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Old 20-06-2019, 09:33 AM   #31
Uncle Bob
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Originally Posted by Luddite View Post
"• The static loaded position of the suspension is closer to the rebound stops, and so there is less suspension movement available before topping-out. So that occurs more often.
• The preload force means that when the suspension does top-out, it does so in a harder fashion."
Yeah but that's the STATIC i.e. without rider position! It's the suspension's position WITH a rider that's way more important! Unless the bike is going around on its own it's a bit irrelevant.

As for the second point, it's kind of true, but that's what rebound damping is supposed to control.

Reading this thread it seems that emphasis is perhaps being put on certain elements of suspension setup and not considering the combined effects of the actual equipment and how it's setup as a whole.
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Old 20-06-2019, 10:26 AM   #32
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Yeah but that's the STATIC i.e. without rider position! It's the suspension's position WITH a rider that's way more important! Unless the bike is going around on its own it's a bit irrelevant.
.
Sorry, but I disagree completely, if you have no static sag you are compromising the bikes ability to use it’s suspension safely, believe me, you do not want your bikes suspension topping out when the suspension goes light when you are at speed etc.
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Old 20-06-2019, 10:32 AM   #33
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With respect, I think you might be incorrect there. Static sag alone will not stop the suspension topping out. The suspension can still top out regardless of what your preload is set to, it's not a 'top out prevention device'.

One of the reasons for setting 'sag' is so that with your weight on the bike the forks\shock have enough travel\range to decompress as well as compress. But they can both still technically top out.

If preload, and therefore (rider) sag, is set correctly, there will be enough travel in the fork\shock for the suspension to move up and down, then compression\rebound damping controls the rate at which that happens.

If all that is setup properly (in combination with the correct spring) then top out\bottom out shouldn't happen, but none of that really has anything to do with static sag. As far as I can tell anyway.

Sorry Bob, but having been involved in racing myself and helping others with bike setups, builds etc, you NEED static sag, it suspends the weight of the bike before the rider gets on.
If you have no static sag on the front of the bike it will be nose high, will not corner correctly etc etc, really it will just run you off the road.
Don’t take my word for it give Maxton, K-Tech, Ohlins, Wilbers etc a ring and ask them.
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Old 20-06-2019, 10:53 AM   #34
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Sorry, but I disagree completely, if you have no static sag you are compromising the bikes ability to use it’s suspension safely, believe me, you do not want your bikes suspension topping out when the suspension goes light when you are at speed etc.
Having no static sag does not mean your bike will definitely top out, unless the bike is riding itself around. Is it?
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Old 20-06-2019, 11:06 AM   #35
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If you have no static sag on the front of the bike it will be nose high
Are you sure? What if there's no static sag on the shock either? Will the nose still be high then? ;-)

As per one of my last posts, I think what's happening here is that people are hanging on to snippets of information they've got about elements of suspension setup without necessarily considering the role they play in the overall setup, or the effects that other parts of the setup have on them.

It was just a question though (about why people think static sag is relevant). It'll be interesting to get the views of all those people you mention, but no doubt there will be differences of opinion from them too.

EDIT: Plus it's important to note when we're discussing this, I refer to 'static sag' as the amount the bike suspension sinks under its own weight with no rider, and 'rider sag' as the amount it sinks with you on it. I get the impression that the terminology is being mixed up.

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Old 20-06-2019, 12:45 PM   #36
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I'm in no way (and certainly wouldn't profess to be) a suspension expert. I rely on proven experts like the two I've quoted above if I want to know anything. So a few words on their qualifications...

Niall Mackenzie is a successful former racer with 7 500GP podiums and 3 BSB championships. He has a wealth of experience on a wide range of machines under a wide range of conditions.

Tony Foale is a professional engineer, Bachelor of Technology and Master of Engineering Science. Sometimes, when a person is an acknowledged expert on something, people say "Oh, he wrote the book on that". Well, when it comes to motorcycle suspension and chassis design, Tony Foale actually DID write the book on that! (Check out his website https://motochassis.com/ there's a lot of useful information and interesting articles there.)

When people with that experience and those qualifications say the same thing, I tend to believe them.

Quote:
Originally Posted by Uncle Bob View Post
Yeah but that's the STATIC i.e. without rider position! It's the suspension's position WITH a rider that's way more important! Unless the bike is going around on its own it's a bit irrelevant.
Not actually irrelevant because, although the suspension may be compressed with the rider on board, that is not a constant state. There are times when the rider's weight is effectively removed from the equation. For example

• (on the rear shock), under heavy braking when all weight is transferred to the front
• (at both ends), going over a rise in the road like a hump-back bridge
• (at both ends), dropping into a hollow or pothole

Quote:
Originally Posted by Uncle Bob View Post
As for the second point, it's kind of true, but that's what rebound damping is supposed to control.
Up to a point, but if you're increasing rebound damping to control the results of insufficient static sag, you'll just be creating other problems elsewhere. For example, on a washboard surface, the suspension may tend to "pump down" over a series of bumps as the spring fails to return to it's static position before hitting the next bump, perhaps eventually even bottoming out.

Better to minimize the topping-out by setting the correct sag than masking the problem with excessive damping.

Quote:
Originally Posted by Uncle Bob View Post
Static sag alone will not stop the suspension topping out. The suspension can still top out regardless of what your preload is set to, it's not a 'top out prevention device'.
Correct, any suspension set-up can top- or bottom-out given the right extreme conditions. But, by having the correct static sag, you will minimize the times that happens. That's what Tony Foale wrote:

"• The static loaded position of the suspension is closer to the rebound stops, and so there is less suspension movement available before topping-out. So that occurs more often."

Quote:
Originally Posted by Uncle Bob View Post
If preload, and therefore (rider) sag, is set correctly, there will be enough travel in the fork\shock for the suspension to move up and down...
Also correct. But how do you know when it's set correctly? With my DU737, the "correct" setting was between 25-40mm so my original 26mm was "correct" according to the book. It wasn't until I also checked the static sag that I was able to arrive at the correct setting for my weight. Correct rider sag will, by definition, also include the correct static sag.

While suspension experts like the one Mossleymonster visited will no doubt be able to set the correct dynamic sag without also checking the static sag, the fact that they haven't checked it doesn't mean there isn't any or that it's not important to the overall set-up. I would still recommend that the home twiddler, without the experts' training and experience, still checks both figures to ensure that the final set-up is correct.
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Old 20-06-2019, 01:07 PM   #37
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Here is a link to the Ohlins suspension setup booklet. Very simple and easy to follow.
This is the rule of thumb I use in setting up my road and in the past my race bikes, along with other information collected from Chris at K-Tech etc.

https://www.sscycle.com/docs/default...l.pdf?sfvrsn=0

Last edited by chris.p; 20-06-2019 at 01:10 PM..
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Old 20-06-2019, 02:09 PM   #38
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Also correct. But how do you know when it's set correctly? With my DU737, the "correct" setting was between 25-40mm so my original 26mm was "correct" according to the book. It wasn't until I also checked the static sag that I was able to arrive at the correct setting for my weight. Correct rider sag will, by definition, also include the correct static sag.
Well, yes and no. You said that you backed off the preload to give you an extra 10mm, but that 10mm really only counts when you're on the bike, right? Because surely only a mad man would 'tune' a bike's suspension for when the rider isn't on it!?!

So what I'm saying is, instead of thinking of it as 10mm static + 26mm rider, the adjustment method is the same i.e. wind off a bit of preload, therefore isn't it the same as basically 36mm rider sag? Because ultimately where the bike rests in its travel is one of the crucial parts of this.

Guys, the fundamental question here is: What is the point of static sag? The inference being that it's just an 'extension' of rider sag. In other words, where your suspension rests in its travel with you sitting on it, and therefore surely the most important measurement.

I think this is probably what mossleymonster's sus guys were hinting at. It's interesting. And let's not forget that the term 'correct' in the context of suspension can be quite subjective. I mean, if it tops out, bottoms out, dives, squats etc. it's obviously not 'correct', but beyond that it's about feel.
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Old 20-06-2019, 02:26 PM   #39
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Originally Posted by chris.p View Post
Here is a link to the Ohlins suspension setup booklet. Very simple and easy to follow.
This is the rule of thumb I use in setting up my road and in the past my race bikes, along with other information collected from Chris at K-Tech etc.

https://www.sscycle.com/docs/default...l.pdf?sfvrsn=0
Thanks Chris that's really good info.

The way they describe it, setting up the suspension unweighted (static sag) is important for setting the geometry of the bike as a starting point. Although obviously as soon as you sit on it that all goes completely out of the window if the other parts of the system are wrong!

Usefully, they go into detail about how to get those other bits 'right' too.
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Old 20-06-2019, 02:34 PM   #40
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Searching the rest of the interweb for answers has led me to this thread:

https://www.pistonheads.com/gassing/...f=74&t=1497711

Very interesting reading!
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Old 20-06-2019, 03:38 PM   #41
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Thanks Chris that's really good info.

The way they describe it, setting up the suspension unweighted (static sag) is important for setting the geometry of the bike as a starting point. Although obviously as soon as you sit on it that all goes completely out of the window if the other parts of the system are wrong! :chuckle.
Once static sag is set the rider sag can be checked, if it is out you need a different spring that will then suit the riders weight., problem solved.
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Old 20-06-2019, 04:50 PM   #42
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Originally Posted by Luddite View Post
I'm in no way (and certainly wouldn't profess to be) a suspension expert. I rely on proven experts like the two I've quoted above if I want to know anything. So a few words on their qualifications...

Niall Mackenzie is a successful former racer with 7 500GP podiums and 3 BSB championships. He has a wealth of experience on a wide range of machines under a wide range of conditions.

Tony Foale is a professional engineer, Bachelor of Technology and Master of Engineering Science. Sometimes, when a person is an acknowledged expert on something, people say "Oh, he wrote the book on that". Well, when it comes to motorcycle suspension and chassis design, Tony Foale actually DID write the book on that! (Check out his website https://motochassis.com/ there's a lot of useful information and interesting articles there.)

When people with that experience and those qualifications say the same thing, I tend to believe them.



Not actually irrelevant because, although the suspension may be compressed with the rider on board, that is not a constant state. There are times when the rider's weight is effectively removed from the equation. For example

• (on the rear shock), under heavy braking when all weight is transferred to the front
• (at both ends), going over a rise in the road like a hump-back bridge
• (at both ends), dropping into a hollow or pothole



Up to a point, but if you're increasing rebound damping to control the results of insufficient static sag, you'll just be creating other problems elsewhere. For example, on a washboard surface, the suspension may tend to "pump down" over a series of bumps as the spring fails to return to it's static position before hitting the next bump, perhaps eventually even bottoming out.

Better to minimize the topping-out by setting the correct sag than masking the problem with excessive damping.



Correct, any suspension set-up can top- or bottom-out given the right extreme conditions. But, by having the correct static sag, you will minimize the times that happens. That's what Tony Foale wrote:

"• The static loaded position of the suspension is closer to the rebound stops, and so there is less suspension movement available before topping-out. So that occurs more often."



Also correct. But how do you know when it's set correctly? With my DU737, the "correct" setting was between 25-40mm so my original 26mm was "correct" according to the book. It wasn't until I also checked the static sag that I was able to arrive at the correct setting for my weight. Correct rider sag will, by definition, also include the correct static sag.

While suspension experts like the one Mossleymonster visited will no doubt be able to set the correct dynamic sag without also checking the static sag, the fact that they haven't checked it doesn't mean there isn't any or that it's not important to the overall set-up. I would still recommend that the home twiddler, without the experts' training and experience, still checks both figures to ensure that the final set-up is correct.
Your absolutely spot on in my opinion , makes the most sense to me .
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Old 21-06-2019, 10:14 AM   #43
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set My two penneth, I've had the static sag several times by, the guy who owns the shop where it came from, he rides motorcross. Teut Wien in Preston, he does all the suspension for one of the national short circuit series. Maxton set my forks up on their dyno. Finally by Daz at Mick Gardner racing set the bike up with me on it.

It's better now than it's ever been.
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Old 22-06-2019, 09:12 AM   #44
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Am pleased we got that sorted 😉
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