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Progressive Fork Springs, XS1B
- Thread starter Ipa62
- Start date
I have to compress mine a bit more, because I weigh more nowadays, and I run with a little higher sag. The fork cap threads will engage before you get to that initial compression. AND, this can't be done off the bike. Our early models' fork caps clamp down on the top bracket. Maybe a piss-poor pic may help here.
Like 5twins suggestion of using a T-handle driver, I use a 1/2" sliding-T breaker bar, with a short extension and socket, similar to this. Gives good control.
Like 5twins suggestion of using a T-handle driver, I use a 1/2" sliding-T breaker bar, with a short extension and socket, similar to this. Gives good control.
Our early models' fork caps clamp down on the top bracket. [/QUOTE said:How bizarre !!
Riding around today on our streets and country roads, I watched the movements of the fork lowers. I'm running OEM straight rate springs. The majority of fork movement, from the laden sag position, was 1.25" (32mm) and less. Of course, a bit more while jumping curbs and cattle. And, a lot less on the smooth roads.
I would expect a progressive to allow a bit more travel, maybe 1.5" (38mm), if that typical street ride stayed within the progressive's soft zone.
The question is: At what point would one want the progressive spring to transition from soft to stiff?
I would expect a progressive to allow a bit more travel, maybe 1.5" (38mm), if that typical street ride stayed within the progressive's soft zone.
The question is: At what point would one want the progressive spring to transition from soft to stiff?
Installed the progressive springs yesterday, not to difficult with a little creative persuasion. To measure sag I put a wire tie around the upper shock tube, not too tight, just tight enough to stay in place once the lower tube pushes it up. I weight about 215, climbed onto the saddle, feet on pegs, hands on grips, forks didn't even budge. Next, I stood on pegs, hands on grips and shifted my body weight as far forward as possible, sag was maybe 6-7mm. Now I'm kind of scratching my head. Next, on the saddle, hands on grips, feet on ground, bike positioned about 8" from wall, pushed forward with feet and bumped the front wheel against wall, had about 55mm of fork travel. Ok, maybe that doesn't mean a whole lot, but at least I know the springs/forks are doing something.
I'm not completely sure what all this means, but my initial thought is that the springs are too long and the soft end of the spring is far too compressed to be effective. Based on my earlier measurements the soft end of the spring has 26 spaces at 1.85mm width, about 48mm total travel, when installed the soft end of the spring compresses about 50% of it's available travel, my guess is that the remaining 50% of travel takes more force to compress than the first 50% and perhaps a greater amount of force than what is needed for compression of the coarse end of the spring. I suppose I could remove the spring and put it back on the treaded rod and compress it and take some more measurements, but then this really doesn't help to get the length of the spring correct so that there is some amount of sag with rider on the bike.
I'm not completely sure what all this means, but my initial thought is that the springs are too long and the soft end of the spring is far too compressed to be effective. Based on my earlier measurements the soft end of the spring has 26 spaces at 1.85mm width, about 48mm total travel, when installed the soft end of the spring compresses about 50% of it's available travel, my guess is that the remaining 50% of travel takes more force to compress than the first 50% and perhaps a greater amount of force than what is needed for compression of the coarse end of the spring. I suppose I could remove the spring and put it back on the treaded rod and compress it and take some more measurements, but then this really doesn't help to get the length of the spring correct so that there is some amount of sag with rider on the bike.
I would expect that to change, at least to some degree, after a good chunk of miles. And those garage maneuvers are a long way from the real world, potholes, force of braking and turning. I just never met a new set of progressive springs that I didn't like when installed with all of the force that I could muster.
Scott
Scott
Yes, for now. See if they settle a bit.
As it is, it appears that your laden sag and installed length are quite close to each other. The geometric solution here would be to cut off 1.5" from the spring post in the lowers. But, that can't be done.
Adjustments would be restricted to:
Cutting the coarse spring.
Cutting the fine spring.
Addition of spacers.
Any combination of the above, including all of them.
This is a complex quadratic, much worse than Canadian salad dressing.
Old hat stuff, I'm sure, for the suspension folks.
It'd take me awhile to conjure up a formulae...
As it is, it appears that your laden sag and installed length are quite close to each other. The geometric solution here would be to cut off 1.5" from the spring post in the lowers. But, that can't be done.
Adjustments would be restricted to:
Cutting the coarse spring.
Cutting the fine spring.
Addition of spacers.
Any combination of the above, including all of them.
This is a complex quadratic, much worse than Canadian salad dressing.
Old hat stuff, I'm sure, for the suspension folks.
It'd take me awhile to conjure up a formulae...
Realistically the only solution seems to be to cut the springs, I calculate about 40mm, and from the coarse end. If this is too much I could always add spacers. For now I will ride it and see how it goes. Only concern is that the rebound from compression might be kind of hard on the forks, hopefully the dampening will slow things down.
One last thought, wouldn't it be sweet if there was some type of mechanical adjustment built into the cap for setting the sag. Maybe I'm over thinking this.
One last thought, wouldn't it be sweet if there was some type of mechanical adjustment built into the cap for setting the sag. Maybe I'm over thinking this.
Well, from my guesstimation, I figure that your first 64mm of fork travel will be in the soft zone, the remainder 66mm will be in the stiffer zone.
Whutcha can do, is to put the spring back onto the allthread, and squeeze it down to the installed length. Now, if the installed length is indeed the same as the laden sag, it makes this a bit easier.
Now, suppose that you wanted laden sag to be 1/3 of fork travel, or 1/3 of 130mm, = 43mm. What you would do is to mark the spring 43mm from the end, as the cutting mark. The spring will exert the same force at that cut position. However, when you remove the spring from the allthread, it'll stretch back out, and that marked position could be as far out as 50mm.
With this in mind, cutting off 40mm now will give you something less, maybe 35mm lower. That's about where mine is now.
Of course, the travel to fine coilbind will be different after that cut, would need to find that with the allthread trick again.
Fun, huh?
Whutcha can do, is to put the spring back onto the allthread, and squeeze it down to the installed length. Now, if the installed length is indeed the same as the laden sag, it makes this a bit easier.
Now, suppose that you wanted laden sag to be 1/3 of fork travel, or 1/3 of 130mm, = 43mm. What you would do is to mark the spring 43mm from the end, as the cutting mark. The spring will exert the same force at that cut position. However, when you remove the spring from the allthread, it'll stretch back out, and that marked position could be as far out as 50mm.
With this in mind, cutting off 40mm now will give you something less, maybe 35mm lower. That's about where mine is now.
Of course, the travel to fine coilbind will be different after that cut, would need to find that with the allthread trick again.
Fun, huh?
Hey, Pete. I understand that it requires a bit of finesse, and a license. Down here, we just slather everything with Ranch dressing, .........blindfolded...
...sort of like bahhh-b-cue sauce...
Another thinker.
Given that a progressive spring's motion dynamics have the finer windings doing most of the initial compression/rebound, then becomes essentially a solid lump of steel when at coilbind,
and one would want to minimize unsprung mass,
Would you install the spring with the finer coils on top, or bottom?
Given that a progressive spring's motion dynamics have the finer windings doing most of the initial compression/rebound, then becomes essentially a solid lump of steel when at coilbind,
and one would want to minimize unsprung mass,
Would you install the spring with the finer coils on top, or bottom?
Hmmm....well, I suppose to be strictly correct, you would want to "lighter", less dense portion of the spring down low near the front axle which would dictate placing the tighter wound coils at the top of the fork leg (which is what the instructions say, in fact). Really though, the effect on unsprung mass of the orientation of the spring would be extremely small because the fork slider, front wheel, axle, brake assemblies weigh SO much more than a small portion of the spring. Those components totally swamp (or is it sewer ...or perhaps...cesspool...this week
) the weight of the spring.In engineering, we would refer to this as a "higher order effect" which means that when you do all the math to determine the natural frequency of the spring-mass-damper front end assembly of the bike, the effect of spring orientation would only be found in the higher order terms of the quadratic equation - which have MUCH smaller values.
Speaking salad-dressing-wise that is....
Haha, good one, Pete.
Reminds me of Maxwell's quaternions.
Then, I guess that bug carcass on my lowers won't upset the suspension...
Reminds me of Maxwell's quaternions.
Then, I guess that bug carcass on my lowers won't upset the suspension...
+1
