Fork overhaul

dwalby said:

maybe I haven't thought this through, but as long as you get some compression in the forks with the current spacers, the difference between the sag you have now and 30mm sag, is the amount you want to shorten the spacers. I think whatever preload you apply through the spacer length, translates into that much less upper slider travel to reach equilibrium. If you add 10mm to the spacer length, the upper slider now has to move 10mm less to support the weight of the bike by compressing the spring, and your ride height goes up by 10mm.

edit: this assumes you change the spacer length in each fork by the same amount, and don't just change one of them, but I think that's fairly obvious.

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Problem is I'm getting ZERO sag and could probably cut a little off the length of the spacers and still get ZERO sag. Should have known the spacers were way too long when I was struggling so much to get the caps back on the tops. What I did was incorrectly assume that the new springs with spacers and washers should equal the length of the old springs. Just doesn't seem to be the case with my bike. I thought that was what I was supposed to do, but perhaps I incorrectly read that when it was advice for the 1300 forks.

But I get your point about the equilibrium....just I haven't found the correct length of the spacers yet that would get me to that point.

Looks like I've just got to tinker with it a bit. During my second attempt, I'm going to try to follow the instructions that came with the Sonic springs. The instructions do mention that the new spring/spacer comber might be shorter than stock because the stock setup have a lot of preload to keep sag within reason with the softer stock springs.

Although this process is a bit time consuming and frustrating, I now know about 2,000% more about suspension setup than I did a week ago.

If you measure your old springs with the original spacers you'll have a feel for 'close'.
Then if you use a piece of PVC you can cut spacers to the size you want.

Mark said:

If you measure your old springs with the original spacers you'll have a feel for 'close'.
Then if you use a piece of PVC you can cut spacers to the size you want.

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That's what I thought too, but not the case with my bike. Sonic instructions are calling for a general starting point of only about 1/2" of preload which is FAR less than the stock setup. I'm guessing I cut the spacers about 2 inches too long the first time. Hoping I get lucky and have better results on my 2nd attempt tonight.

Motherfudger Following Sonic's instructions for 1/2" preload, I'm getting 44 mm of sag. Looks like 3rd time is (hopefully) going to be the charm.

Climbingaz said:

Motherfudger Following Sonic's instructions for 1/2" preload, I'm getting 44 mm of sag. Looks like 3rd time is (hopefully) going to be the charm.

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Hey, now that you're getting closer, I was thinking about a few things. Was the 30mm sag a recommendation of Sonic? If so, you may find you don't like it all that well after trying it, so you could end up changing it again. A good way of doing several adjustments back and forth is to pre-cut a set of spacers out of 1" PVC pipe. Also, for fine tuning you can just change the left fork, and leave the right one alone. (This is the case on the ST1100 non-ABS forks, where the left is a standard fork and the right is a cartridge fork, so the left is easier to change. I know some of the ABS models have larger diameter forks, but don't know about the internals, so the story may be different there) Keep all the plastic off so the fork caps are in plain view, and you should be able to swap out the left spacer in a matter of a few minutes, test ride it for a while, and try again.

dwalby said:

Hey, now that you're getting closer, I was thinking about a few things. Was the 30mm sag a recommendation of Sonic? If so, you may find you don't like it all that well after trying it, so you could end up changing it again. A good way of doing several adjustments back and forth is to pre-cut a set of spacers out of 1" PVC pipe. Also, for fine tuning you can just change the left fork, and leave the right one alone. (This is the case on the ST1100 non-ABS forks, where the left is a standard fork and the right is a cartridge fork, so the left is easier to change. I know some of the ABS models have larger diameter forks, but don't know about the internals, so the story may be different there) Keep all the plastic off so the fork caps are in plain view, and you should be able to swap out the left spacer in a matter of a few minutes, test ride it for a while, and try again.

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Well, late last night I went through my third attempt and think I might be just about dialed in. My original target for 30mm of sag was what was recommended from Sonic (well, actually they say between 30-35mm for street riding). And my goal of 30mm was without all my gear on. Well, I did a bit more research and watched a few videos from Dave Moss (do a youtube search), and he recommeds 35-40mm for street riding. Less than 35mm for the track. So anyways, on my third attempt, I accomplished about 38mm of sag. I think this is going to give me a reasonable basis to actually button the bike all back up and go for a ride to see how I like it.

And like you mentioned, although my bike is an ABS model, the left-side fork is way easier to work with. With a little cursing, I think I might actually be able to change the spacer in the left fork without taking it off the bike.

Now I completely understand why having non-adjustable forks sucks ballz! :

What are you guys running for sag?

Climbingaz said:

Well, late last night I went through my third attempt and think I might be just about dialed in. My original target for 30mm of sag was what was recommended from Sonic (well, actually they say between 30-35mm for street riding). And my goal of 30mm was without all my gear on. Well, I did a bit more research and watched a few videos from Dave Moss (do a youtube search), and he recommeds 35-40mm for street riding. Less than 35mm for the track. So anyways, on my third attempt, I accomplished about 38mm of sag. I think this is going to give me a reasonable basis to actually button the bike all back up and go for a ride to see how I like it.

And like you mentioned, although my bike is an ABS model, the left-side fork is way easier to work with. With a little cursing, I think I might actually be able to change the spacer in the left fork without taking it off the bike.

Now I completely understand why having non-adjustable forks sucks ballz! :

What are you guys running for sag?

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I came from the sportbike world, so I have mine setup pretty sporty. Its been many years since I measured it, but I seem to recall something like 20-25mm.

For sure you can change the left spacer while on the bike. Jack up the front wheel to get the weight off of it and you can easily compress the fork spring, spacer, and cap in one quick motion. I have a 17mm hex driver on a ratchet/extension, so its easy that way. If you're using a L shaped allen wrench then that might be a different story.

I measured it tonight and its closer to 40mm. The 20-25mm was the difference from being on the sidestand to upright with me on the bike (175lbs). I think I remember now that a few years ago I decided to back off the preload a bit, and put in heavier fork oil instead. I think at one time I had 5-10mm less sag than I do now, so I was probably at 30-35mm before, certainly no less than 30mm.

dwalby said:

I measured it tonight and its closer to 40mm. The 20-25mm was the difference from being on the sidestand to upright with me on the bike (175lbs). I think I remember now that a few years ago I decided to back off the preload a bit, and put in heavier fork oil instead. I think at one time I had 5-10mm less sag than I do now, so I was probably at 30-35mm before, certainly no less than 30mm.

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Yeah, I was going to say...at 20-25mm you must be racing your ST in the Isle of Mann.

I'm thinking that I'll probably be coming in closer to 40mm full of gear. But went out for a ride this morning for the first time and it feels SOOOOOO much better than before. I might enlist a buddy to come over and do another sag measurement with me to double-check my figures, but I think it's good enough for now. And for my own memory, as the bike sits now I'm running about 20mm of preload, 38mm sag, using 10wt oil at the 130mm level on the 1.1kg Sonic springs.

Really appreciate all the feedback and help from everyone!

Has anyone tried using a bigger spacer with the oem springs? since they are a progressive type spring surely putting in bigger spacers would adjust the front sag and stiffen up the springs? also what diameter spacer (pvc pipe?) would you need in the 43mm st1100 abs2 forks?

broc11 said:

since they are a progressive type spring surely putting in bigger spacers would adjust the front sag and stiffen up the springs? also what diameter

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a) no 'new' spacers with my Hyperpro springs (same with the Wilbers ones), simple drop-in and re-use the OEM parts; b) keep in mind that taller spacers can impact the avail suspension travel...

ST1100Y said:

a) no 'new' spacers with my Hyperpro springs (same with the Wilbers ones), simple drop-in and re-use the OEM parts; b) keep in mind that taller spacers can impact the avail suspension travel...

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Hi Martin, trying to save a bit of cash here LOL, are the hyperpros the exact same lengh as the oem springs then? a friend of mine has suggested just putting in bigger spacers to stiffen up the oem springs,not sure what to do just, thanks

I understand the issues, but it goes beyond 'stiffening'... in old, worn fork springs the structure has changed, adding taller spacers will increase preload by compressing the soft/tight wound area... means loosing comfort (sore wrists and that) and messing up the ratio... and 'ratio' is the thing, in this the fork springs ought to match the rear spring... sure will taller spacers change the 'feel' of the front, but that's your experiment then, and all the small bumps and cracks in the tarmac will torture your wrists and forearms (and I know from experience that you'll have some patchworked roads over there )... the Hyperpro springs had (almost) the same length then the (used) OEM ones, and being 'progressive' meant a slightly increased effort was required to get the caps back on ;-) But not by much, so unobstructed movement of all coils is still avail, small bumps get properly absorbed.

ST1100Y said:

adding taller spacers will increase preload by compressing the soft/tight wound area... means loosing comfort (sore wrists and that) and messing up the ratio... and 'ratio' is the thing

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Thank you, this is doing my head in,sorry for all the questions,I don't know enough about it, and how to get the right amount of sag etc, the wilbers 640 came set with 16mm preload and 11 clicks rebound based on the weight I gave them,240 lbs rider,80% solo riding.
I had a 2up ride with that shock setting and didn't adjust anything and it was fine, I think, I suppose I should be adjusting it a bit for 2up.
I'm just debating if it's worth putting hyperpros in and if I will notice much difference,the oem springs are very 'plush' and comfortable,but I suppose they are sagged with my weight,
I don't know how to measure/set sag, just sitting on the bike and pumping the forks up and down with the front brake on they feel very soft and springy,

on my Vfr on the other hand, doing the same thing the forks springs feel at least twice as stiff,and the rebound is slower. all I done to them was changed to 10wt fork oil,still on oem springs,though the preload adjustment is very handy on the vfr,backed it of a bit and that left her more comfortable.

ST1100Y said:

I understand the issues, but it goes beyond 'stiffening'... in old, worn fork springs the structure has changed, adding taller spacers will increase preload by compressing the soft/tight wound area... means loosing comfort (sore wrists and that) and messing up the ratio... and 'ratio' is the thing, in this the fork springs ought to match the rear spring... sure will taller spacers change the 'feel' of the front, but that's your experiment then, and all the small bumps and cracks in the tarmac will torture your wrists and forearms

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Martin, if I'm not mistaken adding preload has no effect on how much the spring compresses, just where the compressed spring is positioned inside the fork tube. This affects only the ride height because it directly affects where the lower slider is positioned within its available travel. The spring compresses the same amount with or without preload, based on the weight applied on the forks and the fork spring rate. To use a simple example if you have 100kg on the front end, and the spring rate is 1mm/kg, with no preload the spring will compress by 100mm. If you preload the spring by 50mm, that applies a preload force of 50kg. Now apply the same 100kg load, the first 50kg load will not compress the spring at all because of the opposing preload force, and then the remaining 50kg of load will compress it by 50mm. So now inside the tube the spring is still compressed by 100mm but instead of that 100mm compression being measured from the fork cap (no spacer initially) its measured from 50mm below the fork cap because the preload spacer is now inside. So the only change is the ride height is 50mm higher than the previous case because the spring location has been moved downward by 50mm by the preload spacer. The lower fork tube, which puts the force on the other end of the spring, is now 50mm lower in its travel than with no preload.

So your comment about the softer coils being bound due to the preload spacer being inserted is not correct, the spring is compressed the same amount in either case.

What makes it feel stiffer and more harsh has something to do with a change in the oil dampening response due to the higher ride height. I've never been able to pin down exactly how it happens, but many years of experimentation and empirical data agrees with your comment that it will get more harsh feeling, but its not due to the spring. After years of wondering about the cause, I was finally able to produce the exact same symptom with a fully adjustable front fork on a modern sportbike, by simply increasing the rebound dampening without changing the spring preload at all.

broc11 said:

Hi Martin, trying to save a bit of cash here LOL, are the hyperpros the exact same lengh as the oem springs then? a friend of mine has suggested just putting in bigger spacers to stiffen up the oem springs,not sure what to do just, thanks

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1. remove left fork cap
2. measure existing spacer
3. cut longer spacer from 1" PVC pipe
4. replace spacer and fork cap
5. test ride bike

6. repeat steps 1-5 with varying spacer lengths until satisfied with ride qualities

this technique worked fine for me, but you're 70lbs heavier than I am, so there may be a practical limit where you will be better off with changing to a higher rate spring, can't answer that question for you.

Also, using just the left fork is OK for small adjustments, but if you start making bigger ones then you will probably want to increase the spacer length on the right fork as well. Ideally you'd want the same preload on both forks, but that's not 100% necessary and changing the left spacer is way quicker and easier than the right spacer.

this experiment is basically free, so you have nothing to lose by trying it.

dwalby said:

Martin, if I'm not mistaken adding preload has no effect on how much the spring compresses, just where the compressed spring is positioned inside the fork tube.

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Well, here is what I've been told about this matter, thus how I understand it: already the OEM springs are '2-step progressive', the narrow wound area (on OEM about 100~150mm in length) is the 'soft' part, the wider wound upper section is the 'stiffer' thus harder part. When compressing the spring its 'counterforce' to expand will raise proportionally with the travel of its compression; however will the form/shape of this force-curve/graph depend on various factors, like composition of the steel, wire diameter, heat treatments/hardening, ratio between narrow and wider wound section, etc... so it could be a nicely parabolic curve, it could also form an elevating angle first with a sudden and steep upward tilt at some point...
When putting load on our '2-step design' spring, the narrow wound/softer part will compress first, until its wires bind, eliminating the 'softer' part so only the wider wound/hard part of the spring remains avail for suspension. (And by adding preload spacers you'll narrow, yet might eliminate this softer part of the spring, leaving only this wider wound hard/stiffer part functional)
When I got my Wilbers fork spring set I'd to notice their appearance: the narrow wound section was only 50~80mm long and compared to the rest of the steel wire used, the soft part was very dark/blackish, so some heat-treatment/softening process can be assumed. And their performance while installed felt as if the soft part was already compressed down to like 15~ 20mm remaining travel, so every time I ran over some unevenness in the road surface it felt like 'bam!' a hammer hitting the handlebar when the springs banged on their obviously much harder, wider wound section... really uncomfortable... tried everything from 15W, 10W, 7W yet even 5W oil, but no avail, sore wrists after ~1 hour of riding... telling the suspension guru who'd done the installation about this, he just nodded, told me that he'd expected this and recommended the 'linear wound progressive' springs, offering a much milder characteristic curve, better suitable for my application then the 'race track style 2-step progressives'...

ST1100Y said:

(And by adding preload spacers you'll narrow, yet might eliminate this softer part of the spring, leaving only this wider wound hard/stiffer part functional)

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No, that is not true. The load on the spring is exactly the same with or without preload, its the weight force applied to the front wheel. As long as the load force is greater than the preload force, then preloading the spring doesn't put more force on the spring, it just changes the travel distance required by the lower slider to reach equilibrium. (re-read my previous post example, the spring compresses 100mm in either case so the coil binding condition is exactly the same in either case) Draw a diagram and I think you'll agree that the weight force doesn't change, so the spring reaction to that force can't change either. The only change is the location of the spring inside the fork relative to the top of the fork tube, so you get a different ride height.

dwalby said:

No, that is not true. The load on the spring is exactly the same with or without preload, its the weight force applied to the front wheel. As long as the load force is greater than the preload force, then preloading the spring doesn't put more force on the spring, it just changes the travel distance required by the lower slider to reach equilibrium. (re-read my previous post example, the spring compresses 100mm in either case so the coil binding condition is exactly the same in either case) Draw a diagram and I think you'll agree that the weight force doesn't change, so the spring reaction to that force can't change either. The only change is the location of the spring inside the fork relative to the top of the fork tube, so you get a different ride height.

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This being the case then why don't people just put in a bigger spacer on the oem springs? instead of buying replacement springs.on my vfr I just screw up or down the preload adjuster on top of the forks,and it's amazing how much difference a few turns make to the harshness of the suspension feel.
I think changing to 10 wt fork oil will stiffen the rebound up a good bit,making her less bouncy. also I have rebuild kit coming for the anti dive valve,so that should stop her diving so much when braking.
At the end of the day I have the pan for touring,2 up sometimes and I don't push her that hard in corners, if I want a good blast through the twisties I have the vfr.
Just now when I am doing a refurb on the forks I want to get it done as right as I can the first time. It's a pity I can't get a ride on a pan with different fork springs to see if I'd notice the difference.

broc11 said:

This being the case then why don't people just put in a bigger spacer on the oem springs? instead of buying replacement springs.on my vfr I just screw up or down the preload adjuster on top of the forks,and it's amazing how much difference a few turns make to the harshness of the suspension feel.

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The harshness is due to differences in the oil dampening response because you now have a higher ride height and the position of the dampening orifices have changed inside the fork. I'm not claiming the fork response won't change, I'm only making the claim that the spring compression distance is the same regardless of spacer length. Springs compress a given distance in response to a force applied, and that force is the weight on the front wheel, which doesn't change simply because of the spacer. If you had a transparent fork tube you'd see the spring inside compressed to exactly the same length, but its overall position is changed by the length of the spacer.

and to answer your question about why don't people just put a bigger spacer in with the OEM springs, they do. I'm one of them who has done it (see post #36 of this thread), there are many others as well who have done it. But you reach a practical limit if you have a very large load on the front wheel. First of all, packing 150lbs of preload into the fork just isn't practical from a leverage/strength perspective, and if you have a substantially heavy load which requires that much preload the spring will be compressed more than it was designed for. So you go to a higher rate spring so that the distance the spring compresses is back in line with what the bike was designed for.

If you have the ability on your VFR to adjust the fork rebound dampening with a screw on the top, do me a favor and give it a few turns to the stiffer setting direction. (make sure you measure how much you changed it by so you can put it back) My experience shows you'll get that same harshness without changing the spring preload at all.