vanzen@rockerboxer.com wrote:Alterations to the internals of a forks system will impact the handling behavior of that forks system.
Pretty obvious, that.
Altering that system without an understanding of the effects will very likely be problematic
either in terms of cost or safety...
Perhaps you are able to calculate the cumulative effects of your random proposed changes
or perhaps you will risk your safety to pursue the "trial and error" approach.
But then you will be the one asking the questions,
and I will be the one to say that, if you need to ask –
Houston, we have a problem.
Love those Euro-bars, eh ?
Good luck with the Motorcycle Handling, Chassis Design, Engineering, and Physics –
crash course !
Hello Vanzen
What I'm asking for -( and not affraid to ask) is advice from people like you who have probably a better understanding than most on the subject in question . What I would like would be educated responces and not replies that evaid the specifcs like a politician - surely that is what this forum is all about - sharing knowledge.
I want to shorten a pair of K75S forks to fit my Mono - I'd only be shortening the stanchions by 34mm but yes the internal volume would have to be addressed, the geometry I think would be no different than you have used on your bike so what else is there that would be different ? Get the oil level right and the damping will be the same, spring rate hasn't changed and so as far as safety is concerned I just need to make sure that the new circlip groove is as was - what else would be different - I'm just asking! as yes I really do like my Euro bars!
OK, Nourish, apparently you are dedicated to the more difficult of 2 paths of action !
Given that later (post-84 mono) 247s and early Ks used a very similar forks system design
I would begin my research there –
i.e. Studying and cataloguing the specific differences between the two systems –
Stanchion length, Spring lengths, spring rates (K-bikes are heavier), and spacer lengths.
This information could then be used to replicate a known working system within the shortened K-stanchions
and establish a practical point of experimental / tuning departure –
re: volume
Typically, I use a ruler to measure the fork oil in an "unknown" forks system.
6" from the top of the stanchion with forks compressed and springs removed will be a preliminary setting.
Forks action will be very sensitive to changes in the amount of oil used.
Lower levels reduce internal air-pressure build up as the forks compress.
Higher levels increase pressure rise, reduce braking dive and the chance of bottoming.
re: changing preload
Preload will principally affect ride height, sag,
(25 - 33% of the available suspension travel (spring compression)
should be used initially to avoid both bottoming-out and topping-out the suspension)
and to a lesser extent, suspension travel and the imposed load needed to initiate suspension movement.
Thanks for your reply Vanzen.
I spoke to someone at Hagon about their progresive spring lengths and he talked to me about oil levels and what altering that does and said a good place to start was with a 140mm air gap so in the same ball park as your 6".
The kids were out this afternoon so had a bit of peace and quiet and took some time to study the part drawings of the K forks and finaly understood what I'd read in a magazine article, the K75S uses a 50mm spacer below the damper tube and in this article it talked about "moving the damper up into the fork leg to effectively shorten the fork length"(?) - so now my understanding is that this spacer was machined down 20mm, lowering the damper tube and stanchion down into the slider. This would also lower the bump stop leaving the same fork travel and keeping the spring length the same as standard. So as you advised, measuring the fully extended fork length of the K legs and that of the Mono and less the difference that the thicker cast yoke will take up there is only 20mm difference - as mentioned in that article.
So in effect the ride height can be set by this spacer(within reason) seperate from preload - too good to be true?
I presume that in this instance preload or sag dealt would be dealt with once it's all put together and not some complicated calculation?
Cheers
Even though you don't understand how geometry works, you will be ok............... if you just don't ride it and only admire the retro look from your easy chair.
If you really want to ride it, then start shoving the tubes upwards a bit at a time until you get neutral steering.
It is your bike, do as you wish, but you asked for advice and have gotten some very good advice, esp from vanzen.
Ask the Indians what happens when you don't control immigration.
