Page 3 of 4 FirstFirst 1234 LastLast
Results 31 to 45 of 59

Thread: Set up for the long one.

  1. #31
    Join Date
    13th April 2007 - 18:26
    Bike
    06 scrambler,xrl,
    Location
    In town. Crap
    Posts
    4,155
    Blog Entries
    1
    Neil, remember that even the best suspension guru's like Robert or Paul Thede (Race Tech founder) acknowledge that their job is to set suspension up with "the least amount of compromise".
    But their is always compromise. Don't fall into the trap of over thinking what the forks/shock are doing in an attempt to nullify every type of load factor.
    What may be 95% tuned for ruts, will have you cursing as you go into soft sand etc
    Just my opinion.

  2. #32
    Join Date
    2nd March 2004 - 13:00
    Bike
    FransAlp 700
    Location
    Nelson
    Posts
    14,484
    Quote Originally Posted by That looks like fun View Post
    Just went out to the garage and poked both shocks (front and the other end) with a stick and niether of them sagged and I never got a static shock so the sprung vs unsprung wieght must be in balance with the power output of x squared by the root of the tree in the middle of the field 2 men plowed on a moonlight night.
    I think
    What's the wind direction?

  3. #33
    Join Date
    1st March 2007 - 11:30
    Bike
    2014 R1200 GS, 2007 DR 650
    Location
    Whakatane
    Posts
    1,473
    Quote Originally Posted by tri boy View Post
    Neil, remember that even the best suspension guru's like Robert or Paul Thede (Race Tech founder) acknowledge that their job is to set suspension up with "the least amount of compromise".
    But their is always compromise. Don't fall into the trap of over thinking what the forks/shock are doing in an attempt to nullify every type of load factor.
    What may be 95% tuned for ruts, will have you cursing as you go into soft sand etc
    Just my opinion.
    I agree completely.
    I'm just trying to get a feel for the rules to get to the starting point. I fully understand that the tuning starts in earnest from there.
    There are some widely used rules of thumb, one of which I have mentioned repeatedly. I've simply been trying to figure out how to apply it in a particular case. Fran set me straight and at the same time explained why R.T. set it up the way he did.
    However, if you read back, you will see that the question that I asked was very simple. "If we carry a heap of luggage, should we treat it as static or dynamic loading?"
    Most of the respondents, me included, got it wrong.
    Brent, there was no question of over-thinking it - we are dealing with the absolute basics here. The most basic suspension adjustment we have is changing the spring rate. Get that badly wrong and there is nothing else we can do that will compensate for it.
    I may not be as good as I once was, but I'm as good once as I always was.

  4. #34
    Join Date
    16th July 2008 - 20:36
    Bike
    92 R80 GS
    Location
    NEW PLYMOUTH
    Posts
    804
    Here's my 10cents worth. I ride with a pillion nearly all the time and quite often luggage. I have a stiffer spring so i can get the static sag somewhere in the picture with the bike loaded then the race sag is in the ballpark with rider and pillion. Without the stiffer spring winding preload in doesnt accomplish much. Even with the ride height set up right it still unweights the front end. No problem with traction tho. IMO the only time you would treat the luggage as race sag is if you were carrying it on your back

  5. #35
    Join Date
    16th July 2008 - 20:36
    Bike
    92 R80 GS
    Location
    NEW PLYMOUTH
    Posts
    804
    What rear shock do you have ? modified stock or Ohlins ?

  6. #36
    Join Date
    13th April 2007 - 18:26
    Bike
    06 scrambler,xrl,
    Location
    In town. Crap
    Posts
    4,155
    Blog Entries
    1
    I'd treat the extra weight as static.
    Own a couple of springs, and change them to suit load conditions. ie, full blown Aussie trip, and change back to the lighter spring for NZ weekend adv rides. MHO

  7. #37
    Join Date
    1st March 2007 - 11:30
    Bike
    2014 R1200 GS, 2007 DR 650
    Location
    Whakatane
    Posts
    1,473
    Guys, if you are fitting stiffer springs to carry the extra load, then you are treating it as part of the rider load, not the static and it's by definition.
    Question - how is a pillion passenger different from a big load of luggage? (Don't tell the wife I said that.) I can understand what Colin said earlier that putting the load on the rider's back instead of the bike, needs adjusting for as the rider's legs can be part suspension. However, the pillion doesn't get up on the pegs or move around much, if at all.

    So how is the pillion load different to a heap of luggage?

    Consider what we do to set the bike up.
    Imagine a completely bare bike. The first thing we do is set the static sag by adjusting the preload - typically so that the sag is about 10% of total travel.
    We then add the rider and if the spring is rated properly, the total sag will be about 30% of total travel, i.e. the rider adds 20% more sag.

    Now put some baggage on and repeat the process.

    Adding the baggage will have increased the static sag, so we increase the preload to bring it back to 10%.
    Add the rider whose weight hasn't changed and the total sag will again be 30% (Hooke's Law) The rider will always increase the sag by 20% for this spring.

    Add more baggage and repeat.

    You get more preload but no reason to change the spring and it will stay that way so long as the extra load is treated as static. The extra preload is carrying the baggage and you still get your 10%/30% measurements.

    Now look at it the other way.

    Set the bike up completely bare as before i.e. 10 static and 30 with the rider aboard.

    Now add the rider and baggage as well and where it is mounted doesn't matter. The static sag hasn't changed but the rider/luggage sag will now have increased alarmingly. The static sag is still correct. Take the rider/luggage off and check it. We don't need to change the preload then.

    The only way to get the rider sag back to where you want it is to fit a stiffer spring i.e. to treat the luggage as rider load.

    My Triumph is set up this way as it gets most use 2 up. It has an aftermarket shock and more importantly a stiffer spring. Putting an extra 65 kg or so in the panniers has exactly the same effect as putting Nicky on the pillion seat.
    I may not be as good as I once was, but I'm as good once as I always was.

  8. #38
    Join Date
    15th September 2008 - 16:53
    Bike
    1999 BMW R1100GS / 2012 WR 250 R
    Location
    Inglewood
    Posts
    838
    Just read all that and now my brain hurts.
    Wind is from the South East Quadrent Nordie, where did I leave me orange juice, Im off to lie down

  9. #39
    Join Date
    16th July 2008 - 20:36
    Bike
    92 R80 GS
    Location
    NEW PLYMOUTH
    Posts
    804
    Depending on the weight of the luggage you will get to a point with the standard spring where no matter how much preload (and there is a maximum) you give it you cant get the static sag set right or if you do then the rider sag is wrong. With a lighter spring your compression damping will have to be increased to compensate for the increased load . Increasing preload doesnt make the spring stiffer, just alters the force required to initially compress it. A heavily preloaded spring may mean the shock is harsh in its initial travel.
    At the end of the day I think which ever way you look at it you need a heavier spring and ya have to shag around with settings till it works best for you. Ive read some interesting debates online about suspension and without trying all the options its hard to say that something wont work better
    I'm happy with the spring weights on mine GS but its not good on the gravel corrugations. In talking to Robert and Dennis at CKT the shock has to much high speed rebound and packs down over the corrugations.
    In Alaska I had an Ohlins in my Dakar with a stiffer spring. Kelvin had a stock shock and even with his preload at max mine rode 50mm higher in the rear. We both hit a set of frost heaves and the impact in his sheared a subframe bolt off.

  10. #40
    Join Date
    13th April 2007 - 18:26
    Bike
    06 scrambler,xrl,
    Location
    In town. Crap
    Posts
    4,155
    Blog Entries
    1
    Just buy another spring already

  11. #41
    Join Date
    1st March 2007 - 11:30
    Bike
    2014 R1200 GS, 2007 DR 650
    Location
    Whakatane
    Posts
    1,473
    Quote Originally Posted by Phreaky Phil View Post
    Depending on the weight of the luggage .................................................. .......................shock and even with his preload at max mine rode 50mm higher in the rear. We both hit a set of frost heaves and the impact in his sheared a subframe bolt off.
    Phil,
    To answer an earlier question, I have Ohlins front and rear.
    Secondly, I don't disagree with a thing you say, but I didn't want to bring damping rates into this discussion as it is complicated enough already.
    Lastly, both you and Brent are saying that you would treat a big luggage load as a static one but in the same breath are saying that you have heavier springs to cope with exactly that situation.
    I was simply pointing out that in doing so you are contradicting yourselves. If you are stiffening the spring to cope with the load then by definition you are treating it as a non static one. I was also (obviously unsuccessfully) trying to explain why this is so.

    I know I sound pedantic, but by understanding that the load is NOT a static one, I can now add any size luggage load to my bike that I want and by taking a few simple measurements using the existing spring, I am able to calculate the spring rate of the new one that I need.
    As I said earlier Nordie gave me the key and I have the answer that I wanted.
    I may not be as good as I once was, but I'm as good once as I always was.

  12. #42
    Join Date
    16th July 2008 - 20:36
    Bike
    92 R80 GS
    Location
    NEW PLYMOUTH
    Posts
    804
    I think you have to look at the springs and damping together. From a different perspective, there are two basic types of road condition that affect the suspension. First, a bump in the road. The rear wheel is forced upward. the extra weight on board is not affected by this. The spring and comp damping limit the upward movement and the rebound controls its decent.
    Second. Dips or holes in the road. The wheel and whole rear of the bike drops into the hole or dip. With the greater mass the spring and damping have to control the compression. The more mass on the back, the faster compression. Wind up the preload, once the spring is compessing it has no effect. only stronger High speed compression damping will help. This wont be good on the first type of bump. With a heavier spring, it has more resistance to the comprerssion and the high speed compression damping can be lighter.
    I'm not sure that will make any sense, buts its interesting trying to put thoughts from your head into text !!

  13. #43
    Join Date
    15th September 2008 - 16:53
    Bike
    1999 BMW R1100GS / 2012 WR 250 R
    Location
    Inglewood
    Posts
    838
    Ok, you win I will show that I can be serryus. Forget sag, rebound, static and all that stuff. Lets look at "Sprung" vs "Unsprung" weight. Any weight not supported by the springs, eg wheels, tyres, etc can be taken straight out of the equation as we have little control over that (unless you mount your load to the axles somehow, but why? ) Everything else is "Sprung weight" Regardless of if the weight is carried high, low, forward, back or by those poor buggers plowing the field. If it is supported by the springs it becomes part of the sprung weight. AND THE SPRINGS HAVE TO BE STRONG ENOUGH TO SUPPORT SAID SPRUNG WEIGHT while maintaining the ride height characteristics of the vehicle. This is so the suspension has the correct amount of travel to go up and down goodo So now that we have the load carried and supported properly shall we look at the real problem.............
    Yes the vehicles damping devices (thats shock absorbers to ewes), righto, away ya go sort them out

  14. #44
    Join Date
    15th August 2004 - 17:52
    Bike
    KTM 2T & LC4
    Location
    Rather be riding
    Posts
    3,326
    Okay, there's a bit of misquoting/misinterpreting throughout this thread I'll try to be clearer.

    Quote Originally Posted by Bass View Post
    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.
    No, actually I'm with Robert all the way on this, and that's what I was trying to say... which is what Nordie said clearly. Also, the required spring rate never depends only on the rider's weight; I think you wrote to the contrary a couple of times - not sure if I'm misinterpreting why.

    I agree mostly with what Nordie wrote. The critical difference: static sag matters; it matters because it tells you if the spring is correct. To achieve the correct rider sag (bike/rider/luggage total load irrespective of mounting point) you could have one of these three options:

    • too light spring too heavily preloaded
    • correct spring & preload
    • too heavy spring too lightly preloaded

    Once you have the rider sag set, checking the static sag tells you which of those three scenarios (springs) you have. At this point, choosing whether to include the luggage in the static sag is utterly critical to your analysis. (And without the luggage mounting options, static sag is still critical - it is no more or less academic than the whole rest of the exercise.) With the luggage firmly mounted to the bike, the luggage only uses the bike's spring so you need more spring there. Mounted to the rider, the luggage also uses the rider's leg springs, so the bike's spring can be lighter.

    But we are only talking about theoretical ideals: it is only the starting point. Tune from there as you see fit.
    Cheers,
    Colin

    Quote Originally Posted by Steve McQueen
    All racers I know aren't in it for the money. They race because it's something inside of them... They're not courting death. They're courting being alive.

  15. #45
    Join Date
    15th August 2004 - 17:52
    Bike
    KTM 2T & LC4
    Location
    Rather be riding
    Posts
    3,326
    Quote Originally Posted by Bass View Post
    Lastly, both you and Brent are saying that you would treat a big luggage load as a static one but in the same breath are saying that you have heavier springs to cope with exactly that situation.
    I was simply pointing out that in doing so you are contradicting yourselves. If you are stiffening the spring to cope with the load then by definition you are treating it as a non static one. I was also (obviously unsuccessfully) trying to explain why this is so.
    I don't think they are contradicting themselves. But I don't yet understand your explanations - yet we might be saying the same thing in different words Will think about it some more tomorrow. At this stage I am thinking that the two sag measurements interact to give you the answer, and that changing the load doesn't influence one without the other; it is their relationship that is important.

    Easy:
    Static sag = bike
    rider sag = bike + rider

    Hard:
    Static sag = bike + luggage
    rider sag= bike + luggage + rider
    OR
    static sag = bike
    rider sag = bike + luggage + rider

    In either of the "hard" cases, luggage being moved in/out of static sag changes both configurations as the ratio & relationship between the two sags changes. Note: you cannot simply use rudimentary algebra to cross off each occurrence of luggage in the first "hard" case to make it resolve to the easy case... Rider & static sag occur at different positions in the shock's rising rate, for starters... and that's just the first curvilinear example that popped in to my head.

    I think your examples re: the Trumpy & pillion don't compute, because although you invoke Hooke's law (correct, as far as a linear load on a spring goes) you omit the rising rate suspension. The rider will not always increase the sag (sag = travel measured after linkage applied) by 20% for that spring. Yes the rider will always increase the load and thus compression on the straight-rate spring by a consistent amount; no that does not translate to an equal linear change in travel through the linkage to your sag. Admittedly the curve is fairly slight at that part of the travel, but it isn't flat.

    Make sense?

    With each 1 turn (1.75mm) change of preload to the rear spring of the 640A, I don't get a consistent (linear) change in static sag. Between 8 & 15T it yields 3.5-5.3mm of static sag change per T, and 0.4-6.0mm of rider sag per T. No weights changed, just preload consistently and the output varied by the rising rate. Try it on your bike.
    Cheers,
    Colin

    Quote Originally Posted by Steve McQueen
    All racers I know aren't in it for the money. They race because it's something inside of them... They're not courting death. They're courting being alive.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •