NC35 Fork/Yoke and Geometry Settings

[Neosophist]

Yeah I agree, I will be getting the shock rebuilt for my weight and riding style in the new year but was just hoping that people could pass on their experience with shimming the rear/dropping the front and the effects that it had on handling

depends on how / where your riding the bike?

Are you trying to shave seconds off pb lap times or just popping to the supermarkets?

[fourfingers]

It didn´t affect handling , as I took the measurement on a rolling frame whitout engine, just to get base geometry measurements.
If you lower the forks (raise front) you are increasing rake angle, wheel trail and base therefore better stability.
If you raise the forks (lowering front) you are decreasing rake angle, wheel trail and base therefore more agility.
Take care when lowering your front end as the front tyre might end up rubbing on your lower rad under hard breaking.

[Neosophist]

from memory don't the forks have a groove for the circlip to go in? when the circlip is in you can only slide the fork so far up until it is stopped and its the correct "factory" height.

[fourfingers]

Correct, that is what i did. The circlips sit below the standard clipons.
IMHO that should be a good starting point, if you want to mess with geometry.

[SPOONDIDDLY]

Yeah I agree, I will be getting the shock rebuilt for my weight and riding style in the new year but was just hoping that people could pass on their experience with shimming the rear/dropping the front and the effects that it had on handling

depends on how / where your riding the bike?

Are you trying to shave seconds off pb lap times or just popping to the supermarkets?

It's for a bike that is being set up for the track.
I will do some experimenting to see what works best for me, however just wanted to hear some first-hand experience from others

[fourfingers]

I just do some track days now and then, so I don´t have the skills to judge about geometry settings. Having said this, I think it is best to leave forks unmolested and test geometry settings by raising the rear.
In case you don´t have an adjutable length shock, from the nc35 HRC manual:

(4)Rear Shock - Height Adjustment
Unscrew nuts placing rear cushion bracket to cross pipe.
To adjust a height, set the plate(build your own as pg1-14ae.jpg) between the cross pipe and Shock
bracket and screw tighten.
Using 1mm thick plate makes adjusting about 3mm body height on RR acceleration.
It is recommend to make two each kinds of plates, 1mm thick plate and 2mm thick plate

You also have the drawings on the manual, and they are easy to make with a drill and a saw.
I´d go for one each 1mm, 2mm, and 3mm plates, as you will get the same adjustment range with fewer plates.
OEM Shock hasS 308mm between centers.

[Neosophist]

sounds like a fair way to start.

some advice would be to get one of the suspension setup people who often visit the track days to help you get the bike setup optimally (espeically if you are new to getting the bike set-up.. they can shave hours off pissing about)

Rick O sells an adjustable rear linkage i believe.. id get the front forks setup as stock and the schok / linkage in and get somebody in the know to help you dial it in, ideally best at the track, do a few laps to get warmed up then do a few timed laps and adjust and repeat, youll soon get a feel for what works and what doesnt... make note of the base setup though as it will give you a solid foundation to go back to if things get weird.

[fourfingers]

Neo, I´m not sure about Rick Oliver making and adjustable link (dogbone). He does fixed jackup dogbones for the nc30 and the HRC replica trilink+longer dogbone.
I made some adjustable dogbones a while ago, based on Michael Rhuel´s ones.

Adj_shock_link_DSC04572

To the best of my knowledge, it is not a good idea to raise the rear end shortening the dogbone. It will make the rear wheel even more progressive than the stock setup. By progressive I mean the rear wheel will need much more force to move upwards towards the end of the stroke than at the beginning. That is fine on a street bike, as it will cope with a pillions weigh without bottoming, but not as good for a track bike, as a solo rider will probably never use the full stroke of the rear shock, being unable to overcome the exponential(progressive) force needed towards the end of the stroke.
Here is where R O HRC replica is useful, giving the rear wheel a much more linear ratio.



In this graph I have plotted the rear wheel displacement in mm(x axis horizontal), vs the Wheel force Rate in New/mm to move the wheel along the stroke (y axis vertical), for four different cases.
1 nc35 satandard dogbone 108mm shock lenght308mm spring 140Nmm(red)
2 nc35 dogbone 103mm shock lenght303mm spring 140Nmm(blue)
3 nc35 dogbone 108mm shock lenght316mm spring 140Nmm(green)
2 nc35 HRC link dogbone 130mm shock lenght309mm spring 85Nmm(purple)

I have modified dogbone lengths and shock lenghth acordingly to keep the same rear height.
You can notice, the shorter the dogbone, more force per mm is needed to compress the wheel towards the end of the stroke(progressive).
With the HRC link, the force needed to move the rear wheel is much more uniform (linear) along the entire stroke.

On a side note, some people say the bmw s1000rr sachs shock will work with the hrc link, but after reading Dan Kyle´s post http://www.s1000rrforum.com/forum/kyle- ... -mean.html It looks like that shock is just crap. Very poor rebound properties, and compression adjusters interfering with other adjusters settings.
It will be nice if Tony(DM) could chime in and give us some tips on revalving shocks.

Cheers