Rear Spring Preload/Sag issue (Wilbers)

Originally had this in a different thread, but wanted to raise it as a separate topic.

Some opinions/advice sought if I may please.

About a month ago I got a new Wilbers rear shock & spring fitted to my GRiSO. All custom built according to rider weight, riding style etc and thus is supplied with what is deemed the correct spring rate, preload and valving. Been happy to date, but managed to bottom-out the rear on a bump which got me wondering about ride height. So, when picking the bike up from being serviced, I got the rear sag measured, and it was apparently about 50mm. That's about 15-20mm too much from what I have been led to understand.

Now, I know that just cranking up the preload should help with the sag issue, but for what was a pretty expensive piece of custom-made kit, is this type of variation acceptable? Should it have been more accurate out of the box as such? Have I potentially been provided with a spring that's too light? According to the specs card that came with the unit, the pre-load was set at 14mm from the Wilbers factory (if this means anything to anyone).

In fairness, I'm due to go back to the installer in a few weeks and they are going to look at it then, so I need to give them the opportunity to address the issue. However, if this situation should ring alarm bells, I'd be keen to know. Should I perhaps be demanding a different spring?

Thanks,
Brent.

All springs must have pre-load when installed. 14mm is acceptable.

Based on the theory your GRiSO has 120mm (claimed) rear wheel travel the following would apply;
Rider sag (your fat ass dressed in battle armour on the bike) should be 25-30% of total travel.
That would be 30-36mm. However, every Guzzi I've owned has had less travel than advertised.

I would recommend a max of 30mm total sag.
1. Adjust the pre-load until you get this measurement.
2. Measure static sag, how much the bike settles under its own rate from "topped out". Ideally this should be 6-8mm.

If static sag is greater than 10mm it would indicate the spring rate is too hard.
If static sag is 0-3mm, it would indicate the spring rate is too soft.

Are you sure you haven't got that arse about Wayne?

Wayne is right Pete, if the spring rate is too soft, you wind on more and more pre load to hold the bike and rider up, and end up with little or no static bike sag. The shock can "Top out" on bumps or under hard braking afecting handling. I'm up to a 115 nm spring on the noisey one and still need to go higher. ( or lose weight )

I'm obviously not understanding.

Do you want another frame Ron?

Thanks guys, but I'm with Pete here in that the static sag explanation is confusing me. Assuming the same preload settings, the further the bike settles under its own weight, the softer the spring I would have thought?

NO! You have to stick ya tongue out the other side of your mouth, and think backwards.

When a spring is TOO SOFT to hold YOU up, you will wind on excessive amounts of preload to set RIDER SAG at 30mm (or less for track bikes). When you hop off that excessive pre-load will push the bike up until it tops out the suspension. Then you have zero static sag.

When a spring is TOO HARD, you cannot get 30mm RIDER SAG, so you will wind off the 14mm spring pre-load (that Wilbers set at their factory) to almost zero. But then you will get 20mm static sag.

Your bike needs 8/30 to not only support your weight when stationary, but also to keep your balls off the rear tyre when hitting bumps.

You are already complaining of bottoming out, adjusting pre-load may help but if you get 0/30 static/rider sag, spring is too soft and it will continue to bottom out.

QUESTION. Have you dialled in the damping?
Does your shock have hi speed and lo speed compression damping? Or just a single compression adjuster?

Ghezzi, thanks. I sort of get what you're saying. The shock has both high and low speed compression damping adjustments. Again, these were set by Wilbers as the baseline allegedly for my specs. I was told to let the shock settle in for a few hundred kms prior to adjusting them. That advice sounded reasonable. Anyway, I don't have an issue with how the compression damping feels.......it's firm, yet controlled and compliant if that makes any sense.

My underlying fear is that the "solution" will involve winding on more preload, and applying a few clicks more compression damping to reduce the risk of bottoming out. End result will be that the comfort level deteriorates to what the bloody original Sachs unit was which drove me to tear it out to begin with.

Assuming, for a moment, that the sag is approx 20mm too much, I have no idea how much additional preload would be required to fix it. I still have visions of the original spring with the preload adjusters wound down to buggery and the awful ride that it gave.

My recent experience with fitting an Ohlins shock confirms exactly what Ghezzi is saying. It has a heavier spring (105 nm) than the original Sachs unit but my static sag is now in the sweet spot defined by Ghezzi. In comparison I had the preload on the Sachs cranked up close to max to cope with my weight, resulting in only a few mm of static sag. The picture is complicated slightly by the fact that the Ohlins is about 10 mm longer but the difference is obvious and measurable. Suffice to say the ride, steering and handling is immensely improved. Correct me if I'm wrong but you don't actually say what the preload setting is on the new shock, as installed. I wouldn't be afraid of winding on a bit more if it was set low in the range to begin with.

It is likely you have a spring close to the stocker.

1. What specs have you got regarding it? Stock is 9.6kg.
2. How much do you weigh with your helmet, jacket, gloves and boots on? (No, pants are not optional)

Comfort and compliance are regulated by damping characteristics, Sachs had none to speak of.
Just be aware you now have 12,000 possible combinations of damping settings. Write down in a little pocket book your impressions of ride quality/handling.

First record factory settings by counting the clicks to "Hard", then wind back same.
Then adjust only one item +2 clicks and ride. Record your thoughts. Then go -2 clicks from stock.
Put it back to original settings and then repeat with another adjuster.

You will soon find which direction each setting needs to go to improve the ride. Experiment again by another click or two.

Thanks gents. I don't have any specs for the spring rate on the new unit. I'll have to source this via the supplier. In terms of preload, all it says on the spec sheet (for the new unit) is that preload has been set at 14mm, but without a meaningful reference point, this doesn't mean much to me.

My riding weight (fully kitted) is just shy of 85kg, so I'm clearly not built like a wine barrel! Visual inspection of the new spring looks as though the coils are actually slightly thinner than on the stock spring, but this could be an optical illusion due to the different colour of the coil (blue) compared to the red stock one. My gut feel is that the new spring is certainly no heavier than stock, and possibly a tad lighter.

Ghezzi, in terms of the damping settings, I'm reluctant to start playing with these until I sort out the sag issue. If there's one common theme in all the various suspension setting threads out there, its that I need to get the sag correct before playing with damping, otherwise I'll end up chasing my tail. Once the sag is correct, I'll definitely be keen to try some variations on the damping settings.

OK, so you are a fly weight and not a lard arse like most us old farts (averaging 90 to 100+kg)

The stock GRiSO spring (9.6kg) would have been pretty close to a perfect match for you.
14mm pre-load just means your Wilbers spring was installed on the body and compressed 14mm from its free length.

You have a suspension linkage system with a rising rate starting at approx 3:1 ratio.
Meaning for every 1mm the shock (& spring) compresses, the rear wheel moves 3mm.
Therefore, if you want 20mm less sag with your skinny butt on the bike, you need to add around 7mm more pre-load.

1. Jack bike up with rear wheel off the ground (suspension topped out).
2. Measure length of the spring, = X.
3. X -7mm is your target.
4. Adjust rings with a 'C' spanner that fits, or butcher it with a screwdriver n hammer.

Generally the threads have a 1mm pitch, 7mm = 7 full turns.
Now measure RIDER SAG again ..................... minor adjustments from here.
When rider sag is 28-30mm (two man job for accuracy), check static sag and report back.

Better still, ride it and smile.

Thanks Ghezzi. You are the suspension Yoda!

I've asked the supplier to obtain the spring rate specs for my Wilbers. The only info that came with the unit was a numerical reference "95 - 130" per the "Spring" description which doesn't mean anything to me.

By the way, does rider sag per your note include the full sag from fully topped-out to once a rider is on board?

Yep.
Top out = X
Rider sag = X -30mm
Static sag = X - 7mm etc
Measured vertically from the axle to some point on the frame/bodywork.
I find it easier to put a piece of masking tape on the bike with a horizontal pen line.

Any future measuring do the same. Max distance is unimportant, just rider sag and static sag.

In terms of the Wilbers spring specs, I've just been told that it's 95N (presumably that's 95 Newtons). Using the intergalactic power of Google, I found a conversion formula which tells me that 95N = 9.7kgs (per millimetre?). This would suggest that the new spring is the same approx rate as the original stock spring. For my weight then, perhaps it's about right??? So, should mean that the preload just needs to be wound up a bit to fix the sag.

Gents (and Ghezzi)
what sag do you reckon for the forks?
sorry if this is posted elsewhere, I can't see it.
I'm on all stock, at least for now.
Cheers

Basically, generally, approximately;
Rider sag = 25-30% of total travel.
Static sag= 25-30% of Rider sag.

Be aware, Moto Guzzi's advertised/claimed specs regarding suspension travel are usually "Bullshit.

Pete Roper wrote:

I'm obviously not understanding.

Do you want another frame Ron?

Sounds good Pete I'm out in western NSW for work this week, bugger all phone coverage. Call you when I get home.

ghezzi wrote:

Basically, generally, approximately;
Rider sag = 25-30% of total travel.
Static sag= 25-30% of Rider sag.

Be aware, Moto Guzzi's advertised/claimed specs regarding suspension travel are usually "Bullshit.

Thanks Ghezzi

Brent,
To reply to your original post, I found the same thing when I took delivery of a Wilbers shock for my 2013 GRiSO.  The preload as delivered resulted in the sag with me on the bike to have used up half the available travel and I'm light.  I don't know why this would be the case as the shock should be delivered with a spring and damping selected for the riders weight and riding style.  I added two full turns of preload to get it into the proper range.  The 95-130 number means that it is a progressive spring.  Mine was 100-150 which surprised me as I thought they would fit a lighter spring at my weight.  I ended up reducing the high and low speed compression damping to give me a more compliant ride as well.  I suspect they are not very experienced in dialing in  their shocks to fit this bike for the  preload to be that far off as delivered.  That being said with the preload adjusted to give the proper sag and the compression damping reduced I'm happy with the performance.  I have a previous post on this on the forum for reference.
cheers,
Tod

I doubt if anybody could guess correct pre-load setting during assembly.
Do you have stock exhaust or Titanium system?
Do you have a lithium battery?
Do you have luggage system fitted?
Have you changed front ride height?
Are you tall or a short arse?

All these things will have an impact on the weight, weight bias and sag.

The reason I quoted "Basically, generally, approximately; Rider sag = 25-30% of total travel", is 25% if you prefer a sportier ride and 30% for comfort. Race bikes will often have less than 20%.

Like wise the damping settings. Even when my suspension guru would set sag and damping by bouncing the bike while it is stationary, I will still change it a click or two after the first ride. His settings are inclined towards 200HP, 55 degrees lean, slicks and fastest lap times. I always add rebound to soften the kick up the arse etc.

As an update, I dropped my bike back into the suspension shop for two purposes. Firstly, to get Matris cartridges fitted to the front forks.......come this far, so might as well do the whole thing I reckon. Secondly, get them to look at the rear sag issue. Will get it measured & adjusted properly when I call past again once the front forks are done.

I still have a nagging doubt about the rear spring rate, and whether Wilbers has stuffed this bit up for me. OK, I'm a lightweight (85kgs in riding gear), but visual inspection suggests it's going to need a decent bit of pre-load at the rear to bring it back up to circa 30mm sag. Might be a battle to have them change the spring if it looks and feels wrong. We'll see I suppose.

Matris tell me the 46K shock I ordered should have between 40mm and 45mm 'sag'. As delivered and fitted I have 8mm static sag and 19mm rider sag (27mm overall). Does their recommendation of 40mm to 45mm sag mean overall - ie. from suspension topped out to suspension settled with rider on board, or is the 40mm to 45mm the rider sag in addition to 8mm static sag (or whatever it is when I have backed off the preload to achieve the rider sag?)
I am guessing that it should be 40mm to 45mm overall - ie. 8mm-10mm static and then 32mm to 35mm rider sag. If this is correct then I think I need to find at least 13mm additional sag (to get 40mm overall) so need to wind off 4.33mm preload, which i think is 4.33 full 360 turns? N'est pas?
My shock came with a 135N spring (13.76kg) which Matris are adamant is correct for 103kgs rider.
Theior recommendation for 40mm to 45mm sag seems differnet to conventional thinking of 30mm to 35mm sag but perhaps their theory is stiffer spring set up with more around 10mm more sag will improve the ride quality...

40-45 Total sag with your arse. But those numbers fly in the face of ancient wisdom (not mine) so I'm staying out of this argument. I'm just old, belligerent, resistant to change ................. other than modifying the crap out of Bella.

what Ghezzi says