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Offline djmrmagic

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Setting Preload on DDC *Issues*
« on: June 23, 2018, 08:34:04 PM »
Hi All,
OK I managed to talk the Mrs in helping me out setting the sag / preload etc

Bike was on a level drive
Engine was running
DDC set to soft
1 up was set
Bike in road mode
I'm about 14st (90kg)

So I held the bike level, No Load, Mrs measured height=47cm
I then sat on the bike, Mrs measured height = 43.5cm
So negative spring displacement = 3.5cm, book says 2-2.4cm so I need to increase preload so it raises 1-1.5cm

Now I turned the preload adjuster about 5 turns, sat on it again and measured and it was the same (43.5cm), tried again another 5 turns, same height, I literally turned and turned, I was thinking that the nut was just spinning, when all of a sudden, it started tightening up, but I only got a couple of turns from when it started stiffening until I couldn't turn the nut any more......anyway when we measured again the height was 45cm, so all good.

When we measured the front it needed adjustment too, and the adjustment was the same, turning the preload did f-all until right near the end of the adjustment, when I literally had 2 turns from stiffening to tight....


So my question is.....is this normal to have the preload nuts turn and turn and seem to do nothing until the end of the adjustment?

Couple of mates coming over on Monday so I will ask the to double check for me

Offline Rivets

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Re: Setting Preload on DDC *Issues*
« Reply #1 on: June 24, 2018, 08:54:42 AM »
After 9 months of ownership I did the same 2 days ago and being slightly heavier than you I did the same only when I reached fully in I was as still a few mm short of the required range at the rear. Front ok so I think it left the factory set up for an oompah lumpah !!

Offline djmrmagic

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Re: Setting Preload on DDC *Issues*
« Reply #2 on: June 24, 2018, 11:14:15 AM »
Ahh that has made me feel a bit better.....thought I was doing something wrong.

I didn't think I was "heavy", now I know what girls feel like when they are compared to size 0 models....is the average bike rider 85kg, that's bloody small!

Think it means, either go on a diet (never happening) or get stiffer springs (expensive)

Offline SimonS1KR

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Re: Setting Preload on DDC *Issues*
« Reply #3 on: June 24, 2018, 12:12:07 PM »
I must admit that Ive never really understood BMWs instructions for setting sag, but the behaviour you describe fits with how a linear spring would work. Apologies if I use any incorrect terminology here.

Total sag consists of static sag (caused by the weight of the bike) plus rider sag (caused by the additional weight of the rider). Assuming that the preload does not overcome the static sag (such that the suspension doesnt squat at all under the weight of the bike), then it should have no effect on the rider sag, which is governed only by the spring stiffness. So, if you want to change the rider sag (which is what BMW want you to measure) then you have to change springs. The total sag would reduce in this situation as youd be reducing the static sag by increasing the preload.

Alternatively, if the preload adjustment can overcome all of the static sag and more, then it would be possible to affect the rider sag that BMW want you to measure. In this case, you wouldnt see any change in the rider sag until the last few turns on the adjuster, once the static has reduced to zero.

Now, I always thought that an amount of static sag is required to prevent the suspension from constantly topping out over irregularities in the road.

As Im way more than the ideal 85kg in gear, I pretty much have my preload adjustment maxed out front and rear to try to get the suspension working as close to the optimum range as possible. I havent checked any measurements recently (nearly 3 years) so Ive no idea what my static, rider and total sag numbers look like.

Maybe someone who knows more about the vagaries of motorcycle suspension could chip in and tell me Im completely misunderstanding the sag concept and that BMWs rider sag measurement makes some kind of sense please?  :087:

Offline djmrmagic

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Re: Setting Preload on DDC *Issues*
« Reply #4 on: June 24, 2018, 02:32:33 PM »
ahh ok bad choice of words on my part....what i was trying to say was,

 that i was setting the bike up so that the negative spring displacement when loaded with rider was in bmw specs 😀

Offline SimonS1KR

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Re: Setting Preload on DDC *Issues*
« Reply #5 on: June 24, 2018, 03:24:27 PM »
Sorry if that came across as a criticism djmrmagic, I wasnt trying to say youve done or said anything wrong.

I was just trying to explain that I dont quite understand how the BMW rider sag method works. If they were asking us to take all of the weight off the suspension (wheels off the ground) as the starting point then measure the difference with the bike plus rider on the suspension (i.e. measuring the total sag), then it would make more sense to me. But as BMW are asking us to take the rider sag measurement that I thought is dictated by spring stiffness, Ive never quite understood the logic.

Simplistically, I always thought preload is the means to get your total sag to the right point in the suspension travel then changing the spring stiffness is the way to get keep your suspension travel between the stops without bottoming out.

Offline djmrmagic

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Re: Setting Preload on DDC *Issues*
« Reply #6 on: June 25, 2018, 09:52:05 AM »
lol...no probs I have thick skin :)

Its all a bit confusing, and I don't know why their adjustments don't allow for fatties like us  :P

Offline Skaterboy

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Re: Setting Preload on DDC *Issues*
« Reply #7 on: June 30, 2018, 05:47:41 PM »
Sounds about right similar issue as you but alas slight heavier. Igot pretty close to required settings not sure if mentioned above but need a to done after a ride as oil up to temp.

Offline Brian the Sn@il

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Re: Setting Preload on DDC *Issues*
« Reply #8 on: August 10, 2018, 04:24:13 PM »
is this the nut on the top of the front forks ?
I keep turning and turning ( CLock wise)  it just spins forever ?
Im 100KG so maybe ive broken it ?

Offline alxsterling

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Re: Setting Preload on DDC *Issues*
« Reply #9 on: August 10, 2018, 07:24:01 PM »
*Originally Posted by Brian the Sn@il [+]
is this the nut on the top of the front forks ?
I keep turning and turning ( Clock wise)  it just spins forever ?
I'm 100KG so maybe I've broken it ?

@Brian the Sn@il
The preload adjuster on bikes with DDC is found on the right fork cap. It's the black hex (15mm?) adjuster w/ rings on the cylindrical tube.
Those rings indicate your front fork preload position.



If you spin it clockwise you increase preload which decreases sag (makes bike sit higher) - counterclockwise decreases preload which increases sag.

Your adjuster would be broken if it just spins and the number of rings doesn't increase or decrease. At either end of the range you should reach a stop point. I believe from factory the bikes come with either 5 or 6 rings showing in the front but for whatever reason the adjuster hardly affects sag. The first time I tried to set mine I thought it was broken cause I kept turning it and nothing happened to my sag numbers. You may have to spin the adjuster quite a bit to notice any measurable changes.

Go for a 30 min ride with a friend, come back and measure your sag numbers in mm with the bike on, level, set to soft / 1 up, and with you off and then on the bike front and rear. From there calculate the difference between static and rider sag and figure out if your in spec or not. Adjust the preload knob's 2 turns at a time till your in spec & then fine tune it (anywhere in the range should do just keep it consistent). If you get to the end of your preload adjustment range and your still out of spec you'll probably need a respring and maybe an oil viscosity change to support that since revalving isn't possible on the R w/ DDC as far as I know.
« Last Edit: August 10, 2018, 07:31:01 PM by alxsterling »

 


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