Preload confusion

Scarfall

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Hi guys,

I have been riding a '16 F800GS for a few months and it's the first bike I've owned with a preload adjuster.

I wanted to make my bike just right for me. So I watched a few videos and tried to put my hand.

I am 6'2 weighing 187lbs. The adjuster was originally turned completely to the right. This somehow just feels right, the right seat height when stopped and low speed moving, kinda like my legs don't have to move much.,My first measurement was an unloaded rear, on its centerstand at 236mm, and loaded with my weight and gear at 203mm, giving me a sag of 33mm. The interwebz says my rear suspension travel is 215mm. So 30% of that should be around 64.5mm. It needs to be stiffer, right?

Dialling the adjuster counter-clockwise made the bike feel smoother on acceleration. Rattles less on washerboard roads. Cornering feels more planted to then road, but for some reason I don't feel cornering with less preload?

So this is all making me wondering. Anyone got some tips on how to properly set the preload on this bike? What are your settings? Anyone with a similar body measurements?
 
I've never used suspension travel length in the sag calculation; only static sag and rider sag.
I suggest the susp travel length topic is the root of the confusion. Also focusing on the seat height. Ignore these.

Static sag: a) Measure with bike unloaded, wheel off the ground. b) Bike unloaded, off stand, wheels on the ground.

Assuming it's a standard spring it should cope with your "typical" weight.
Pre-load set to max cannot be right. Trust your riding sensation: less pre-load gives better handling.

I'll let someone else pitch in with recommended sag measurements.
 
Last edited:
It is a black art

My understanding which is limited i accept is that a spring has a certain amount of boing in it

Appluing preload takes some of the boing out so according to the load applied with rider, passenger etc the boing factor can be adjusted accordingly

You need some boing in the spring so max preload should not feel right for a bloke of your weight

The spring does much of the actual suspension work with the shocker assisting it with damping and compression etc so having a spring which is correct for your weight is ideal then you can play with damping compression and rebound
 
I would have thought very simply, with the bike upright on its wheels unloaded, measure from the bottom of the number plate to the floor.

Repeat sat on the bike, feet on the pegs. You'll need someone else to measure and you'll have to to hold yourself upright on the bike with fingers against a wall or similar

The difference should be about 10-15mm

similar to this this https://www.maxtonsuspension.co.uk/downloads/manuals/gp10/6.STATIC SAG.pdf

Too little or no sag when you get on and the suspension isn't working until you hit bigger bumps. Too much sag and the shock will bottom out too easily
 
If you've got 33mm and want 64mm you need less pre-load. It will make it ride lower, less ground clearance so more chance of touching something down when cornering, it may also make it steer a bit slower.
If it feels right as it is it's what suits you, it's worth trying with the pre load wound off but may not be better.
If it's right with full pre load it may be worth trying a slightly higher rated spring with less pre load, that'll give you some adjustment for passenger/luggage carrying.
 
I've never used suspension travel length in the sag calculation; only static sag and rider sag.
I suggest the susp travel length topic is the root of the confusion. Also focusing on the seat height. Ignore these.

Static sag: a) Measure with bike unloaded, wheel off the ground. b) Bike unloaded, off stand, wheels on the ground.

Assuming it's a standard spring it should cope with your "typical" weight.
Pre-load set to max cannot be right. Trust your riding sensation: less pre-load gives better handling.

I'll let someone else pitch in with recommended sag measurements.

Right about the sag but in general less preload does the opposite of giving better handling. Obviously too much preload will make it feel odd but it’s very common to tweak a bit more preload on the rear when a bike won’t turn without a lot of persuasion - it sharpens the nailing on the front. The VFr1200 and first edition Triumph Tiger 1200 were lardy bikes that turned in slowly and benefitted from a bit more rear preload.
The BMW stock factory one-up suspension settings are (allegedly) meant to be for an 85Kg rider with no luggage, so assuming the shock isn’t sagging because the spring is knackered it should be easy enough to adjust preload up or down to compensate.
 
Google how to set static sag. It's easy to do.

Once set this is your 'base' setting and is how the manufacturer will have deemed is correct for the bike.

In therory, as you add weight (pillion/luggage) you increase the preload preportionaly to maintain that sag. In other words the bike maintains the same ride height and doesn't drag it's arse like a dog with worms when loaded up.

Now.......there may be other reasons why you'd play with the preload. You've already noticed that decreasing the preload makes the steering less precise, you didn't imagine that, it does. So if your prefernece is for a quick steering bike then by all means keep increasing the preload beyond it's 'correct' sag setting until you get it how you like it. This is because raising/lowering the preload changes the trail of the bike (another way of achieving the same is to raise/lower the forks in the yokes).

The preload setting will not have any effect on ride quality or damping unless you have it wound up sooooooo high that the spring is effectively locked solid or has little travel left.

FWIW on pretty much any bike I've owned with OEM suspension I've ended up running higher preload just 'cos my preference is for a quick steering bike.

Andres
 
Andres, if you want a quicker steering bike then simply lift the forks around 5-10mm (lowering the front) but loading your rear spring with potential energy which you then only compensate for with too much rebound will affect traction and much more.
BUT if it feels right for you then great although many prefer to run with little preload. If anyone's running max or min preload then they have the wrong spring :)
 
Andres, if you want a quicker steering bike then simply lift the forks around 5-10mm (lowering the front) but loading your rear spring with potential energy which you then only compensate for with too much rebound will affect traction and much more.
BUT if it feels right for you then great although many prefer to run with little preload. If anyone's running max or min preload then they have the wrong spring :)

That's a good point and not something I'd ever considered; agreed about dropping the forks, something I've done as a matter of course on every SM I've built :thumb2

Andres
 
It is indeed a dark art.

I eventually set my 1190 up to just how I wanted it, but it looks weeks and weeks. I would regularly drive the same length of good road (lots of undulations and corners) with the tools i needed to play with rebound and compression.

A small eureeka moment for me, was that for a spring to work, it has to be compressed somewhat in the first place. When I started on this journey, I was trying to soften off the rear and couldn't get my head around the fact that the more I 'unloaded' my rear spring, the harsher the ride was becoming. It turned out that I was unwinding a spring that was pretty much fully unwound in the first place, and I got to the stage where suspension was rock hard because the spring wasn't actually doing anything! :blast I needed to compress it, to make it 'work' to get a softer feel .....


Agree with Tim about different springs - I was on the cusp of my working parameters I guess, and could have ideally done with a firmer spring.

To the OP ..... what I would be careful about doing is using your rear spring to make you fit the bike. That is arse about face! If you want more leg room, then higher seats, lower footage hangers etc, bar risers etc. But altering suspension to make you fit the bike will just fuck up the handling ..... :thumb2
 
It is indeed a dark art.

I eventually set my 1190 up to just how I wanted it, but it looks weeks and weeks. I would regularly drive the same length of good road (lots of undulations and corners) with the tools i needed to play with rebound and compression.

A small eureeka moment for me, was that for a spring to work, it has to be compressed somewhat in the first place. When I started on this journey, I was trying to soften off the rear and couldn't get my head around the fact that the more I 'unloaded' my rear spring, the harsher the ride was becoming. It turned out that I was unwinding a spring that was pretty much fully unwound in the first place, and I got to the stage where suspension was rock hard because the spring wasn't actually doing anything! :blast I needed to compress it, to make it 'work' to get a softer feel .....


Agree with Tim about different springs - I was on the cusp of my working parameters I guess, and could have ideally done with a firmer spring.

To the OP ..... what I would be careful about doing is using your rear spring to make you fit the bike. That is arse about face! If you want more leg room, then higher seats, lower footage hangers etc, bar risers etc. But altering suspension to make you fit the bike will just fuck up the handling ..... :thumb2

The reason it felt harsher when backed the pre load right off was because the suspension was only beginning to work when it was already further down it's stroke. Progressive damping does just that :)
 
The reason it felt harsher when backed the pre load right off was because the suspension was only beginning to work when it was already further down it's stroke. Progressive damping does just that :)

yes yes yes .... I know that (now!!) :D
 


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