rear shock aftermarket spring rates? hagon 2810's

[Chuck78]

What rate are they???

[Toasty]

1kg/mm, firm but still comfy. I had them on my 550, on a heavier bike I think it would be about perfect.

[salty_monk]

I calculated quite carefully how much spring travel was available before I cut mine....

Basically as long as the spring has more than enough compression left (gaps between the coils, calculated by taking the accurate dia of the wire x number of coils from the free length of the spring) for maximum fork travel then it won't bind.

Preload can affect it (Sag won't as when the fork sags you use part of the available travel versus preload which compresses the spring with zero travel). I set mine up with pretty much zero preload but left myself a good 1.5" or so spare as I have the adjustable preload caps on the 1100 forks which can apply about 3/4" of preload should I want it.

I ran the progressive springs with virtually no preload in my old fork (no emulators) & it was fine but you can use a lighter spring with emulators for better small bump sensitivity etc & still not get the dive.
Most people are using a spring rate that is too hard in order to firm up the fork under braking - it's a compromise when you can't adjust the damping properly!

[Chuck78]

Toasty, I may consider those springs. With my bike in it's current state and setting it up for aggressive riding, that would probably be fine. How long uncompressed are they? I suppose I could chop my OEM springs and add a short section of them instead of a spacer in order to drop the rate slightly if I wanted, although that would be adding a slight bit of weight over a slightly thinner coil wire if that's how Sonic adjusts their rates (vs shorter spring for stiffer). If the price is right, I am more interested, as it is #1 one size stiffer than I had intended initially, and #2 I was going to skip the springs for now because I am really broke and pouring all the money I can scrounge up into the bike for our May trip to the West Virginia mountains

[Toasty]

Well it looks like I have a buyer for those springs, I can let you know if it doesn't work out for some reason.


Btw the springs from Sonic are very short, the PVC spacer ended up being pretty long.

[Chuck78]

I pulled the springs out of one of the 81 GS650G fork legs. As I had read from others' posts, it has a short tightly wound progressive spring maybe 4" long (1/4 of it is very very closely wound and the rest is still a lot tighter wound than the main spring) , and then a much longer, more loosely wound spring, with a spacer in between. So this setup actually has THREE different progressive steps in the spring rate. I have yet to pull apart the 1977 GS750 forks to see if it has a thicker wire diameter than the 650, as it is a heavier bike by about 40 lbs.

The main spring is 410mm long, 25.4mm diameter, 41 active coils plus the flat ends, and 4mm thick wire. The smaller spring is about 3.7mm wire. main spring has about 6+mm of space between each coil, so that leaves about 234mm of travel with a minimum length at max compression of 176mm.

This calculates to about 35 lbs-in (6251 N-m) for the main spring, with a force of about 320lbs per each spring to compress to the bottom out point. This leaves 9.2" of travel in the spring total. I suppose I could cut a few coils out of it still, maybe 2+" worth, which ends up about 13.5-14" total - about what Salty said his ended up being. 4" of travel plus 1" of pre-load plus about 1" of sag plus up to 1" of cushion leftover. Cutting this extra 2" out may arrive me at the 42lbs-in as Salty said with his, although his springs may have been in a GS1000 I suspect, so maybe different as they fit in 37mm forks and may be larger o.d. as well as thicker wire. Dan?

[Chuck78]

cutting out 2" or 50.8mm would equate to 5 coils cut. 359mm total length 36 coils 204mm of available compression to bottom out (8" of travel), with 155mm compressed length. This translates to 39.6lbs-in with 318 lbs required to bottom out, getting closer to where I want it!

cutting 7 coils is 340mm free length, 34 coils, 192mm of available travel to bottom-out (7.5" of travel to bottom-out), 148mm fully compressed length, equates to 42lbs-in!

I'm not certain on the total travel of our forks, so this may be the max that I would want to cut out of that spring, but with 1" preload, 1" of sag, and a hypothetical 4" of travel, I could potentially cut more coils if needed. I doubt the spring is still as strong as it was when new, so at 34 coils, I would guess that it is about 38lbs-in.


9 coils cut... 32 coils 320mm free length 180mm available travel to bottom out (7") 140mm compressed length = 44.6 lbs/in and 315lbs force required to fully compress spring. 7 or 8 coils cut would be my max I think, without knowing for certain how much travel the fork will really have.

700lbs total bike and rider with fluids and maybe some gear, with the front brakes SLAMMED on at a high speed stop nearing a nose wheelie, pushing against springs that are 630lbs total to compress... well now...? The stock spring without the second shorter (and progressive) spring would take 640lbs to compress total, although I doubt under most any riding condition on my bike that I would have no weight at all on the back wheel, even under hard braking. Whaddya ya guys think of these figures????? I plan to get my bike down to 480-490 lbs with fluids by next year, it's at about 533lbs now (557 wet weight from factory), and I'm 155lbs max with boots and jacket! 688lbs total plus gear currently. With battery and starter delete and all mods and parts swaps that I listed in my "Shaving pounds to add performance" thread, I may get to sub-490lbs by winter,

[salty_monk]

Mine is using 37mm 1983 GS1100E fork legs in a GS1000 triple (triple is virtually identical actually).

If I remember correctly the spring is about 26mm dia & your wire dia sounds about right. The Progressive for the same model is 1" dia & the wire is about 1mm thicker from memory.

If you get the spring rate right you should not need any preload....

You are about 10lb lighter than me.... Your bike sounds like it will ultimately be lighter than mine too.
Sounds like you could get rid of 7-8 coils & be somewhere close.

What is the internal dia of that fork & the external dia of your spring? I think I have a set of GS1000 stock springs that you could have to play with...

Your comment about spring strength is not applicable - that affects free length only over time and you are calculating it "real world" not against it's stock figures.

[Chuck78]

Well it turns out that cutting 9 coils to get 44.6lbs/in converts to .7964kg/mm, so basically just a hair under the lower rate of Sonic's! Without doing full mathematical calculations, 10 coils would be about 45.8lbs/in, 11 coils approximately 47.2lbs/in or. 84kg/mm, and would be about 12mm less travel total than 9 coils cut, so about 6.5" total travel including sag. I'll have to look into suspension travel amounts to make sure I'd be comfortable with this, but I'd say much shorter is pushing it darn close.

[Chuck78]

11 coils cut would be 168mm or 6.62" travel, 30 coils at 300mm free length (11.8"), 132mm compressed length. 47.5 ft-lbs and 314.4 lbs force to bottom spring out. that's .85kg/mm, sounds perfect other than the 6.62" of travel being really close. Any thoughts? Maybe 9 or 10 coils would be my max... an extra 12 or 18mm of travel would be nice as a safegaurd. I'll have to check the travel on the fork with the spring removed to get a better idea. I think the dampening system will bottom out and that will tell me the max travel I need to concern myself with. Tomorrow...

I do recall reading some reviews of people saying the GS650G was one of the sportiest bikes of it's kind from that era as far as handling goes. The rear shocks even had adjustable dampening on them! Maybe they learned and started experimenting and putting stiffer springs in them in the 80's? I figured 35 lbs/in would be the max I could get out of a stock spring after chopping. Getting into the 40's was a very pleasant surprise! With cartridge emulators, I think I''ll be pretty set after chopping 9 or 10 coils!

Dan, what's the wire diameter on those springs of yours? Mine are 1" exactly, 25.4 spring o.d. with a 4.0mm wire diameter. I will pull a GS750 spring out in the next few days and see what wire diameter it is. I'll check my fork i.d. tomorrow as well to see if 26mm will smoothly fit. Thanks for the offer!

[Chuck78]

I made a little free time this evening and pulled the GS750 fork springs out, after a long week of work and having to take my wife to the ER for a chopped off fingertip from cutting veggies for dinner last night.... The walls of the fork tubes are almost 5mm thick! 25.4mm springs are the max to fit into the 35mm fork legs for sure. Here's the specs of what was in my bike. two coils, same as the GS650, one tighter spaced for a progressive setup.

shorter tightly wound/spaced spring:
much tighter than the GS650 spring as far as spacing, thicker wire, and about 2" longer than the 650's, at a total of about 6".

longer spring - 2" shorter than the GS650G but more&thicker coils and more tightly wound:
363mm free length (14-1/4")
25.1mm outer spring diameter
4.3mm coil wire diameter
43 active coils
4+mm free space between coils

[Chuck78]

'77 GS750 SPRINGS to 48.5lbs/in or .87kg/mm!!!!!!!

WOW, AWESOME!!!! The main GS750 spring without the smaller progressive spring is 48.56 lbs/in or 0.867 kg/mm by itself as it is stock according to the spring rate calculator on the Pontiac GTO/Trans Am guy's website!!!!! NICE! This makes it super easy, just ditch the auxiliary coil in favor of a PVC spacer to go straight rate! Much easier than the single oem progressive spring setup that needs cut, or even the two spring setup like the GS650 that needs the main spring cut more...

I have a total of 164mm (6.54") free distance between the coils, uncompressed. Wow, this is too easy! Not sure what years or models started using the single spring with one end tighter spaced, but these older springs take all the work out of it! 5.5" total travel is needed, this spring before preload has 6.5" of travel available, PERFECT!!!! Score!! Saved $90 shipped for some Sonic's!!!!




Should I figure pre-load based on lifting the front end up until the fork is topped out, and measure for my spacer from that point? It's 6-1/8" to the top of the fork tubes, and the threaded cap is 1" long, so flush with the top means 1" pre-load when assembled IF I should measure from the fork being topped out. Both original springs total length came to this height, although ditching the softer spring will probably require slightly less pre-load IF my sag was correct before, but I didn't check.
Are there going to be any negative effects on handling if I run this front setup with the stock rear shocks? I have some GS1100 shocks to compare the springs with at least, maybe swap them on if the springs are stiffer. Maybe I can set more preload on the rear shocks if still running the originals while waiting on the 20kg slimline spring Hagon 2810 adjustable dampening shocks that are on birthday wish list?


If I ever do my project idea of a 449cc 10.25:1 GS400 or 463cc 10.5:1 compression GS425 project, I'm compiling a lot of awesome take-off parts for it! I can chop the 650 springs as planned for the GS750 forks for that bike to run a single twinpot caliper and 310mm Blackbird CBR1100 rotor, maybe my original GS750 swing arm and spare rear disc brake setup, as well as spare spoked wheels and some used DID 2.15ft/2.5rr alloy rims!

[salty_monk]

What's the diameter of that 750 spring?

[Chuck78]

25.1mm o.d. and 4.3mm wire diameter. the GS650G springs measured just under 25.4mm o.d., and that is about the max diameter you can fit into a 35mm fork.

[Chuck78]

I just tried to fit a SCH40 3/4 PVC pipe spacer into the 35mm forks, and it's just a touch over 1" and doesn't quite make it... 3/4 cpvc pipe is smaller diameter - 7/8" o.d., so it's either going to be a section of that or else a chopped aluminum 25.4mm bicycle seatpost. I have a steel bike post here now but no aluminium...