Colorado VDR Harescrambles suspension setup?

[Starkman]

OK, I've done 5 harescrambles at VDR. I have to ask if my bike is bad or is it normal. At the higher speeds it will tank slap and become very harsh in the front. To the point that it hits my wrists so hard on small sharp edges that I almost can't hold on to the bars.

My bike is a 2001 CR250R and I'm 195 lbs and have been going faster every race, I had the suspension done by Racers Edge and he put the right springs in and did some work to the forks to help with the harshness. At the last race I pushed the forks down in the trees by 3 MM with no change to the slapping but it doesn't turn as good.

I know it's old but I have it and it was cheap so is this normal for that bike? TIA, I'm an old roadracer and this is new to me.

[RMSpeed6]

Cure...

[Grinstead_77G]

Gotta agree with the photo above.

I've been running the same Scotts Damper since 2003 - Just keep moving it from bike to bike. And I'm still running it even on my new 2012 CRF250R because the stock steering damper (at max) doesn't have enough dampening to handle the VDR HS ruts and bumps at speed without head-shaking. Just dial in the amount of control for the conditions and charge!

[mjskier]

While a damper helps a lot, if you have extreme head shake your suspension is suspect.

My crf 450 (07) had quite a bit of shake on acceleration bumps. Changing the valving helped tremendously.

Searching the net at the time, it sounds like too much compression damping would cause head shake.

Anyway, you might want to talk with Mark Wright. He is the local rep for Pro Action and he races most of the HS.

[Dizman]

Installing the Scott's dampener is a game changer. I installed one about 5 years ago and it made a world of difference. No more head-shake on the high speed sections, and it has saved me a number of times from augering in the front wheel in heavy-powdery dirt. Adjusting the suspension will also help. Go as soft as you can stand on the compression (minimal bottoming-out), and increase the rebound dampening.

[coyote9090]

unfortunatly it is "normal" for that bike if the suspension setup is right its not as bad as you decribe but still there.

I race the same bike and its taken half of the summer to get the suspension to work for me. Im down to a small shake of the bars on the high speed section on the north fence at VDR.

Im going to install the damper for the next race to get rid of the rest you are more than welcome to try it out if i can make the next race.

[Thorny]

Try softening the rebound on the forks just a click or 2, and you can also try increasing the race sag of the shock 1-2 turns of pre-load.

Head shake is usually caused by incorrect setup in 1 of those 2 areas.

[Starkman]

Thanks for all the help.

I just measured the sag and it's at 25mm. A couple of races ago the lock nut on the shock was loose so I tightened the spring to 25mm of sag. I raced at CORE with CORCS and didn't have any headshake but that was nothing like VDR. For the last VDR race I increased the fork compression and rebound by 4 clicks because I was bottoming on the jumps at practice the week before (didn't run the back 40 just the track). Sounds like from you all that I should loosen the shock preload some and soften the compression in the fork.

I can't help but wonder if newer bikes have the same issue and if I should just find something newer for next year instead of spending 600 bucks on a damper?

[mjskier]

My understanding is that you control bottoming on jumps with the oil level in the fork, not with the clickers.

Air compresses, oil doesn't. So more oil, less air, more resistance to bottoming out.

[RMSpeed6]

My understanding is that you control bottoming on jumps with the oil level in the fork, not with the clickers.

Air compresses, oil doesn't. So more oil, less air, more resistance to bottoming out.

Not trying to be a jerk, but that's completely incorrect.

[mjskier]

Not trying to be a jerk, but that's completely incorrect.

Well, if you don't want to be a jerk, then offer an explanation instead of just making a blanket statement. I'm willing to be educated.

My understanding comes from the troubleshooting scenarios in the "race Tech Motorcycle Supension Bible":

- Bottom too soft, mushy on landing. Does it feel good otherwise? then oil level is too low.

This affects mostly the last 1/3 of travel.

[Bmotoman]

Raising the oil level does help with bottoming resistance to a certain extent but not for the reason you stated. You're correct in that liquids are non-compressible when compared to air.

The fork has a set volume inside filled both with air and oil. By adding oil you decrease the volume of air and the available space it has to occupy when the fork is compressed (volume inside fork leg that doesn't contain oil) so the pressure the air exerts on the inside of the fork during compression increases which increases the bottoming resistance.

There is a limit though in that if too much oil is added you'll experience hydraulic lock; where the available space isn't enough to overcome the decrease in volume when the fork compresses resulting in a very harsh, bottoming feel even when not using full travel.

Usually an increase of 10-20 ml of oil is best if experiencing bottoming.

[mjskier]

Thanks Motoman.

So if you were to take things to the extreme (on a dual chamber): Fill the fork to the max with oil, then compress it all the way so that all the excess oil flows out, then close it up and go riding. Would you have the maximum amount of oil that you can use without experiencing hydraulic lock?

[Bmotoman]

Technically yes. The volume of oil inside the fork would be just enough to allow the lower fork leg to achieve full travel at the circumstances when you originally filled the fork.

The problem with that is it doesn't allow for any air in the fork or account for the thermal expansion of the oil or air during the suspension action. If the bleed screw was undone then there would be an overflowing of oil and the fork would experience hydraulic lock once it was in use.

It is best to stay relatively close to the recommended volume listed in the service manual +/- ~10-20 ml before I would recommend a re-valve to get the required damping. This is more of a fine tuning procedure than a miracle solution. It's good for adjusting to track conditions, a local track has very quick, short, g-out take offs that when hit at speed seemed to cause bottoming of the forks regularly. I was happy with my suspension setup under most conditions so I increased the oil volume 10ml to increase bottoming resistance.

[Bmotoman]

As for the original OP's problem, the sag should be around 100mm, the sag being so little will load the front and can make it more skittish. Too much compression or not enough rebound can cause head shake. Too much compression doesn't allow the suspension to absorb the bumps quickly enough for the speed traveling. Not enough rebound damping can cause headshake when the fork rebounds too quickly from the spring force.

This is going to take some testing to determine which one is the cause. Go out to a rough section where the headshake is occurring and do some setting adjustments. Adjust the compression in both directions 2 clicks per adjustment (softer and stiffer) and run the section a couple times to see if that fixes it. Now stay at your best comp setting and repeat the process with the rebound until your satisfied with the setup. If it can't be dialed out with the clickers then it's time for a re-valve or if your clickers are at an extreme (full closed/open) which means the valve setup is too far off for the rider/application.

[husky390or]

Use this to check your sag. It's been my experience that if sag is not set correctly, the rest of the bike will not handle worth a damn.

http://www.tootechracing.com/suspension_tips.htm

[Starkman]

Use this to check your sag. It's been my experience that if sag is not set correctly, the rest of the bike will not handle worth a damn.

http://www.tootechracing.com/suspension_tips.htm

Thats cool, it's a CR like mine.

I guess the process is to set sag with the rider on the bike. 4" from this graphic...

Thanks for the help all this has been very informative.

[husky390or]

Thats cool, it's a CR like mine.

I guess the process is to set sag with the rider on the bike. 4" from this graphic...

Thanks for the help all this has been very informative.

Just remember, when you are setting the sag, be sure to stand up on the pegs of the bike. It's very important that you do this.

[Big Pollock]

Husky-

I thought race sag was how different I looked like after the hare scramble than I did starting?????????

Bryan

[husky390or]

Husky-

I thought race sag was how different I looked like after the hare scramble than I did starting?????????

Bryan

LMAO. That's a different kind of sag buddy.