Gearing change WTF, someone care to explain?

The theory that I know and which should be true, is that the speed on the
bike is "read" from the front sprocket, and changes to the sprocket should
affect speedo accuracy.

Changes to the sprocket SHOULD NOT result in changes to indicated
speed vs revs on the bike, right? If I had 62mph at 5000 revs, I should
have 62mph at 5000 revs with -1 or +1 at the front too, right?!

This WAS TRUE on my Kawasaki 650R (ER6F) when I went +1 on the front.
Indicated speeds remained the same, GPS indicated speeds went up, making
the speedo more accurate.

The speedo on the FZ6 is said to be around 7% off, which I confirmed
(somewhat) with radar traps around town, at speeds from 40 to 60mph.

I've read here (and on other forums) that going +1 at the front should
make the speedo accurate to about 1%.

So what really happened?
Today I got my +1, put it on, went for a ride and tried 2 android apps
(which locked on to 8-9 satellites, which should be enough) and I still
had a 5-6% indicated error in comparison to the bike's speedo. Ok, maybe
it's the phone.. I should try the radar traps.

..BUT

I got different indicated revs vs speeds now, and this, from what I've
come to understand over time and with experience on the last bike,
should not have happened, right?

My 62mph (100km/h) went down from 5000 revs dead on to 4600, more
or less.

WTF is going on here?

Why is there a change in revs vs speed on this bike, and there wasn't
one on the 650R? AND, is it possible that my speedo is still indicating
5-7% off?!

Thanks everyone.

the speed sensor is based on the speed of the front sprocket. The ER6F likely had a speed sensor directly on the wheel, hence it stayed true.

Decreasing the tooth count on the front (or increasing on the rear) will make the speedo over-read (and the odo too).

I have -1 on the front, and my speedo reads around 10-15% over actual speed.

greg said:

the speed sensor is based on the speed of the front sprocket. The ER6F likely had a speed sensor directly on the wheel, hence it stayed true.

Decreasing the tooth count on the front (or increasing on the rear) will make the speedo over-read (and the odo too).

I have -1 on the front, and my speedo reads around 10-15% over actual speed.

Click to expand...

Um, yeah, thanks, but shouldn't mine read more accurate now compared
to before? And also, if the reading is based off the sprocket speed, the
indicated speed vs revs shouldn't have changed, right? That's the WTF
I'm trying to figure out. Why isn't the 62mph at the 5000 mark as before?

Also, I'm rather sure the 650R had the reading on the sprocked, same
as fz6.

If you can post the specific year, model , etc I may be able to find on a parts fisch how your Kawasaki speedo was set up. The closest I could find, at least on the US parts list, was a 650, not a 600.

As noted above, the shaft that the sprocket rides on is what is monitored (with a sensor) by the ECU and sent up to the speedometer.

A larger front sprocket, physically, will LOWER the RPM's (the engine is now turning slower for the same speed) at the same speed. And yes, going up one in the front should correct the speedometer.

Something not mentioned, is the rear sprocket STOCK?? If that's been changed to a larger or smaller sprocket from stock, that will affect the speedo just like the front sprocket.


Yamaha Motorcycle Parts 2007 FZ6 - FZS6W ELECTRICAL 1 Diagram

Part #12 is the electronic speed sensor for the FZ6

You said yours was 7% off, but mine seems to be more in the neighborhood of 10% off with all stock gearing and sprockets.

So it might have changed quite a bit and you didn't realize it.

TownsendsFJR1300 said:

If you can post the specific year, model , etc I may be able to find on a parts fisch how your Kawasaki speedo was set up. The closest I could find, at least on the US parts list, was a 650, not a 600.

Click to expand...

It was a 2007 Kawasaki ER6F ABS (EU spec), called Ninja 650R in the USA.

TownsendsFJR1300 said:

As noted above, the shaft that the sprocket rides on is what is monitored (with a sensor) by the ECU and sent up to the speedometer.

A larger front sprocket, physically, will LOWER the RPM's (the engine is now turning slower for the same speed) at the same speed. And yes, going up one in the front should correct the speedometer.

Something not mentioned, is the rear sprocket STOCK?? If that's been changed to a larger or smaller sprocket from stock, that will affect the speedo just like the front sprocket.

Click to expand...

Yes, that was the first thing that I checked after I got off the bike actually,
it's a 46T.

Xavias said:

You said yours was 7% off, but mine seems to be more in the neighborhood of 10% off with all stock gearing and sprockets.

So it might have changed quite a bit and you didn't realize it.

Click to expand...

If my 2 local radar traps are accurate, it was around 7%, maybe 8%.
But yeah, you could be correct.

I STILL actually wonder the most about why the speed vs revs relation
changed.

There isn't a speedohealer or something similar installed, is there?

dpaul007 said:

There isn't a speedohealer or something similar installed, is there?

Click to expand...

Nope!

Just recapping. You have a 17t front sprocket, 46t rear sprocket, and your indicated speed is still ~7% off from GPS?

I know cruising in 6th gear at 60ish MPH, my RPMs are right at 5k. How RPMs dropped to 4600 at the same indicated speed and gear....um, did you install a 7th gear?

dpaul007 said:

Just recapping. You have a 17t front sprocket, 46t rear sprocket, and your indicated speed is still ~7% off from GPS?

Click to expand...

Yes.. 5-6%. 17/46T.

dpaul007 said:

I know cruising in 6th gear at 60ish MPH, my RPMs are right at 5k. How RPMs dropped to 4600 at the same indicated speed and gear....um, did you install a 7th gear?

Click to expand...

Yeah, 62mph (100km/h exactly) was SPOT ON 5000 revs.
Now it isn't, but should be.

I'll go check on the speed traps.

Cortez said:

I STILL actually wonder the most about why the speed vs revs relation
changed.

Click to expand...

I'm also a bit confused by this. I'm just trying to visualize the effect on my old 10-speed bicycle...when you go up to a larger sprocket up front the speed your are traveling remains the same but the speed you have to pedal is lower (rpms).

I just took a short ride with GPS and some speed traps.
They're close.

Speedo is still off and from what I can tell, as much as it was before.

Did anyone actually do the 17T mod and CONFIRM the 1% error or
was this all done with math?

I had at least 10 separate runs. I'll do kmph since that's what I've
got on my bike, the percentage is obviously the same.

At 60kph, the "best" I got out of the radar speed trap was 55.
GPS was jumping between 53 and 55. That's 7,5%

Went to another trap, tried a 50kph run, had 46-47 on the trap
and GPS. That's 5% at best.

At a ride before, I set the GPS to record the maximum speed, and
I kept it at 100kph (62mph) pinned for a short time. GPS said 94,X.

That's 5-6%.
I checked the 62mph/100kph revs again, they're around 4600.
They were at 5000 before. This should have changed.

Is there a way to mount the speed sensor.. incorrectly?

Cortez said:

Did anyone actually do the 17T mod and CONFIRM the 1% error or
was this all done with math?

Click to expand...

I have it done on mine and it's right on. I really have no idea what's going on with yours, though.

dpaul007 said:

I have it done on mine and it's right on. I really have no idea what's going on with yours, though.

Click to expand...

Can you confirm that your indicated speeds vs revs have not changed?

TownsendsFJR1300 said:

Yamaha Motorcycle Parts 2007 FZ6 - FZS6W ELECTRICAL 1 Diagram

Part #12 is the electronic speed sensor for the FZ6

Click to expand...

Can this senzor be mounted in more ways then one?
Rotated differently?
Anything to make it work.. well.. worse?

I can live with this 5-6% error, but I really wanna know why the rest of the
gang here has the same indicated speed vs revs, and I don't!

Your old Kawasaki had an electrical speed sensor,(similar to the FZ set up) part #21176:

Kawasaki Motorcycle Parts 2007 EX650A7F Ninja 650R ENGINE COVER(S) Diagram

I'm assuming the tire sizes are stock, a wrong sized diameter would screw things up... I also have to assume the clutch is NOT SLIPPING as the engine would rev higher than it should at a given speed... One last basic question, I have to assume you are in 6th gear, maybe count them just to make sure..

Yours, should, be a lot closer with the set up you have.. I guess its possible the sensor could be bad, but it'd be a first that I've heard of.... Perhaps check the connector where it'll plug into the main harness, possible corrosion and ALL the speed signals aren't getting sent?? Guessing here, disconnect the battery for S&G's for a re-set (likely won't do anything but your problem is very odd)...

Should you not be able to get it straightened out, a "Speedohealer" is not hard to install and can be adjusted for it to be dead on.

TownsendsFJR1300 said:

Your old Kawasaki had an electrical speed sensor,(similar to the FZ set up) part #21176:

Kawasaki Motorcycle Parts 2007 EX650A7F Ninja 650R ENGINE COVER(S) Diagram

I'm assuming the tire sizes are stock, a wrong sized diameter would screw things up... I also have to assume the clutch is NOT SLIPPING as the engine would rev higher than it should at a given speed... One last basic question, I have to assume you are in 6th gear, maybe count them just to make sure..

Yours, should, be a lot closer with the set up you have.. I guess its possible the sensor could be bad, but it'd be a first that I've heard of.... Perhaps check the connector where it'll plug into the main harness, possible corrosion and ALL the speed signals aren't getting sent??

Should you not be able to get it straightened out, a "Speedohealer" is not hard to install and can be adjusted for it to be dead on.

Click to expand...

Yeah, everything is fine, tire size, clutch not slipping and definitely 6th gear.
I've tried a couple of times, since I only know speeds in 6th.

3000revs - 60kph
4000revs - 80kph
5000revs - 100kph - dead on, all 3.

Now I'm around 65 at 3000, 85 at 4000, and 105 at 5000.
Speedohealer is a solution for sure, but shouldn't be needed as I obvisouly
have some sort of an issue here that we can't get around.

Not worth that sort of money in my book either, I did the math for correct
speed on all my bikes on the fly, I can continue doing it, but it's annoying
knowing it should be different then it is.

EDIT: Current 5th gear is rather close to what 6th used to be in terms of speed vs revs.
5th gear 4000 revs = 78kph now - used to be 6th gear 4000 revs = 80kph.

It's like I added a 7th gear to the stock setup.

Also, gearing commander site says 100kph (62mph again) revs should be over 5100 on
the stock setup, and around 4800 on the 17T setup. I've got around 4600 showing, and
GPS says 95.. when I bump it up to GPS indicated 100kph, it'll be more or less 4800 like
gearing commander says.

So.. everthing seems to be in order, other then the indicated speed vs revs being screwed up.

I don't know what year your bike is and if you have access to any electrical testing equipment.

In the manual(section 8 07-09 Yamaha manual), it does show how to test the speed sensor and what the parameters are for it to pass.

PM me if you want access to those #'s, won't cost anything but some time and knowledge to check...

BTW, should you pop for the Speedohealer, its easily removed and can be put on your next bike. I still have the stock gearing, with the Speedohealer, compared to the GPS, at 60 MPH, its within .2-.3 MPH on the high side (with the settings I programmed in)

I like to know exactly how fast I'm going as there is a little lag time with the GPS and of course the speedometer is much easier to read...

TownsendsFJR1300 said:

I don't know what year your bike is and if you have access to any electrical testing equipment.

In the manual(section 8 07-09 Yamaha manual), it does show how to test the speed sensor and what the parameters are for it to pass.

PM me if you want access to those #'s, won't cost anything but some time and knowledge to check...

BTW, should you pop for the Speedohealer, its easily removed and can be put on your next bike. I still have the stock gearing, with the Speedohealer, compared to the GPS, at 60 MPH, its within .2-.3 MPH on the high side (with the settings I programmed in)

I like to know exactly how fast I'm going as there is a little lag time with the GPS and of course the speedometer is much easier to read...

Click to expand...

I can get the bike back to the shop, I'm sure they'll do the check if they
know how so I'd appreciate the PM.

The bike is a 2008 FZ6n S2 w/ABS.