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Re: hello from nyc! [Re: whatwobbly] #149018 09/15/20 08:52 PM
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skypupbob Online Content
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You got it ,springs and or spacers for sag. Oil weight and or emulators for dampening.
The sag should be between 25 to 30 percent of overall travel when you are on the bike with riding gear on.

Re: hello from nyc! [Re: skypupbob] #149022 09/15/20 10:44 PM
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whatwobbly Offline OP
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Originally Posted by skypupbob
You got it ,springs and or spacers for sag. Oil weight and or emulators for dampening.
The sag should be between 25 to 30 percent of overall travel when you are on the bike with riding gear on.


Thanks for the concise explanation, bob. I have tried reading Racetech's book on suspension, as well as some of what Lee Parks has written, but have yet to convert what I have read into any practical knowledge.

I will search the forum to check out other posts about XT suspension tuning. Are there any reference materials--such as charts or guides--anyone can recommend regarding understanding the what changes can be made to springs and spacers and what effects those changes would have?

*Edit* The point about suspension tuning has brought to mind another characteristic of my new-to-me 2005 XT that differs from my prior 2006 XT. When I am riding my 2005 XT over speed bumps or pot holes, I hear a distinct sound of what sounds like air being forced through a valve, or of some sound of compressed air.

The factory manual had a spec for PSI in the forks, and I recalled the manual stating that the PSI in the forks in adjusted by prying off the caps on the fork and releasing the air from the valves. I may be wrong, however. The manual is kept at my garage (which is in another neighborhood), so I cannot look it up right now.

I did try removing the black plastic caps on the end of my forks, and all I found were smooth metal caps without any valve. Next time I am with the bike, I will take a picture.

Does anyone have any idea what is the sound I hear when I go over a bump? Is fork PSI something that may be related to this, or is it a symptom of bad fork seals? There is still a lot that I am learning about diagnosing problems and mechanical issues.

Thanks!

Last edited by whatwobbly; 09/16/20 04:23 AM.
Re: hello from nyc! [Re: whatwobbly] #149024 09/16/20 01:47 PM
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Given that the XT's suspension is largely non-adjustable, there isn't a whole lot of info other than rebuilding the forks and replacing the shock. The XT's stock suspension is soft, so upgrades are almost always toward increasing spring rates, especially if you're an average size American or bigger.

The stock springs and damping are designed to work together as a system. When you change one, it affects the other. "Upgrading" to stiffer springs without changing the valving (fork or shock) can result in a system that's overdamped in compression and underdamped in rebound. Changing forks without changing the shocks can result in front/rear imbalance.

When you stand on the pegs in a normal riding position and bounce on the bike, the front and rear should move up/down together. If you change one end and not the other, you can get a teeter/totter effect where one end moves faster than the other, which can cause other problems. You really need 2 friends to help set up a suspension. One to hold the bike upright (unless you've got trials rider balance skills) and another to watch as you bounce it. Pay attention to both the compression and rebound speed of both ends. The bike should remain level as it moves up and down.

Another test is to go for a ride and find a long, sweeping, preferrrably flat corner you can take at moderate speed. Once you enter the corner, you should be able to nearly let go of the bars (hold the throttle for constant speed) and the bike just continue to track around the corner with basically no input. It shouldn't try to stand up or fall over on it's own. Tire profile and pressure can have a big influence on this. This is something I used to do when I rode sport bikes. Every time I changed tires (2-3x per year) I'd have to tweak the settings a little to keep the bike stable.

Adding spacers to either forks or shock only affects the pre-load (static sag) but doesn't change the spring rate. So if you're bottoming out the forks, adding spacers may help a little but the more pre-load you add, the more harsh the ride becomes. Adding pre-load means it takes more force to get it to move, but you're back to the same spring rate once it starts moving. You sacrifice smoothness over small bumps for a small benefit on big ones.
You can put a zip tie on the forks and shock shafts to see how much travel you're using.


This shall pass, be still and know.
2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.
Re: hello from nyc! [Re: whatwobbly] #149030 09/16/20 05:21 PM
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whatwobbly Offline OP
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Thanks for such a detailed answer, peejman. It sounds like there are going to be quite a few things I will need to consider regarding my issue with front-end handling. I have a few friends I can recruit to help me check the sag.

Overall, it is helpful to hear that I do not need to resort immediately to rebuilding my front wheel, as the answer may possibly be found in how I set my front and rear suspension. I will need to carefully look into how everything is set up.

As the previous owner claimed to upgrade the front fork springs, would it be possible to match the new spring rate via adjustment on the rear suspension without having to replace the rear shock with a cogent shock? One additional problem is that I do not know the front spring rate, nor do I know if the previous owner did other modifications that he did not mention (such as modifications to the front fork spacers).

Re: hello from nyc! [Re: whatwobbly] #149031 09/16/20 05:59 PM
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good q&a going here, i'll just add some detail on fork spacers. haven't been inside my xt forks yet (have stiffer springs i'll install at some point too) but, my klr had metal spacers. you can swap that out for schedule 40 pvc pipe (the thicker, high pressure stuff). this is much easier to trim that the steel spacer, especially with a tool like this;

https://www.harborfreight.com/finger-release-ratcheting-pvc-cutter-62588.html?cid=paid_google|||62588&utm_source=google&utm_medium=cpc&utm_campaign=&utm_content=&gclid=CjwKCAjw74b7BRA_EiwAF8yHFPrHSUV03n1D2GCQuf84JLIVG8urjRVFnlDVgGQjnRHGeN4oZigOehoCUS8QAvD_BwE

measure your sag on the fork and determine if you need a longer or shorter spacer to correct. in my case, i started at a length of pvc the same as the stock steel and trimmed about 1/4" at a time until i got down to correct sag. you may need to start with a longer spacer. nice thing about pvc, it's cheap and easy to work with in case you make a mistake.

Re: hello from nyc! [Re: peejman] #149034 09/16/20 08:04 PM
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whatwobbly Offline OP
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Thanks for describing your experience with adjusting front fork sag by means of adjusting the spacer, ptxyz. It really helps illustrate the discussion about suspension adjustment.

Originally Posted by ptxyz
measure your sag on the fork and determine if you need a longer or shorter spacer to correct. in my case, i started at a length of pvc the same as the stock steel and trimmed about 1/4" at a time until i got down to correct sag. you may need to start with a longer spacer. nice thing about pvc, it's cheap and easy to work with in case you make a mistake.


Is there a correct process for checking and adjusting sag, front and rear? Best to start with the front, move to rear? Or each sag measurement is irrespective of the other, and can be completed in either order?

One question I will need to research more is the sound coming from the front end when I go over a bump. I am going to see if I can recreate it when the bike is still and I just push down firmly and quickly on the handlebars.

Originally Posted by peejman
You can put a zip tie on the forks and shock shafts to see how much travel you're using.


I will do this and try to report back with the results. Thanks for recommending this.

Re: hello from nyc! [Re: whatwobbly] #149041 09/17/20 05:33 PM
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front or rear 1st doesn't matter. i enlisted my wife to help measure, pick a fixed point both above and below where things move. an example would be the front axle and lower triple clamp. lean the bike over onto it's sidestand far enough to completely unweight the suspension and measure (much easier on the xt than the klr, the klr than the blackbird...). sit on the bike with your gear and balance (had my hand on the clothes dryer...) and re-measure.

think of something nice to do for said spouse for their repeated measuring as you trim, install and trim again your spacers...

Re: hello from nyc! [Re: ptxyz] #149050 09/20/20 05:23 PM
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Originally Posted by ptxyz
front or rear 1st doesn't matter. i enlisted my wife to help measure, pick a fixed point both above and below where things move. an example would be the front axle and lower triple clamp. lean the bike over onto it's sidestand far enough to completely unweight the suspension and measure (much easier on the xt than the klr, the klr than the blackbird...). sit on the bike with your gear and balance (had my hand on the clothes dryer...) and re-measure.

think of something nice to do for said spouse for their repeated measuring as you trim, install and trim again your spacers...


That's pretty much what we did. Bounce a little to minimize the effect of friction in the suspension. And don't think of these as hard and fast rules, they're just to get you in the neighborhood. Tweak until you're happy, it'll be a little different for everyone.


This shall pass, be still and know.
2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.
Re: hello from nyc! [Re: whatwobbly] #149051 09/20/20 06:44 PM
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Regarding front end "knock" that may be the head stock bearings and/or fork tubes. What I'd do is get the bike on a cement floor (like in a garage) and lock the front wheel with the brake lever. Move the bike forward/backward (front wheel locked) and see if you hear/see any looseness. Doing this will put translational forces on the fork tubes and head frame. It also works the front suspension. The spaces (X2) in each fork tube can wear causing sideways movements in the tubes. After a while this causes the seals to leak and you'll see fork oil bleeding. As for the head stock bearings, you can put your finger on the span and feel slop in there. There should be none. Or the noise(s) could be coming from something rattling behind the headlight cowling, caliper or bracket(s). Also wheel bearings being worn out. Just take the weight off the front wheel and see if there is any slop. It should be tight side to side. Just a few things that are easy to check. Good luck.


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