Spring selection?



26 replies to this topic
  • MX_Tuner

Posted October 04, 2001 - 04:19 PM

#21

I can't think of any advantages of running that much sag if your spring is correct for your weight. It would make the bike more stable at speed but I can't think fo any other advantage. I've never had an instance to run more than 100mm. I've run as low as 90mm at times but I rarely run into a problem I can't easily deal with at 100mm.

For the kicking sideways tendency, I'd look closely at things like rear wheel alignment. I've seen swingarms with the alignment marks off significantly from one side to the other. When I have a question of side to side alignment, I have one of those Motion Pro chain alignment tools that attaches to the rear sprocket and has a bar to sight down the chain with. Other possibilities are bent axles, worn swing arm bearings, worn wheel bearings, etc.

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MX Tuner

[This message has been edited by MX Tuner (edited October 04, 2001).]

  • Boit

Posted October 04, 2001 - 05:40 PM

#22

After giving this more thought, I need to make a correction. My rear wheel doesn't kick more to the right than the left on jump launches. It's just that the one that bit me kicked the rear to the right and that was burned in my mind. What I have been catching myself doing more and more is using the seat-bounce technique to prevent kicking to either side. I think you were right on the money Dave when you mentioned using the throttle correctly just as I launched. By standing, I believe that the wheel is unloaded just prior to leaving the lip and I get a bit of wheel spin which makes the wheel kick to the side. By seat-bouncing, I get maximum bite and no kick. Does this sound reasonable?

MXTuner; Checking the bearings was first on my list as culprits but everything is in top shape. I'm very anal about bike maintenance and even went so far as to disassemble everything the minute I got home from taking delivery of my machine. I used Bel-Ray grease and carefully went through the entire rear end plus the steering stem before riding the first time. I just checked an hour ago that my swingarm has no side-to-side play, my axle is not bent..etc. My inclination here is to suspect that this kicking is a combination of poor technique in conjunction with improperly setup of my suspension(imbalance). As Dave pointed out, the kicking could be due to too much or too little in rebound on the shock. MX-Tech's site talks about this but it appeared to have a contradiction. I'm sure I just need to re-read it.

As far as the alignment issue, you bring up a good point. I've never felt comfortable using those marks on the axle block either. I think I'll take your advice and acquire the Motion Pro alignment tool.

Thanks for the input.

  • DaveJ

Posted October 05, 2001 - 02:57 PM

#23

Boit,

Yea...I guess it sounds correct. But you shouldn't have to work so hard with your body to keep the bike under control. The bike should launch from any jump smoothly and evenly regardless of body position (well...in most cases).

Play with your settings. Like I said, a video camera can do wonders for spotting the details.

And the MX-Tech.com site reads a little weird. Proceed with caution.

DaveJ

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  • MX_Tuner

Posted October 05, 2001 - 03:03 PM

#24

If the rear end is consistently kicking over jumps, the rebound may be too soft but not too stiff. Usually, the rider won't even relate it to a rear set up situation since the symptoms is the front drops and they continually have to over correct for the front being too low. Just the opposite is also true. If you see someone whose front is always too high over jumps, chances are his shock rebound is too stiff.

Think of it this way. The rear end *has* to kick back some on the take off of a jump. Once I get the forks working well, have the rear sag set and have the compression in the ballpark, I set the rebound to control the attitude of the bike in the air. I'll adjust the rebound a couple clicks at a time until the rider gets the definite sensation one way or the other, just so they know exactly what they're feeling for. Then we'll go back in the right direction until we get a nice neutral jumping bike. This is assuming we aren't dealign with any unusual circumstances that might affect set up.

Once we get the rebound set for jumping, we can make an assessment as to whether the shock needs revalving. Some guys will cook through stadium whoops and need lighter high speed rebound. Most mortals can deal with the stock shock valving

Of course, there are other variables that can control the way the bike jumps. Does this only happen on this one particular jump? Any other unusual sympotms that might be related?

------------------
MX Tuner

  • az426

Posted October 05, 2001 - 05:59 PM

#25

for anyone else: there is a pretty good explanation of setting "sag" and "racesag"
and a little about those clickers on the
motocross action web page.

  • Boit

Posted October 06, 2001 - 02:43 PM

#26

Yeah, it has been this one particular jump that is causing me a problem. It's a routine double with a very short approach coming out of a 90 degree left. It's very difficult to get traction so I short-shift into 3rd to increase tractability. Even then, if I use a little too much throttle I get wheel spin, plus it's very choppy. So far I'm able to get enough speed to clear it but I want to jump a few feet further and land where it's smoother and get set up for the next corner. I've tried both standing and seat bouncing and the seat bouncing works best. I'm going to experiment with the rebound and see what happens.

  • MX_Tuner

Posted October 06, 2001 - 04:22 PM

#27

One other variable I run into is peoples method for setting the rear sag. Most all manuals say to sit on the seat for the "rider on board" measurement. I have the rider stand on the pegs instead of sitting down. This eliminates the variable of where the rider sits. This can make a substantial difference in how the sag is set. I had a guy with a KDX and was setting the sag. I'd make an adjustment, measure and have to go back the other way. Adjust again and I'd have to go back the way I originally started. Kept going back and forth and finally realized he wasn't sitting in the same place for each measurement. Even if the rider sits in the same place, it is hard to determine if this is really where the rider normally sits, and in what circumstance. Measuring with the rider standing makes setting the sag much more reliable.

------------------
MX Tuner





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