will vary rpms in the real world if you chose to sit in one of the spots that the engine is not at it's happiest, could be fuel pooling in the intake, a slipping clutch and so on for various other glitches.

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