BMW K bikes (Bricks)


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1Back to top Go down   fork travel Empty fork travel Sun Nov 28, 2021 12:19 pm

arbalest

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Spec's say front wheel travel is 185mm. Is that the unladen travel from droop to full compression? I am considering modified fork legs in a version of a leading link fork for my sidecar rig. I'm shooting for about four inches of travel. I would like to shorten the fork tube considerably, using a cut down stock fork spring. Cutting down the fork spring has two advantages. First the spring rate increases with decreasing length. The question is, how much can I shorten the spring to get my four-ish inches of compression with the correct amount of rebound?

    

2Back to top Go down   fork travel Empty Re: fork travel Mon Nov 29, 2021 5:01 am

92KK 84WW Olaf

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From my limited thoughts I cant see that you can cut the spring. I dont s the travel as a problem but damping and springs need to be matched. you dont mention the forks type, some of the Ks have one stanchion compression and one rebound but I dont see leading link units doing that.


__________________________________________________
1992 K100LT 0193214 Bertha Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 106,950 miles Deceased.
1983 K100RS 0011157 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 58,200 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 48,061 miles.
1983 K100RS 0004449 Odette R100 colours 58,000 miles. Sprint fairing now 61,190 miles

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

3Back to top Go down   fork travel Empty fork travel Mon Nov 29, 2021 7:02 am

arbalest

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92KK 84WW Olaf wrote:From my limited thoughts I cant see that you can cut the spring. I dont s the travel as a problem but damping and springs need to be matched. you dont mention the forks type, some of the Ks have one stanchion compression and one rebound but I dont see leading link units doing that.
Early 85 K100

    

4Back to top Go down   fork travel Empty fork travel Mon Nov 29, 2021 7:08 am

arbalest

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92KK 84WW Olaf wrote:From my limited thoughts I cant see that you can cut the spring. I dont s the travel as a problem but damping and springs need to be matched. you dont mention the forks type, some of the Ks have one stanchion compression and one rebound but I dont see leading link units doing that.
Just looked at the K100 damper rods. The damper rods are wholly contained in the lower leg. The damper is a hydraulic damper controlled by orifice diameter. It has no relation to fork travel (to my untrained brain).

    

5Back to top Go down   fork travel Empty Cut it in half Mon Nov 29, 2021 7:00 pm

stanthomas

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I would cut the spring in half then make up to the required ride height with a spacer. Maybe try just a third off to start with.

There is more to it however. The cut end of the spring will not be properly formed but you could fashion a cap with a spring shaped ramp to give proper support. And then there's the fork free length - the damper rod stops the fork over extending so you'll need to rework that too so there's a little bit of preload on the spring at full extension.


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K100RS 16V '91
    

6Back to top Go down   fork travel Empty fork travel Mon Nov 29, 2021 7:09 pm

arbalest

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stanthomas wrote:I would cut the spring in half then make up to the required ride height with a spacer. Maybe try just a third off to start with.

There is more to it however. The cut end of the spring will not be properly formed but you could fashion a cap with a spring shaped ramp to give proper support. And then there's the fork free length - the damper rod stops the fork over extending so you'll need to rework that too so there's a little bit of preload on the spring at full extension.
There are nylon looking caps that have the ramp for the end of the coil. The springs have tangential ends, the springs will not stand by themselves. Cutting the springs a little at a time sounds like a good idea.

    

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