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Offline Noggie

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My DDC modification story, heavy rider modifications.
« on: September 28, 2017, 04:01:07 PM »
This is my story trying getting the DDC suspension to better suit me and my weight.

It will be a long post as I want to get as much information in here as possible for future reference.

First lets get some basics out of the way.



Target:

A DDC suspension better suited for a 100kg rider.


Riding experience with stock DDC setup, all preloads set to max.

Fast compression too hard, causing a harsh rough ride, suspect this is because the spring is too weak and the shock is hydro locking causing it to go rock hard on fast compression.

Slow compression too soft. Causing the bike to be unstable when pushed through corners, weight distribution is not evenly distributed between the forks and shock making the bike unpredictable in corners. High fork compression causing excessive fast brake dive when braking and risk of bottoming out the forks.



Bottom line. I dont trust the suspension and it affects my riding. Have not dared to take the bike on a track day because of this.



OEM spring rates:

Rear: 9kg/mm or 88Nm/mm
Forks: 0,85kg/mm or 8,3Nm/mm

Forks:

Status with OEM springs max preload.

Sag: 24mm (76mm from lower casting, 100mm without rider)
Total length of fork 130mm. (above fork seal to lower casting)

Suspension range i.a.w BMW manual 120mm, placing bottom out 10mm above lower casting.
Measured lowest zip tie position on normal road use, 14mm from lower casting.
I am in theory 4mm from bottoming out the fork on the street. According to Dave Moss you want to be between 10-20mm from bottom out. Anything below 10mm is in the danger zone.



After conferring with TripleTuning in Germany I was recommended 9Nm/mm fork springs (0,92kg/mm), just 0,7kg/mm stiffer than stock. 
Springs were changed at the bikes 20.000km service and a fork service was done at the same time and I moved the fork tubes up from 2 to 3 bars to see how that was.


Rear shock:

Recommended rebuilt to Wilbers WESA system, at 1000, this retains DDC functionality, and give you an additional quick and slow compression adjuster for individual fine tuning.

Just a spring swap was possible, but not recommended as it would not work properly as the electronics and internals of the shock also had to be modified.


I have this scheduled as a winter project as the shock has to be removed and sent in to be rebuilt.

I will update this post with information second quarter of 2018.



Result with just fork springs:

I got the bike back from service with pre-load at 2 visible bars, fork tubes with 3 visible bars.
How is the bike handling?
Well, the front is much better, feels more controlled in the corners, brake dive may not have changed much with regards to distance it drops, but it drops a lot slower and feels more controlled and confident inspiring.
Moving the fork tubes from 2 to 3 bars was a mistake, the bike turns really easy, but it became awful riding slow and in queues, I was constantly correcting the bike with steering inputs.

This would probably be a good idea for a bike that see a lot of track use, but as a daily rider the loss of stability was not something I personally liked. This is my personal opinion, yours may differ.

I moved the fork tubes back to the stock 2 bar position after a 250km test ride.



Changing just the fork springs has upset the balance of the bike, and that is something I expected. 
The electronics appears to be struggling to cope with a stiff front and soft rear. After all they do work in conjunction with each other and the stiffer front appears to result in the rear being softer that it should because of the way the DDC works.

Im not comfortable pushing the bike in the corners as the rear is very soft and I dont like the balance of the bike.

Riding normally is no issue, but I do feel more up/down movement of the rear, cant say if its the same as before and if its just the forks moving less that causes me to notice.
 It does feel like the rear is pivoting around the front though.
I did try two helmet mode and while the rear became much stiffer, I did not like how the rear acted. I believe that is because the compression dampening is just made harder by the shock, and it is now even more prone to hydrolocking.

Zip tie position with 9Nm/mm fork springs and preload set to two visible bars (4 turns out from hard), was 25mm after several emergency braking tests, which should place me 15mm from bottom out, which is good, 11mm higher than stock springs, well above bottom out and in the safe zone according to Dave Moss.


As a test I removed all preload, fork tubes set to stock, ran single helmet mode and repeated my emergency braking tests with suspension at the soft setting.
The zip tie still remained at 25mm. Im quite happy with this result.
 The bike also handles well with no preload, and moving the fork tubes back to stock did increase the stability.

SAG.

I guess this is going to be the big question.

With no preload: 13mm

With 5 turns of preload (50%): 9mm

With max preload: 6mm

Note that these may not be 100% correct since the rear is very soft and probably takes more of the weight. For now I have set it for 3 turns in from soft, which gives me 10mm sag.



Not sure I would recommend just changing the front springs, I think changing both front and rear at the same time is better.



Result of rear shock modification.

Will be updated second quarter of 2018

Offline lospsi

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Re: My DDC modification story, heavy rider modifications.
« Reply #1 on: September 28, 2017, 06:41:43 PM »
Its a bit confusing to me how you measure sag.
To my knowledge, there are 2 sag values, static aka the compression of the suspension by the bike itself and the dynamic (or rider) sag aka the compression of the suspension with the added rider weight. About 5-10mm of static and 30-35mm of dynamic sag are considered good values.

So, if I understood correctly, you had 24mm of dynamic sag with OEM springs topped out. That was too stiff and possibly explains the harshness of the rider.
It also seems weird that such a low increase of spring rate made so much difference.
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Offline Noggie

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Re: My DDC modification story, heavy rider modifications.
« Reply #2 on: September 28, 2017, 06:56:46 PM »
BMW measure sag differently.
It's specified in the manual around page 79.
You measure the bike standing straight on its own weight, and then with the rider on it.
So it's rider sag minus static sag.

The manual specifies that this measurement should be 6-10mm, I had 24mm with stock springs so it was way to soft.
With the new springs I can get within BMW spec.

As an engineer, the fluid inside the shock has to pass through holes in the cartridge that slows down the movement.
If the spring is too weak, the oil has to take up the energy the spring can't.
On quick compression the holes are then too small restricting the oil flow too much, so much that the oil can't flow fast enough causing it to lock up and go hard.
That is why the spring must be matched to the load applied, and why the stock spring gives me a harsh ride on quick compression, and becomes too soft when the load is applied gradually, like in corners or braking.
« Last Edit: September 28, 2017, 07:03:03 PM by Noggie »

Offline lospsi

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Re: My DDC modification story, heavy rider modifications.
« Reply #3 on: September 28, 2017, 07:49:30 PM »
I haven't read the manual but it seems that it says the same but posts a different number. So, if I understand correctly, the number you posted (24mm) is the difference between static and dynamic? If so, 6-10mm is way off and 24mm is correct.
See here how I measure my bikes.
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Offline Noggie

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Re: My DDC modification story, heavy rider modifications.
« Reply #4 on: September 28, 2017, 10:32:40 PM »
Then I suggest you read the manual, page 77-79.

I know how you normally measure sag, like that Dave Moss video, but thats not how BMW do it.
BMW don't care about static sag on the DDC.
According to the manual, you should hold the bike vertical, ignition on, DDC in "Soft". Then take a measure of the fork. i.e 100mm
Put the rider on the bike and re-measure, say you get 90mm, this gives you a sag of 10mm
BMW specifies in the manual that the difference between the bikes own weight and with the weight of the rider should be 6-10mm for the forks, and 20-24mm for the rear shock.

With stock springs I have 24mm where BMW say I should have 6-10mm.
With the new springs I now have 10mm, and can adjust to 6mm if I want to.

Offline miles

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Re: My DDC modification story, heavy rider modifications.
« Reply #5 on: September 28, 2017, 11:40:30 PM »
I'm really looking forward to reading about your experiences with the Wilbers shock. Their information online doesn't say that it retains DDC functionality- they claim it retains WESA, and in BMW speak, ESA is a completely different animal from DDC.

That ambiguity has kept me from wanting to pursue that avenue at all... I'm just not convinced. For that reason, I'm pleased that somebody else is stepping up to be the guinea pig.

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Offline Noggie

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Re: My DDC modification story, heavy rider modifications.
« Reply #6 on: September 29, 2017, 12:23:44 AM »
*Originally Posted by miles [+]
I'm really looking forward to reading about your experiences with the Wilbers shock. Their information online doesn't say that it retains DDC functionality- they claim it retains WESA, and in BMW speak, ESA is a completely different animal from DDC.

That ambiguity has kept me from wanting to pursue that avenue at all... I'm just not convinced. For that reason, I'm pleased that somebody else is stepping up to be the guinea pig.

Yeah, I hope it plays out well in the end.
I'm kind of thinking this is an abbreviation and system name confusion.
While ESA probably means Electronic Shock Absorber, DDC is Dynamic Dampening Control.

As a technical person (9 years as an aircraft tech and 10 years in drilling controls for oil rigs) I believe this is down to definition.
DDC would be the name of the whole system, the forks, the shock and the electronic control modules.
something called an ESA would be a single component in the DDC system.

From talking to Wilbers the WESA shock absorber rebuild changes the spring to match rider weight, then changes both the internal hydraulic cartridge of the shock, and the electronics.
My guess to make it work better with the BMW DDC controller.
It also ads a fine-tuning ability for fast and slow compression, while I doubt I will be using that much, track users may find that helpful.

I'm currently debating with myself if I should send in my own shock, or buy a used one of ebay and have that modified so that I have the option of returning the bike to stock, mostly for when I'm selling the bike..... But you never know.

Offline lospsi

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Re: My DDC modification story, heavy rider modifications.
« Reply #7 on: September 29, 2017, 09:25:28 AM »
*Originally Posted by Noggie [+]
Then I suggest you read the manual, page 77-79.

I know how you normally measure sag, like that Dave Moss video, but thats not how BMW do it.
BMW don't care about static sag on the DDC.
According to the manual, you should hold the bike vertical, ignition on, DDC in "Soft". Then take a measure of the fork. i.e 100mm
Put the rider on the bike and re-measure, say you get 90mm, this gives you a sag of 10mm
BMW specifies in the manual that the difference between the bikes own weight and with the weight of the rider should be 6-10mm for the forks, and 20-24mm for the rear shock.

With stock springs I have 24mm where BMW say I should have 6-10mm.
With the new springs I now have 10mm, and can adjust to 6mm if I want to.

I forgot that your bike has DDC, which probably works way different. Then again, to me the numbers still seem odd. Hope you figure it out!
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Offline Noggie

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Re: My DDC modification story, heavy rider modifications.
« Reply #8 on: September 29, 2017, 11:54:51 PM »
*Originally Posted by lospsi [+]
I forgot that your bike has DDC, which probably works way different. Then again, to me the numbers still seem odd. Hope you figure it out!

Yeah the DDC is special.
I was approaching this like you in the beginning, and I found out that I was very close to the standard way of measuring sag, ignoring the BMW way.
But as I got to know the bike and started to push harder, I realized that BMW was probably on to something.
I felt the fork bottom out a couple of times, and installed a zip tie, that's when I found out how close I was.
A friend riding behind me when we was pushing it through some twisty roads said he noticed that my rear was moving a lot and appeared very soft.
So in July, after 14 months of ownership I made the decision to do something about it.
Fork springs first as I could do them during a mid-August service, and season here up north usually ends in October, so I figured I could spread the cost by doing that during the winter.

When April comes and the season starts I should have everything ready to go.

Offline RideRedWA

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Re: My DDC modification story, heavy rider modifications.
« Reply #9 on: October 07, 2017, 12:30:28 AM »
Subscribed to this. I'm your same weight and going through the exact same thing. I love all of the tech on this bike but it is not working for me right now. Willing to put some money in to get it sorted but would prefer to not drop in loads of cash.

 


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