Gearing change WTF, someone care to explain?

[gocartone]

You need to be more clear with what you are saying with RPM vs speed. Are you saying the SPEEDOMETER said 62mph at 5000rpm, and it now says 62mph at 4600rpm? Or are you saying that the GPS/radar said 62mph at 5000rpm, and now it's 62mph at 4600rpm? Did you do the test as accurately before the change as you are now?

Also remember that not all bikes are the same percentage off when coming off the assembly line, so using some numbers other people found with their bikes is not always going to be true for your bike (hell, car speedometers are +/-2.5% from the factory, a 5% difference from the low to the high side, which is 58.5mph to 61.5mph, and they are much more accurate than bike speedometers!). That's without considering how much tires vary in size from one to the next.

 

[Cortez]

You need to be more clear with what you are saying with RPM vs speed. Are you saying the SPEEDOMETER said 62mph at 5000rpm, and it now says 62mph at 4600rpm? Or are you saying that the GPS/radar said 62mph at 5000rpm, and now it's 62mph at 4600rpm? Did you do the test as accurately before the change as you are now?

1) The bolded part.
2) Yes, same way, radar traps, but didn't try GPS.
I had 7% error at 62mph which is the only speed I tried.

Also remember that not all bikes are the same percentage off when coming off the assembly line, so using some numbers other people found with their bikes is not always going to be true for your bike (hell, car speedometers are +/-2.5% from the factory, a 5% difference from the low to the high side, which is 58.5mph to 61.5mph, and they are much more accurate than bike speedometers!). That's without considering how much tires vary in size from one to the next.

Yeah, true, different errors.. but one thing is a constant, everyone is looking
at 5000 revs at 62mph, and I'm not, but should be. That's the reason for
"WTF" in the subject of the thread.

 

[Cortez]

I just found this:
"I went with 17 front/ stock rear. It reduced 6th gear rpm approx 500 rpm"

Here:
higher gearing? - Sportbikes.net

A bit too late to register there and ask the guy, but he basically wrote
that the 17T swap dropped the revs by about 500 in 6th, or, exactly
what happened to me.

Seems like it's gonna turn up to be the norm, and that people who think
they have the same revs weren't actually paying attention.

 

[jspansel]

I just found this:
"I went with 17 front/ stock rear. It reduced 6th gear rpm approx 500 rpm"

Here:
higher gearing? - Sportbikes.net

A bit too late to register there and ask the guy, but he basically wrote
that the 17T swap dropped the revs by about 500 in 6th, or, exactly
what happened to me.

Seems like it's gonna turn up to be the norm, and that people who think
they have the same revs weren't actually paying attention.

Thats how it works on every other bike I have owned... That is why people do it, to lower cruising revs on the highway. Same speed, little lower rpm.

 

[outasight20]

Well, this thread has thoroughly confused the hell out of me. I have the 17T sprocket. When I first changed it, I confirmed that the speedometer was very close to dead on with GPS. Before it was 6-7% off. This was with a new rear tire.

Keep in mind that if you have a worn out rear tire, your speedometer error will increase as you are travelling less distance with each revolution of the rear tire. It isn't much, but can add a few percent to the error.

Finally, if the speed sensor is coming off of the transmission output shaft, then the speedometer is based ONLY on the current gear and RPM, and will NOT be affected by the size of the front sprocket. This is why I am so confused right now. It is simply not possible that your indicated speed and RPM went out of sync with a sprocket change.

If someone can prove me wrong and show how the indicated speed and RPM can be affected separately, please go right ahead.

 

[Cortez]

I'd love to know how this happened, but it did. I can record it.

My rear tire is probably around 1/3 worn.

 

[FinalImpact]

I have an Excel sheet that crunches the numbers. Forum won't take Excel but it will take Word Docs - SO, Download and SAVE AS, Removing the ".DOC" extension LEAVING the ".XLS" extension and wallah - crunch numbers for your Tire size, RPM, GEAR, SPROCKET Count....

Let me know if you have questions.

 

[FinalImpact]

See Above Post by me... This is just a tool. Take it or leave it.

 

[Cortez]

I know what the changes are, I knew them before I decided to buy the 17T,
you're missing the point which is.. the bike should still read the same speeds
at same revs, and it isn't.

That's the "issue".

I've used the gearing commander site to death before getting the 17T
sprocket. Same with my last bike.

 

[TownsendsFJR1300]

I know what the changes are, I knew them before I decided to buy the 17T,
you're missing the point which is.. the bike should still read the same speeds
at same revs, and it isn't.

That's the "issue".

I've used the gearing commander site to death before getting the 17T
sprocket. Same with my last bike.

"the bike should still read the same speeds
at same revs, and it isn't."

Sorry, but your absolutly INCORRECT in your thought process.

If you change either sprocket, up or down, the speed vs revs ARE GOING TO CHANGE. The engine is NOW, (with the larger front sprocket), turning the REAR WHEEL FASTER, as the front sprocket has a LARGER DIAMETER.

IE, just ride a bicycle with multiple gears and change gears. Your pedals are either going to go faster or slower depending on the gear you change to, same principle..

 

[Cortez]

"the bike should still read the same speeds
at same revs, and it isn't."

Sorry, but your absolutly INCORRECT HERE. If you change either sprocket, up or down, the speed vs revs ARE GOING TO CHANGE.

IE, just ride a bicycle with multiple gears and change gears. Your pedals are either going to go faster or slower depending on the gearing..

REAL SPEED will change, but indicated will not, this was confirmed multiple
times in the thread already.

The speed sensor is taking a reading from the front sprocket.
I've already changed +1 on another bike (also mentioned) and it DID NOT
change the speed vs revs (INDICATED, once again), just made the speedo
more accurate.

This should have happened here too, like it did to everyone else's bike.
That's the whole point of this thread.

 

[outasight20]

REAL SPEED will change, but indicated will not, this was confirmed multiple
times in the thread already.

The speed sensor is taking a reading from the front sprocket.
I've already changed +1 on another bike (also mentioned) and it DID NOT
change the speed vs revs (INDICATED, once again), just made the speedo
more accurate.

This should have happened here too, like it did to everyone else's bike.
That's the whole point of this thread.

On my way to work today, I confirmed that at 60 mph indicated in 6th gear, my RPM were right around 5,000. This was with the throttle open. There is a difference of about 200-300 rpm as indicated by the digital tach when you are accelerating or decelerating past a given speed. Perhaps this is where your error is coming from? I believe it is simply from a small amount of lag in the system.

 

[FinalImpact]

I know what the changes are, I knew them before I decided to buy the 17T, you're missing the point which is.. the bike should still read the same speeds at same revs, and it isn't.

That's the "issue".

I've used the gearing commander site to death before getting the 17T
sprocket. Same with my last bike.

Two things would change this; speed'O healer and slipping clutch. I guess yours is special! Perhaps you need a new means to measure speed!

View attachment 48031 :BLAA:

 

[Cortez]

On my way to work today, I confirmed that at 60 mph indicated in 6th gear, my RPM were right around 5,000. This was with the throttle open. There is a difference of about 200-300 rpm as indicated by the digital tach when you are accelerating or decelerating past a given speed. Perhaps this is where your error is coming from? I believe it is simply from a small amount of lag in the system.

Negative on that, since I was able to read it correctly at 5000 revs before,
and it's as accurate as can be just over 4600.

I've got the analogue tach!

 

[FinalImpact]

Not to derail your thread - but on another topic.....

The R6 is using the the same 180/55/17 rear tire.
The primary, secondary and all 6 gears have a different ratio. It works out like so.

MPH at 6000 RPM stock gear and tires…
FZ6 - - R6
27.7 - 29.4
40.5 - 38.0
50.6 - 45.5
59.1 - 52.5
66.2 - 59.0
72.7 - 66.0

 

[FinalImpact]

"the bike should still read the same speeds
at same revs, and it isn't."

Sorry, but your absolutly INCORRECT in your thought process.

If you change either sprocket, up or down, the speed vs revs ARE GOING TO CHANGE. The engine is NOW, (with the larger front sprocket), turning the REAR WHEEL FASTER, as the front sprocket has a LARGER DIAMETER.

IE, just ride a bicycle with multiple gears and change gears. Your pedals are either going to go faster or slower depending on the gear you change to, same principle..

Scott, he is saying the crank all the gears in between (1-6) are FIXED and DIDN'T Change in relation to the output shaft - thus, the BIKE will be traveling at a faster speed but the FIXED VALUE of all those gears I just mentioned remained the same - therefore the RPMs should still match the output shaft just as they did before the change.

I suspect the issue is the imposed load. As you increase the load it drops the RPMs. Increasing the sprocket diameter increases the load.

 

[Cortez]

Scott, he is saying the crank all the gears in between (1-6) are FIXED and DIDN'T Change in relation to the output shaft - thus, the BIKE will be traveling at a faster speed but the FIXED VALUE of all those gears I just mentioned remained the same - therefore the RPMs should still match the output shaft just as they did before the change.

I suspect the issue is the imposed load. As you increase the load it drops the RPMs. Increasing the sprocket diameter increases the load.

Why didn't it happen on my kawasaki then?
This is pissin' me off!

 

[outasight20]

Unplug your gauge cluster and ride the damn thing!

 

[Cortez]

Nah!
Too expensive.

 

[TownsendsFJR1300]

Scott, he is saying the crank all the gears in between (1-6) are FIXED and DIDN'T Change in relation to the output shaft - thus, the BIKE will be traveling at a faster speed but the FIXED VALUE of all those gears I just mentioned remained the same - therefore the RPMs should still match the output shaft just as they did before the change.

I suspect the issue is the imposed load. As you increase the load it drops the RPMs. Increasing the sprocket diameter increases the load.

I agree with most of what you say BUT AS SOON as the sprockets are changed, the TRUE SPEED in relation to RPMS WILL CHANGE..

IE, if you could put a 50 tooth front sprocket on the engine, RPMs WILL BE LOWER FOR THE SAME SPEED, more chain is being pulled, thus spinning the rear tire faster...

You know as well as I do, change a sprocket #, the speedometer will also change. Put bigger tires on a car than stock, the speedometer READS LOW...