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Old 01-06-2005, 10:41 PM   #1
Fresno OP
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Triple clamp offset

I'm replacing my triple clamp with an Emig so I can have a steering stabilizer. The stock offset is 18mm but I've been told to move up to 20mm. What does increased offset do? Do I need more offset? My riding is 50/50 dirt/asphalt, but I'm fairly conservative in the dirt and sand. Looking more for stability than getting the bike sideways.
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Old 01-06-2005, 10:49 PM   #2
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Quote:
Originally Posted by Fresno
I'm replacing my triple clamp with an Emig so I can have a steering stabilizer. The stock offset is 18mm but I've been told to move up to 20mm. What does increased offset do? Do I need more offset? My riding is 50/50 dirt/asphalt, but I'm fairly conservative in the dirt and sand. Looking more for stability than getting the bike sideways.
It reduces trail and quickens the steering. If you can feel the difference of 2mm (.080") I would be surprised. With the steering stabilizer, the reduction in trail should amount to fuck-all. Post some pics when you are done.
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Old 01-07-2005, 07:30 AM   #3
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Quote:
Originally Posted by Jinx
It reduces trail and quickens the steering. If you can feel the difference of 2mm (.080") I would be surprised. With the steering stabilizer, the reduction in trail should amount to fuck-all. Post some pics when you are done.

Actaully increasing offset from 18mm to 20mm will slow steering and is intended to help prevent the bike from "puching" into corners, and to add stability in high speed/sandy stuff.

I would also be surprised if the offset was really all that noticeable outside of racing conditions...just a guess though
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Old 01-07-2005, 09:17 AM   #4
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I went from 20 to 18 on my 300 and could absolutely feel the difference. course, that was a 230# bike on single track. Much more 'flickable'

IMO going to 20 on the street makes a bit more sense - as does the stabilizer. I've gotten the wobbles before up around the century mark, I'm thinking either of these mods would have helped....

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Old 01-07-2005, 09:55 AM   #5
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Emig

Extra offset is KEY especially if you ever run 17" rims as I do. The asymmetric dampener is also amazingly good. This bike turns SO much better now.

JM
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Old 01-07-2005, 10:42 AM   #6
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Check the math again, mates. Increasing offset moves the front axle, and hence the contact patch, forward. Since rake and rolling radius of the front wheel are constants, you wind up with less trail, which results in quicker steering, and by definition less stabillity. But that is probably just enough to overcome the baseline drag of the steering damper.

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Old 01-07-2005, 02:48 PM   #7
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Triple Clamp offset

The offset is the difference between the center of forks to the center of steering head. More offset, more straight line stability. Less offset, quiker turning. Less offset actually moves forks back in triple clamps. Have personally changed 3 KTM EXC's to 18mm from stock 20mm. Makes a difference in tight stuff. Motocross SX guys even go to 16MM.
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Old 01-07-2005, 03:14 PM   #8
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Quote:
Originally Posted by Chipper
More offset, more straight line stability. Less offset, quiker turning.
Sigh, dirt bike guys.

(pssst, you have it backwards, mate)
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Old 01-07-2005, 03:47 PM   #9
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Quote:
Originally Posted by Jinx
It reduces trail and quickens the steering. If you can feel the difference of 2mm (.080") I would be surprised. With the steering stabilizer, the reduction in trail should amount to fuck-all. Post some pics when you are done.

It INCREASES RAKE and slows the steering so the bike doesn't KNIFE into corners and what not. Helps gobs in the sand.
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Old 01-07-2005, 04:42 PM   #10
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Quote:
Originally Posted by motozilla
It INCREASES RAKE and slows the steering so the bike doesn't KNIFE into corners and what not. Helps gobs in the sand.
Sigh, dirt bike guys.

Increasing offset actually reduces rake, if no other adjustments are made. As the offset increases, there is a vertical component as well as a horizontal one, that actually drops the steering head a little.

Look, there seems to be a lot of confusion about stability, response, and rider comfort. I even read some of the stuff on Emigs's site, and it was gibberish from a physics standpoint (but is probably based on very valid real world experience, and more about that later). So I guess owning a CNC machine does not mean that all the laws of physics are repealed.

Stability and response are mortal enemies. A drag bike or a Bonneville Liner are stable, but they are not responsive. A Trials bike is very responsive, but it sacrifices stability to achieve it. You would not want to thread a bike with a Top Fueler's geometry through an observed Trials course. You would not want to ride a trials bike at 200 MPH. So you can very easily have either too much stability, or too little, it all depends on the function of the bike.

And everything in between a Liner and a Trials bike is a compromise. Longer wheelbases increase stability and decrease response. A large polar moment of inertia increases response and decreases stability. Big tires increase stability and decrease response. And, as sure as BMW makes crappy final drives, increasing trail increases stability and decreases response. And adding offset does not increase trail, it reduces it.

So what are you feeling? Who are you going to believe, your own experience or that tosser Jinx? Well, to start with, I would appreciate it if you would stop calling me a tosser. Thank you. And secondly, there is no real disagreement. Because we are now at what matters most, what all these little measurents are supposed to produce, And that is rider comfort.

And by rider comfort, we are not talking about a better seat. We are talking about whether the stability/response trade-off matches your riding style. You can make a bike too stable, particularly an off road one. Excess trail will lead to a stronger corrective force every time the front wheel points anywhere but dead ahead. So is this bad? I t certainly can be.

Say you are riding a trail at a fair old clip. the surface is hardly smooth and level, therefore your front wheel will be constantly reacting to that surface and rarely pointing straight ahead. Now, with too much trail built into the geometry, every time one of those little irregularities pass under your front wheel, the corrective force will attempt to make the wheel turn back to center, And you will feel this a series of very annoying left/right jerks through the bars. Which reduces rider comfort as to how well the bike can be controlled. There is too much stability, not enough response, and the whole thing feels very mucked up and unpleasant.

Same thing with sand. Too much corrective action from the steering geometry will prevent the tire from following the surface naturally. It will try and maintain one arc regardless, which is felt as that dread "knifing" feeling.

An F22 is unbelievably responsive, but to attain that is it so dynamically unstable that it will literally break apart in the air if it were not for the flight computers constantly adding just enough stability to maintain controlled flight and structural integrity. And a good steering damper is our less-than-$30M answer to a flight computer. It adds enough stability, on demand, and otherwise allows a very high level of response.

So the correct term for increasing offset is: It makes the bike handle better. It feels better so you say it is more stable. But it is not, it is just better balanced now between stability and response to make you more comfortable. Which feels like stability, but isn't. Words matter, and so do all those little numbers. And you can look it up for yourself if you don't want to take some tosser's word for it, but increasing offset reduces trail and reduces stability. But it might well feel better that way.

So increased offset may be just what the doctor ordered to allow you to gas it up in confidence, and that is what the whole deal is really about. And this is probably where people like Emig (and others) are invaluable. They know what works. But I would die a happier man if they learned how to explain it correctly. Cheers.
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Old 01-07-2005, 04:48 PM   #11
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Daymn, here is the Jinx I know and love
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Old 01-07-2005, 04:52 PM   #12
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Jinx - It seems the confusion is over the definition of 'offset'. Whatever offset you are referring to, it seems that we all agree that if the change results in more trail, the bike will steer slower and be more stable in a strait line. While I am no geometry expert for dirtbikes, we move trail around quite a bit on our roadracers, and even small changes can make a big difference at speed. On our SS bikes we shorten trail by sliding the forks up in the T clamps, thereby steepening rake. Or we raise the back end for the same purpose. But back end changes can affect traction because of the swingarm angle. So we constantly are searching for the right balance at various tracks.

We have gone so far as to steepen it to the point where the front wants to tuck because under hard braking and fork compression, the fork angle gets too steep (reverse trail?). Then we've gone the other way (too much trail by sliding the forks all the way out and lowering the back) resulting in the bike running wide on the exit, preventing the rider from pulling the trigger until real late. Basically, the thing won't turn. Damn stable on the banking, though. More trail, more stable. Less trail, quicker steering and less stable.

The offset I was imagining on this thread was at the triple tree. Some machines allow for increasing trail by moving the front axle forward through an adjustable T clamp axis. More offset up there increases trail because you are lengthening the rake. -pantah
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Old 01-07-2005, 05:14 PM   #13
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Quote:
Originally Posted by Pantah
Jinx - It seems the confusion is over the definition of 'offset'. Whatever offset you are referring to, it seems that we all agree that if the change results in more trail, the bike will steer slower and be more stable in a strait line. While I am no geometry expert for dirtbikes, we move trail around quite a bit on our roadracers, and even small changes can make a big difference at speed. On our SS bikes we shorten trail by sliding the forks up in the T clamps, thereby steepening rake. Or we raise the back end for the same purpose. But back end changes can affect traction because of the swingarm angle. So we constantly are searching for the right balance at various tracks.

We have gone so far as to steepen it to the point where the front wants to tuck because under hard braking and fork compression, the fork angle gets too steep (reverse trail?). Then we've gone the other way (too much trail by sliding the forks all the way out and lowering the back) resulting in the bike running wide on the exit, preventing the rider from pulling the trigger until real late. Basically, the thing won't turn. Damn stable on the banking, though. More trail, more stable. Less trail, quicker steering and less stable...
Good stuff, mate.

And proving again why pavement is for racing, and dirt is for growing potatoes. Lord save me from these heathen dirt bikers and thier heresies.

I am referring to offset as defined in this sketch as d=offset

which is the distance measured normal from an axis drawn thru the steering head to a parallel line intersecting the front wheel axle. And you are quite correct that it does not matter if this number is generated via T-Clamp offset, or by offsetting the axle from the forks. The number is the number.

Quote:
Originally Posted by Pantah
The offset I was imagining on this thread was at the triple tree. Some machines allow for increasing trail by moving the front axle forward through an adjustable T clamp axis. More offset up there increases trail because you are lengthening the rake. -pantah
You had me until this bit. If you are talking of dropping the axle (vertical), and therefore increasing rake, with everything else being equal, trail will indeed increase. But if you are talking of moving the axle forward (horizontal), with everything else being equal, the the trail is decreased as the contact patch of the front tire has moved forward = less trail. But I may not be seeing the axle movement you describe correctly. But anything that moves the tires contact patch forward, while leaving the rest of the geometry pretty much as it was, decreases trail. And this is what increased offset does, regardless of at the T-Clamp or the fork legs.
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Jinx screwed with this post 01-07-2005 at 05:21 PM
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Old 01-07-2005, 05:41 PM   #14
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angle of the dangle

Jinx - With the offset I am referring to, the axle moves forward and the contact patch less so. Basically the T-clamp adjustment allows the tuner to extend the fork angle beyond the steering head angle. It gives more or less rake then the steering head dictates (a fine tuning adjustment). As I interpret it, adding offset kicks out the fork angle. The reason the active word is 'adding' is because modern bikes have increasingly steep head stocks. It seems the dirt guys always mean lengthening the rake back out when they want to change geometry.

But the truth is, you have sucked me into pontificating about something for which I am ill equipped. It was fun, but from now on, it's all in the angle of the dangle on my part, and I'll have another brew. -pantah
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Old 01-07-2005, 05:47 PM   #15
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Quote:
Originally Posted by Pantah
Jinx - With the offset I am referring to, the axle moves forward and the contact patch less so. Basically the T-clamp adjustment allows the tuner to extend the fork angle beyond the steering head angle. It gives more or less rake then the steering head dictates (a fine tuning adjustment). As I interpret it, adding offset kicks out the fork angle. The reason the active word is 'adding' is because modern bikes have increasingly steep head stocks. It seems the dirt guys always mean lengthening the rake back out when they want to change geometry.

But the truth is, you have sucked me into pontificating about something for which I am ill equipped. It was fun, but from now on, it's all in the angle of the dangle on my part, and I'll have another brew. -pantah
-pantah
Thanks, mate, that makes sense. And I think I will join you.
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