Lowering links and pullrods etc

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KDXer
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Lowering links and pullrods etc

Post by KDXer »

I attended a suspension seminar today and it got me thinking about pullrods and lowering links. Does anyone do anything to counteract the difference in the front end geometry and clearance ?? Does anyone have issues with the rear fender and tire kissing each other ?? Probably over thinking it all but in theory it seems (to my pea sized brain) it would just lower the back end causing the steering rake to change, sag and tire to fender clearance to change also. Your thoughts on this are appreciated...

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krazyinski
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Post by krazyinski »

yes lowering the rear will increase trail and effect the handling.
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canyncarvr
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Re: Lowering links and pullrods etc

Post by canyncarvr »

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KDXer wrote:I attended a suspension seminar today and it got me thinking about pullrods and lowering links. :shock: Does anyone do anything to counteract the difference in the front end geometry and clearance ?? :razz: Does anyone have issues with the rear fender and tire kissing each other ?? :butthead: Probably over thinking it all but in theory it seems (to my pea sized brain) it would just lower the back end causing the steering rake to change, sag and tire to fender clearance to change also. :rolleyes: Your thoughts on this are appreciated...

Cheers,
Trev...
:shock: I don't now about 'anyone', but I didn't. I used Devol rods, a difference of 1.5mm, so didn't bother changing the front. If longer rods like Koubas are used, I would assume the forks could come up in the clamps. The Devols lowerd my seat height by something like 5/16"

:razz: I have no problems with tire/fender interferance. I've munched the rear light wire a time or two..but never has the tire hit the fender.

:butthead: Overthinking? You? You're kidding, right?

:rolleyes: Certainly any change to the height of the rear has a corresponding effect on the front. All that trail, rake and stuff and the steering quickness, stability apply.

You did miss the most important (besides the obvious 'lower') part of the long rod approach. It changes the geometry of the suspension, too. The leverage angles/moment arms change. The amount of shock travel (actual rod movement) I believe increases with a given wheel input in the KDX. That may be backwards? MY pea brain isn't quite sure of the physics of that one. Ask Idaho Charley about it. I recall reading that in a Devol description of their pull rods...that they improved shock action. I don't take that to mean the shock moves LESS.

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Post by OverTheHill »

You can adjust the sag to make up for some or all of the difference. For instance, if the links lower the rear by 1.5" without rider, you could reduce the sag from 4" to 2.5" to keep the stock geometry. Normally you would lower the sag to 3" (leaving the rear .5" too low) and slide the forks up .5" to keep the stock geomety. Rear wheel movement will have more leverage on the shock/spring so you may need a stiffer spring and shock adjustments.
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Post by canyncarvr »

To each his own..and if you like it, fine and all...

But...misadjusting the sag to 'fix' a height issue is generally considered not a good idea.

The shock works when setup in a particular (and known) fashion. 4" of race sag is not a number derived from how tall the bike needs to be.

I guess if you're using links to lower the bike instead of reworking the shock (the right way to do it), hosing the shock action by setting the sag to a bogus figure is six of one, 1/2 dozen of another.

Certainly, anyone is welcome to set their bike up any way they wish.

Uh...completely btw, but if you change the shock sag to 2.5" (less than 4") how does that make the bike shorter? :wink:

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Post by KarlP »

I've been following this thread with interest.
I've got a '95 KX125 that I put my KDX forks on. You can probably figure where the KX forks went.
The kx is a wee bit high in the back, low in the front, and the shock spring seems way too hard for the forks. Very strange ride at speed.
I want to lower the rear about 1.5". It has 93 mm rods on it now.
I was going to make two sets, one at 99 mm and one at 105 mm. If I knew exactly what length I needed to drop it 1.5"......
Maybe I should not be so lazy and start measuring and figuring. It's just geometry.
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Post by canyncarvr »

Yeah. 'Ya lazy bum. It's just geometry, and everybody knows pies are squared!!

Which means, 'I have NO clue how the pull rod length relates to seat height and couldn't figure it out but empirically.'

Well, longer=lower, but I don't know how the progression works.

The outcome will depend on the unitrack configuration, too. It's been said that most knuckles are the same KX-KDX wise, but I have no idea if that is so or not.

My guess (based on my Devols) is the 99s will be a lot closer to what you want than will the 105s.

Good luck!

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Post by KarlP »

Oh, hey, by geometry I meant put the bike on a stand, take the bolt out of one end of the rods, move the swingarm up an inch and a half, and see how short the rod ends up being. I guess that's tape measure work.

I'm not looking for perfection, I just need to get the back end down a bit. It's just a dinking around bike.

I really am that lazy, and averse to too many numbers.
I think longer rods increase leverage on the shock, meaning more wheel movement per inch of shock movement but I could be wrong; I'm just one of those damn Engineers you hear about. If you want to know shear loads on the anchor bolts of a 150,000 gallon liquid nitrogen tank during a seismic event in a particular geographic area, I can probably tell you.

How the linkage on a KX or KDX works I'll leave to the Japanese
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Post by canyncarvr »

Great! I've been worried sick over that big N tank in my back yard and what will happen to it NEXT time the ground shimmies. I have NO faith in those tie wrap things. Not even the BLACK ones!! (UV resistant and all yanno)

So....' move the swingarm up an inch and a half, and see how short the rod ends up being.'...

Making the bike lower (moving the swingarm up) will make the rods shorter? Not if longer rods make the seat height drop.

Just razzing.

I'm averse to numbers myself. That's why I make every effort to ensure my checking account never has any numbers IN it.

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Post by KarlP »

:grin:
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Post by Indawoods »

Forget the links... get the shims to lower it!
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Post by KarlP »

Inda-

What shims?
I've never heard of that......
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Post by Indawoods »

*** Administrator //***
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"People ate cows a thousand years ago for the same reason we eat them now. Cause they are easy to catch.We're not savages,we're just lazy. A cheetah could taste like chocolate heroin. But will never know. Those bastards are fast!!! "
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