Suspension Blues!!!


4 replies to this topic
  • Dune7

Posted February 25, 2006 - 07:43 AM

#1

I am 6'4" and weigh around 255lbs . I have changed my XR650R stock springs with 11.5 KG for the Rear shock and .49kg for the Forks. I am using Motul 7.5 for oil. I also have the added weight of an Acerbis 6.0 gal tank so you can see I have my baby working hard!! (nearly all riding is in the desert dunes around Dubai)
This was a 2 step process:- I started by changing the back spring, it works like a dream. I then add the long range tank and have a serious problem with forks bottoming and getting a little head shake. So I fit a SRC fork brace, cool no headshake , solid as a rock in the softest of sand. Recoil and damping are still in the stock "click" positions ie: midway. Only problem I have is the bottoming foks.

Step 2: I changed the stock fork springs for 0.49kg Racetech springs and this unleashed the devil in the handling. (Clickers still in stock position) changed oil for Motul 7.5 wt. The front wheel "washes" at the slightest hint of a rut or bump and when I get in slightly rutted sand tracks in the desert the bike get headshake like a recovering alchoholic gets the DT's!! In other words the bike is all over the place.
Now before someone says check back in the forum for previous mails I have and problem is that most are telling me the theory behind all this suspension stuff but I am a firm believer in practice/experience over theory.

Can someone help me with a step by step from back to front suggestion on how I should go around setting my suspension so I can love my Pig again. I have a sore arse and "arm pump" after a a serious 130 km through the dunes and I don't love her very much anymore!

Can some please help.???? :thumbsup:

P.S: I have the 11.5 Kg rear spring and some guys observed that the bike seemed to be riding low, now that could be my "fat ass" that causes that ....but how can I get the race sag set ( ...preload...??)

  • ewbish

Posted February 25, 2006 - 08:44 AM

#2

First, make sure your clickers are all in the OEM position.

Set your race sag-3.9 to 4.1 inches is a good range. To do this, measure from the axle bolt to the seat bolt on one side while bike is on a crate and rear wheel off the ground. Then take it off crate and you sit on bike with feet on pegs. I also like to stand up and jump up and down on the pegs a couple of times to make sure everything settles. With somebody holding the bike upright, and your feet still on the pegs, have somebody measure from the same axle bolt to the same seat bolt. To adjust this, use the adjusting rings on the top of your shock. If you have more than 4.1 inches, you need more preload, tighten the rings (this shortens the shock). If you have less than 3.9, back off (lengthen the shock) some.

Now, on your forks. You have the heavy spring, so I'd use the book recommended oil weight and volume. This is a good baseline. From there, I'd:

Back off all damping, rebound and compression. You want no damping at all.

Rebound: the more damping, the SLOWER your forks/shock return to original height from a compressed state. If you "pogostick" off jumps, you want more rebound damping.
Compression: the more damping, the SLOWER the forks/shock compress. If you are feeling like the slightest bump makes you sink, or you bottom easy, crank up the compression damping.

So, with all damping backed off, start riding the bike, and make incremental changes. I prefer my bike set up with the least compression damping I can stand, and almost no rebound damping. This is my prefereed "desert" setting, it soaks up rough terrain, handles small jumps, and keeps the wheels on the ground. If you like to jump, you'll want more damping. When you like it, check your race sag again and readjust if neccesary. Make sure you write down how many clicks you went.

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  • 1Hondalover

Posted February 28, 2006 - 06:26 PM

#3

Do what I did. Fill out the form, send it with your forks and shock to Precision Concepts. Get it back in one to two weeks and put it back on. Go riding and haul butt. Finish the first loop and wonder how you ever rode without it.

It's kind of like a Scott's Stabilizer.

  • Supplicate

Posted February 28, 2006 - 07:31 PM

#4

instead of me trying to put into words everything I've learned about suspension, here is a link and a quote from two separate sites:

http://www.borynack..../suspension.htm

Bruce knows his stuff when it comes to the BRP

and here is a quote:

Im a "self-proclaimed-gypo-suspension-expert" I've done more with less than almost anybody, and this info Im offerin really works! Put on yer crash-helment, grab a beer, take notes, and make yer bike work for you! Here we go!

THIS IS FOR A BIKE WITH A LINKAGE TYPE REAR SUSPENSION ONLY

SUSPENSION has only 1 job! That is to give you the best ride possible, while providing you with total control over varying terrain at break-neck speeds! No sweat rite?

If your bike does not do this, then read-on because soon,,,it will! Hell,,,mine does!

Step #1. is to set the FREE-SAG! This is free, and nothing else will mean squat if this is not done 1st.

Lift the rear wheel off the floor, (can be done tiping it on the kick-stand) so the rear suspension is fully extended. Measure the distance from the center of the axle to a known point like the fender mount bolt up near the seat, or anywhere on the sub-frame as dirrectly above the axle as possible, and adjust the shock rings til ya get it to sag 1" (25mm) Once ya have the spring tension set so it sags 1" under its own weight, go to the next step.

Now fill the tank with fuel, and go "suit-up" in ALL yer gear!

Ya need 3 people (includin you) ta do this so get help. Once ya have 2 helpers, get on the bike. 1 helper is to steady the bike so ya dont fall over, and the 2nd. helper does the measureing. (all you gotta do is pretend that yer goin fast) Get up on the pegs, lean over the bars and pretend that yer at light-speed. Have the #2 helper measure the distance between the same two points you measured from before and, write this down. This distance MUST fall in the 3-4" range. If it does not,,,ya have the wrong spring for yer weight. (highly un-likely) If ya have LESS than 3" of sag, the spring is too stiff for yer weight,,,and if ya have MORE than 4" of sag,,,it's too soft.

Once ya have the SAG set properly, we will move on to the tuning (clickers) of the rear shock. We aint near-done yet but once we get the rear outa the way,,,we'll start on the front and THAT's where the magic really is.


Now that the "sag" is set properly, ya need ta adjust the compression and the re-bound dampening on the shock. Your owners manual will tell ya which is which. Set the "clickers" on both at nominal. ( usually about 1/2 way) Inother words, if it has 10 positions on compression, set it at 5. Ride the bike as ya always do for a while and see if it bottoms out. If it does, go to 6 and try it and so-on. If it doesnt bottom, back it off to 4 and try that. The object is to get the softest ride possable without excessive bottoming. Bottoming out sometimes on really big bumps is ok.

Now that ya have the compression set, ya need ta set the
re-bound. This keeps the shock from extending too quickly after it's been compressed. (like when ya leave a jump and the rear wheel leaves the ground) Ride the bike again and notice if the seat is smackin ya in the rump or the rear of the bike is "kickin up". If it is doing that, then go 1 click tighter on the re-bound adjuster and try it again and so on. If it's not kickin up, loosen the clicker a notch at a time til it does. Once ya notice that it's startin to kick,,,tighten it 1 notch. The object here is to get the back wheel back on the ground as fast as possable, while at the same time not lettin the rear kick-up.

Once you've done all this, you will probably never have ta do it again, and never need ta spend any money for an after market shock. The suspension on your new bike NOW was winnin super-crosses, moto's, desert races etc. 10 years ago properly set-up, and ridden by pro's. For the average racer,,,it's all ya will probably ever need


my only other suggestion is to keep playing with your settings, change one thing a little at a time until it works right and then move on.


and BTW, I'm 6'6" but weigh more then you, only have an 12kg spring and its on the money for me.

edited to fix the spring rate i said.

  • Supplicate

Posted February 28, 2006 - 07:32 PM

#5

Do what I did. Fill out the form, send it with your forks and shock to Precision Concepts. Get it back in one to two weeks and put it back on. Go riding and haul butt. Finish the first loop and wonder how you ever rode without it.

It's kind of like a Scott's Stabilizer.

or give Rob Barnum a call, he has some kick ass valving for the 650R.





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