RT suspension settings question (Ohlins on 1150RT)

[GMC]

Installed new (actually used) Ohlins struts on the 1150RT this week (and have been posting a little on other threads during the process, but figured a new thread for this question was more appropriate).

 

My 2 questions are as follows, and sorry for the length of the post/questions:

 

1. Easy one first - on the rear suspension, I noted that i needed a little less static sag. How far "down" (clockwise) can I twist the hydraulic pre-load on the Ohlins before i should be concerned? I dialed-in about 15 full turns to get the sag just right, and it seems like there's plenty still to go, which is very unlike the stock BMW strut i removed. I'm thinking thats bad, but maybe no big deal on the Ohlins system?

 

When I first checked rear sag with the new Ohlins and found it needed less (about 3/8" less), I figured I'd pull the strut back off and move the adjustment rings on the spring, assuming I'd want things set right that way first, and then i'd be able to fine tune with the hydraulic pre-load adjustment mounted on the side of the bike. The previously installed, stock hydraulic pre-load adjustment from BMW gave a limited, small amount of adjustment before it reached the end of its travel, so i assumed the same for Ohlins. But in reality, when starting to screw down on the Ohlins I was able to twist that knob seemingly forever, which worried me. It gave good results, and seems to have more to go (good, for when i add a passenger), but does that sound normal for the Ohlins to have that much more adjustment available?

 

2. The even dumber question, and more difficult to write without too many words.... Ohlins indicates I want a max static sag of about 1-3/8" (using inches, as that's the tape i'm unfortunately using) up front. My initial reading gives me about 2" of static sag. Hmmm... ok, back off the tension on the spring (c-spanner wrench), right? Seemed to get worse. Oh, I guess I tighten it? So I crank it the other direction, and it seemed to get better. Got static sag down to about 1-3/4" with max adjustment on the spring (adjusted almost all the way "tighter"). Better, but still too much in theory. So i put the stock strut back on for comparison, and it gives about the same, approx 1-3/4" to maybe 1-7/8" sag. I then put the heavier spring("heavy duty" option spring from Ohlins that I have sitting there) back on the ohlins shock, re-installed that setup, and it gives more or less the same result as stock. Huh?

Now I've just managed to really confuse myself...Shouldn't i be seeing some larger changes here with all those options?

Other factors to mention: when i started swapping struts and making lots of adjustments, I ceased torquing the upper and lower shock bolts for expediency, so there could be some slop there, but i assume its "uniform slop", meaning its got roughly the same impact on all the different options i'm trying.

 

2a. Should I be tightening the tension on the spring to decrease (front shock) sag, or loosening the tension (loosening = counterclockwise tension ring = longer spring)?

 

2b. Since the stock setup seemed to give me approximately the same amount of sag, is it possible that I'm just not measuring sag appropriately to be able to compare the numbers to Ohlins recommended numbers? I'm measuring vertically up from the middle of the front wheel bolt to a fixed point on the fairing above. Maybe i have the wrong front sag numbers from Ohlins for BMW telelever suspension? (i noted some posts regarding the GS that were a good bit larger, but that makes sense for a GS vs an RT)

 

 

some other qualifying remarks:

I've been mainly using "static sag" thus far simply because I have not had easy access to a helper just yet. I did do one "rider sag" measurement, and the delta (increase) in sag between the static number and the rider sag number is about what you'd expect from Ohlins numbers... in other words the rider sag adds about 10mm (roughly, but you get the point). I'll certainly do my final, main adjustments using rider sag, but using static sag to get things in the ballpark, when i'm working solo.

 

As more back story, which should be mostly irrelevant, I bought the struts used and removed the heavy springs and replaced them with new "normal" springs, as recommended by Ohlins, the springs that normally come on the BM124/125. So the setup now is a truly "normal" BM124/125 setup.

[Selden]

GMC : More preload = less static sag. The usual "rule of thumb" is that static sag should be ~30% of total suspension travel +-5%. I set the preload on my rear shock such that I got the desired static sag with zero turns with empty side cases. That leaves the entire range of the hydraulic adjuster to compensate for luggage, a passenger, etc. Riding 2-up, I add 10-15 turns of the adjuster knob. You don't mention your weight, but from your description, it sounds like your springs may be too light.

 

Also, check that the reservoir for the hydraulic jack on the rear shock is full; if it is, when the suspension is completely unladen (i.e., on the center stand), there should only be a turn or so from all the way out before you feel resistance. If there is more, turn the knob all the way out, invert the reservoir, remove the banjo bolt, and add more oil. Jack oil or power steering fluid seem to work well.

 

The other variable is damping. I like to start on the soft side (adjuster backed most of the way out, then increase damping 2 clicks at a time until the ride starts to feel harsh, then back off 1 click. It can take a lot of miles to find the point that is right for you.

 

To keep track of settings, after I get damping to where I want it, I put paint marks on the damping adjuster knobs. For the hydraulic jack for the rear shock, I put a mark at zero preload, then count turns when adding more preload for a passenger, luggage, etc. Without these reference marks, it's really easy to get lost.

[GMC]

thanks Selden-

I'm actually quite light, at 160lbs, which is part of the puzzle. its unanimous that the heavy springs for me are way overkill, so I replaced them.

What you propose sounds like the reasonable path forward, but there are still lots of questions. I read up beforehand on the topic, but now that i'm into this i'm reading more, and its still confusing, which sounds common....

 

Increasing pre-load via the spring rings (tightening those rings with C-spanner), if i understand properly, should mainly just effect ride height, and not the sag as much (maybe), since they are constant rate springs. But all the same I'll be doing what you've indicated. I'll increase the spring pre-load on the rear so that hopefully I have more of my hydraulic pre-load adjustment available for use. that should also increase ride height a bit in the rear (unless i'm still confused on that).

 

The front end is the tougher one, as my issue on that end doesn't really make sense to me. I think perhaps I"m just doing something wrong, and may just have-at-it again this weekend and see if i can get more sensical results.

[mrduck]

Try an old dirt bike trick on the front. Put a zip tie around the fork leg, shiney part,unload the front-on center stand- then gently put the bike down on the wheels. Back up on the stand, measure the amount the zip tie moved, there's your sag. The tighter the spring, the less sag.

I would suggest on the rear, remove all tension on the remote shock adjuster, then set the sag with the spring tensioner on the shock.

 

And to get even more confusing, your rebound setting (in my humble opinion) is more important and gives more feedback than the compression setting. Keep working with this, get the sag close and the rest will come.

 

At least that's how it used to work in the off-road world, and has worked well for us with the Ohlins.

 

Good luck

 

Don J

[GMC]

thanks Don -

good call, and now that you mention it thats what i did many years ago on the front forks on a bike i had where i had done some fork work... forgot about that zip tie deal. I don't remember being nearly as confused on that job years ago, but i think at that time things were all fairly close from the start, so not much needed to be done or figured out (= less thinking), and my standards were low...

cheers

[Twinsig]

Had mine rebuilt last spring by Fast Bike Ind. At my weight 175lbs. per the dyno, front shock is 18 clicks (counter clockwise) off of full stop (clockwise), rear is 17 clicks.

Dont know if this helps, good luck bro.

One thing I read in Lee Parks book 'Total Control': Fine tuning shock adjustments can only be determined when the shock/bike is at its performance limit.

[GMC]

thats perfect... getting it all in the ballpark is the key, so i can mess with it over time, especially once our wx starts to turn from cold and wet to something better.

 

During the winter I tend to ride the RT like full dresser, as i end up just sitting on it in my winter gear, enjoying the electric jacket, heated grips, bigger windscreen, etc., and with focus on staying warm and getting from A to B. Sunnier/warmer weather then (finally) comes and its like the bike changes, though in fact it doesn't, its just me that changes, as I start to ride it like a motorcycle and less like a generic wheelbarrow. Every spring i surprise myself remembering (one more time again) how relatively fun the RT can be to ride, after treating it like a pack mule each winter season.

 

So the trick now is to get the suspension in the ballpark, then can start dialing it in later in the year.

thx

[GMC]

To close my own loop:

 

Finished install of the Ohlins this weekend (along with other annual maintenance).

Suns out, ready to test ride, but awaiting one last part (bad relay) via mail to get her back on the road.

 

Had a good review of way too much info on suspension during this process. So much is written on it that its hard to see the forest for the trees, but its a good process to go through now and then, and answers are there to be had. Re-emphasizing such things as what sag really is (seemingly the most mis-understood piece), and the various other variables is all good.

But the bottom line for someone looking to just get things basically set up with new Ohlins (etc) is as others here on this thread (and elsewhere in the forum) have described. Tweaking it to perfection is a different deal, and I don't pretend to have that knowledge.

 

For the basic setup (much easier if you get your struts new from Ohlins/Elka/Wilbers, etc, where they come somewhat close to where you want them out of the box, but not for me with a spring change), its a simple matter of checking sag, and then adjusting the rings accordingly.

-"Tightening" the ring (seemingly compressing the spring) will reduce sage, and visa versa. Never mind the reasoning behind all that... thats where the rubber hits the road.

- there's a roughly 2:1 ratio of sag change to ring/spring adjustment change. So tightening the ring about 1/8" gives about a 1/4" sag change. Roughly.

- twinSig gave a good starting point for rebound damping of about 17 clicks out from fully "tight" or clockwise for a starting point. others have suggested 14. No set answer there, but 12-17 seems to represent a good ballpark to get someone on the road and not be totally out of whack.

- A lot, in fact most of the seemingly wise suspension folks that I followed online advise that the static sag number is not worth much, but i disagree only insofar as if you're like a lot of folks and mainly work alone in your shop, its a lot easier (possible) to work with static sag at first to assure you're in the ballpark, then use a helper later to do the more important rider sag.

- for RT-P owners only: remove the damn police sub-frame up front! Maybe there's a good argument to keep it, but I haven't seen a good reason yet, other than for those that use it as crash protection (which I can't argue with, but not my preference). Save the time wasted thinking about it and just remove it, or at least cut away the piece that spans in front of the front strut (then deburr, and clean up however you like). You can modify the frame to accommodate the shark fins, or buy the shark fin brackets used or from BMW, etc. This will remove weight, make access to the strut change from almost impossible to very easy, make accessing the alternator and belt as easy as it should be, and so on.

- the "dirt bike trick" that many speak of makes the front sag measurements way easier than dangling a tape measure from a fixed point to a moving point. I don't know why i didn't remember that until late in the game, but thanks to those who reminded me. Zip tie on slider body/shaft ("forks") with slider all the way extended, then gently let down, then jack back up to measure the movement to check either static or rider sag.

- Some mention the difficulty of removing the bottom bolt on the rear strut. Loosening the rear exhaust bracket, removing rear wheel, and using a shallow depth alan socket proved to work fine for me. Since you may have to remove and re-install the rear strut multiple times (since you can't reach the adjustment rings when installed), its worth while assuring you have easy access, whatever that means for you. My motorcycle floor jack (harbor freight cheapy) worked great for supporting the rear swingarm.

 

Nothing special here, just closing the loop for anyone interested.