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Setting Front Sag on Modern Sports Bike

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  • Setting Front Sag on Modern Sports Bike

    I've come to the conclusion that setting the sag on the front end is a bit different when you have top out springs in your forks.

    These forks actually work both ways so the neutral position is when the forks are extended with no weight ... that is with the front wheel off. So I reckon you measure the extension when the fork is in that neutral state then set you rider sag at 35mm-40mm for track work.

    Yesterday I set my sag the usual way and the bike was worse. It dived more on the front and didn't feel as composed under brakes. Backing off the preload made it better.

    Any ideas? ... am I barking up the wrong tree?
    I'll be riding for you #52, my dear son, Cameron Taylor Elliott 1985-2009
    2008 CBR600RR and 2010 GSXR750 Track Bikes, KTM530EXC Enduro bike wrist breaker

  • #2
    Bark up Marty Moose's tree!

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    • #3
      It would be handy if, just occasionally, when someone asked anything about suspension we got more than "PM MartyMoose!!1!!" as a response.

      Yes, he's great. But some people like to learn what their machines are doing and be able to tune things themselves armed with half a clue and a spanner. "PM MartyMoose", "Call Russel at DynoTime", "ShortSteve can help" are great for people who want to set up for one type of riding and never touch it, but it's not a great deal of use when someone wants to learn how to DIY so they can tune it over a week's riding, or change the settings between road and track.

      Scott52 - think about this. You've set your suspension halfway not because of spring tension but so that from a "neutral" position the forks can compress and extend about equally to track the road nicely. Regardless of load, that position is what gives you the travel range. I'd be setting sag to the middle as per usual and, if it feels like shit, be looking at compression and rebound adjustments.

      Of course I could be completely wrong, if I am, someone please educate us.
      "Once upon a time we would obey in public, but in private we would be cynical; today, we announce cynicism, but in private we obey."

      Comment


      • #4
        The old adage was set the rider sag at about 1/3 of the full travel ie. 35-40mm as most bikes have around 110mm to 120mm front travel. But that was the old days when you had one spring. Now we have two springs ... the main spring and a top out spring the works against the main spring. If you take the front wheel off you'll find that you can pull the fork down about 20-40mm against the top out spring. When you let go it shoots back up again to what I've called the "neutral position.

        I prefer to learn and understand these things myself and make my own adjustments ... outsourcing every thing to "experts" is not that satisfying. It doesn't help you grow as a "man". Men are supposed to fix things.
        I'll be riding for you #52, my dear son, Cameron Taylor Elliott 1985-2009
        2008 CBR600RR and 2010 GSXR750 Track Bikes, KTM530EXC Enduro bike wrist breaker

        Comment


        • #5
          Simple set up guide...

          Set your just as you have done by adjusting preload, once you have set your sag to the suit your weight. If you can't get your static sag and rider sag in the right readings (either too far apart or two close together) you will need either a heavier or lighter spring. Once you have your sag settings you won't need to touch your preload again, from here you need to use your rebound and compression dampening to do the rest.

          If it's diving too much add more compression dampening to control dive. Until you are satisfied with how it behaves under brakes. Can't get enough dampening? add more oil or replace with heavier for oil.

          Then set about adjusting rebound to control how it behaves when it comes back up.
          Trying to think of a wise and sincere signature quote, but the only words that leap to mind are, "TITTY SPRINKLES"

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          • #6
            For what it's worth Scott, we had a top out spring in the rear shock of the ZX-6R which we ended up removing - could not get the suspension to work at all, the springs seemed to act against each other continually and gave the overall result of a rigid plank in the rear of the bike.

            Though it was awesome how sideways you could get it with a locked out shock hahaha.

            Comment


            • #7
              Originally posted by Nigel View Post
              For what it's worth Scott, we had a top out spring in the rear shock of the ZX-6R which we ended up removing - could not get the suspension to work at all, the springs seemed to act against each other continually and gave the overall result of a rigid plank in the rear of the bike.

              Though it was awesome how sideways you could get it with a locked out shock hahaha.
              Actually Nigel the top out spring is part of the 30mm Ohlins cartridge ... I dare not interfere or question all those Swedish Mechanical and Hydraulic Engineers that designed these things. Those kind of experts I'm happy to deal with and accept they know best because of the countless R&D $$ they've spent.
              I'll be riding for you #52, my dear son, Cameron Taylor Elliott 1985-2009
              2008 CBR600RR and 2010 GSXR750 Track Bikes, KTM530EXC Enduro bike wrist breaker

              Comment


              • #8
                Its only an issue if you wind into the top out springs while adjusting your loaded sag. Some top out springs are longer than others. The one in a std 07 CBR thou is very long about 70mm(total) from memory. It operating range is about 40mm.

                Set it about 35-45mm loaded from the neutral position I think you are barking up the right tree Teknic suspension has a great pdf doc on this from their website. Although he does recomend less loaded sag.

                Terry Hay messed around with "reactive suspension" with very long top out springs a few years back where the main spring fought a huge top out spring all the time, some loved it I have mates who swear by this but I've only seen this idea used on off road bikes.

                Turbo the bikes load on the suspension should be controlled by the spring for the most part not the comp damping. If its diving too much use a harder spring ,add preload or oil level. The comp should control the bikes reaction to bumps if you add comp to stop dive then it won't work well over bumps. I know plenty of racers who add comp to stop dive but they always run into handling issues (patter) and lack of feel becuase they are runing very little bypass on their adjusters.

                MM

                Comment


                • #9
                  Originally posted by Marty MOOSE View Post
                  Its only an issue if you wind into the top out springs while adjusting your loaded sag. Some top out springs are longer than others. The one in a std 07 CBR thou is very long about 70mm(total) from memory. It operating range is about 40mm.

                  Set it about 35-45mm loaded from the neutral position I think you are barking up the right tree Teknic suspension has a great pdf doc on this from their website. Although he does recomend less loaded sag.

                  Terry Hay messed around with "reactive suspension" with very long top out springs a few years back where the main spring fought a huge top out spring all the time, some loved it I have mates who swear by this but I've only seen this idea used on off road bikes.

                  Turbo the bikes load on the suspension should be controlled by the spring for the most part not the comp damping. If its diving too much use a harder spring ,add preload or oil level. The comp should control the bikes reaction to bumps if you add comp to stop dive then it won't work well over bumps. I know plenty of racers who add comp to stop dive but they always run into handling issues (patter) and lack of feel becuase they are runing very little bypass on their adjusters.

                  MM
                  I have the 30mm Ohlins cartridges that include the top out spring. I have 0.95 main springs ... which are about right for my weight of 78kg.

                  We're singing form the same hym book because I'm going to set the rider sag back to about 35-40mm from the neutral position ... which is where I first had it and it felt good and gave you confidence to push it harder into the corners. The extra preload that I tried yesterday to get the sag at 35-40mm from the fully extended position ... ie with the top out springs compressed made the bike worse.

                  Thanks for your thoughts.
                  I'll be riding for you #52, my dear son, Cameron Taylor Elliott 1985-2009
                  2008 CBR600RR and 2010 GSXR750 Track Bikes, KTM530EXC Enduro bike wrist breaker

                  Comment


                  • #10
                    Originally posted by Marty MOOSE View Post

                    Set it about 35-45mm loaded from the neutral position I think you are barking up the right tree Teknic suspension has a great pdf doc on this from their website. Although he does recomend less loaded sag.


                    MM
                    I have found this. AM only just getting my head around what happens, but find 30-35mm works best FOR ME, any further and the bike seems to drop in too quickly but be too heavy on centre to tip in. control dive and extension with comp. Good luck and happy learning

                    oh, pm MM
                    yes, i am ignorant
                    yes, i am a prick
                    no, i don't care
                    you make me sick

                    Comment


                    • #11
                      Scott, ignoring the impact of the top out spring and given you are using a constant rate (rather than progressive) spring, then doesn't changing the amount of pre-load simply change the ride height of the front? So, given your weight and that of the bike is more or less constant, when you brake the rate and amount of front end compression will be the same regardless of what pre-load you dial in.

                      What will change is where the fork moves within its usable range. If your fork was bottoming out, then dialling in 10mm more pre-load will help, but the front will also ride 10mm higher. This will increase rake angle and change how it steers. If you then slid the forks 10mm up through the triple clamps, you would be back to the same rake angle.

                      I have read somewhere that setting sag is only a starting point for suspension tuning. There is no perfect amount of sag. As long as your setup allows adequate operating range for the fork, you change pre-load or sag to get the handling your want.

                      What was the handling issue you were trying to cure?

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                      • #12
                        I was just trying the increased preload and less sag. It was handling well before ... I guess I was fiddling to see what would happen. I need to take the wheel off to see how much the top out spring compresses the forks so I know what point the rider sag is at.
                        I'll be riding for you #52, my dear son, Cameron Taylor Elliott 1985-2009
                        2008 CBR600RR and 2010 GSXR750 Track Bikes, KTM530EXC Enduro bike wrist breaker

                        Comment


                        • #13
                          It is interesting that the adjustment you made should not have changed the rate or amount of dive and increasing ride height should have increased rake, so it shouldn't have been less stable on the brakes????

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                          • #14
                            It will Nevr you are spot on, but if you wind into the top out spring and measure the height (sags) you will find you can add preleoad for little ride height change. Scott don't bother just measure from the unloaded position. You can chase your tail in circles with this stuff, just make sure you measure and record changes and you know what effect each change has on the chassis. That way if you have an issue like tucking, pushing, running wide etc etc you can make good decisions to fix the issue. Use the Kiss rule

                            MM

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                            • #15
                              Originally posted by nevr2old View Post
                              It is interesting that the adjustment you made should not have changed the rate or amount of dive and increasing ride height should have increased rake, so it shouldn't have been less stable on the brakes????
                              The initial dive when hitting the brakes seemed to be more/faster which unsettled things ... the weight transfer from rear to front was too quick. If I go back to 5 turns (5mm) of preload that I had before it will be fine. As you said yesterday I like tinkering with things to see what happens.
                              I'll be riding for you #52, my dear son, Cameron Taylor Elliott 1985-2009
                              2008 CBR600RR and 2010 GSXR750 Track Bikes, KTM530EXC Enduro bike wrist breaker

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