Author Topic: Advice on setting up suspension  (Read 1730 times)

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Offline nzmike

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Advice on setting up suspension
on: December 23, 2020, 11:14:33 PM
Hi all,

Took delivery of my F900R (in Hockenheim Silver & Red) about 4 weeks ago and so far I've only been able to go on a few rides around 120-150km but am finding on the twisties when the road surface is a little bumpy or broken up the rear suspension feels a bit harsh and skittery so I have a couple of Q's:

1) Could this be caused because the bike is new and the mileage (so far) is so low? i.e: can I expect the suspension to soften up a bit as I ride it more?
2) If not then should I be setting the pre-load or the damping or both?  I'm thinking it's the dampening but not 100% sure. I'm slightly on the heavy side at 95kg/210lbs for my height (I'm only 168cm/5' 6") but not sure how to work out what means for adjusting the suspension.

I am also finding the seat just a bit too high so would reducing the preload a bit bring the height down?  My layman's understanding is that pre-load is the amount of "sag" it allows before you sit on the bike so am hoping I can reduce the height just a little (I'm only looking for ~ 1cm or 1/2 inch) without affecting the ride quality too much.

I had to google the difference between preload and dampening and TBH I'm still not sure I really understand the difference or how to adjust it correctly so any thoughts would be much appreciated - and please excuse my ignorance, I clearly need to do a lot more reading on this stuff!
Last Edit: December 23, 2020, 11:17:27 PM by nzmike

Online rcb78

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Re: Advice on setting up suspension
Reply #1 on: December 24, 2020, 02:26:28 AM
So I'm going to cover some of the basics since there's not much you can adjust with the stock setup.  First, look up how to check sag on the rear, there's more than enough info already written all over the internet and while it's simple, it takes a bit to explain.  The front forks are not adjustable, so you'll have to take them as they are and realize that the changes you make to the rear need to balance with the front.
While sag does affect how tall the bike is, DO NOT USE IT FOR THAT.  Sag is used to partly to tweak steering geometry by how the bike is tilting front to rear.  Lowering the front (raising the rear) makes the bike want to turn more easily and vice versa for raising the front or lowering the rear.  Getting on the gas will lift the front and getting on the brakes (front in particular) will drop the front.  So you sag needs to work within these constraints to ensure the steering input is not only good for your riding style, but safe too.  Screwed up sag can make you do weird things going into and coming out of turns.
Another function of sag is having enough travel stored in the suspension (what you're 'sagged') to let the wheels drop into potholes and road imperfections without the suspension topping out.  This gives some degree of ride quality.  Too little sag and the ride can be rough, too much sag and you'll bottom out that much easier.
Rule of thumb for a street bike is somewhere around 25mm-30mm of sag in the rear with around 30mm-35mm in the front.  Slightly more (or equal) sag in front vs rear is what you're looking for.  So  measure the front first (google it) and then adjust the rear to fall into that range, then test ride and adjust as needed.  But if you find you're making adjustments way outside those ranges then you've gone too far.
Damping is a little more simple, again since you only have rebound damping in the rear.  Turn the adjuster in (CW) to add, out (CCW) to subtract damping.  Adding rebound damping makes the wheel slower to recover from a compression stroke.  Hit too many bumps in a row with too much rebound and the wheel will never recover and will sit on a more compressed spring, this can make for a harsh ride.  Too little rebound makes the wheel bounce back too quickly and the bike will feel like it's a pogo stick over every bump.  Since you can't adjust the front, you're trying to match the rear to  what the front is preset to.  Ideally, you want as little rebound as needed to keep the bike feeling planted.  Find out where you are right now by sitting on the bike (stand over), drop your weight onto the seat and the quickly stand again.  Does the bike just return up and stay there, does it come up and go back down again?  Adjust the rebound out until it bounces, then add it back in until it 'just' settles on the top of the rebound.
Google as much as you can, watch some Dave Moss videos on YouTube and play around with settings.  Once sag is set you leave it alone.  Rebound can be adjusted as needed for the desired handling and road conditions.

Offline nzmike

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Re: Advice on setting up suspension
Reply #2 on: December 24, 2020, 02:50:57 AM
Wow, great reply - thanks so much for the detailed info.... I clearly have a lot of reading and learning to do! 

I know it sounds crazy not to know anythng about it but all the bikes I've had in the last 7 years or so since I came back to riding just felt perfect from the get go (I guess they're so well engineered these days it's no surprise) and the bikes I had in the early 90's (when I last rode "big" bikes) definitely did not have anything so fancy as adjustable suspension!

I'll try out your tips and also watch some of those Dave Moss videos out over the next few days and do some testing - it'summer here so no issues going for a few rides to test out any changes.  A pal of mine here in Sydney suggested taking it to a suspension tuner - he had the same issue with a bike he bought and he said the guy tuned the issue out completely for around AU$100 which I think is pretty good value.

Online rcb78

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Re: Advice on setting up suspension
Reply #3 on: December 24, 2020, 04:00:20 PM
For a setup as simple as the F900, I'd expect to pay half what your friend did unless the person only has a flat rate.  Don't forget that we only have two adjustments, not the 6, 7 or even 8 like high end suspension setups can have.  The exception would be if he actually helped mess with the front end too, such as giving advice for re-springing and re-valving.

It may seem complicated, but it's pretty simple once you wrap your head around it.  I also just checked the owners manual for your bike (I have the xr) and it does provide starting point for preload and rebound.  The preload suggestion should be close, but still double check.  Then add or subtract rebound based on if you added or subtracted preload from the recommended setting.  The two are somewhat related since rebound is a function of the springs reactive force.

Oh, and on the Dave Moss videos, don't pay too much attention to how he reads tire wear, that will only be useful on a track.  Pay more attention to how he sets the damping, and don't fixate on just his videos, there's a lot of good info out there.

Offline Burnie10

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Re: Advice on setting up suspension
Reply #4 on: October 29, 2021, 09:39:03 PM
I know I'm replying to an old thread here, but has anyone actually measured their suspension settings.  I've got the TE version so nothing really to adjust manually.  There's effectively 2 buttons, one for preload & 1 for damping. I leave preload on rider only, anything else & I can't touch the ground because it's too high.  I change the rebound between Road & Dynamic based on town riding vs faster open road riding. I'm normally very anal when it comes to setup & I experiment with settings, especially rebound & compression where available, I was however very supprised to put the measurements I'd taken from my bike into my spreadsheet. It is either a massive coincidence the settings are like this or BMW have done a shed load of research to get it this close.