Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Suspension pre-load discussion, pro's and con's

Discussion in 'Technical and Troubleshooting Torque' started by Goose, Mar 9, 2005.

  1. Just after some info into the effects of spring preload adjustment.

    Not the best setting, but rather the pro's and con's of soft vs hard. I recently set my rear preload to full hard from dead neutral and I find its more comfortable.
    Last night I had a huge rear brake lock up. I don't think I would've locked the brakes normally and I was just thinking thats its probably related. Could some of you infinatly knowledgable guys help me out with this? :D

  2. Hmmm, the explanation is too involved for here but yes, increasing rear spring preload will give SLIGHTLY more front weight bias, hence with less weight on the rear it could be more sensitive to braking forces. If you get a better ride with the spring preload wound up, leave it like that, just use more care on the brakes, me thinks ;-)

    The road is more of a headache than the race track as always with suspension, it is a compromise, comfort v road holding v traction and high speed v low speed, grrrr
  3. How about:

    As your spring was pre-loaded its reactive abilities were diminished because of reduced suspension travel available to handle the bump you hit which caused the huge rear brake lock up.

    Confused? I am :-k

  4. Did he hit a bump??????
  5. Dont think i hit a bump... i was too busy avoiding smacking into the car in front of me who had locked up for the car in front of him who was doing an illegal u turn :roll: to notice, but i dont think so
  6. Ok make that 'slight road undulation'

  7. Your probably right, I might have gone over a slight bump or dip. Do you reckon it'd be worth setting it back up neutral pre-load? or just not be such a day dreamy knob next time :D
  8. Umm Nova,

    Increasing pre-load shouldn't decrease suspension travel. It just increase the force at which it starts to work.

    If anything when you are sitting on the bike the rear suspension should be longer because you are compressing it with the same mass yet it requires more force to compress it each addition mm.

    The downside to too much rear preload is:
    1. the steering can become too quick
    2. Bumps are harder on your arse/ back.
    3. if you don't have compression and/or rebound control then you can get a pongo effect..

    Advantages are:
    1. You get quicker steering
    2. you can solve a vague feeling on the front and ro rear
    3. you may get more ground clearance (depending on you bike design)

    The rear brake, well now you know about it, just use less
  9. ...what ibast said.

    Somewhere on bikepoint.com and also buried in sportbikes.net [huuuuge sportsbike site] are some excellent guides to suspender set up.


  10. So to dial out the pogo effect what should I be doing with my preload and rebound? That's all i got to work with. Trouble is I have an aftermarket spring and a rebuilt shock so the standard settings don't apply. I think the rear is 10.something kgs and I've got it set two notches from the bottom and have it pretty soft on the rebound, at the moment.
  11. Increase you rebound. This stops the spring doing too many cycles.
  12. I've done race car suspension for some 20 odd years (in fact, thats what I have done for a living for quite a long time) and I just wanted to point out that you can't increase the rate of a spring unless the shock is topped out (this excludes changing the actual spring). By raising the mounting point on the base of a spring all you are doing is raising the bike height.....the spring rate remains the same. Changing the bike height will transfer some weight forward and it will also reduce droop travel.

    Just for example, if you have a 50kg/cm spring and the spring is 30cm long free height. If the "fitted" length (meaning fitted to the shock) of the spring is say 20 cm then the fitted spring rate would be 500kg/cm (50kg/cm X 10cm). If you have a 1:1 motion ratio and the rear weight bias is say 75kg then this spring would move 0.15 cm or basically hardly at all (and feel as hard as a rock). The shock in this case would be for all intents and purposes "topped out". (Althought this is an extreme example I hope you get the idea).

    The effective spring rate is equal to the spring rate divided by the motion ratio. In other words if you have a 150kg bike with say 50 per cent weight bias (static) on the rear i.e 75kg and a 50kg/cm spring and the motion ratio (or leverage ratio whatever you prefer) is 1:1 then the bike spring would compress 1.5cm (as will the shock from fully extended height).

    If the motion ratio is increased by moving the shock/spring assembly furthur towards the front on a swing arm then the motion ratio is increased. Say we move the spring right up under the seat, then we may have a 4:1 motion ratio...which means that our 100kg/cm spring will compress 6cm.

    Anyway I hope I haven't confused everyone. I don't have enough room here to explain it all. If you want a better explaination then I'm happy to show anyone how it all works (in a visual presentation on a computer)...I have a suspension program that will show you exactly how all this works.
  13. Hey Tack... great reply.

    Hope you don't mind me pointing out an irony?! You ride a GPX250 [I used to too!] which interestingly actually has a variable spring constant spring in the rear shock [gets stiffer the more compressed it is] and zero adjustment possibilities... lol.

    BTW I loved my gpx... very under rated well sorted bike.


  14. Hi Tack,

    This suspension program sounds good. It is something you can share with us?
  15. As I said, too much to explain here ;-)
  16. How does the spring rate change from 50kg/cm to 500kg/cm by adding pre-load? I know that real world springs don't completely adhere to Hooke's Law but this is wild :shock: :wink:
  17. ... I think it was a typo. 500 kg force would be the resultant force after 10cm of compression....
  18. Thanks for clearing that up.

    How silly of me to think that someone with 20 years experience could make such a simple mistake :wink: :LOL: :LOL: :LOL:
  19. the suspension program is called susprog. It is available off the internet for anyone to download but to be fully functional program you must buy a licence (which I have).

    The program itself is adaptable but really is a 4 wheeled vehicled program. It's just that I can adapt it to show you how spring rate, motion ratio, frequency, shock length and travel work.
  20. As for the 500kg/cm spring rate is concerned....a spring increases it's rate for every cm that it is compressed. So a 50kg/cm spring that is 30cm long and is compressed to 20cm becomes 500 kg....this works like this.....compress spring 1cm...spring equals 50kg/cm...compress 2cm..spring= 100kg/cm
    3cm=150 ...4cm=200...5cm=250..6cm=300...7cm=350...8cm=400...9cm=450...10cm=500.