Hi All,

As per the sig, I get around on a ZX12R. Unfortunately I spend most of
my time riding in straight lines at highway speeds on the F6 freeway.
It bugs me that in order to accurately sit on 110km/h I need to
indicate about 122! This is not my first rodea, and I know this is
pretty normal for motorbikes (ever since my ZZR250!).

However, being a such a powerful torque-monster, and considering I
almost always live on the highway, what if I threw a smaller sprocket
on the rear and dropped the revs plus brought the speedo closer to
reality? There's a 45 on there now (with an 18 on the output shaft
AFAIK) - suggestions? Anything I need to be careful of? Yes I know
accelleration will be compromised…it's got 1200cc and lots of wild
horses to spare (it scares me now!).

Shiny side up peeps!
--
James
ZZR250==>ZX9R==>Hiatus==>ZX12R

Centurion wrote:
> On 2011-11-22 02:19:24 +0000, Centurion said:
>
>> Hi All,
>>
>> As per the sig, I get around on a ZX12R. Unfortunately I spend most of
>> my time riding in straight lines at highway speeds on the F6 freeway.
>> It bugs me that in order to accurately sit on 110km/h I need to
>> indicate about 122! This is not my first rodea, and I know this is
>> pretty normal for motorbikes (ever since my ZZR250!).
>>
>> However, being a such a powerful torque-monster, and considering I
>> almost always live on the highway, what if I threw a smaller sprocket
>> on the rear and dropped the revs plus brought the speedo closer to
>> reality? There's a 45 on there now (with an 18 on the output shaft
>> AFAIK) - suggestions? Anything I need to be careful of? Yes I know
>> accelleration will be compromised…it's got 1200cc and lots of wild
>> horses to spare (it scares me now!).
>>
>> Shiny side up peeps!
>
> BTW the service manual says that should be 46 on the back.

Put the 46 on the back, that will make it slower for the same revs.

On 22-Nov-11 13:19, Centurion wrote:
> Hi All,
>
> As per the sig, I get around on a ZX12R. Unfortunately I spend most of
> my time riding in straight lines at highway speeds on the F6 freeway. It
> bugs me that in order to accurately sit on 110km/h I need to indicate
> about 122! This is not my first rodea, and I know this is pretty normal
> for motorbikes (ever since my ZZR250!).
>
> However, being a such a powerful torque-monster, and considering I
> almost always live on the highway, what if I threw a smaller sprocket on
> the rear and dropped the revs plus brought the speedo closer to reality?
> There's a 45 on there now (with an 18 on the output shaft AFAIK) -
> suggestions? Anything I need to be careful of? Yes I know accelleration
> will be compromised…it's got 1200cc and lots of wild horses to spare (it
> scares me now!).

This might help.
http://www.gearingcommander.com/

This might help too
http://www.amcmotorcycles.com/conten...er.html#p14142

Nev..

"Centurion" wrote

> Hi All,

> As per the sig, I get around on a ZX12R. Unfortunately I spend most
> of my time riding in straight lines at highway speeds on the F6
> freeway. It bugs me that in order to accurately sit on 110km/h I
> need to indicate about 122! This is not my first rodea, and I know
> this is pretty normal for motorbikes (ever since my ZZR250!).

> However, being a such a powerful torque-monster, and considering I
> almost always live on the highway, what if I threw a smaller
> sprocket on the rear and dropped the revs plus brought the speedo
> closer to reality? There's a 45 on there now (with an 18 on the
> output shaft AFAIK) - suggestions? Anything I need to be careful
> of? Yes I know accelleration will be compromised.it's got 1200cc
> and lots of wild horses to spare (it scares me now!).

That very much depends on where your speedo pick-up is from. Unless it
picks up from the gearbox output shaft, no amount of sprocket changes
will correct the indicated error margin. If the speedo is driven from
the box output shaft you will need to increase your wheel speed by 10%
to make your speedo accurate. This will mean reducing your sprocket by
4-58 teeth, or increasing your output sprocket to 20 tooth.

Theo

"Theo Bekkers" wrote
> That very much depends on where your speedo pick-up is from. Unless
> it picks up from the gearbox output shaft, no amount of sprocket
> changes will correct the indicated error margin. If the speedo is
> driven from the box output shaft you will need to increase your
> wheel speed by 10% to make your speedo accurate. This will mean
> reducing your sprocket by 4-58 teeth, or increasing your output
> sprocket to 20 tooth.

reducing your rear sprocket by 4 to 5 teeth, not 58.

Theo

On 2011-11-22 10:20:48 +0000, Nev.. said:

> On 22-Nov-11 13:19, Centurion wrote:
>> Hi All,
>>
>> As per the sig, I get around on a ZX12R. Unfortunately I spend most of
>> my time riding in straight lines at highway speeds on the F6 freeway. It
>> bugs me that in order to accurately sit on 110km/h I need to indicate
>> about 122! This is not my first rodea, and I know this is pretty normal
>> for motorbikes (ever since my ZZR250!).
>>
>> However, being a such a powerful torque-monster, and considering I
>> almost always live on the highway, what if I threw a smaller sprocket on
>> the rear and dropped the revs plus brought the speedo closer to reality?
>> There's a 45 on there now (with an 18 on the output shaft AFAIK) -
>> suggestions? Anything I need to be careful of? Yes I know accelleration
>> will be compromised…it's got 1200cc and lots of wild horses to spare (it
>> scares me now!).
>
> This might help.
> http://www.gearingcommander.com/
>
> This might help too
> http://www.amcmotorcycles.com/conten...er.html#p14142
>
> Nev..

Thanks Nev That works nicely (the first link). I think I'll try to
solve the speedo error with a final drive modification as it will lower
the RPM where I spend most of the riding and hopefully reduce the fuel
consumption (although 4000RPM is probably not much more efficient than
4500RPM due to volumetric inefficiencies at low RPM etc). We'll see

--
James
ZZR250==>ZX9R==>Hiatus==>ZX12R

On 2011-11-23 03:18:18 +0000, Theo Bekkers said:

> "Theo Bekkers" wrote
>> That very much depends on where your speedo pick-up is from. Unless it
>> picks up from the gearbox output shaft, no amount of sprocket changes
>> will correct the indicated error margin. If the speedo is driven from
>> the box output shaft you will need to increase your wheel speed by 10%
>> to make your speedo accurate. This will mean reducing your sprocket by
>> 4-58 teeth, or increasing your output sprocket to 20 tooth.
>
> reducing your rear sprocket by 4 to 5 teeth, not 58.
>
> Theo

Hi Theo,

Thanks for the tip. Figured that's what you meant As for the
pickup, it's from the gearbox output shaft. So essentially and long as
I can make the outputshaft turn 10% slower, but maintain rear wheel
RPM, I should correct the speedo and reduce RPM for the same km/h. Or
am I smoking crack?

--
James
ZZR250==>ZX9R==>Hiatus==>ZX12R

On Fri, 25 Nov 2011 14:09:59 +1100, Centurion <(E-Mail Removed)>
wrote:

>On 2011-11-23 03:18:18 +0000, Theo Bekkers said:
>
>> "Theo Bekkers" wrote
>>> That very much depends on where your speedo pick-up is from. Unless it
>>> picks up from the gearbox output shaft, no amount of sprocket changes
>>> will correct the indicated error margin. If the speedo is driven from
>>> the box output shaft you will need to increase your wheel speed by 10%
>>> to make your speedo accurate. This will mean reducing your sprocket by
>>> 4-58 teeth, or increasing your output sprocket to 20 tooth.
>>
>> reducing your rear sprocket by 4 to 5 teeth, not 58.
>>
>> Theo
>
>Hi Theo,
>
>Thanks for the tip. Figured that's what you meant As for the
>pickup, it's from the gearbox output shaft. So essentially and long as
>I can make the outputshaft turn 10% slower, but maintain rear wheel
>RPM, I should correct the speedo and reduce RPM for the same km/h. Or
>am I smoking crack?

=================

Onya bike

Gerry

"Centurion" wrote

> Hi Theo,

> Thanks for the tip. Figured that's what you meant As for the
> pickup, it's from the gearbox output shaft. So essentially and long
> as I can make the outputshaft turn 10% slower, but maintain rear
> wheel RPM, I should correct the speedo and reduce RPM for the same
> km/h. Or am I smoking crack?

It's better for the chain if you increase the drive sprocket to 20
teeth. Chains prefer larger sprockets. It's also probably cheaper.

Theo

On 24-Nov-11 11:06, Centurion wrote:

> Thanks Nev That works nicely (the first link). I think I'll try to
> solve the speedo error with a final drive modification as it will lower
> the RPM where I spend most of the riding and hopefully reduce the fuel
> consumption (although 4000RPM is probably not much more efficient than
> 4500RPM due to volumetric inefficiencies at low RPM etc). We'll see

I owned an '03 ZX12R for a couple of years. You're talking about a bike
which makes about 180HP.. You're never going to get great fuel
consumption. I used to get 6.5-7.5 L/100km just putting along at 100kph
in top gear and 7.5-9 L/100km when the riding was more spirited.

Nev..