Set up for the long one.

**Bass** · 9th July 2010, 08:27

Eddie's picture at the start of the Gunbarrel Highway has brought an old problem back to mind.
I have often wondered whether we got the suspension set-up right when we did the Oz trip. Specifically, I have wondered, when setting the suspension, whether the luggage should be treated as part of the bike or part of the rider. In other words, should it be on the bike or not, when setting the static sag?
Normally it doesn't matter that much as we don't carry much luggage and we are not going to change the spring to accomodate a tail bag anyway. However, when setting up for a big one, there could be 50 kg of luggage aboard, which has real consequences. Let me illustrate with some simple numbers.
A common rule of thumb when setting the suspension is that the static sag should be about 10% of the total travel and the rider sag around 30%. The difference between these numbers (20%) is the compression forced by the rider weight. If this is the rider only (say 100 kg) then it wil require quite a different spring than if the same travel is rider + luggage (say 150 kg).

So which is it guys and why?
I can think of good reasons for doing it both ways.

**warewolf** · 9th July 2010, 09:10

Mounted to the bike = part of the bike, include in static sag.
Carried by rider = part of the rider, include in rider sag.

If it is carried by the rider (ie backpack) then like the rider's weight, it is supported by the "suspension" in the riders legs in addition to the mechanical suspension of the bike. In this scenario it is easier to move the bike around as you aren't moving the luggage too.

Further thought: whether the luggage is on the bike or rider will only affect the preload. In each case the overall load is the same, meaning the same spring.

**Bass** · 9th July 2010, 09:32

Originally Posted by warewolf

Mounted to the bike = part of the bike, include in static sag.
Carried by rider = part of the rider, include in rider sag..

This is what i figured as well but is NOT what Robert Taylor did for us. I need to go and talk to that man and see what I can learn.
If you don't include the luggage in the static, with a big load there's a good chance that the bitch won't sit on the side stand when you get off, DAMHIK!

Originally Posted by warewolf

Further thought: whether the luggage is on the bike or rider will only affect the preload. In each case the overall load is the same, meaning the same spring.

You would think so, eh?
Think about the set up procedure though. We set the static and then the rider sags.
Once the static is correct, the only way to adjust if the rider sag is wrong, is to change the spring.
In one of the cases I suggested, the luggage is included in the difference, in the other, it is not. It all comes down to what we include in that 20% compression between static and rider sag.

**Taz** · 9th July 2010, 12:03

Surely you can just keep adjusting it til it feels right. I'm sure even with Rob Taylors best guess at your riding style and conditions you may encounter you'd still need to make adjustments to his settings along the way? I would include the luggage in the static.

**Bass** · 9th July 2010, 12:33

Originally Posted by Anthrax

Surely you can just keep adjusting it til it feels right. .

Well maybe............

Originally Posted by Anthrax

I would include the luggage in the static.

This is the key and why I asked the question.
If the luggage is part of the static load, then the required spring rate depends only on the rider's weight, meaning preload adjustment is all that is necessary and yet Robert fitted us with stiffer springs.
If the luggage is part of the rider weight (and for a long trip, it could be as much as 50% of the total rider + luggage weight) then a spring change will almost certainly be necessary.
So Colin's, your's and my instincts are at odds with what Robert did and so far I can't figure out why.

This is all based on my assumption that we should have about 10% static sag and 30% rider + static sag under all conditions, but I'm no expert. That could be complete bullshit.
It also feels wrong to say (as I am doing) that regardless of how much luggage I put on, I don't need to slot in a stiffer spring because the luggage is part of the bike, not part of the rider. So obviously, there is something that I haven't got my head around yet.

**Taz** · 9th July 2010, 12:44

You might find it impossible to get the correct static sag within the original springs adjustment range when the bike is weighed down with luggage. Therefore to bring the sag into spec may require a change in spring rate. Remenber there is a finite amount of range when winding the spring down. Sure you may have some thread left on the body of the shock but that does'nt mean you can use it all.

**That looks like fun** · 9th July 2010, 12:50

KISS A simple philosophy that works. I have seen people mess around with suspension and steering, tyre pressures and all sorts of things when at the end of the day they have a riding style or load that is completely outside the parameters of what they have set up. Ask a simple question before you start changing things "is this bike designed for this" Chances are not many bikes are made to be loaded to the rafters with panniers so wide they need a pilot vehicle and then ridden up a vertical hill with overweight riders and pillions simultaneously shitting on the seat. I don't claim to be the worlds best rider (not even second best), I adjust the suspension so that the I feel like I have control of the bike, not the other way round. Saves on carrying around a set of scales, some cable ties and a calculator in every pocket

**Bass** · 9th July 2010, 13:11

Originally Posted by That looks like fun

simultaneously shitting on the seat.

Could get messy!!!!
Don't mistake my intent here - I am pretty satisfied with the way I have it set up.
However, I have an interest in the theory and am trying to fill some gaps in my knowledge.

**Bass** · 9th July 2010, 13:14

Originally Posted by Anthrax

You might find it impossible to get the correct static sag within the original springs adjustment range when the bike is weighed down with luggage. Therefore to bring the sag into spec may require a change in spring rate. Remenber there is a finite amount of range when winding the spring down. Sure you may have some thread left on the body of the shock but that does'nt mean you can use it all.

That's possible but unlikely.
Your luggage is unlikely to weigh more than a pillion passenger and the manufacturers usually give enough adjustment to allow correction for the weight of a pillion.

**dino3310** · 9th July 2010, 13:30

Originally Posted by Bass

Could get messy!!!!
am trying to fill some gaps in my knowledge.

i use beer for that

**warewolf** · 9th July 2010, 14:08

Originally Posted by Bass

You would think so, eh?
Think about the set up procedure though. We set the static and then the rider sags.
Once the static is correct, the only way to adjust if the rider sag is wrong, is to change the spring.
In one of the cases I suggested, the luggage is included in the difference, in the other, it is not. It all comes down to what we include in that 20% compression between static and rider sag.

What I am saying is that once you have the correct spring, moving the luggage from bike to rider or vice versa means only a preload change. Essentially the spring must support all the weight - bike, rider, luggage - at the correct rider sag, but the preload says "how far through the stroke are we positioning the dead-weight of the bike (ie everything below the rider's legs)?" which is static sag.

Edit: because the luggage should always be factored in, if you are setting up for a big trip with big luggage.

**Bass** · 9th July 2010, 17:34

Colin, I do understand where you are coming from. You and I really are going to have to organise a discussion over a beer at some stage. Some of the info you have posted in the past has been invaluable, especially the numerical descrition of linkage performance.
In this case, your point of view (and I cannot say that you are wrong) begs the question that if the total load does not change (and it doesn't in shifting the load from the bike to the rider), then why is any adjustment at all necessary? After all, the spring is carrying the same load regardless of where it is attached.

**NordieBoy** · 9th July 2010, 19:05

Originally Posted by Bass

Colin, I do understand where you are coming from. You and I really are going to have to organise a discussion over a beer at some stage.

I'll referee.

Typing out loud here...

Hmmm...

Static sag...
So the suspension can extend into dips/holes without topping out.

Rider sag...
So there's enough suspension travel left to prevent bottoming out all the time.

Sooo....

The spring rate needs to be set for the race sag (rider + luggage). At this point the static sag is just academic.
Damping also needs to be set for the total weight.

So it doesn't really matter if the luggage is attached to the bike or the rider.
The difference is that the luggage attached to the rider is higher (bad) but moves with the rider (good) but fcuks the riders back (bad)..
When attached to the bike it's static over the back end (bad) but low (good) but can fcuk the bikes back (bad).

Therefore: Spring rate and damping for total weight carried and reinforced backs.

I need a milo.