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So confused... Ninja 250, same gear, same speed, different rev speeds???

fuzzybabybunny

fuzzybabybunny

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So my new Ninja has an odd issue. When I'm cruising at 70mph in 6th gear, some days it revs at 8.75K RPMs and other days it may rev at 9.25-9.5K RPMs... uhhhhh....

I've verified that I am indeed in 6th gear and at 70mph in each instance.
The only other thing that I can think of that would vary RPMs is clutch slipping, but this can't be the case on a new Ninja with proper oil changes, can it?
 
satyajitmenon said:
This.
Click to expand...

An assumption that I could be entirely wrong on:

1) This is a traditional manual gearbox, with a clutch.

If that's correct, then it doesn't matter if you have a headwind/tailwind/diplodocus on the pillion.

For a given speed and gear, then engine can't spin any faster or slower unless you change the gear yourself, or the clutch is slipping. Otherwise the drivetrain is in lockstep from each revolution of the engine to each rotation of the driven wheel.

But I can't imagine the clutch would be slipping that consisently (or if it was, I can't imagine it would do it from long!)...
 
dug777 said:
An assumption that I could be entirely wrong on:

1) This is a traditional manual gearbox, with a clutch.

If that's correct, then it doesn't matter if you have a headwind/tailwind/diplodocus on the pillion.

For a given speed and gear, then engine can't spin any faster or slower unless you change the gear yourself, or the clutch is slipping. Otherwise the drivetrain is in lockstep from each revolution of the engine to each rotation of the driven wheel.

But I can't imagine the clutch would be slipping that consisently (or if it was, I can't imagine it would do it from long!)...
Click to expand...

Motorcycles have a sequential gearbox with a clutch.

I seriously doubt there is anything wrong with your bike. Does your bike have a digital tach or an analog tach? 8.75k to 9k isn't much of a difference, I wouldn't worry about it. If your clutch was slipping it would be more evident on take off, not at speed on the freeway.
 
Did you do the last oil change yourself? If so, did you use the correct oil? The wrong oil can make wet clutches slip.
 
dug777 said:
An assumption that I could be entirely wrong on:

1) This is a traditional manual gearbox, with a clutch.

If that's correct, then it doesn't matter if you have a headwind/tailwind/diplodocus on the pillion.

For a given speed and gear, then engine can't spin any faster or slower unless you change the gear yourself, or the clutch is slipping. Otherwise the drivetrain is in lockstep from each revolution of the engine to each rotation of the driven wheel.

But I can't imagine the clutch would be slipping that consisently (or if it was, I can't imagine it would do it from long!)...
Click to expand...

Yeah that's my opinion too-- gear 6 is the same ratio no matter how you get there (IE if you went gear 1, 2, 6, 70mph is still going to be the same RPM). If you have headwind then the engine will put more gas into the chambers to produce more torque, if tailwind less. But the engine RPMs will be the same no matter what, if you're going at 70mph.

I'm not aware of continual clutch slipage (that it's even possible) but hey, who knows.
 
Most likely cause: Some days you're still in 5th.

With a sequential box it's easier to forget which gear you're in.

ZV
 
Zenmervolt said:
Most likely cause: Some days you're still in 5th.

With a sequential box it's easier to forget which gear you're in.

ZV
Click to expand...

my bike doesn't have a gear indicator, so i sometimes forget. right now i really only know speed vs RPM for 6th gear, and i can tell where 2nd is when i downshift... but otherwise it's a bit of a crapshoot 😛
 
Zenmervolt said:
Most likely cause: Some days you're still in 5th.

With a sequential box it's easier to forget which gear you're in.

ZV
Click to expand...

My first thought was that I'm in the wrong gear, so I try to upshift and I can't because I'm already in 6th. I also count off the clicks as I upshift from 1-6 to verify that I am in 6th.
 
Greenman said:
Did you do the last oil change yourself? If so, did you use the correct oil? The wrong oil can make wet clutches slip.
Click to expand...

I changed it myself, but I used the correct oil. 10w40 motorcycle oil and the oil indicator level shows correct level.
 
JulesMaximus said:
Motorcycles have a sequential gearbox with a clutch.

I seriously doubt there is anything wrong with your bike. Does your bike have a digital tach or an analog tach? 8.75k to 9k isn't much of a difference, I wouldn't worry about it. If your clutch was slipping it would be more evident on take off, not at speed on the freeway.
Click to expand...

The reason I began noticing this in the first place is because I realized that the engine was making more noise at 70mph than usual. I've driven stick cars for 10 years and know to listen to the engine to guage RPM. I look down at my analog tach and it's at 9.5K. Normally it's at 8.75K RPM and sounds quieter. I try to upshift thinking that I'm in 5th but it won't go anywhere. Some days it does this and some days it doesn't.
 
BassBomb said:
or the clutch isnt slipping, you are just having to drive harder to keep teh same speed because of more resistance?
Click to expand...

That still won't change the RPM - we're talking about revolutions per minute of the engine, not the amount of load on the engine.
 
jlee said:
That still won't change the RPM - we're talking about revolutions per minute of the engine, not the amount of load on the engine.
Click to expand...

Huh?

If you want to maintain 100 mph in any given gear, the difference in RPM needed would be huge, given for example, a hill climb versus a steep drop.
 
MJinZ said:
Huh?

If you want to maintain 100 mph in any given gear, the difference in RPM needed would be huge, given for example, a hill climb versus a steep drop.
Click to expand...

that is what i was thinking... i mean i can cruise at 3000rpm on highway, a hill comes if i dont put the throttle down and get to 3500 my speed will drop , thats kinda what im thinking of
 
BassBomb said:
that is what i was thinking... i mean i can cruise at 3000rpm on highway, a hill comes if i dont put the throttle down and get to 3500 my speed will drop , thats kinda what im thinking of
Click to expand...


Because the transmission downshifts. It's basic physics here. The engine is connected to mechanical gears. When the engine spins at 3k, the output will spin at a constant rate. Go up a hill, yes more load is pressed on the engine and if you don't add more throttle to maintain that speed you will slow down. As you slow down the engine spins lower. Why? Because it is mechanically connected to the wheels. 3.5k in top gear would net more speed. 2k, slower.


As for the bike. Try going down into 5th and back in 6th.
 
Demo24 said:
Because the transmission downshifts. It's basic physics here. The engine is connected to mechanical gears. When the engine spins at 3k, the output will spin at a constant rate. Go up a hill, yes more load is pressed on the engine and if you don't add more throttle to maintain that speed you will slow down. As you slow down the engine spins lower. Why? Because it is mechanically connected to the wheels. 3.5k in top gear would net more speed. 2k, slower.


As for the bike. Try going down into 5th and back in 6th.
Click to expand...

I dont believe its downshifting
 
MJinZ said:
Huh?

If you want to maintain 100 mph in any given gear, the difference in RPM needed would be huge, given for example, a hill climb versus a steep drop.
Click to expand...
We're talking about a manual transmission. The RPM of the motor is the same for a given speed and gear. Period. End of discussion.

Unless there is something wrong with the clutch causing it to slip continuously to keep a steady RPM (unlikely). A worn clutch is obvious under acceleration, not a constant load, like on the highway.

I doubt a flat tire would affect the RPM that much. Especially if it fluctuates up and down that frequently.
 
As you're shifting up from first through sixth just take not of the change in RPM in each gear. As long as you are seeing the change it's actually shifting.

If you see the change in all gears make a note of the specific RPMs of 70MPH in 5th and 70MPH in 6th. If your unusually high RPMs match your 5th gear RPMs then it might be having trouble getting into 6th gear.

Like some others have said, the RPMs needed to go 70MPH in 6th gear should be a constant whether you are driving uphill or downhill or against the wind or in a box with a fox.
 
BassBomb said:
I dont believe its downshifting
Click to expand...

At the very least, it's disengaging the lockup clutch on the torque converter, which permits the torque converter to slip (input pump spins faster than the output turbine). In a torque converter, that slippage allows torque multiplication, but decreases efficiency. In almost all modern automatics there is a lockup clutch that physically locks the input pump to the output turbine in higher gears when there's low load on the engine. That allows better highway mileage while preserving the ability of the torque converter to act as a fluid coupling (necessary to allow the car to be in gear and stopped with the engine still running) and to multiply torque in lower gears when the lockup clutch is disengaged.

Typically when the lockup clutch engages there is a 300-500 RPM drop in engine speed.

Unless the clutch is slipping (or the torque converter is not locked), engine RPM in a given gear at a given speed will always be constant. Uphill, downhill, tailwind, headwind, light load, 50,000 lb trailer, doesn't matter.

Gear X at speed X is RPM X. Now and forever. Amen.

Here endeth the lesson. 😀

ZV

EDIT: Theoretically there would be very slight (probably <50 RPM) variance from new tires to worn out tires because as a tire's effective diameter changes, the overall gear ratio changes slightly. However, in the real world, that's not enough to matter or even for most people to notice.
 
Last edited:
If you barely pull the clutch lever in does it disengage or do you have to pull it almost all the way in before it disengages?
 
Zenmervolt said:
Most likely cause: Some days you're still in 5th.

With a sequential box it's easier to forget which gear you're in.

ZV
Click to expand...
This...

KnightBreed said:
We're talking about a manual transmission. The RPM of the motor is the same for a given speed and gear. Period. End of discussion.

Unless there is something wrong with the clutch causing it to slip continuously to keep a steady RPM (unlikely). A worn clutch is obvious under acceleration, not a constant load, like on the highway.

I doubt a flat tire would affect the RPM that much. Especially if it fluctuates up and down that frequently.
Click to expand...
...this...

Zenmervolt said:
Unless the clutch is slipping (or the torque converter is not locked), engine RPM in a given gear at a given speed will always be constant. Uphill, downhill, tailwind, headwind, light load, 50,000 lb trailer, doesn't matter.

Gear X at speed X is RPM X. Now and forever. Amen.

Here endeth the lesson. 😀
Click to expand...
...and this.

[/thread]
 
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