Standard (Sachs) Rear Spring length vs Wilbers, Ohlins etc

Hi all.

Trying to find what is the standard length of the rear spring (Sachs shock) for the GRiSO. Is it a 160mm? Reason I ask is that my Wilbers is a 130mm. Hmmmm.

Thanks.

Hi Brent....
Can't answer the Sachs as I sold my OE shock & can't find the photo of the naked springs together !....but in case it helps the Matris has approx 6 inch (150mm), and the Stelvio - I've got one & may put back on GRiSO - is approx 7 inch (180 mm)....

The Sachs looks longer than the Matris in pics I took at time (even allowing for possible preload differences) ..& I even wrote in my notes somewhere that the travel (exposed bit of damper) isn't any longer on the Matris (in fact the whole thing looks more compact)

[You must be registered and logged in to see this image.]

Actually found this in forum [You must be registered and logged in to see this link.]

Says stock Sachs has a free length 180mm....sounds about right looking at my photo compared with a 150mm

Thanks Paul. So, suppose this begs the question as to what the effect is, if any, of a spring that is 50mm shorter than stock? So long as there’s capacity on the preload thread to adjust the correct level of preload (up or down), does it matter at all?

I took a stocker and ran the adjustment to the end. It feels loose and uncompressed and I measured it at 7-1/4 inches. Here is a picture on my workbench and an older photo with one next to a stock stelvio:

[You must be registered and logged in to see this image.]

I don't think a spring that is 50mm shorter than stock spring should go on a Sach shock. The Wilbers (and Ohlin) shocks are a different design and have much shorter springs. And while those shocks will fit the GRiSO (eye bolt to eye bolt length is the same), the springs will not fit a Sach shock.

See page 2 of my post [You must be registered and logged in to see this link.]

(sorry couldn't figure out how to link an exact post) Page down to the racetech link and springs from other bikes that fit.

If you are trying to be thrifty, like I am/was, you can pick up a used shock spring from some other bike that has the same size as the GRiSO (but rated higher).

For example, a 2006 Suzuki GSXR 750 has a 95 N/mm spring that will work on the GRiSO's Sach shock.

Agree you'd likely struggle with 50mm different....Also worth looking at ID/OD . I think Sach is 2.25 inch ID (same on Matris, just shorter). New replacement springs cost about 30 gbp in UK giving you lots of choice for rate/length/colour !

Thanks gents. For clarity, I’m not attempting to utilise a different spring on a Sachs shock. I already have a Wilbers on the bike. The Sachs has been consigned to the dustbin of history. My query was more around the issue of why the Wilbers spring is so much shorter, and whether this design carries any inherent disadvantages.

Regards,
Brent.

Ahh, Ok. Theorizing.

So any shock that goes on a GRiSO should have the same shock stroke (unless a person is trying out a slightly more travel Stelvio shock) ... so as long as a spring is long enough to support that stroke, I don't see any big disadvantage or advantage of a longer one.

So I'm not sure of our shock stroke, maybe in the 35mm range. So if a 130mm and 150mm and 180mm spring all support 35mm of movement (after preload) then I don't think any "extra" spring (like on the 180mm one) is helping anything out vs a shortie 130mm.

And with our "normal" straight rate springs, any say 5mm of movement requires the same amount of pressure, whether it is the first 5mm or the last 5 mm.

I would assume some metallurgist spring theorist might have some extra info on that last 5mm as the spring becomes coil bound (smushed all together) ... but hopefully the shocks with 130mm length springs are designed to not even get close to being coil bound.

So my speculation is if a shock can handle a 150mm - 170mm spring ... and you tried a 150mm spring and a 170mm spring (same spring rate, preload set to same bike sag) you couldn't tell any difference the the shocks performance as you rode the bike. And I'd speculate that the top racer guys couldn't either.

That 35 mm or so rear stroke should translate to about 110mm rear wheel travel.....55 mm up & down....I'm still trying to make it do that properly

[You must be registered and logged in to see this image.]

Indeed, the rear shock has a very limited travel. If I had my time again, I'd order the Wilbers with the optional extra 10mm eye to eye length which (I believe) would bring it a lot closer to the Stelvio length. The extra ride height at the rear would be nice (I'm about 6'1 height in the old scale). Mind you, that optionality was never offered to me at the time which is a little disappointing, but probably reflects that a lot of shops/suppliers don't really appreciate the finer technicalities of the GRiSO setup. They look at the product chart, find the model that fits, and that's what you get.

Also, noting that I have a 95nm spring on my Wilbers, I did enquire about a replacement spring. Was thinking a 105nm would be about right (riding weight about 84kgs), but seems that Wilbers only offer a 100nm or a 110nm (in the 130mm length that is).

Plenty of generic springs around (just check you match the ID of the Wilburs, but I'm guessing will also be 2.25 inch) .....here's a 5 inch 105n/mm one local to me

[You must be registered and logged in to see this image.]

Jesus, £26. I was quoted $220 Australian rupees for a replacement Wilbers!

Brent S wrote:

Thanks gents. For clarity, I’m not attempting to utilise a different spring on a Sachs shock. I already have a Wilbers on the bike. The Sachs has been consigned to the dustbin of history. My query was more around the issue of why the Wilbers spring is so much shorter, and whether this design carries any inherent disadvantages.

Regards,
Brent.

I have a Eibach spring on my Wilburs shock. The spring supplied from Wilburs which was set to my weight was terribly soft.

We found an Eibach fitted the Wilburs and  is 150 mm . Longer than the 130mm Wilburs Same as a Matris and shorter than the Sachs 180mm

We kept swapping springs until only minor preload was required to achieve correct static and rider sag.

Its not perfect and needs more tuning but post COVID19 when I can work to earn enough for motorcycles again I will visit Pet Ropers mate in the ACT...


[You must be registered and logged in to see this image.]

Question for the gang, for the rear shock adjustment, which one is which? I see a top flathead screw head, and a bottom flathead screw head and the knurled nut, which ones are compression, rebound, preload?
I am learning lots from utube, on suspension tuning,
Thanks very much!!
Gord

In User Manual for stock one...

[You must be registered and logged in to see this image.]

Thanks for speedy response Paul!! I forgot to mention I searched two versions of GRiSO manuals, they both skip over this information, then I thought I found a utube but no luck.
I will print this off and add it to my old hard copy version the one that tells me to use 5w40 for motor oil,
Happy new year to you all!!
Gord