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setting suspension sag

Discussion in 'Norton Commando Motorcycles (Classic)' started by SteveBorland, Aug 3, 2018.

  1. SteveBorland

    SteveBorland

    Joined:
    Nov 15, 2010
    As a follow on to my earlier post about rear shocks, I was wondering ow people setup the static sag on the front. I've a set of Landdowne internals in otherwise standard forks, and I think I need to get a bit more static sag. At the moment it does not seem to move much at all, and I've been advised to aim for around 15-20mm.

    The only way I can see of doing this is to shorten the spring, but this will then affect the spring rate.

    What do the gurus say on this?
     
  2. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    I am no guru , just barely I rider ... I do have the JRB Lansdowne fork setup with black chrome Hagons out back ... I was so pleased with the improvement it never occurred to me that I should worry bout static sag .... prolly not going to either ... but very interested in what the expert gurus have to say ....
    Craig
     
  3. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011
    Advised by who?

    Is there something amiss with the ride and handling? If not, why mess?

    Shortening a spring will increase the rate, do you want to do that? It will never be a neat installation either.

    The best way to do what you are suggesting it is to buy shorter springs that need to be installed with a spacer, then adjust the spacer length to get your sag. I have done this on several Japanese bikes. It was never as good as sending the fork legs to Maxton!

    If you can find springs of the right diameter and length you can get from around 8.5nm to 10.5nm rated springs in 0.5nm increments, straight wound or progressive, do you know what you want? You can calculate based on bike weight and your weight with riding gear. There are calulators available on line to help you.

    Clearly a lighter rate spring will exhibit more natural sag, but increasing the spacer size may offset the natural sag. So you sag may appear correct, but you spring rate may not be!

    Any change in springing will need you to reset your Lansdowne dampers to suit.

    I seriously suspect none of this will give you a magic carpet!
     
    Last edited: Aug 3, 2018
  4. RoadScholar

    RoadScholar VIP MEMBER

    Joined:
    Dec 28, 2008
    I set sag at 25% to 30% of the shock/fork travel, that is with my weight squarely on the motorcycle, initially. I take the motorcycle on my "test" track at varying speeds and varying road surface conditions to see at what speed the suspension begins to feel vague. I add more or less damping and/or more or less spring pre-load and test again and keep at it until I achieve the compromise I understand and can live with.

    I like to ride the Norton on New England back roads between 40 and 70 MPH, below that the suspension feels a bit stiff, above that the handling becomes less responsive, unless the road is smooth. The same setup feels decent near the ton on the freeways, but I spend very little time on the big 6 lane freeways unless I'm stuck in transport mode.

    Suspension systems on most production motorcycles are price point systems with decent operational bandwidth. Systems based on high end forks/shocks have a much larger operational bandwidth. Until real active suspension becomes practical and affordable, it will remain true that if you set up a suspension system for a comfortable, responsive ride at 40 MPH it will become progressively more unresponsive above that, conversely if you set up suspension to give manageable control at 100 MPH, it will be very uncomfortable at, say 40 MPH, maybe even a tad dangerous.

    No free lunch lads.
     
    xbacksideslider likes this.
  5. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011
    That may work well, but it isn't 'static sag', which is without rider weight. the OP says someone has advised him on static sag at around 15-20mm. We have no idea how qualified that person is regarding Norton Commando suspension. Ideal static sag varies depending on application. I have been adjusting the sag on a 500 single race bike I have, to be told by the shock maker that for the weight and size of machine, top class racers are currently setting zero static sag.

    As a useful comparison perhaps he should measure the loaded sag as you say? Once he has converted 25% to 30% of travel to a Commando Roadholder figure!

    At the very least, compared to the static sag it should give an indication of how suitable the springs are for his weight!
     
  6. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011
    Another approach to finding out what is happening with front suspension is to put a zip tie around each fork leg, not too tight, it has to move. Set the zip tie against the dust seal and ride.

    Ride different roads, check how far the zip tie moved, note, reset. You can also try hard front brake applications to get an idea of full travel with this configuration. Does it bottom out?

    This will all give you information about what is happening.

    Unless you get some extreme variance it won't tell you what to do to get it right, but it will give you a guide to the effect of spring changes.
     
    xbacksideslider and oldmikew like this.
  7. RoadScholar

    RoadScholar VIP MEMBER

    Joined:
    Dec 28, 2008
    My post says initial setting, a good starting point. When the motorcycles I set up like this, initially, are completely unladen they, almost always, have zero static (unladen) sag.. My goal is to ride somewhere inside the suspension travel, not on it or at the bottom of it, within the speed range I like for the roads I enjoy.
     
  8. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011

    And I havent disagreed with you, your goal is sound, but we risk confusing the OP when discussing static sag and any other sag!

    You comment also further supports a view that what the OP already has is probably fine, and that the 'expert' who has advised him may not have the experience of his particular machine.
     
    Last edited: Aug 4, 2018
  9. SteveBorland

    SteveBorland

    Joined:
    Nov 15, 2010
    I'm a little surprised about the somewhat unhelpful tone of some of the replies.

    The four people I was talking to at Spa this year were 2 rather fast blokes on Seely Nortons (they also ride Commandos on the street), one who rides Ducati's at the Isle of Man and a well known irish roadracer, so yes I do think they know what they were talking about, and they all race (or have raced) a considerable number of different machines. The advice was given to establish a good start pont for the suspension settings as part of the approach to sorting out a rather nasty wobble on some of the faster curves on the track. Since I really have very little experience in playing with suspension settings, I asked their opinion. I've never bothered much about this before since the bevel Ducati is very stable everywhere on the track.

    I may have used the wrong term in my question, I was referring to the sag with the rider on board.

    It does seem though that no one bothers to adjust this value on Roadholder forks?
     
  10. gortnipper

    gortnipper VIP MEMBER

    Joined:
    Nov 11, 2013
  11. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011


    Seems I should not have worried about us confusing you with references to static and loaded sag, you already were! Sorry for that, I have no intention to be unhelpful.

    15mm to 20mm loaded is very different to 15mm to 20mm unloaded.

    I suspect the reason no one bothers much with Roadholders for sag settings is because it is a well trodden route to use standard springs, even if an improvement can be had by changing them. Also not many riders will be challenging their chassis with runs around Spa, which will challenge just about anything.

    It is impossible to know who advised you other than what you tell us. I have been involved in racing and other motorsports for over 40 years. You may be surprised to know that I have met 'experts' who talk utter bollocks. I have learnt to apply a reasonableness filter and often seek the simpler alternative. If you found some good ones that know standard Commandos, well that is good.

    So with your new comment about nasty wobbles in fast sweeps, maybe first check the basics. How are your Isolastics and particularly the head steady? Which head steady do you have? Might also be worth mentioning which frame and head angle you have. How are your tyres and pressures?

    Very little translates from a rigid mounted Seeley to a Commando. My experience with a production Commando in race conditions was always not to fight it in long sweeps, or, it developed a nasty wobble!

    Relaxing your grip on the bars may have had a positive effect. Equally moving your weight might improve things. What bar and footrest set up do you have?

    Bevel Ducati's can be fairly stable most everywhere, they are not full of rubber between front and rear wheels and are subsequently not so much of a compromise on handling.
     
    Last edited: Aug 5, 2018
  12. SteveBorland

    SteveBorland

    Joined:
    Nov 15, 2010
    I know it's a complex thing, trying to find an ideal (or at least acceptable) setup, which is why I did not post a question about how to fix a wobble in a fast corner :)
    As you mention, there are many factors which will affect how the bike handles. I've several different things lined up for this winter, including some machining work on the iso mounts to ensure the ends are actually true. I do not intend to do the whole hog of stripping the bike and sending the frame off to be trued (well, at least not at the present moment), but there's quite a number of things that can be done to remove possible problems. Reading through the website of Parallel Engineering (http://www.parallelengineering.co.uk/) is informative.

    Here's some details of my current setup. It's an 850 MkIIa, standard frame and fork clamps, with Landsdowne dampers in the front forks, Hagon shocks on the rear. A Dave Taylor type headsteady from RGM with the Mk3 spring arrangement and vernier type engine isos. Tyres are Roadriders, AM23 in road compound, pressures were 29/32 psi front/rear. i'm using clipons and rearsets of course, together with a PR tank and seat but no fairing. I do think the PR tank is a bit long though, placing too much weight rearwards. I've always tried for a relaxed grip on the bars, following some interesting experiences on my first real bike, a Honda 550 four.

    I've experimented with diferent iso settings, riding styles and body placement, and found that (as expected) tight iso clearances, keeping power on through the curves and placing as much weight as I can on the front tyre definitely reduced the problem, allowing me to give it considerably more stick through the curves. I still did not feel happy about running through Blanchimont flat out though - this to me will be the acid test.

    I think the comments about a good starting point for the sag measurements which I recieved from the four independent sources are vaild though. A Commando is still a 2 wheeled vehicle with suspenson, just with a few more variables after all. I would be very interested in hearing what sort of settings you aim for though on your bike.
     
  13. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Steve, if you do change the shocks, and especially as you ride on the track, you might want to consider 10mm longer ones. That’s what I recently fitted under advice from Maxton. It feels good, but I haven’t had it on the track again yet.
     
  14. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011
    The thing I have always found about a relaxed grip is that after 40 odd years it still doesn't come naturally, all sorts of things can cause you to tighten up, and I have to check myself occasionally and loosen up! I found that with a Commando this even means that if you are laid over and the bars flap a little, you really need to let them! Make sure your throttle action is a light as possible, heavy throttle springs and sticky cables demand tighter grip!

    I have never ridden Spa, but I understand running flat through Blanchimont takes more than a good handling bike!

    The settings from my current bike won't help a lot, because it is a Rickman. The Rickman is more stable than most bikes through long sweeps, the issue with it is changing direction! It is a bit physical and it is through slower corners that it typically loses out to the Seeley. I don't run a steering damper, you don't mention one.

    I have also concentrated on weight over the front, my Maxtons are 50mm over the original fit, any longer and you have an issue with chain run over the swinging arm pivot. I would certainly follow Maxton/Fast Eddie's advice and go longer, it will help with weight over the front. Hagons are OK, I have ridden a PR replica at Cadwell with them on, with a standard front end, no problems, but springing just may not be right for you. (which is what you suspect anyway) For somewhere like Spa you might want to run your chain as long as you can! And make sure chain tension is correct as it can have an interaction with the suspension on a Commando.

    You don't mention your own weight, but mention of working physically to get weight over the front and finding the PR tank longs suggests you may be smaller than me? If you consider Maxton make sure you are equiped with all the weight data and riding style info you can when you talk to them. Don't buy without talking first.

    Static sag is similar to the 15mm to 20mm front, less rear, but the Rickman is lighter than a Commando, on the downside I am 100kg in leathers and boots. But a Rickman is long, rider weight quite well back. I run race tyres with lower pressures, but I also run a 90/90 front, 18", steers easier than the 110/80 18" front available as an alternative. I always preferred the narrower 19" front on a Commando, some don't, but if you run same size front/rear you might try that.
     
  15. SteveA

    SteveA VIP MEMBER

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    Dec 20, 2011
    One thing you don't mention is the fork build state, and what actual springs and oil quantity and viscosity you have in at the moment.

    Fast Eddie's solution is a bit extreme, it is obvious from road and race users that Lansdowne dampers can be made to work very effectively. There are several threads on here regarding Lansdowne dampers. Bear in mind I have no reason to assume the problem starts with the front suspension.

    But it is possible to rebuild the legs and introduce problems with stiction, alignment etc. Also look at threads talking about JSM 'turcite' bushes.

    Just a thought before changing springs.

    And when thinking about changing springs, with reference to the AN website, they supply one fork spring from '68 to '75 including PRs!

    Just read a Ducati thread about shortening springs and fittings spacers, to stiffen the front!
     
    Last edited: Aug 6, 2018
  16. SteveBorland

    SteveBorland

    Joined:
    Nov 15, 2010
    Thanks for the very interesting comments. I didn't find that the bars flapped about, it was more a case of the bike doing a sort of waggle / roll movement, its a bit disconcerting to me.

    Ive also had comments about a steering damper, both for and against. I might try one of the cheapo ones from Ebay, just to see how it affects things, but generally I feel it's more a matter of masking a problem rather than solving it. On the other hand, if it works.....

    I'm about 1.8m (6ft) and probably 85kg with all the gear on. I feel as if there's a bit too much weight bias on the rear wheel, so perhaps a different tank / seat would help with this. (Depending on how the Caswell coating holds up, this may occur automatically next year!).

    I'm running 19" WM3 rims with 90/100 tyres on both ends, perhaps a 90/90 front would be better, but I'm not really unhappy enough to change it now. I really just want to gather some input to help decide what to do over winter. I do need to ride the bike more to get really familiar with its quirks though. Then there's the whole gearing question which also needs to be looked at and carbs etc.
     
  17. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    'Relaxing your grip on the bars may have had a positive effect.'

    Whenever I ride my bike on a race circuit, it takes me about 5 laps before I relax and start riding it properly, then it is almost up to race speed - and that is with a Seeley which is fairly rigid. If you are not used to riding your Commando fairly quickly, it might take you longer to adjust.
     
  18. SteveA

    SteveA VIP MEMBER

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    Dec 20, 2011
    One man's flappy bars are another man's waggle/roll..... really, that sounds familiar to me.....even as if the front tyre is skipping off the tarmac at high lean angles...relax and don't back out of the throttle.

    Totally agree on steering dampers, I prefer not to, and have managed fine without one on a couple of GSXR750s that 'experts' said needed one! Not with a decent suspension set up they didn't. The trouble is a cheap one may not really give you the info you want. I have one on my 'Fury' 500 single in a monoshocked BSA Fury/Triumph Bandit Frame. The only effect adjusting it has is to make it harder or easier to move around in the paddock!

    I think you are going to struggle to find an alternative spring, and I suspect apart from a good check of oil and stiction it will be fine until you have settled in more. Rear end can be improved with more money!

    Look at Cosentino's spring options! Suggests that apart from standard you only want to go a fair percentage stiffer!, but the cartridge system does have adjustable preload to allow you to set sag.

    Japanese sport bike springs just don't get down to these numbers! Around 9nm is more common.

    http://www.cosentinoengineering.com/index_files/Page450.htm
     
    Last edited: Aug 6, 2018
  19. xbacksideslider

    xbacksideslider VIP MEMBER

    Joined:
    Aug 19, 2010
    It bears saying that the reason that we want sag is to give the forks room to extend. That is, when the road throws the machine upward, we want the forks to extend down so the wheel stays connected to the road surface.
     
    SteveA likes this.
  20. gortnipper

    gortnipper VIP MEMBER

    Joined:
    Nov 11, 2013
    Steve - Maybe go chat with a suspension tuner? I have a mate who does a lot of track days on his SV1000 track bike. He blew a motor in his street bike and then he bought another that had had a tuned suspension with a reptuable guy here in NZ. His impressions of the two bikes were night and day - and worth every penny.

    I dont know who these guys are, and if they are near you - but they popped up in a quick search - https://ma-servicecenter.dk/motorcycle/suspension.aspx
     

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