Suspension sag on 2016 bike - these look weird

[SteveThackery 3,090]

 

This isn't aimed at you Steve as there are plenty of other posters on here who bash anyone round the head who suggest that altering pre-load affects softness of ride.  But I found it interesting tonight that I have found two specialist suspension websites at least who fall into the same trap (if that's what it is).

Here's a quote from Hagon's site:

"Hagon Twin Shocks with 3 position preload adjusters are supplied set at their softest setting"

and

Turn the HYDRAULIC PUMP HANDLE clockwise to increase the spring pre-load for heavier riders or luggage.

Turn clockwise to harden and anti-clockwise to soften the ride."

 

and here are the guys from Progressive Suspension in a video (at about 45 seconds in) saying that they like to run softer or firmer preload 

https://www.youtube.com/watch?v=2DO-qJj95tE

Mike

 

 

Mike, you are welcome to aim at me as often as you like!!  

 

I've just started the third year of my BEng(Hons) in Motorcycle Engineering, which gives me access to countless text books on this sort of thing.  One of the most accessible is "Sportbike Performance Handbook", 2nd edition, by Kevin Cameron:

 

"When thinking about preload, always remember than adjusting preload up or down simply changes the height at which the bike rides.  It does not make suspension stiffer of softer.  [....]  A stiffer spring is made with either thicker wire [...] or fewer coils."

Edited October 11, 2016 by SteveThackery

[Mike5100 2,061]

Yeah - I know, I know Steve    But it doesn't help when some specialist suspension manufacturers are saying the opposite.  Either they are doing it from ignorance (unlikely) or because they know the customer is using the wrong term but they don't want to confuse them ..... or the books are wrong and changing the ride height DOES make the ride softer or harder in some way.

Mike

PS How does your book define 'static sag'?

[SteveThackery 3,090]

I think a lot of this is about lazy terminology, especially when it's spoken by professionals.  However, it's also worth pointing out that just because someone works at a suspension specialist doesn't automatically make them an expert themselves.  Many of these small, specialist companies rely upon many years of accumulated practical experience rather than an in-depth understanding of the physics, mechanics and engineering.  I know of a very small outfit that specialises in restoring magnetos, and it does an excellent job.  However, the guy in charge has only the most superficial understanding of electromagnetics.

 

When it comes to motorcycle sport, it all comes down to the rider in the end.  Very few riders have degrees in physics or engineering, so their feedback needs a lot of interpretation by the team mechanics.  If the rider notices that the bike sags less when they first get on it, they set off thinking "the suspension is stiffer" (rather than "they've raised the bottom of the spring") and that thought colours their subjective impressions of the bike and the feedback they give at the end of the race.

 

That's why science and engineering is not built upon subjective data, but upon some basic physical laws and a lot of objective data.  And that is how we know what effect raising the bottom of the spring has; subjective data is just so unreliable and inconsistent.

[SteveThackery 3,090]

Cameron uses the term "sag" rather than "static sag":

 

"This is a very important concept related to ride height.  Sag is the distance that a bike settles when normally loaded with fuel and rider, measured from the fully topped height.  [...]  When you set sag, you are determining how much suspension travel will be available for bump absorption.  Sag is typically set at one-fourth to one-third of total travel."

 

My lecturer differentiated between "unladen sag" and "loaded sag", referring to without and with the rider, respectively.

[SteveThackery 3,090]

Incidentally, if you ask why bikes have adjustable preload when all it does is alter the ride height, not the stiffness, it's because the bike must be able to cater for a wide range of loads, from a skinny Japanese teenager to two obese Americans.  The adjustable preload allows the static sag to be set correctly for this wide range of users.  In particular it matters if you sometimes carry a passenger and other times not: you need to adjust the preload to maintain the optimum static sag.  That's why so many tourer bikes make it easy to change it using dashboard controls.

[Mike5100 2,061]

Incidentally, if you ask why bikes have adjustable preload when all it does is alter the ride height, not the stiffness, it's because the bike must be able to cater for a wide range of loads, from a skinny Japanese teenager to two obese Americans.  The adjustable preload allows the static sag to be set correctly for this wide range of users.  In particular it matters if you sometimes carry a passenger and other times not: you need to adjust the preload to maintain the optimum static sag.  That's why so many tourer bikes make it easy to change it using dashboard controls.

Sounds like you are defining static sag then as when the bike is loaded up with riders and luggage - which is how Racetech define it, but everyone else defines it as with just the bike's weight on its own.

I prefer your lecturer's definition - no room for misinterpretation

Mike

[SteveThackery 3,090]

Sounds like you are defining static sag then as when the bike is loaded up with riders and luggage - which is how Racetech define it, but everyone else defines it as with just the bike's weight on its own.

I prefer your lecturer's definition - no room for misinterpretation

Mike

 

No, that's how Cameron defines it.

 

As for myself, I'm intelligent enough to understand that the sag can be measured in either of the two conditions,  and all you need to do is specify which.

 

However, I believe Cameron's to be the most defensible definition.  Nobody cares how much a bike's suspension sags just under its own weight.  Why would you?  It's not like it can drive itself anywhere.  The only sag that matters is when there is a rider on board.

 

The "static" bit just refers to the starting point for the suspension when the bike and suspension are not moving.  It is relevant because the bike always averages to that point when it is moving, so we know how much travel we have - on average - for absorbing bumps.  Hence we are interested in it.

 

Incidentally, there is no way "everyone else" defines static sag as being without rider.  In fact a quick google search shows the terminology to be in disarray.

 

These use the Cameron definition (with rider):

 

"Static sag is a measure of how much your bike settles on its suspension with you on board."  http://www.sportrider.com/ask-geek-set-your-static-sag

 

"Static sag is not an Indian dish, but the free play in your suspension between fully topped out (maximum extension) and normal resting position at a standstill."  (Accompanied by photos showing the rider on the bike).  http://www.visordown.com/features/how-to-do-just-about-anything/how-to-set-up-your-bikes-suspension

 

This site uses the term to mean the unloaded sag:

 

"RIDER SAG is the difference steps 1 and 3. This is the amount the bike drops when your heavy arse sits on the bike.

STATIC SAG is the difference between step 1 and step 2. it is how much the bikes weight acts on the rear suspension or how much you can lift the bike rear without the rider on it before it tops out."  http://www.gostar-racing.com/club/motorcycle_suspension_set-up.htm

 

There are many more examples of each.  Also, the above has introduced the term "rider sag", and I've seen another talking about "racing sag".

 

Clearly the definition of "static sag" varies, so it's silly to get hung up about it.  All we have to do is make it clear whether we are talking about with, or without, a rider.  And I would repeat my initial point: why would we care what the unloaded sag is?  We never use the bike without a load.

Edited October 11, 2016 by SteveThackery

[embee 7,288]

I agree with Steve, let's use clear terms on this forum, "bike only" and "bike plus rider" or similar clear terms. One reason you might be interested in both values is that it gives an indication of whether the spring stiffness is appropriate for the rider weight, you could for example have the correct sag with rider aboard but with a soft spring and lots of preload and thus very little sag with the bike alone so it's likely to be topping out over crests. Conversely you could have very little difference indicating the springs are too stiff (high rate).

 

... and no, no amount of fiddling with preload will change the stiffness of the spring, that's just the physical design of it. Given springs on a given bike will always sit at the length which provides the required force, adjusting preload simply alters the height of the bike at which the springs reach this condition.

 

I also agree about the level of understanding sometimes, that's where I like o use terms like mechanic, technician, or engineer. Nothing wrong with any of them, just need to have the appropriate level of understanding of what you're trying to do.

[SteveThackery 3,090]

.....you could for example have the correct sag with rider aboard but with a soft spring and lots of preload and thus very little sag with the bike alone so it's likely to be topping out over crests.

 

That's a very good point which I hadn't thought about.  One of the disadvantages of softer springs would be more chance of topping out, which sounds counter-intuitive but makes perfect sense.

[Mike5100 2,061]

I'm quite pleased with myself because I had more or less worked out that bit above but then didn't post it because I thought it was probably wrong.

Another thing to think about Murray.  If the springs were dual rate then even at 71mm of rider sag there would still have been quite a bit of travel left in the soft part, meaning quite a smooth ride on smooth roads.  But my experience with the Showa DBV forks right from the off was a jittery jiggliness so that on smooth roads (for instance a motorway), when I approached a road sign the headlight illumination was thrashing up and down like a mad thing.  Only improved a bit if at all with 5wt oil.

However - if they are behaving as a progressive fork then at anything more than the 71mm of travel they may already be into a considerably higher rate area of the whole spring?

It would be interesting if David who is photographing the 2014 forks in another thread, could take the relevant dimensions, and if they differ from the 2016 OEM spring it could indeed explain why I liked the older model's supension.  Edit - I have just looked at his post and from the pictue of the spring it looks to me like its has almost 18 turns of looser windings and 14 of tighter ones.  This is different from the new spring

Mike

Edited October 11, 2016 by Mike5100

[fred_jb 10,265]

I'm coming a bit late to this discussion, but finding it very interesting, as I have had a few trials and tribulations myself with suspension on both my NC and subsequently my Versys. I also found a lot of inconsistency in terminology out there, so you have to be very selective in what advice you follow. I tend to agree with Steve's comments about measuring sag with rider on board as being most relevant to our type of riding. Maybe in racing, with a fixed and known rider weight, changes can be made by working with bike only sag measurements, knowing that the effect when adding the rider will be predictable, but this is not sensible for more general purpose riding, for example when trying to work out if your suspension has sufficient adjustment to cater for both solo and two-up riding, and what the best settings for each would be.

 

I think a lot of the apparent inconsistencies people are seeing are due to the simpler suspensions not having the ability to have different damping mechanisms for fast and slow compression conditions, so the damping, particularly when non-adjustable, is a fixed compromise which cannot be optimal for all conditions.  Damping which is compliant enough to absorb the fast jiggles of broken road surfaces without transmitting them to the rider might be to too compliant and wallowy for larger slower undulations, and vice versa.  In this respect, it is interesting that the new Showa "Dual Bending" NC front suspension, which I would expect to have at least some ability to respond differently to fast and slow compressions, is not meeting expectations.  I was interested to read reviews of the new Harley 2017 range which say that they have also been fitted with the Showa forks and that the suspension is improved as a result.

 

One area which remains a total mystery to me is what effect the common use of rising rate linkages has on rear suspension adjustment and the perception of "hard" and "soft" when changing preload.   I agree that preload does not change spring rate, it should just be used to make sure the spring is working in the optimum range of movement. However, if preload is wrongly set, either deliberately or through lack of adequate adjustment, then I would think that it might cause the linkage to be working in the wrong part of its range of movement, which might cause the apparent spring rate, as modified by the rising rate linkage, to vary from optimum and give a perception of harder or softer springing.

 

I found measuring sag loaded with rider, pillion and luggage was essential to work out why my Versys was handling badly when fully loaded. It turned out that despite being marketed as a bike good for two-up touring, the rear suspension had too soft a spring.  This meant that when loaded the rear sag was well over 50% of available movement.  This was also changing the geometry and making the front feel excessively light, particularly at slow speed. This was greatly improved by fitting a Nitron shock which Nitron had customised for my requirements with a higher rate spring and a remote preload adjuster. I still had some issues with unstable steering at low speeds when heavily loaded, but in the end I suspected this might be due to some frame flex during the larger steering movements required during low speed maneuvering.

Edited October 11, 2016 by fred_jb

[SteveThackery 3,090]

 

One area which remains a total mystery to me is what effect the common use of rising rate linkages has on rear suspension adjustment and the perception of "hard" and "soft" when changing preload.   I agree that preload does not change spring rate, it should just be used to make sure the spring is working in the optimum range of movement. However, if preload is wrongly set, either deliberately or through lack of adequate adjustment, then I would think that it might cause the linkage to be working in the wrong part of its range of movement, which might cause the apparent spring rate, as modified by the rising rate linkage, to vary from optimum and give a perception of harder or softer springing.

 

 

Funnily enough I decided to avoid bringing the rising-rate linkage into the equation because it complicates things!  I find it's always best to agree the basic principles first, and then add on the complications later.

 

But you are quite right - on this type of suspension, altering the ride height by altering the preload adjuster moves the rising-rate linkage to a different operating point, which has the potential to alter the effective spring rate.

 

We did some measurements last year in the workshop, and actually the rise in the rates we measured was surprisingly small, which raised the question of why the manufacturer bothered.  

 

However, the key point is that they are set up such that the effective spring rate rises as the suspension is compressed, so if you adjust the spring preload to raise the ride height (i.e. what people describe as "stiffer"), you are actually moving the linkage to a softer (i.e. lower effective spring rate) part of its operating range - the opposite of what the rider expects.  Frankly I'd be surprised if a rider could actually tell the difference in effective rate, to be honest.

Edited October 11, 2016 by SteveThackery

[Mike5100 2,061]

 

However, the key point is that they are set up such that the effective spring rate rises as the suspension is compressed, so if you adjust the spring preload to raise the ride height (i.e. what people describe as "stiffer"), you are actually moving the linkage to a softer (i.e. lower effective spring rate) part of its operating range - the opposite of what the rider expects.  Frankly I'd be surprised if a rider could actually tell the difference in effective rate, to be honest.

Bingo.  Well here's one rider who can definitely feel it.  I have explained in several threads that on my bike with the stock rear shock, I was gobsmacked to find that when I raised the preload to its maximum level (7) I drastically improved the ride.  I said it felt about 25% smoother softer ride and that was with just me on the bike.  In fact it was so counterintuitive to me that I suggested there might be something wrong with my shock and it was part of the reason I went for an expensive aftermarket shock.

Mike

Edited October 11, 2016 by Mike5100

[embee 7,288]

I measured the Integra rear linkage and it is remarkably linear, essentially no variation through the available travel. It'd be interesting if someone could measure an X with the longer travel, it appears it will start at a bigger angle away from a straight line (gearbox/swingarm pivot/axle) with the longer shock (Integra is nominally 300mm, I measured 301mm, X is 310mm) so may have some departure from linear. I was measuring using a steel tape, so ignore the odd +/-1mm.

Edited October 11, 2016 by embee

[SteveThackery 3,090]

That linear result you have found is no surprise to me.  I think we could easily get distracted by the idea of rising-rate linkages, when it appears the NC has a pretty linear one.

 

And that brings us back to square one: raising the bottom of the spring simply raises the top of the spring - nothing more, nothing less.  So it increases the ride height and reduces the sag.  What it cannot do is alter the rate of the spring (i.e. make it harder or softer).

[Mike5100 2,061]

That linear result you have found is no surprise to me.  I think we could easily get distracted by the idea of rising-rate linkages, when it appears the NC has a pretty linear one.

 

And that brings us back to square one: raising the bottom of the spring simply raises the top of the spring - nothing more, nothing less.  So it increases the ride height and reduces the sag.  What it cannot do is alter the rate of the spring (i.e. make it harder or softer).

The coincidence of your explanation and the much softer ride I got by 'hardening' the preload is just too impressive Steve.  It would be easily tested by other people who are about my weight winding their preload to level 7 and reporting back.

Mike

[SteveThackery 3,090]

...........and it was part of the reason I went for an expensive aftermarket shock.

Mike

 

Mike, how is your work to replace the suspension going?  Is it all done now, and with satisfactory results?

[SteveThackery 3,090]

The coincidence of your explanation and the much softer ride I got by 'hardening' the preload is just too impressive Steve.  It would be easily tested by other people who are about my weight winding their preload to level 7 and reporting back.

Mike

 

The problem is, it's subjective.  I know from personal experience you just cannot rely on subjective data.  Nor should we discount it completely, of course.  But we should always aim to support it with objective data.

 

We need to set up some kind of jig that will progressively compress the suspension when it's at each of the seven preload settings so we can know for sure the effective spring rate at each point.  It's unlikely any of us has the time or equipment to do such a test, unfortunately.

 

But to summarise,

 

1/ I think the argument is won that altering the preload cannot affect the stiffness of the ride, EXCEPT when a progressive linkage is used.  

 

2/ In that circumstance altering the preload will move the linkage to a different operating point and thus a different effective spring rate.  

 

3/ HOWEVER, raising the preload would normally move the linkage to a softer operating point, which is exactly the opposite of what most riders expect and report (but is in line with what Mike reports).

 

4/ Notwithstanding Mike's super-sensitive backside  , I'm sceptical that most riders would notice the difference due to the linkage, having plotted one in the university workshop and found it to be hardly progressive at all.  (Sorry, can't remember which bike it was now.)

Edited October 12, 2016 by SteveThackery

[Mike5100 2,061]

Well let's get some 2016 model 750x owners to try it.  We need a few because there's me who can definitely feel a softening effect but I'm counteracted by another rider who finds it softest at the zero pre-load setting.

By the way - I have a suspicion that canting the bike forwards by raising the preload may have a noticeable effect, but I don't know whether it would 'soften' things.

Mike

[Mike5100 2,061]

If I wanted to try increasing the preload on my new Wilbers, am I right in thinking that all I need to do is keep checking the unladen sag, so if it goes up by say 10mm then it's likely that the riderless sag and the rider sag will decrease by 10mm (discounting any of the prolink geometry effects).

Thanks

Mike

PS - the reason for asking is that it's awkward to change the preload on the Wilbers and if I can do it while it's on the centre stand it will be much quicker

PPS the other reason is that rear rider sag is 55mm and the front is 35mm and whilst I would have liked to decrease the preload on the front, I can't, so I thought I would try equalising them by increasing the back

Edited October 12, 2016 by Mike5100

[fred_jb 10,265]

If I wanted to try increasing the preload on my new Wilbers, am I right in thinking that all I need to do is keep checking the unladen sag, so if it goes up by say 10mm then it's likely that the riderless sag and the rider sag will decrease by 10mm (discounting any of the prolink geometry effects).

Thanks

Mike

PS - the reason for asking is that it's awkward to change the preload on the Wilbers and if I can do it while it's on the centre stand it will be much quicker

PPS the other reason is that rear rider sag is 55mm and the front is 35mm and whilst I would have liked to decrease the preload on the front, I can't, so I thought I would try equalising them by increasing the back

I don't think you can make that assumption - both the sag due to the bike's own weight and that due to bike + rider will depend on the exact weight being applied.  While the bike only sag may be predictable, and possibly proportional (though not necessarily equal) to any increase in the unladen suspension length (not strictly sag) the bike plus rider sag will depend on the weight of the rider (and pillion if two-up) so in my view is not going to be predictable from the unladen suspension length.   

 

Edit:  In any case with the bike on the stand I'm not sure you will see any increase in length as won't the suspension will be mechanically fully extended regardless of preload setting?

 

If you really want to know what is going on, then there is no substitute for getting an assistant to help you with the measuring while you are on the bike, complete with bike gear and normal amount of luggage.  You can then keep making adjustments and re-measuring until you get the sag into the right area, generally 30-35% of total available travel I believe, and of course road test to check the effect.

Edited October 12, 2016 by fred_jb

[fred_jb 10,265]

When I had the Wilbers 641 on my NC I found the preload didn't make much difference to the feel of the bike, but the damping settings did.  I believe the standard settings for both the fast and slow compression damping as standard is 12 clicks out from fully in (max damping).  From memory I think mine felt better with the slow compression damping on 14 or 15 clicks and the fast compression on about 17 (bearing in mind that Wilbers state there should be no more than 4 clicks difference between the two.  This was with preload set for just rider - at the time my wife wasn't riding pillion, so I didn't have the complications of having to keep changing the preload when carrying a passenger, so like you I didn't pay the extra for the remote preload adjuster.

[Mike5100 2,061]

Thanks Fred.  My problem is I have no-one to help set the sag - or rather only occasionally when I can persuade my daughter to come to our house to help.  and because of other reasons I can't do many test rides at the moment so I am trying to get it right first time in theory, then hopefully when I can get out on the bike it will feel good.

I have built a spreadsheet to record Wilbers adjustments and subjective feel.  It's not clear whether Wilbers set them from fully damped or fully undamped but I have worked from the latter.  I'm currently on 10,10 and 10 from fully off (rebound, highc, lowc) and it's not very good.  It came 12,14,14, and the 'best' I have had has been 10,14,14.  The suspension specialist changed it for me when I complained that the new suspension was no better than the OEM to 12,1,3 but it felt just the same as when I reverted to Wilbers standard setting.  That's why I think I need to get the front back balance sorted otherwise these damping adjustments may not be having much effect.

Mike

[Mike5100 2,061]

Just had a conversation with Wilbers UK agent.  He won't do anything by email so I have now been left even more confused after the phone call.  First the clear bit, he says that all clicks quoted are from the fully closed maximum damped condition.

However when I tried to get to the bottom of which way to turn the adjusters it appears that Wilbers instructions are wrong.  He said all damping is turned towards maximum by turning adjusters clockwise (every manufacturer).

Now that works for the rebound damping if you assume you are lying on the wet tarmac looking up at the  knurled adjuster (but you'd be more likely to be above it).  Anyway this is correct because it's easy to tell which way gives the softest setting and which way locks it solid.

But the little screws on the remote compression adjuster couldn't be viewed any other way than the obvious way and they provide a diagram showing 'open' clockwise and they say turning it clockwise increases the damping.

The only conclusion I can come to is that Wilbers use of the term 'open' is the opposite of their distributors and Wilbers are saying that open the valves increases the damping.

This might seem finnicky but it's obviously fundamental which way round the adjustment is.  I can work it out for the rebound but is there a similar way of deciding which way it works for high and low speed compression?

Mike

[SteveThackery 3,090]

But the little screws on the remote compression adjuster couldn't be viewed any other way than the obvious way and they provide a diagram showing 'open' clockwise and they say turning it clockwise increases the damping.

The only conclusion I can come to is that Wilbers use of the term 'open' is the opposite of their distributors and Wilbers are saying that open the valves increases the damping.

 

 

Mike, I've studied the Wilbers website and I agree with you - the markings for those two screws seem to be wrong.  Normally you would think "open" meant reducing the damping.

 

Until this is clarified, I'd be tempted to go with the generally accepted system of clockwise = more damping.