1200 Des Suspension Analysis

You're right, the active SCU is programmed with a number of "fixed" parameters, since the unit does not have sensors that will adjust the "table" along (rider or rider+passenger weight, relative movements of the suspensions, etc etc). This is the main reason I didn't upgrade my 2010 to the new Ohlins SCU, but I can tell you that I had the same problems as anyone with the rear spring and tried:

- progressive spring. Good, but the progression curve should be really precise, or you will struggle to find a setup that gives you the complete use of the preload, a really good sporty ride when you are alone and a reasonably comfortable ride with a passenger without bottoming up the rear suspension. Really hard task, and you have to add the problem of a probable adapter to suit the spring in length and diameter. The spring used since the m.y.2013 is not compatible if I recall correctly, but I managed to measure it's progression curve and it was softer than my Hyperpro.

- Changed the spring to 100nm. It is simply too hard, the shock doesn't work well almost all the time, maybe it is not so bad with a passenger but I was not satisfied (I am Italian, so I am probably not heavy enough for it with my 70 kg)

- Replaced the spring with an Ohlins 85nm. Linear, of course. You have to set up the dampening very well to avoid bottoming with a passenger, but I prefer this solution in almost every condition. Changing the dampening stacks inside the shock would do the trick, but I didn't try it since the electronic dampening needs to be studied very well.

Last thing: spring's nominal force (100nm, 75nm etc) determines the comfort of the ride (force=millimeters of travel), and on the other side it tells you how much you need to preload the spring (mechanically, with that ring you were talking about) in order to have a good SAG with rider only, and the electronic preload has just 7/8mm of preload to add for the rear passenger (really small range and only if motor oil is in good condition), so if you multiply the spring nominal force x 7 or 8, you should try to choose a spring that reaches a force that could balance the additional weight of the passenger+luggage, really hard task with that small range trying to avoid making the bike completely unridable. This is just one of the reasons I stick with the old SCU: trying to find a balance is not easy at all, and the new active SCU only helps to complicate things. Hope you'll find a good setup for your needs

 

You're right, and it would be interesting to enable or disable the active dampening, just front or rear for example. I changed the front springs too, but that was not so hard since the preload system is manual. If I recall correctly, ohlins Multi's forks have 6nm springs, but can't remember the static preload. I replaced them with 7.5nm ones and I don't regret it at all.

 

I thought the std rear spring was 85 ? I also fitted the 100 for a 2up (plus luggage) trip to the Alps. It sat far too low on the std spring. I also had a custom 90 spring made up. It was made from a 'normal' spring steel as opposed to the silicon steel ohlins use, so slightly heavier in weight and with more coils. I've never actually used it. May finally give it a try as the 100nm spring is too hard for normal riding.

 

May be try backing the preload off to make it softer on urban to use around town (with the heavier spring) so the operating range become more consistent at slower, around town speeds.

Did you find it was also choppy at speed? Or was it just lower speed?

 

Hmm, some good points, but not my experience.
I fitted a 100nm spring to my first bike back in July 2010 following a two-up trip to Germany, and finding it severely under-sprung (I am ~100kgs and Mrs W is ~70kgs).
I still have this spring on my current 2012 ohlins bike.

From memory, both of my springs were the same length. I would need to go check my photos from back then, but I'm sure I would have noticed if they werent.
When I had the preload adjuster rebuilt (seals went) a few years back I added in the order of 3 to5 mm of preload to the spring. In practice this was a mm or two too many, because it has made the bike stiff when solo.
For me this is a compromise I am willing to accept since I can live with a firm bike when solo, but don't want an undersprung bike spoiling my fun when two up on trips.

I too have the ohlins mcu, since around 2014 i think (can't recall, bought it off someone on here). It most certainly does make a difference to the bike even with the stiffer spring. You don't need to swap back to the older mcu to see what difference it makes, just set two riding modes up with all the same parameters (e.g. solo touring vs solo enduro), but set the ones you want to be semi active to value of zero, and using fixed settings on the other. Then you can go ride the same bit of road in both modes. I have done exactly this on my bike although not recently. There was a difference.

As for fork springs, I've never fiddled with them. I was talking to someone recently though and they suggested running the same weight oil but more of it, reducing the air gap, so it reduces fork dive a bit.

 

You're right, we both typed it incorrectly. Standard is 85nm, mine should be 95nm (I'm sorry if I'm not sure, but sadly I couldn't ride the bike for the last year and more). Andreani offered me 90nm and 95nm springs for the rear, I chose the 95 if I recall correctly. The 90 could be a good choice too, but I think it will bottom up a bit too easy when 2up

I replaced both front and rear with Hyperpro's progressive sprigs as first try, I never tried the stiffer front springs with the standard rear spring... Honestly, I had the STD rear spring on for just one year, maybe less. But my bike has also some height changes in the front and in the rear and a longer wheelbase (I hope it is the correct word), it is more similar to the 1260 regarding quotes (when Ducati presented te 1260-17inch bike I couldn't avoid a big laugh ) . It is a bit hard to remember the exact order of the changes at the moment.

I managed to measure the exact distribution some years ago. With roughly 6/7 liters of petrol inside the tank, I measured a 49/51 distribution without rider and luggage, with my 70kg it reaches a 41/59. Changing suspension heights will not change this distribution, I can assure you . Moving the rear wheel back will, and we have room with the eccentric hub.

The problem is that the comfort is independent from preload, al least with reasonable preload values. If a 100nm springs dives 1mm with that force, it will do it anyway even if you preload it 0mm or 50mm. What changes is that you need to go beyond that initial force to see it dive the first millimeter: 100nm preload 10 = 1000nm. If you put a force of 1000 on the spring you will se no diving, if you put 1100 you will see 1mm, 1200 will result in 2mm and so on. It is different if you use progressive springs, since the spring ration changes with diving, so you are actually making it stiffer or softer. But it is not so easy to understand at first

 

Sure, it is too stiff only if you are a 70kg like me. Ducati offered the 100nm spring mainly for other countries, where people often reach 90/100 kg and ride often 2up or with big luggage on the back

I noted the air chamber value of the original setup, but can't find it at the moment. Anyway, you can certainly add oil and reduce the air chamber, obtaining what you were saying, but it will add more stress on the seals and put some "spring work" on the hydraulic part, and it will effect just the final part of the dive. It will prevent or slow down the bottoming, but almost zero difference o really slight difference in the main part of the dive. Replacing the springs will solve both the problems, without causing any stress on the seals

 

With skyhook, and I know it’s likely different but no idea how different, many found the heavier spring would put the bike in the ‘wrong plane’ for the ecu to calculate and it would become very harsh for two up riding. However, if they reduced the preload a little which, on non-active would make it wallow, it actually dropped the system into the right operating parameters and worked far better. With semi active, it’s seems more important to get the bike in the riding operating range than a static one.

 

Does it have a IMU? How many axis? If it has one and does what you are saying, than it must ignore the rotations on the Y Axis. I think it would be really dumb programming if so, but I really don't know how it works at the moment...

EDIT: maybe it has linear sensors on the suspensions? Then it would know the starting static position of the bike and the dynamic ones, I can't understand why someone should feel an harsher ride for this reason... Anyway, it is impossible to understand how a spring replacement will affect an active system, because the hydraulic correction table is calibrated for a value that is a result of the stock spring/ideal rider, and we don't know it. Trying to set up a semi-active system is nothing more than a trial-and-error thing, it is really hard to imagine how it could respond to our interventions because we don't know many of the parameters, algorithms, etc etc

 

Skyhook has lots of sensors and there are IMU's on the bike which I assume are all linked (cornering ABS, traction control, semi active suspension, cornering lights)

 

Ok, I saw on the tech specs that it is a 3 axis sensor IMU, sure it cannot change it's behavior just for a change in front ride height. There must be some reason other than that

 

AFAIK it operates in about 1/3rd of full travel zone best, and adds comp or rebound on the fly (in milliseconds!) to keep the rider as 'flat' as possible and mean that dive and unloading is constant regardless of speed. When you are outside of that (too soft or too stiff) it over compensates. So some who added a former spring, lifted it outside the zone and it added comp/reb and made the actual ride firmer for pillions (theory not fact)

Mine worked better the faster you went. At slow speeds, you felt a lot, at faster speeds fault large potholes can easily be ridden over with almost zero (mostly zero) feeling as the bike adjusted itself (if that makes sense). But I don't know how different the SCU system on the ohlins is

 

In theory, the position of the suspension should not change the hydraulic behaviour, since the hydraulic dampening works with relative motion: speed of the movement * travel=quantity of oil moved. It is a simplification but it like this more or less and I don't know the exact word I have in mind in Italian, I'm sorry... Maybe the flow rate? Anyway, what changes this is the center of gravity height, but it should not change so much for a minor preload variation and for a minor change in the spring. In this last case, it surely change the resistance of the system, so it could result in an overcompensation of the system if you use a stiffer spring, and a undercompensation if you use a softer spring. But again, it is really hard to imagine, since you don't know how much you (and your weight, specifically) are close to the stock value Ducati has built the algorithms around, the only one that works as Ducati wanted in the project. There is another problem too: increasing the rider weight will affect less the front suspension than the rear and in almost every situation, that's the main reason many owners complaint about the rear and not so much about the front. What changes the most in front, is the dive while braking, and the same question as before about how algorithms work is valid here too.

The Ohlins system has less parameters to decide how to change the dampening, so it is easier to experience some strange or different behaviour from the bike, I guess

 

I personally don't think the ohlins mcu has any IMUs within it.
From reading the info when they were released its more to do with what information it can glean (presumably from the CAN bus) relating to speed, gear, throttle position (plus no doubt clutch). It therefore has a stab at adjusting to the conditions, but clearly cannot determine what the road surface is like in terms of grip or smoothness.

There aren't to my knowledge any sensors on the bike or the suspension units to determine travel or current position, certainly in the case of the ohlins. Just look at the TTX rear shock, it effectively has manual controls replaced with stepper motors and a hydraulic spring adjustment platform. These are also dumb in that they don't know their current position, this is why the units have to do a range sweep when battery is connected.
I would assume their forks are just the same (I don't know as I've personally not stripped a pair) - adjust compression and rebound with steppers but no measurement.

I follow what your saying about preload but disagree on some aspects.
I accept adding preload does not change the spring rate, If applying 100kg of weight causes the spring to compress 100mm, 100kg of applied weight will always compress the spring the same amount.
The key to preload is to get the ride height to sit correctly when the static weight of rider (and in some cases pillion and luggage) is in place. If the spring is too soft it wont cure it, it will still compress more than is desired.
The key is to find the right spring rate for the maximum applied load that can accommodate it in all conditions likely to be encountered, whilst still being compliant with the minimum load.
The problem here is a spring that can accommodate the highest load could well be too stiff for the lightest load.

In our case I could easily see the additional weight of pillion and luggage adding 100kgs to the static weight.
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Trying to adjust damping for what might be encountered before you get to it is quite a challenge too.
Consider riding that bike with additional 100kgs on it around a bend at approaching 100mph which will clearly compress the suspension, and hit a bump mid bend.
This is quite a design challenge to overcome for a spring that must also be compliant with 100kgs less load in the same conditions


Neo you clearly know your stuff, and its great to hear someone else talking about this at such a technical level.
p.s. sorry for the long post, sat in a dealers waiting for my car to be serviced and have time to fill

 

Skyhook seems to manage so well at mid corner, large bump high speed.

IMHO it’s jut Ducati wizardry and the special spell only lasts until 2 yrs and 3 months lol