Suspension tuning; S4

[spuggy]

So, I don't know a single thing about Ducati suspension tuning I didn't read here - and only know enough to be dangerous. So could use advice from someone who knows what they're talking about

My M900ie Dark handling was pants when I got it. The (non-adjustable) forks were too stiff & didn't have enough (any?) damping, the rear was lowered and soft/saggy/bouncy - like it was worn out and had been owned by someone under 5ft tall; had to bend my knees when flat-footing it... Fitted S4 front forks dropped slightly in the yokes, and a Nitron R2 with a spring spec'd for my weight, and it transformed the bike. It'd fall into corners - but went round them like it was on rails, and soaked up bumps like they weren't there. Sorted.

My M900Sie was saggy as crap at the rear (Ohlins) shock; jacked it up with slugs on the hoop (front already dropped), and increased pre-load until static sag was correct; much, much better. Ohlins doesn't seem as good as the Nitron to me, but could just be it needs a stiffer spring...

My S4; I've been riding it and was not especially thrilled by the handling at first; don't know why it had tire pressures of 36 in the front and 38 rear, but I can tell you that doesn't seem like an improvement on the factory settings to me...

Now I'm not actively trying to avoid leaning the bike(!), what I notice next is weight distribution changes on slow greasy roundabouts. As you roll tiny amounts of power in as the line straightens (from literally slightly over idle speeds, I can still hear clutch knock), I can feel the front suspension unloading.

Yeh, the S4 is noticably more powerful than the injection 900s - but I mean with the smallest amount of throttle you can realistically feed in. This feels more like a suspension issue than "clumsy ham-fisted git tries to wheelie banked over"...

Oh, also the 900s fall into the corner quite quickly - but predictably/linearly.

Unless I'm imagining it, the S4 seems to fall into corners slow at first and then quite abruptly speed up the deeper the lean angle gets. Does this suggest anything in particular, or is it maybe a foible of the different frame? It's not scary, but seems odd.

So, the bike's got 21K on it. I'm pretty confident before I look that the rear spring will be both way too soft and won't have enough pre-load. I don't have any way to adjust the pre-load right now, but am intending to check rebound & compression damping is set per factory settings and adjust the pre-load to get sag somewhere in range Real Soon Now. Checking fork oil levels (or even changing the oil) might not be a bad idea either.

Just how good is the adjustable Sachs shock? I'm thinking 21K could be getting to about where it needs a service - right? - and if I need to yank it for a spring change, I could easily be tempted to get another Nitron R2 with the appropriate spring rate anyway...

Thoughts?

[Wasta]

Have a look at Dave Moss Tuning on youtube. Very helpful videos and the guy knows his onions

[alan s4]

Could be as simple as the tyres. When I first got my S4 it felt exactly the same, the bike was fitted with sports oriented tyres, the profile (esp the front) was "pointy".

Changed to Michelin Pilot Roads (with a far rounder profile) and the handling was much more neutral.

What tyres have you got fitted?

[Darren69]

What front tyre profile do you have on it? I imagine the shock will be past it's best by now as you say and maybe that's the cause? What's the ride height set at? As standard they are too low and the tie bar if never adjusted is likely to be seized but you can change that if you're doing the shock anyway, you can get longer ones as well from other models.

I fitted an Ohlins (DU046) to mine and the spring is too soft for my weight but it still handled fine and I could get it in the ball park with the pre-load adjustment, a Nitron would probably be just as good with the correct spring.

[Darren69]

As Alan has also said, that was the issue with my 748. It had been fitted with a different profile front and although a correct fitment was not the OEM one and did not feel good to me. It felt like the front was dropping away if you leant too far over, it wasn't but it just felt like that as it dropped too fast. Had fitted a standard profile front when I had a new set of tyres and no longer a problem.

[Mr Gazza]

Sounds like you know more about suspension than your modesty allows.

I imagine you have already adjusted the tyre pressures? If not I would start there with something like 32 front 36 rear, which works well on my M900Sie but might need a pound or so more on the heavier S4?

Next I would look at the tyres themselves starting with the date stamps. I would change anything more than 5 years old as a matter of course, or even getting near that if they feel hard and stiff or show any sign of degradation/cracks.
Also look at the wear pattern, as they may well have prematurely flatted if they were run with too much pressure? Even a virtually invisible flat on the rear will induce horrible handling characteristics, which usually gets blamed on the front.
If the rear has a flat then the front will most likely have corresponding "pyramidal" wear which can also be hard to spot, but will play up the handling, particularly at that roll in point, but usually be okay when cranked right over, which you seem to allude to?

Next, and in short order I would change the fork oil, as you obviously intend to do. It might explain the apparent lack of rebound damping as you accelerate? Low oil might facilitate some compression damping as the forks go down into the oil, but they could be coming out of the oil on the way up and so loose rebound damping?... Possibly?

Even good suspension will struggle against the above faults, so it's always best to check the background (cheaper) things first and go from there.

[slob]

Doesn’t matter whether your suspension is Sachs, Ohlins, Nitron or A.N.Other. As well as having an approximately correct spring rate, it’s going to want servicing periodically, the oil passes through many heat cycles, starts to fill up with particles worn from internal bushes and starts to cavitate at which point your damping is £@!&ed. Most manufacturers suggest changing fork oil every 2 years, most owners just don’t.

[spuggy]

Thanks guys, some great input there.

Ride height; not lowered. Higher than both/either of my 900s when I got them, I'd say. Comfortably balls of both feet, probably, haven't really tried.

Tyres... Ah yes, I'd mentally glossed right over the tyres....

Bike's done 2000 miles in the last 8 years, according to the MOTs. My buddy said he found a 2008 date code on the front; just went out there and I can't find any dang date codes on either... They're not damaged or cracked, otherwise I wouldn't have ridden on them (I'm stubborn and stupid, not insane ).

Tyres are mis-matched, however - Pirelli Diablo front, and Maxxis Battlax rear. They seem to have similar (round) profiles and don't look obviously flat-spotted, but they were certainly over-inflated @ 36 front/38 rear. Reduced to the figure I like in the 900s - 30/34. Does feel better.

I've not been keen to explore the limits of adhesion with them, but they seem fairly well-behaved.

So; ordered a front-lift arm for the Abba. baby needs new boots. Michelin Pilot Road you say?

So, game plan looking like; replace tyres. Drain/replace fork oil, check front/rear suspension settings are "normal".

I bought a used R2 on flea bay; it's for the injection 900s (eye-to-eye 330mm, rather than 305mm stock for the S4), but it does have an Ohlins "fat knacker" spring.

Nitron quote 5 week lead time for service/supply new just now, but have dealers that can do faster. So I thought I'd snag the spring to put on the Sachs, check/set the compression/rebound, and send the R2 off for a service/get re-worked in the meantime.

Y'all say to jack up the rear on an S4 as well? Presumably to quicken the steering? I'm old - stable bikes with slow steering don't bother me at all

[Darren69]

I jacked mine up to remove the rear bias that is standard on these and the early ones too would appear to be the same. It was enough to restore a more neutral 50/50 weight bias front to rear and made a big difference to how the bike felt in corners, I may have increased the front bias slightly I also fitted clip-ons, but enough to make a noticeable improvement to front grip feel and how the bike stays where you point it, instead of running wider on exit. It's not as planted as say my 748 is mid corner, but it's as good as I think I can get it.

[spuggy]

Originally Posted by Darren69

As standard they are too low and the tie bar if never adjusted is likely to be seized but you can change that if you're doing the shock anyway, you can get longer ones as well from other models.

I fitted an Ohlins (DU046) to mine and the spring is too soft for my weight but it still handled fine and I could get it in the ball park with the pre-load adjustment, a Nitron would probably be just as good with the correct spring.

Hmmm, if I'm not mistaken (I looked in vain for a used DU046 for my Dark), that's from the 900ie bikes - eg 330mm eye-to-eye, rather than the 305mm spec'd for the S4?

The Nitron R2 I got used (complete with a weight-appropriate spring) is actually 335mm eye-to-eye (with the adjustable bottom fitting wound all the way in).

I was intending to get it serviced & shortened; but now I'm thinking maybe I should just leave the length alone. Even noodling just fitting it as-is and seeing what it feels like...

Just out of interest, what model/lengths tie bars are commonly used to achieve the same jacking effect with the stock shock length?

Originally Posted by Darren69

I jacked mine up to remove the rear bias that is standard on these and the early ones too would appear to be the same. It was enough to restore a more neutral 50/50 weight bias front to rear and made a big difference to how the bike felt in corners, I may have increased the front bias slightly I also fitted clip-ons, but enough to make a noticeable improvement to front grip feel and how the bike stays where you point it, instead of running wider on exit

Hmm - I don't really crave ground clearance or quick steering, but yeh, running wide on exit seems like a trait best corrected to me.

[chris.p]

I would think that a extra 25mm is far to much over the standard 305mm, it will make the front end too twitchy, 10 to 15mm is more manageable, this will make the bike stop running wide etc and be a more pleasant ride with easier turn in etc.

[Darren69]

Originally Posted by spuggy

Hmmm, if I'm not mistaken (I looked in vain for a used DU046 for my Dark), that's from the 900ie bikes - eg 330mm eye-to-eye, rather than the 305mm spec'd for the S4?

The Nitron R2 I got used (complete with a weight-appropriate spring) is actually 335mm eye-to-eye (with the adjustable bottom fitting wound all the way in).

I was intending to get it serviced & shortened; but now I'm thinking maybe I should just leave the length alone. Even noodling just fitting it as-is and seeing what it feels like...

Just out of interest, what model/lengths tie bars are commonly used to achieve the same jacking effect with the stock shock length?



Hmm - I don't really crave ground clearance or quick steering, but yeh, running wide on exit seems like a trait best corrected to me.

DU046 is the correct one for the S4 and 620 and others:-

https://www.desmo-racing.com/en/shoc..._358-2390.html

Tie bar was an aftermarket one for a 999SBK from Peter Dorsch Racing which maybe called MVS nowadays.

[spuggy]

Originally Posted by Darren69

DU046 is the correct one for the S4 and 620 and others:-

Yes, I was correct about the 330 length for the M900ie, and completely wrong about the DU046 being correct for it. Probably just as well I didn't find one...

In penance, I post a small part of the Ohlins catalog that shows how wrong I was:

Originally Posted by Darren69

Tie bar was an aftermarket one for a 999SBK from Peter Dorsch Racing which maybe called MVS nowadays.

Ahhh. Those guys. MVS Performance... They used to have a lot of interesting pieces.

In fact, I used to really like their billet swingarm end plates, and their alloy or carbon/alloy adjuster plates. I blame Dirty - I never knew they existed until he told me, and then I just couldn't look at the factory parts anymore without cringing... .

Sadly, when I went to buy a set for the S4, found out they've been closed since 2018....

I managed to find these on Flea Bay, which are quite acceptable:



But couldn't find a source for billet swingarm adjuster caps - anyone know anyone else doing those?

Luckily, my only remaining set of factory ones are only mildly scabby right now, so it's not as urgent as the adjuster plates (which were both scabby and bent/damaged)...

[jerry]

The S4 as standard is not a good handler ,, and its not the Sachs shock that is the main culprit its the front forks ,, they look fully adjustable ,, but its not ,, the preload and compression work but the rebound is not connected to the cartridge ,, even putting in decent springs and a shim upgrade wont make much difference ..

The standard front forks are very cheap showas ,, I spent a lot of time and money trying to improve them with hyperpro springs , different oil weights and adjustments but they were flwad design due to NO rebound circuit .


I fitted an Ohlins DU46 to rear with remote adjusters and it did help a bit but in the end I changed front forks to Superbike forks off a 996 with Kteck valves and shims mods installed and ohlins 8.5 springs ,, now its perfect also needed new yokes etc ..

[spuggy]

Originally Posted by alan s4

Could be as simple as the tyres. When I first got my S4 it felt exactly the same, the bike was fitted with sports oriented tyres, the profile (esp the front) was "pointy".

Changed to Michelin Pilot Roads (with a far rounder profile) and the handling was much more neutral.

What tyres have you got fitted?

Ding! Ding! Ding! Winner winner, chicken dinner!

New set of MP Road 2's fitted. I wasn't there, but the tyre chap (who rides bikes/does track days) took one look at the front and said, unprompted "yeh, that's farked". (profile worn unevenly, steeper one side than the other).

Wasn't supposed to be far from a laptop this W/E, but took it for a spin anyway when we got the wheels back...

Even taking it easy (letting the pads relocate, sipes still glossy with mould release agent etc), vastly improved. Taking it off vertical, quickly lost the "no mommy, I don't want to" reluctance on my part - because it no longer pitches in abruptly while the front seems to telegraph that it's washing out and going away.

So, new tyres == win.

One strange thing; tyre guy filled them with 2.75 bar and 3 bar (I measured 40 psi front and 45 rear). Of course, I bleated that factory pressures were 2.1/2.2 bar. "Try it" was the response.

I figured they couldn't be any worse than the crap that came off, so rode it like that for a few miles before dropping pressures to 36 psi front and 38 psi rear.

Here's the odd thing; didn't really notice any significant difference between the two pressures at the rear (perhaps slightly more prone to tramline/follow road imperfections at the lower pressure).

However, with the higher pressures, the steering seemed fast, sharp, precise. Lowering the front pressure - it still steered well (maybe slightly slower) but still precise and tracked well, softer ride (well, duh) - but also more "wallowy" - like a hint of head-shake transiting the apex I didn't notice before.

Curious... Think I need more miles/testing to figure out how much is imagination and how much is increasing confidence causing me to be less cautious as the tyres scrub in and they feel better/I trust them more, but it's got me wondering...

I'll try the handbook figures next, but I think I may revisit higher pressures at some point. At least until the suspension gets baselined and/or a little better sorted. Because now it seems very obvious that the front suspension is saggy/soft with lots of travel - and very little compression or rebound damping. Starting to think there may be no oil in them... Various tools showing up for that soon, and I'll fit a fresh rear shock with an appropriate spring too.

Maybe if I'm lucky, the bushes will be worn and there'll be a reason for the poor damping. Yeah, I know they cheaped out on the rebound circuit on these Showas - but I have the exact same forks on the Sie and the Dark, and they feel fairly reasonable there..