Fork Spring Mod

[Guest]

Hey all, need some direction. So I'm trying my hand at cutting my stock fork springs for my 80' 1000G and putting the PVC spacer in. So I've cut the springs, 3" off the tightly wound end but now I'm scratching my head as to how long of a PVC spacer to put in. I was reading threads and 'I think' I'm supposed to put in a length of spacer that will bring it all to the stock length of the spring (what would have been smart is if I had measured that length before I cut them). I'm guessing I replace the entire space, the 3" I cut off and the stock metal spacer by one PVC spacer. I guess I can just measure the metal space, add 3" and go from there and do the rebound test but maybe there is an easier way. If someone can chime in on this it would be appreciated.

 

[Steve]

Did you have any kind of spacer in there along with the stock spring?

If you did, add the lengt of that spacer to the 3" that you cut off the spring.

Be sure to measure your "sag", you might need more length than that, even.

.

 

[Guest]

Yes there was the stock metal spacer in there. So like you say, add the length of the original spacer to the 3 inches I cut off then measure my 'sag' and adjust the length of the spacer as needed.

 

[Steve]

Yep, that's pretty much it, but you can't measure the "sag" until you get it all put back together, so be prepared to open them up a few times.

.

 

[Guest]

Got it, thanks Steve.

 

[Steve]

No problem, that's why we're here.

Time to catch a nap now, before "work" tomorrow.

.

 

[salty_monk]

If you want to get technical you can use this to calculate spring rate rather than trial & error.

http://www.pontiacracing.net/js_coil_spring_rate.htm

I think you will need to chop off more than 3" & actually you are better off chopping the loose wound end not the close wound end in a lot of cases.

The way a progressive spring works is that it starts of with a number of coils (say 50) when the close wound ones bind (i.e. all join up) they are now solid & act just like a spacer so your spring is now a 40 coil spring (10 close wound coils) & thus a higher spring rate.

What you have done by chopping the close wound end is change your initial spring rate but not changed the rate of the overall spring.

If you play about with the figures in the link you will understand it better. I did a huge amount of research on this. It's quite difficult to get to the rate of a Sonic or terminal rate of a progressive (50lb/inch on a progressive for the GS1000 once the close end binds) using a stock spring as you end up with a spring about 10" long only!

Dan

 

[bwringer]

Yep -- you can easily end up with binding if you cut very much off a stock spring, and you probably still won't have an acceptable spring rate. Stock spring rates are very, very weak.

You should be OK with only 3" cut off, but I wouldn't cut any more. And it will be better than it was, although probably still far from ideal.

To this day, all the Japanese manufacturers still very commonly sell bikes with spring rates too weak to even hold up the bike, let alone a standard humanoid or two. No one has any clue why they do this.

On the sporting models, they do pay more attention to suspension, but many bikes still arrive on our shores set up for the underaged anorexic Japanese ballerinas they apparently employ as test riders.

Sonic Springs in the correct rate are only $80 and will transform your bike's front end. Worth every penny and then some.

Progressive brand springs are more common and more expensive, and also an big improvement from stock, but they come in a "universal" progressive spring rate that is not sufficient for anyone over 150-180 pounds. Faster and/or larger riders will be better off with straight-rate Sonic springs.



To get back to your original question (sort of), assuming you have the proper spring rate (which you probably don't), you cut spacers so that you will end up with 1/2" to 3/4" of preload when the fork caps are installed. Since you likely do not have the proper spring rate, you'll need to make your spacers so that you end up with some greater amount of preload, maybe 1 to 1.5 inches or more to at least achieve proper sag.

 

[Sandy]

I think as a general start point you want the spring/spacer combo to just sit slightly above the top of the fork tube so you have to push down a bit on the cap to get the threads started. From there you can add washers to fine tune it stiffer or cut a little more off to soften it. Just remember at full extension you still need some, even just a little pressure, on the fork caps when they're screwed in all the way. If the spacer is too long and sticks up too far it's a real bear to get the caps on.

 

[Guest]

I think as a general start point you want the spring/spacer combo to just sit slightly above the top of the fork tube so you have to push down a bit on the cap to get the threads started. From there you can add washers to fine tune it stiffer or cut a little more off to soften it. Just remember at full extension you still need some, even just a little pressure, on the fork caps when they're screwed in all the way. If the spacer is too long and sticks up too far it's a real bear to get the caps on.

Thanks for this info Sandy, because I did not measure the spring 'before' I cut it, duh, aaannnddd..I threw the spacer in the same bucket with all the other spacers from 850's, 750's, 1000E's, etc, etc...nice one if I do say so myself. Looking at the tutorial on Cliff's site from 'Mr.Matchless' I was able to figure out which was the right one, lol:-\\\ Sure appreciate all the info/research salty and bwringer, I'll be curious to see what she feels like when she's back on the road. In the end this may be a lost cause and I will just throw in a set of progressives as I'm not doing this to save money but to experiment with something I've never done. 'bwringer' I've never used a set of Sonics, are they really that much better than the progressive? I'm only 170 lbs but this bike in particular is going to be for touring 2 up with full luggage as well as hauling my skinny but around on my own.

 

[bwringer]

You're in the weight range where Progressive brand springs would also work well for you and be a bit more comfortable than straight rate springs.

Straight rate springs would give you a bit less brake drive and more linear response if you're riding really hard. About $10-$15 less, too...

If you're going to add a fairing up front, don't forget to account for the weight of the fairing. In that case, I'd definitely go for the straight rate springs in the next higher rate indicated for your weight (there's a calculator on the Sonic site) or maybe add the fairing's weight to your own when using the calculator. You might also email Rich, the owner of Sonic Springs, for advice. He responds quickly, and he's GS owner, racer, and a member of the GSR forum.

 

[Guest]

You're in the weight range where Progressive brand springs would also work well for you and be a bit more comfortable than straight rate springs.

Straight rate springs would give you a bit less brake drive and more linear response if you're riding really hard. About $10-$15 less, too...

If you're going to add a fairing up front, don't forget to account for the weight of the fairing. In that case, I'd definitely go for the straight rate springs in the next higher rate indicated for your weight (there's a calculator on the Sonic site) or maybe add the fairing's weight to your own when using the calculator. You might also email Rich, the owner of Sonic Springs, for advice. He responds quickly, and he's GS owner, racer, and a member of the GSR forum.

Thanks for the input Bwringer, I had actually thought of trying a full fairing on the front to see what it would be like, I think I'll wait until that experiment is sorted out before buying new springs, thanks!

 

[salty_monk]

Progressive springs start at 35lbin & become 50lbin springs when the closely wound coils bind if I remember correctly....

On the 1100 Forks I have I did the calculations to do what you have done using the link I gave you. My springs are now 14" long only (i.e. I chopped off about half the spring). You can't go any shorter otherwise you risk binding at full travel. This gives about 42lb/in springs. I haven't ridden on them yet.

Sonic recommended 0.9kg/mm for me from memory (which is 50l/in the same as the terminal rate on a set of progressives. You & I are about the same weight.
I currently have the progressive springs fitted to stock forks on the skunk & they are about perfect with approx 10mm of spacer sticking out the top of the fork leg. You & I are about the same weight (I'm 165lb). With regular two up riding I think you'll want more spring or a way to add preload (The 1100 forks have preload adjusters on the top but the adjusters don't fit GS1000 forks). The other thing you could look at is cartridge emulators, you can get away with less spring if you have those fitted as you can increase compression damping a little which slows down brake dive etc (which is why I am happy to start at 42lb/in on the 1100 forks as they have emulators fitted).

 

[Guest]

Well according to the calculations I'll be starting with 25 lbs/inch and 56 lbs/inch when compressed, the compressed rate could be closer to 50 lbs/inch as it was a bit hard to get an exact measurement of the spring compressed. All very interesting. Although as Dan mentioned it appears I cut the wrong end, I cut the tight wound end instead of the loose end, I read and read on this subject yet still cut the wrong end, does that make me dyslectic or just stupid?? Anyways I'm glad I'm doing this as it's helping to motivate me to get her up and running.

 

[Guest]

Well according to the calculations I'll be starting with 25 lbs/inch and 56 lbs/inch when compressed, the compressed rate could be closer to 50 lbs/inch as it was a bit hard to get an exact measurement of the spring compressed. All very interesting. Although as Dan mentioned it appears I cut the wrong end, I cut the tight wound end instead of the loose end, I read and read on this subject yet still cut the wrong end, does that make me dyslectic or just stupid?? Anyways I'm glad I'm doing this as it's helping to motivate me to get her up and running.

Naw, you just committed a Homer D'OH is all lol

 

[salty_monk]

Well according to the calculations I'll be starting with 25 lbs/inch and 56 lbs/inch when compressed, the compressed rate could be closer to 50 lbs/inch as it was a bit hard to get an exact measurement of the spring compressed. All very interesting. Although as Dan mentioned it appears I cut the wrong end, I cut the tight wound end instead of the loose end, I read and read on this subject yet still cut the wrong end, does that make me dyslectic or just stupid?? Anyways I'm glad I'm doing this as it's helping to motivate me to get her up and running.

A ton of people have done it the way you did it (me included on a couple of bikes). It's not "wrong" I just wanted you to understand it so you could better figure out what to do.
What you have done is akin to adding additional preload (i.e. you have changed the "start" point but not the final spring rate). It's not precisely the same & I'd need a bunch of graphs to explain it properly (& you'd be bored to tears!)

I also cut off the tightly wound end on my 1100 fork springs as I didn't want a progressive spring but as explained earlier i basically cut those springs in half anyway. (Danger here is that I might find spring fatigue sets in very quickly if I'm unlucky (not many coils left to share the work) but I have seen plenty of bikes (incl my KLR) that use springs that are as short or shorter than 14").

To get the compressed spring length you get a very accurate spring wire dia & multiply it by the number of coils in the spring, no need to actually measure it. I would be very surprised if you have managed to get 56lb/in from a stock GS spring.

 

[Guest]

So when they say compressed length they mean as if there were no spaces between any of the coils at all? and when they are asking for the free length it is the length of the spring only, not with spacers, right? I appreciate all this, like I said it's all very interesting. Punching in 47 coils with a wire diameter of 0.155 and an outside diameter of 1.05 with a free length of 13 1/2 inches means I will have a compressed length of 7.29...so....24 lbs/inch spring rate with a pressure at compressed length of 150 lbs, think I wrote it down wrong the first time. I did the same calculation for a stock spring from a 79 850 (which I think is close to the 1000G) and came up with 18.87 lbs/inch and 137.75 lbs at compressed length. So it's an improvement for sure but not what Sonic or Progressive would be.

 

[salty_monk]

You got it... Progressive is 35lb moving to 50lb when the coils bind (to calculate that you just alter the number of active coils - will be a smaller number).

 

[Wizard]

Full Extension

Full Extension

At the end of the day, you still need to have about an Inch or so, of travel available, in the fork tubes, while Loaded & Riding.
If you hit a Dip in Road, while in a turn, at speed, (I've seen you ride!), the front wheel needs to Extend and stay on the road.
Don't make it too stiff or a rough road (Goat Trails) will beat ya up.
For Touring I've actually backed off on everything, easy rebound, soft springs (low air pressure).

 

[bwringer]

You should have about 2.5 to 3 inches of travel, actually.

Static sag should be set at 2/3 to 3/4 total travel. Total travel on a GS (and most streetbikes) is just over 4 inches. (dual-sports are a bit different -- V-Stroms have about 6 inches of travel, KLR650s about 10 inches.)

Therefore, 1 to 1.5 inches static sag is about right for a GS. when you're traveling down a level smooth road, that's where the suspension should sit.