rear shock aftermarket spring rates? hagon 2810's

[Chuck78]

I am upgrading my rear shocks at some point soon to adjustable dampening Hagon 2810's with their slimline springs. For now I am doing cartridge emulators in my front fork and chopping the stock springs upfront to stiffen the rate to a little closer of being where I want it (I think this ends up around 35lbs/in max (about .72kg/mm???). Eventually I'd like to go with some Sonic straight rate springs. Sonic have a handy calculator on their website that figures total bike weight with fluids, rider weight, any potential luggage on bike, and preferred riding style. With shaving about 60 lbs total of of my bike in the next year, they say I should ride .90kg/mm or 1.0kg/mm springs up front.

Hagon says their replacement spring for my bike would be a 20 kg, and if I am lightening the bike up as planned then an 18 kg would be recommended. If I wanted a softer ride then they said to go with a 16 kg. As you can see the 2 different companies are rating their springs in different terms, and they did not ask for the riding style that I prefer which would be aggressive riding in twisties with some city riding & commuting. Also I am thinking that the Hagon springs are progressive rate. I had planned for Sonic straight rate Springs up front. Maybe progressive front springs should be in order if going with progressives in the rear???? I was pretty set on the 2810 shocks, as for the money and the adjustable dampening, they cannot be beat.

What is everyone's opinion on the rear spring rates to match the recommendation for the front from Sonic? I would think that it maybe not be so good to mis-matched straight right front and progressive rears. Any thoughts?

[John Kat]

I believe Hagon is quoting their springs in Newton/m which is the correct way to do it as we are dealing with forces and not mass.
Strangely I've been using Pounds/inch myself and I chose 125 Lbs/inch springs for my 1100 Kat that suit me fine.
16N/M would give you : 16*25.4/.454*9.81=91.25 Lbs/inch and that's way too low in my opinion.
I computed the strength of the OEM springs on my GS 1000 ST: 116 Lbs/inch
On my Std GS 1000 EC: 130 Lbs/inch.
Don't forget that if you use .95kg/mm upfront ( I do to!) this is much stiffer than OEM and you need to keep the rear in balance

[Chuck78]

No, they specifically said 20 kg was stock for a GS 750. Or at least their standard offering for a GS 750 - at least that is how I interpreted it. They stated the 25mm o.d. front springs they sell for my bike are progressive starting at 5.8 and stiffening to 8.0, no units stated but I assume kg. Apparently the rear shocks springs they sell are not progressive. I will have to check back with them when I have a minute.

[salty_monk]

I use 43lb on the front of my skunk which is about 0.8. Progressives are just under this (38lb) on the start of their travel but then become 50lb when the closely wound coils bind.

Progressives with 1/2" of preload were great without emulators but when using an emulator you can use a lower spring weight. Straight weight is better for use with emulators.

I used progressives on the rear for a while & 95/140's were good for me. 110-150's were too stiff. I like a fairly sporting setup.

I weight 165lb.

Hope it helps...

Your bike weighs about teh same as mine I suspect...

[Chuck78]

So it looks like your preference for front spring falls just under the average of the two progressive spring rates. On the rear, in a straight rate,
Hagon told me their stock offering for the GS750 was 20kg, which translates to 44.1lbs. This was for the rear. This makes no sense compared to what you are saying your real world spring rates are. I emailed them for clarification, but no reply yet.

Salty, would you say around 115 or 120 lbs in a straight rate rear shock spring would do you good?

[Chuck78]

My bike's weight with all fluids was around 550 stock. I've dropped the center stand and have 4 into 1 already, so I'm saving a fair amount of weight in that so far, with much more to come.

1977 GS750B w/oil&gas&fluids 558 lbs dry weight 511.5 lbs

I will be down at least 40 lbs lighter bike weight by summer, with another 20-40 lbs dropped by the end of this summer or next winter. So 518 lbs, with sub-500 lbs in the near future. 155 lbs rider, sometimes I carry gear with me in saddlebags if going on long rides through the Southeast Ohio twisties.

I had planned on getting the 0.90kg/mm Sonic straight rate front springs, which was the lower of their recommendations from Sonic's web calculator that I used when entering my body weight and around a 490lb bike with more sporty aggressive street riding style specified. If I enter in 81 GS650G (the 35mm forks I am swapping on for dual discs), it gives me the option of going down lower to .80kg/mm with the same weight of bike. But for now I will be chopping the max amount possible out of some stock springs since I am dropping a lot of cash on lacing alloy rims in, new shinko tires, twinpot dual discs, carb overhauls, etc. For now, I'll chop probably 5" off the GS750 springs if my past research is still fresh enough in my memory. I have no idea what spring rates are in the 81 GS650G springs I have vs the 77 GS750B springs I have, but I assume the GS750 uses stiffer springs.

Straight rate in the rear from Hagon, any ideas on what spec I would need??? I can surely tell them a figure from other manufacturers and they can just convert it to their measuring methods.

[John Kat]

Hagon told me their stock offering for the GS750 was 20kg, which translates to 44.1lbs. This was for the rear. This makes no sense compared to what you are saying your real world spring rates are. I emailed them for clarification, but no reply yet.

Salty, would you say around 115 or 120 lbs in a straight rate rear shock spring would do you good?

I believe you cannot state that a 20 kg rating corresponds to 44.1 lbs because if Hagon specifies a metric rating for the force ( here in kg) they must also be using a metric unit for distance ( eitheir meters or mm).
So to convert from metric to english you also have to convert the length by which the spring gets compressed with the stated force.
I have an old KZ 1000 manual that states that the rear spring is rated at 2.2 Kg/mm no way near 20 kg....

[tkent02]

Centimeters would make it work out about right.

[John Kat]

Centimeters would make it work out about right.

You are right
20kg/cm is equal to 2kg/mm.
But as I posted earlier you must keep everything eitheir metric or english.

[Chuck78]

Well I had completely forgotten reading about Dave Quinn Motorcycles being the preferred USA Hagon dealer to go to. You pay about $10 more for a set of 2810's from them, but they give you an extended warranty above Hagon's warranty, and every single order from them is a 100% custom fit shock for your application based on your bike model, bike mods and current weight of bike, rider weight, and riding style. They also have cosmetic options available such as stainless housings, partial shrouds, full shrouds, etc.

After looking through their site, they shed some light on the spring rates. As you guys had called out, it does appear that they rate them in Kg/cm instead of kg/mm lbs/in or N-M. It also appears that all of their light and medium weight applications use progressive rates. As Salty mentioned, Progressive the name brand rates their progressive rate springs with two figures, the initial rate, and the stiffer rate once the closer coils are bottomed out. Hagon rates theirs as the median spring rate, meaning splitting the difference between the lower and the higher number. So a 100/140 Progressive (brand) would be called a 120 in the Hagon. Their really heavyweight shocks come in straight rate springs however. And as far as their light, medium, and heavy dampening bodies, I think that since the 2810 is a 3 or 5 position adjustable dampening shock, I think it falls out of any of those categories (correct me if I'm wrong).

Here's some info from their site:

SOFT BODY SHOCKS:
10kg=56lb progressive
12kg=67lb progressive
14kg=78lb progressive
16kg=90lb progressive

MEDIUM BODY SHOCKS:
18kg=100lb progressive
20kg=110lb progressive

HEAVY BODY SHOCKS:
23kg=129lb progressive
26kg=146lb progressive

and straight wound springs for the extra heavy body shocks:

EXTRA HEAVY BODY SHOCKS:
30kg=168lb straight
35kg=196 lb straight

XXTRA HEAVY BODY SHOCKS:
40kg=220lb straight
45kg=250 lb straight

We can supply springs in 194, 214 and 234mm in two shapes:

Slimline with 38.5mmID and 52.5mm (2.125" ) OD
Wideline barrel shaped with 39mm ID and tapered OD 53.5-60mm (2.35")

[Chuck78]

HagonUSA tells me their stock listing for the front fork springs are progressive rate 5.8/8.0 kg-cm springs, and their recommended rear spring is 20kg/cm.
In a straight rate Sonic front spring, Sonic says .90kg/mm (9.0kg/cm) to 1.0kg/mm (10kg/cm) for my very specific input for my modded bike state and rider/cargo weight.
Salty says he is happy with his .80kg/mm (8.0kg/cm) straight rate fork springs, I am thinking that I should probably be going with the 20kg/cm rear springs.

I think from reading posts on chopping fork springs that I can potentially get my OEM springs (if not too shot) up to 35 lbs/in (.72kg/mm), that's almost up to the rate of .58/.80 kg-mm that HagonUSA has paired up with the 20kg/cm rears in their application guide.

Going from Salty's rear progressive spring comparison,

I use 43lb (about .80) on the front of my skunk. Progressives are just under this (38lb) on the start of their travel but then become 50lb when the closely wound coils bind.

I used progressives on the rear for a while & 95/140's were good for me. 110-150's were too stiff. I like a fairly sporting setup.

When using cartridge emulators you can use a lower spring weight. Straight weight is better for use with emulators.

I weigh 165lb.Your bike weighs about the same as mine I suspect

So converting to Hagon's median rating method and kg/cm units, Salty said 8.0kg/cm straight rate fronts with emulators were good for him, and 117.5 lb/in rear springs were perfect but not too stuff for a sporty ride, but 130 lb/in were too stiff in the rear.
So it sounds as if the 20kg=110lb progressive in the rear is going to be the best option for me vs the 129 lb/in which is the next size up.

In the fronts, since going with emulators, it sounds as if I need to decide between .90kg/mm Sonic's and .80kg/mm Sonic's. Going out on a limb, with the 20kg/cm in the rear, if I end up doing a battery and starter delete, the battery is going to me more weight off of the rear shocks (starter is more evenly distributed mid-bike), so that will effectively stiffen the rear a little, so maybe I should consider going softer? or else maybe stick with .90kg/mm in the front as to not have too soft of a front suspension for the rear rate??? Riding chopped stockers may tell me if that is close to what I desire (go .80) or if it is still waaaayyy too soft.

Any advice on the 18kg vs 20 kg progressive rears and the .80kg/cm vs .90 kg/cm front Sonic springs would be greatly appreciated. I think with them being progressive rears, the lower initial rate may buy me a little bit of slack to be able to run the 20kg. Thoughts?


I know going too stiff in the rear with too soft in the front can cause the life-threatening high speed wobble/drift if pushing the ton on the speedo... I don't care to break the ton too often myself, but following my speed demon wife, sometimes I have to! And she tells me "promise me you'll be safe!????! I know how you boys are..." Sheesh!

[John Kat]

I have three different set-ups on my GS 1000's.
Stock, .9 kg/mm in OEM forks and .95 kg/mm in GSXR 1100 86 forks.
Going from stock to .9kg/mm makes the bike feel more taught in the twisties but doesn't change how comfortable the bike feels ( the hydraulic setting does that).
Given the different forks I'm not able to say if .95 makes any difference from .90?
My springs are from RaceTech and if you go to their site you will find a configurator to help you choose.
The total weight of the bike barely changes the rate for the front spring as you will notice.
Going with stronger springs will reduce the travel of the front fork which is good if you ride fast because it limits the variations in geometry as you dive into the turns.
I believe the .8 kg/mm upfront will be a good match for the 20 kg/cm for the rear

[Chuck78]

I wonder how the .90kg/mm would work with the 20kg Hagon progressive springs in the adjustable dampening shocks? I suppose if I wanted it a little stiffer in the rear to match, I could just bump up the rear pre-load? Maybe even cut 1/8 coil out and install a nylon spacer block? Or pay $309.99 for the 2810's from Dave Quinn Motorcycles to get their free spring exchange program (twice they let you swap!) and extended warranty vs $299.99 at HagonShocksUSA.com

For now I am going to swap my 750's springs into the dual disc 650 forks that I have, the GS750 being lightened up by at least 20 lbs from stock, and if they are progressive springs from the factory ('77 GS750B, any ideas if they are?), I'll keep the progressive end intact and cut 5" off the other end and install a schedule 40 PVC pipe section as a shim.

I wonder if I could potentially find a set of springs off of say a GS850G fork (heaviest GS models) and chop them to end up with a desireable stiffer spring rate without going aftermarket? the 750 is the largest with 35mm tubes, so not sure that the larger bikes' springs would even fit, but you never know.

[Chuck78]

chopping stock springs for now, more on front/rear new spring rates?

I just got some MikesXS cartridge emulators today in the mail (woohoo!), but decided with rims/spokes/tires/twinpots/s.s.brake lines/etc I couldn't afford new Sonic Springs for the moment. The emulators were top priority now because the forks are sitting on my bench, and easy to mod now as opposed to after I install them for the dual disc twinpot setup... springs later will be a quickie swap.

I've read posts on cutting OEM fork springs by Salty, nessism, old_skool, and others, so I get the gist of it, but I'm looking for a little more specific advice. I have yet to pull my 77 GS750B springs to see if they are thicker diameter wire stock than the 81 GS650G fork springs on my bench now, but I will undoubtedly use the thicker springs between the two pairs.

Salty said he cut one of his sets down to "around 14" which was close to half as long as before." I've read estimates that down to 10" will definitely be dangerously close to bottoming out, sounds likely to me. Some say 4" or so max travel on our forks, but others speculated more, but I wasn't sure if that was after pre-load and sag are set properly with rider seated on bike, or before sag. Trying to get an idea from people's experiences on what to shoot for. I am thinking I'd need to figure about 6.5" minimum travel of the spring and add to that figure the measurement of the number of coils and compression space between the coils, and that would be the absolute bare minimum that I must stay a little above. Probably impossible to get to the .80-kg/mm or .90kg/mm that Sonic sells, but I think Salty was able to figure approximately .72kg/mm he achieved from a set of GS1100 springs, so maybe .65kg/mm or in the upper-mid-30's in lbs/in would be possible for now until a better upgrade? Any thoughts?



Also looking to seek out more opinions on the 110lb/in (20kg/cm) hagon springs vs the 100lb/in (18kg/cm) median rated progressive springs in the rear matched with either the .80kg/mm or 90kg/mm sonic fronts. I'm thinking the Hagon 20kg/cm spring rate is probably it for what I plan to do, but I wonder if I went with the 18kg/cm of any adjustment of pre-load would get me up closer to the 20 if that was too soft?. I'm down 19-25 lbs approximately on bike weight so far from stock on my 77 GS750B, looking to drop it down to about 500lbs with fluids by next spring, maybe 490 if I go all out.

[Toasty]

I have some Sonic springs that I'm selling, they'll work in your 35mm forks.