Final drive jiggery-pokery

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!

 

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

 

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

This might help too
http://www.amcmotorcycles.com/contents/en-uk/d601_speedo_healer.html#p14142

Nev..

 

"Centurion" 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.

Theo

 

"Theo Bekkers" wrote

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

Theo

 

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

 

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

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

 

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..

 

Agreed. Ideally, I'd increase the teeth on the output shaft as much as
possible, but like most bikes, the clearance around the drive sprocket
is limited.