racer
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Posts posted by racer
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Mind you that I am not necessarily talking about a precise race jet for all seasons so to speak, but, even with mods, modern honda rr motors will operate well around the same needle and screw setting and minor jet changes for weather on the day.
Unless you have major weather system changes from morning to afternoon, the same jet should be ok for school riding all day. This assumes a broken in piston, etc.
If you plan to buy a 125 you should really cultivate some friends in that circle so you don't spend five years learning what could take five races to sort.
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Tell me what year you get, what modifications it has and what track you intend to ride and I'll tell you a jet/needle/airscrew combo that'll work all day every day (barring extreme weather conditions).
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As long as we can ride it.
Yup, not a problem.lol
cheeky git
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Here's a decent overveiw of forks: http://www.motorcyclecruiser.com/tech/fork...logy/index.html
Actually, while highlighting the difference between damper rod and cartridge fork dampers ok, that link wasn't really such a good operational "overview" of forks, in general. Upon further research, those illustrations leave a bit to be deisred IMO. For instance, it isn't clear in their damper rod model illustration that the top of the damping rod/resevoir (that acts as the bottom spring seat) remains stationary wrt the bottom tube while the upper tube slides past it. I found a better illustration here from the Gold Tech Emulator site:
http://www.sportrider.com/tech/146_9502_tech/photo_03.html
and this for the basic damper rod model:
http://www.sportrider.com/tech/146_9502_tech/photo_01.html
Much better with all the little arrows indicating oil flow, clear labels and better quality detailed drawings.
I've got a much better understanding of all of it now. Also thanks to your input harnois.
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*crickets chirping*
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Here's a decent overveiw of forks: http://www.motorcyclecruiser.com/tech/fork...logy/index.html
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Let's say we set the sag at 1.5 inches, then we ride down the road and hit a bump that causes the suspension to compress 1 inch from the sag point and then return to the sag point. Then we crank down on the preload so that we get only 1 inch of sag, then we go out and hit the same bump at the same speed. Once again, the suspension will compress 1 inch FROM THE SAG POINT. Same bump, same speed, same spring, same starting weight on the spring thus same amount of starting spring compression, it will react the same UNLESS we reach top out or bottom out. Preload is just going to make the whole 1 inch of suspension movement resulting from that bump happen at a different portion of the available travel, or in other words, the bike will sit higher or lower as it rolls over that bump. In the context of this scenario it's perhaps not even accurate to call it "stiffer" or "softer" as is commonly said. So far no one has given me any actual mechanical explanation as to how this description is incorrect.
"'it will react the same UNLESS we reach top out or bottom out. "
So, setting sag would seem to be mostly about staying between the top out and bottom out for the rear shock, in the middle of the range so to speak. And, setting greater sag for street riding gives more effective travel range before topping out ... at increased risk of bottoming out?
As for a mechanical explanation of saying the spring is harder or softer, I would say it is a descriptive expression based on the fact that the spring is compressed more under preload. The more compressed a spring is, the more force it will take to compress it further. It is that simple. Starting from top out, x amount of force will compress the spring to the same point no matter the preload, but, with more distance traveled. So, though, while in riding mode, we won't compress the spring any further due to pre-load or experience a "harder" ride, we will alter the potential/effective travel from top out (and geometry of course).
In the case of front end dive under braking, relevant to this thread, if we increase front preload to reduce sag by .5 inches then repeat the hard braking in exactly the same way, then for all practical purposes the front end will have .5 inches less dive. The front end will sit .5 inches higher during the braking and all other times except when bottom out or top out is reached. Changing out the spring could make a much bigger difference, and would allow me to have less brake dive without reducing sag, which is why like you said, it is a much better option - as long as we don't decrease the fork's mid-corner performance.So what defines or limits the bottom out in a standard fork?
Spring binding? Or will the airspace reach a critical compression that will prevent further compression before the spring bottoms out?
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So, what defines the travel of the forks?
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Sweet--you rock! Thank you for the materials. I'll be departing shortly... >: )
>8 }
Bring warm riding gear!
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I understand the shock in the pic is topped out and will never get any longer no matter what you do with the preload. Top out is top out, like you said, it will not change. But bottom out will not change due to a preload adjustment either, thus available travel has not changed. The definition of bottomed out is that the shock has hit that bump stop/bottom stop and can not compress any further. That WILL happen before the spring itself bottoms out, as long as you are in the intended preload adjustment range. Another way to look at it is that the amount of shock shaft (the polished chromy part that disappears into the shock body when the shock is compressed) showing when topped out represents the amount of travel of the shock. No matter what you do with the preload you'll see the same length of shiny shaft at the bottom of the shock when it's topped out.The (compressed) spring is what dictates the travel (even if you hit the bump stop/bottom stop on the shock before binding the spring).
If you hit the bump stop/bottom stop, didn't the bump stop/bottom stop just dictate the travel?
Ah... I see what you are saying now.
If the operational length or travel of the spring is longer than the travel of the shock assembly, the travel will be limited by the top and bottom stops on the shock assembly.
Got it.
Of course, we don't generally go around bottoming out or topping out the shock under normal riding (except under hard braking). And the more pre-load, the tighter the spring, the less travel for the same set of applied forces in actual practice.
If you are running with too much sag, like extra headroom for the suspension to float up, every upward rebound can push the suspension further. So, that is what I meant by 'potential for travel' (which is probably how they "rate" a shock), and then there is the actual amount of travel experienced while riding a given set of conditions and damping settings.
And this is what I was refering to when I said "at the expense of travel and geometry".
And now I get what you meant by moving the spring. You meant with more pre-load you will be running closer to top out. Hence, the shock assembly does not compress as far toward it's bottom out stop (assuming the spring is not pe-loaded very much).
Which brings me back around to stock springs vs racing springs which is where we started. While you may only be dialing 5-10 turns or threads for the proper spring, like I mentioned before, Johnny sportbike rider cranking a couple inches (or more if he adjusts for riding two up) on his stock spring is cranking that spring down WAY more.
And this is where I've been thinking. Of course, for your Penske, the pre-load factor was negligible ... which was my whole point and what I've been on about since page one.
Soo ... what about forks?
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Pre-load will effectively increase the spring rate (essentially at the expense of geometry and suspension travel).
The only way to change the spring rate is to change out the spring. Preload simply changes the amount of sag. This is true as long as you are working anywhere within the safe and relevant preload adjustment range. When you adjust preload you are just changing the position of the spring relative to the top-out and bottom-out points, which changes how much the suspension will sag under your weight and the bikes weight. It should be called a sag adjustment so people would stop being so confused about it.
Your understanding or explanation of what pre-load is or does seems flawed here.
When you adjust or increase pre-load you are compressing the spring and making it shorter by "loading" the spring prior (or pre-) to putting your butt on the bike. You are not "just changing the position of the spring relative to the top-out and bottom-out points".
The comment that "preload simply changes the amount of sag" is oversimplified. So now, in order to try and explain it, I'll write a bunch of nonsense that probably nobody cares about and only makes sense to me.
If we adjust the preload while the suspension/shock is topped out, then yes we are compressing the spring against the top out stop. But, we don't ride around with our suspension topped out all the time, most of the time it is compressed some amount. And perhaps the most important moment for suspension is in the middle of a turn to keep the tires on the ground at maximum lean angle, and in this moment both front and rear suspension are compressed.
So lets evaluate how a preload adjustment would affect the bike while the suspension is sagging or compressed and not topped out. Let's say we get on our bike and while sitting on causing the suspension to sag, a friend cranks down on the preload, the spring stays compressed under the weight of the rider and bike, the amount of weight on the spring is not changing, thus, the amount of compression of the spring itself is not changing. Thus, in this scenario, we are NOT actually compressing the spring, it is just staying compressed under the weight of bike and rider, and we are just moving it down the shock, or in other words moving it closer to the top out point and further away from the bottom out point.
No. It does not move the spring further from the bottom out point, the spring and suspension remain exactly the same wrt the bottom out point. The shock body moves closer to the top out point for the same spring compression and spring compression is the ONLY factor determining how close to the bottom out point the suspension is.
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I still think I disagree with your explanation, or perhaps terminology, of pre-load and suspension; but, until I have more time to sort through and get a better grip on what you are saying above, I will refrain from further comment at this time.
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OK...
If one is compressing the spring against the 'top out stop' when adjusting the pre-load (at static sag = 0), like you say, then one is effectively decreasing the distance the suspension can or will compress from that point (topped out) and the spring will only ever extend as far as that point where you have compressed it against the 'top out stop'. Pre-loaded, the spring is now partially compressed (at 'topped out') and has less distance to travel until it binds or 'bottoms out'. Neither it, nor the shock, will extend more as the shock is 'topped out' and the spring can only compress further from that point of partial compression known as 'pre-loaded'.
In fact, if you added more pre-load while riding in the middle of a corner under some compression, you would effectively shorten the travel even more as you brought the shock body up from the spring and closer to the 'top out stop' for that given compression (thereby also increasing ride height for that given compression). But, the travel decreases.
Please refer to the lovely enlarged photo of a Penske racing shock w/Hyperpro spring installed here:
http://en.wikipedia.org/wiki/Image:Penske_shock.jpg
(Anyone know the color code on that spring? lol)
The shock in the photo is topped out as the pressure of the spring is applying force to the collar. No matter how much you compress the spring, the shock will never extend any further than it is in the photo. Topped out is topped out. And pre-loaded is pre-loaded. The (compressed) spring is what dictates the travel (even if you hit the bump stop/bottom stop on the shock before binding the spring). Full stop.
Otherwise, my spring would flop around on the shock every time I did a stoppie or even lifted the rear wheel under hard braking. That is the whole point of the zero/negative pre-load as it allows the shock to lift off of the spring (assuming a spring shorter than the travel at top out).
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harnois,
My "confused about a great many things" remark was too much. My bad.
racer
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You are saying that adding preload reduces travel? I don't get how. "Travel" to me is a measure of how far the suspension can travel from top out to bottom out, fully extended no weight on it to fully compressed. I don't think this measurement changes when preload is added or removed, unless the preload is cranked down so far that the spring bottoms out on itself, but that'd require settings so grossly out-of-whack it isn't worth talking about. Or are you just saying that the suspension will move less in response to any given bump as a result of increased preload?
Well, there is potential for travel and then there is how much the suspension actually does travel under "normal" riding conditions. I was thinking the latter; but, the former is also true. And you seem to be confusing the two.
The motorcycle is suspended on springs. When you compress the springs, the potential range of motion is decreased. And the actual amount of travel the suspension experiences is also reduced.
Try this: Dial out all the pre-load on your stock suspension and go for a ride. Then crank it back up and go for another ride. That should help clarify things a bit.
Cheers.
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Pre-load will effectively increase the spring rate (essentially at the expense of geometry and suspension travel).
The only way to change the spring rate is to change out the spring. Preload simply changes the amount of sag. This is true as long as you are working anywhere within the safe and relevant preload adjustment range. When you adjust preload you are just changing the position of the spring relative to the top-out and bottom-out points, which changes how much the suspension will sag under your weight and the bikes weight. It should be called a sag adjustment so people would stop being so confused about it.
Your understanding or explanation of what pre-load is or does seems flawed here.
When you adjust or increase pre-load you are compressing the spring and making it shorter by "loading" the spring prior (or pre-) to putting your butt on the bike. You are not "just changing the position of the spring relative to the top-out and bottom-out points".
PS: I am surprised that you have left this post intact considering your apologies and, forgive me, how confused you seem to be (about a great many things....lol).
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You said that you were not sure you remembered what TD said correctly. And you said that you thought it would be interesting to have Max posting here. In any case, I made my suggestion as an alternative to continued speculation about what TD meant or why they said what they said and it was aimed at helping you resolve the questions that you are still posing in qualified or speculatively phrased interpretations of your memory of TD's words to your satisfaction. You've expressed your positive impressions of TD's CS Dept. and you have expressed a clear desire to communicate with Max. So, I just figured why not go ahead and do that? Seems logical. I didn't mean it to be any sort of characterization.
And, besides, maybe he will give you a free primer on motorcycle suspension technology and tuning.
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If ya know how much a spring is compressing under the weight of the rider and bike it makes sense they could deduce from experience roughly how well that spring will work out as far as absorbing bumps for that rider on that bike. When I talked to the dude at Traxxion (someone other than Max don't remember who) and gave him that 3mm of preload number and was asking all the "why" and "how" I was under the impression that it not only helped him deduce that the spring was too stiff, but also deduce roughly how much to change it. When they are helping people through the mail I guess all this math is all they have to go on.
Right. So they could refer to past experience to deduce a range or good starting point ... for you and your type of riding. That was my point.
As for "dragging Max into it", my point was that, for your benefit, you might want to address your questions to TD personally. As YOU have a pre-existing business relationship with TD, they probably would be inclined to discuss the matter directly with you. Customer service and sales and all. In any case, I was not suggesting that you ask Max to "join the fray" or "settle" anything here. And, I would imagine that since it is his profession, he probably wouldn't be interested in holding forth on an internet forum ... for free.
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Pre-load will effectively increase the spring rate (essentially at the expense of geometry and suspension travel).
Since either adding pre-load or switching to a stiffer spring would reduce fork dive when braking, I realize that, especially within the context of this thread, your comment makes perfect sense. Sorry for my negative comments about it before, and for being rude and full-of-myself. We all have our moments.
What do you mean by "at the expense of geometry and suspension travel?" "At the expense of" to me means it will have a negative impact. I understand it will change but do you mean to say that it will have a negative impact? Seems to me it could be negative or positive depending on what you are trying to do. Just wondering if there's something else for me to learn here.
Specifically, I meant "at the expense of" in the most direct sense that it reduces travel and 'alters' geometry. I suppose that might not always be a bad thing under all circumstances; but, I am of the opinion that the geometry as designed by the engineers probably has some value as a starting point ... from time to time ... (lol). And that, for me, the broadest range of adjustment yields greater ease with which to acheive accuracy or better resolution from which to "fine tune", as it were. For example, if your analog radio tuner/dial has a really small knob, it will be more difficult to adjust precisely than if it has a really big knob which makes fine adjustments easier. I don't know if that analogy really gets it, but ...
Anyway ... I believe the primary geometry issue is that, pre-loading the spring adds ride height. Logically, you might think that the overall height will simply sag to the same point relative to ground because you are merely pre-compressing the spring and the spring will only sag or compress as far as it would anyway with you on it. However, as you yourself pointed out before, there is more to the suspension than merely the spring. And I think it is precisely that combined with the fact that you are not on the bike when compressing the spring that is the critical factor.
Ordinarily, the spring compresses under your weight, the suspension moves and the bike sags. So, what happens if you compress the spring without you on the bike to make it sag and sort of "equal out" the suspension?
(Edited for clarity. Will re-post info in better terms later.)
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I am not a suspension expert or 'guru'. What I 'know' is mostly what others with more experience have imparted over the years combined with my own attempts to really understand the 'why' (as opposed to merely going by rote); and, then applying that in practical "real world" circumstances and conditions. So, while, at the end of the day, what I 'know' is generally based on empirical evidence and experience, by the same coin, I listen to the experts and I am always open to more data.
That said, I do not know a scientific reason, based on the physics of springs, that would dictate a flat 8 or 10 mm of pre-load across the board for all springs as "the right number" to set pre-load to acheive proper suspension characteristic, much less using minor differences in a relatively small range of pre-load at the bottom of the scale to ascertain the proper spring rate. Frankly, if your memory is correct, I am a little mystifiied as to why you were told that a spring was "clearly too hard" based on the fact that you were only using 3 mm of pre-load, except possibly that they were concerned that 3 mm of compression might not create enough pressure or stress to hold the spring well. (I believe 'stress' is a more proper term than 'tension' (tensile), ie stress and strain in the engineering usage. )
Logically, to my mind, the more of the spring that is available for action, the better. Perhaps there is a "sweet spot" or more consistent linear range of response in the characteristic of springs which makes the first 10% (or whatever) of compression significantly different than the middle 80% or so. Like, if the response curve was exponential for the first 10% and then subsequently linear for the rest of its compression until it approached binding, that might make some sense to my mind in that you would have more consistency in the middle, eg. it might be easier to tune damping for a broad range of loads and inputs with a more consistent or predictable effect. It should be a simple matter to find some graphs of spring characteristic response curves ... but, for our application and purposes, we then need to think about things like "speed" of stroke and specific impulse or big bumps vs undulations in road and how that might affect any "harmonics", ie. if you hit a bump while cresting or compressing in a dip, etc, etc ... and that is way beyond my expertise ... lol.
In any case, I still don't really see the logic of 3 mm vs 8 mm vs 12 mm or ease of tuning dampening as the way to determine the proper spring rate and I am not getting any intuitive hints from the back of my mind which, while hardly conclusive, leads me to consider the possiblity of more 'practical' reasons for TD's recommendation that may have been either mis-communicated or perhaps merely interpreted within the context of your understanding at that time. I just don't see a direct connection between 3 mm vs 8 mm and the best rate for your weight and riding style. That doesn't mean there isn't one, I just don't know what it might be. Perhaps it is simply a rule of thumb that TD have discovered through practice that what rate works best for them, or what rate their customers say works best for them, seems to fall at or around 8 mm of pre-load. But less than 1/4" seems like a really small difference. And, if 12 mm is OK, why not 4 mm? On the flipside, capturing the spring well seems like a practical issue (and is, in fact, one that those who originally described the 'absolute zero pre-load with room to spare' set up to me also were concerned with, hence, the qualifying codicile to my original remarks to the effect that "I don't know what modifications might be necessary...").
So, my speculating about your memory of a conversation with TD some years ago is hardly going to get us anywhere (lol). The bottom line is that, for clarification on the 'why' of their recommendation(s), I think contacting TD is probably the best course of action. Of course, there are other, less 'brand oriented' and far more experienced suspension experts than Traxxion Dynamics out there. I don't mean to take anything away from them; but, like your experience is a singular event of limited scope, perhaps a wider sampling of a broader, more general, data set would yield some additional insights...?
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Traxxion Dynamics...
Mad Max and I spent several years racing Nationals together before he quit racing to found Traxxion Dynamics. If I wanted a Penske shock, he'd be the man I'd call.
What was the stock YZF spring rated? And how much pre-load did you need to dial in to set the correct sag for the stock shock and spring? I'll bet 8mm is a lot less than the pre-load that was needed to set sag on that stock shock/spring ... like we have been discussing.
So ... it's a bit relative. If a stock machine needs say 40 mm of pre-load for a rider to acheive the correct sag ... 8 mm is practically nothing. Especially when compared to an overall spring length of 6" (175 mm) ... 8 mm ~ 4%.
But let's get to the heart of the matter...
Why do they recommend 8 mm (1/3") and NO MORE THAN 10 or 12 mm (less than 1/2") of pre-load?
Perhaps creating enough tension to capture the spring well without using up too much of the stroke or range? Like, ideally, zero pre-load might be optimum ... but, having the spring flopping around might not be a good idea?
In any case, my gut feeling is that your personal experience probably had a lot to do with what kind of riding you were doing. Why did TD install an 800 lb spring in the first place?
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Cool links and info on "top-out" springs.
From the last link:
"Note: Ohlins racing shocks features a "top-out" spring ... The top-out spring also effects the negative sag, making it difficult to adjust the sag with the shock on the bike."
Thanks for that.
Good luck sorting out your issues with the wiggling rear end.
Yup, not a problem.
Do You Guys Mind If I Bring A 125 2stroke Gp Machine?
in School Questions/General Discussion
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Sounds like you are on the right track. Good luck!