The new 16" front wheel

<div class='quotetop'>QUOTE (skidmark @ Mar 26 2007, 01:42 PM) <{POST_SNAPBACK}><div class='quotemain'>Now you talking Getting the right air gap can take a while and a certain amount of trial and error. What brand of fork are you using? What weight of fork oil are you using? What bike are you on? There are a few suspension 'gurus' that aren't gurus at all, or, what they say works will definitely not inspire confidence in every rider at every level, but they'll still take your hard earned cash.

This guy take money from those that can pay and give free advice too those who can't. A really nice guy who does nothing but suspension. I had a long chat with him only days ago as I had a outer leg with a small dent in making the inner leg stick a little. He checked it for free. Being able to make a living out of such a narrow niche in Norway is remarkable by it self. Having a huge workshop with several emplyees is a sure sign of success and competence. I guess that half of the serious racers in Norway have an Esp1Tech sticker on their forks.

Any way, after my experiments on the track I left the forks to him to service them and short of rebuilding them they worked great. I'm not racing anymore but at that time I used a standard Aprilia RS250. I think they use Shova forks but not sure. I think I used 10W at the time, but not sure. After service he had put 5W in them as they should have.
In fact they were very good after service (or bad before). I first were very satisfied when testing in a bumpy high speed corner where head shake is very common. The front where planted and worked perfect. Only after that first session I noticed that I had forgotten to fasten the steering damper

Btw. no need for any sarcastic comments of my abilities as a mechanic. I know they stink. Not that I get that much real wrong, I just keep forgetting minor details as thightening wheel nuts, fork clamp bolts (actually only 3 days ago) and similar when I put things together again

<div class='quotetop'>QUOTE (crvlvr @ Mar 26 2007, 11:09 PM) <{POST_SNAPBACK}><div class='quotemain'>I agree with Babelfish's analysis. Actually, when the bike is leaned over 60 degrees, a fork must move 2cm along its axis for an effective vertical wheel movement of 1cm. this is a simple trignometric calculation -- Sin 30. See here for more info http://www.ac.wwu.edu/~vawter/PhysicsNet/T...ningOfSine.html

Yeah, I was affraid I was wrong there because I didn't look up the trignomety. So it's not 1.66 but 2 as you said.

<div class='quotetop'>QUOTE (skidmark @ Mar 26 2007, 12:57 PM) <{POST_SNAPBACK}><div class='quotemain'>That’s not entirely correct. The fork does the same thing at 60 degress as it does at 20 degress or any degrees, it’s properties cannot be changed. The fork can only travel on one axis, the only thing that ever changes is the forces acting upon it.
But the angle of that axis is changing with lean angle and that's why the properties change when your viewpoint is the horisontal ground.
<div class='quotetop'>QUOTE <div class='quotemain'>The lesser of these forces being the vertical. The force exerted on the damping in a fork/shock to control the stored energy in the shock/fork spring(s) mid turn on a racing bike is far greater than any force on the vertical axis which is always 1g.
No it isn't. in bumps it change all the time and that's a key factor in what I describe.
<div class='quotetop'>QUOTE <div class='quotemain'>So the first rule is…. but the most important parameter is… These two points sort of go against each other, two different adjustments, different properties. Help me out there.Do you mean when the bike is static?
Same thing. Both descibe the bottoming out. typically tested at the hardest braking point of the track, with or without bumps. That's where they dial in spring rate and turn dampening to just avoid bottoming out.
<div class='quotetop'>QUOTE <div class='quotemain'>Fish I gotta call you on this. Where are you getting your info? You’re assuming a lot of simple physiscs ( action and reaction ) applies which is true up to a certain point. But there’s much more to it than that. You’re not taking the damping in the fork and the amount of energy that can absorb into account at all, and that‘s a pretty damn important factor, how do you account for that? A fork must move 1.66cm?
The description are full of flaws. For example when the bike try to soak up a 1cm bump it doesn't soak it up completly, and the sharper lean angle the less it soaks up, simply because as you said, the properties of the fork are the same while how the suspension and bike "feel" the bump change with lean angle. But it doesn't influence much on my initial statment. The suspension has a much harder job to do when leaned over and works less efficient. As mentioned, it won't soak up as much and that means more movement of sprung mass, more forces, things you don't want when on the edge.
<div class='quotetop'>QUOTE <div class='quotemain'>Totally negligible compared with the factors we're talking about and worth 0.000001s a lap. Slippery forks and trick suspension materials are about about consistancy and predictability of performance as components heat up. Ever feel the shock on a race bike just after the bike's come in, it get's hot.
And one of the reasons for that heat is friction in the bushings that slides between the outer and inner leg. The other part are hydraulic friction.
I'm still unsure of how much influence it has, but with higher corner speed it increase and at a dramatic rate, so I wouldn't rule it out.
<div class='quotetop'>QUOTE <div class='quotemain'>Dude, in my view, there are some serious flaws in your points and I mean that with no offence or patronising intended. You said you were involved in roadracing, well talk to me brother! I love debating tech stuff, much as I might bore some people to death around here and I'm not always right. Just I gotta pull you on some stuff cos I don't get it.

Let's bore them to death

<div class='quotetop'>QUOTE (skidmark @ Mar 30 2007, 11:34 AM) <{POST_SNAPBACK}><div class='quotemain'>Listen you two, for christ sake, would you actually put your protractor sets away
How many GP tracks have got 1cm bumps mid turn, even if they have what you're saying doesn't hold true. Here's the news, you can't build a tyre that is flexible and durable in a racing situation. I was trying to spark a debate but I guess you just got to understand something, that obviously you both don't. I can't stress this enough, you do not want a tyre to flex in it's sidewall at full lean angle. Disregarding the heat/energy produced and the subsequent negative effect on tyre life, the principle factor is feel for the rider. A tyre sidewall moving around is not mechanical, therefore it cannot have any controllable damping and is completely unadjustable therefore unpredictable, in other words the feeling from a tyre like that will be vague, just like some of the responses to a few points in this topic. The only thing that helps the bike track bumps at full lean is the bloody suspension.

Hey, cool down a little will you. Look at the picture an tell me that the rear side wall don't flex. And this is by no means extreme. I've seen pics where there literaly are a few mm from rim and ground. And bad or not that is caused by flex, lots of flex.
What do you mean that tire wall moveing around is not mechanical? It's not adjustable for the spesific tire but that is not the same as upredictable. Rubber and air is a common suspension solution in many applications. Heavy transport often use air. Bicycles use elastomer rubber and air, or only eleastomer in some front forks. Change the elastomer and you have different properties for both spring and dampening properties.
It's been said that the new tire give a larger contact patch. I can't see that happeneing without extreme change of profile or simply because the tire flex more it will create a larger patch.

<div class='quotetop'>QUOTE (crvlvr @ Mar 30 2007, 09:29 PM) <{POST_SNAPBACK}><div class='quotemain'>Based on your analysis it woud be best if the racers rode on solid rubber tires, or better yet, rubber coated metal wheels? Now, they would have no sidewall flex.

Right. That is of cource the reason we use 28-21psi in race tires as oposed to 35-45 in street tires; to avoid flex. Allthough it could be argued that sidewall flex is something different, it is still the softest part of the tire. Flex in sidewall is in fact even what what make even us amatures keping the rubberside down. When we wear the tire all the way to the edge the side wall flex make sure we have a full contact patch available.

<div class='quotetop'>QUOTE (skidmark @ Apr 3 2007, 05:10 PM) <{POST_SNAPBACK}><div class='quotemain'>I’m back so ok you asked for it. We’ve got to put a finer point on a few things, we’re all crossed up here.
Added ‘suspension’ in a front tyre, and an implicit statement the suspension is ineffective at max lean angle. ( I’m going to take it you mean the front fork when you refer to suspension ). I still disagree with both, but anyway.
Correct, I ment the front fork.
<div class='quotetop'>QUOTE <div class='quotemain'>Then…
Here’s where you’re confusing me. As far as I was concerned, suspension is there for that very purpose, to help man and machine go around corners as quickly as possible. You stated that specifically in the middle of a turn, the suspension was ineffective. In other words not effective. How can that possibly be true, I’m still waiting for a more detailed explaination of that one?

See attached pic. This show how much more the fork must travel to totally soak up the same bump. That is the ideal situation where it soak it all up. but of corce it doesn't. In fact, if we for the illustartion leve the stiction out of it, it would travel about as long as it would do straight up. The rest (at 60 deg. the other half of it) are tranferred to the rest of the bike or soaked up by the tire or soaked up by fork bending.
That's the first part, travel or movement. The other is forces. You can replace the meaning of those arows, or vectors as they actually are, from movement to forces. Forces have the exact same problem, and that's why I guess the actual movement of the fork will be the same as straight up. That tell us that at a given vertical force we need twice the force along the forks axis to compress the fork as much as the same bump would do with the bike straight up.

<div class='quotetop'>QUOTE <div class='quotemain'>I got confused again because I’m still thinking the corners are the important part of the racetrack and wondering how can it be the suspension doesn’t work too well in the corners and imagining what this bike must handle like, only to be told that the suspension doesn’t work by far as good in a corner as it does when the bike is straight ( by that I think you mean upright on a straight ). How good (or bad ) your chassis set-up is at any given track will not show up on the straights, it’s irrelevant on a straight but it’ll sure as hell show up in the turns so tell me how it can be working ‘good’ when the bike is straight?

I see your confusion, but unfortunatly it's the way it is. Quite right, the GP guys don't need that $50 000 suspesnision for straight up riding, they need it for the turns, but as long as suspension today are less effective in corners by design, lets's just say it's overkill for straight up riding. Allthough this is a simplifiacation. There are often bumps at the entry or exit of corners. The bikes woulf be spitted out of the track even when straight up with 220hp and no suspension.
Into the corner it's mainly a front job, out it's mainly a rear job.
At this point let me cearify what I mean by less effective by design. It's not only by dseign, it's by the nature of a bike using lean angle to fight the forces in corners. It's pure physics that tell us that suspension working in the bikes axis, regardless of lean angle have a harder job or being less effective with the lean angle. A more effective suspension would have som kind of links to let the tire and main suspension unit always be vertical. Probably with a secondary system dealing with the horisobtal forces. Right now no one has found a solution that can do this without adding to much weight, costs and all sorts of other difficulties.

<div class='quotetop'>QUOTE <div class='quotemain'>Let’s get this one sorted, you say it’s ineffective, doesn’t work well and all the rest. Suspension is engineered with one thing top of the list, corners. Not straights, not when the bike is straight. Corners. That’s what gets me is when you seem to change your mind mid flow and then start talking protractors and angles. 62 degrees, 63 degrees, 59 degrees or whatever. It makes no difference, it’s at that point the suspension must be perfect, period.

And non the less, this is when the suspension is at it's worst. Just explains why they need a guy or to for each bike from Ohlins for something simple as springs and oil.

<div class='quotetop'>QUOTE <div class='quotemain'>Sidewall flex different from what exactly?
Eh lack of words. The rolling surface, can I call it that?
<div class='quotetop'>QUOTE <div class='quotemain'>You’ve got me confused again. We’ve been talking front end all along and about ‘flexing tyres‘, then you throw up a shot of a rear tyre squatting under acceleration. How does that relate to your points on corner entry and a front tyre acting as suspension?
I show that tires flex, something you said in you rprevious post are not wanted. I say it's wanted and designed so. Rear tire load at the exit of turns and front at entries. They do much of the same job that's why it's comparable. They both must handle maximum acceleration forces (braking as negative acceleration) at lean angle. It was the first photo of flex I could find. Please believe me when I say I've seen similar on front tires, to a degree that ther are, lets say, 10mm from the rim to the ground. It looks like there are practically no sidewall left at all, the rim, the rolling surface, the ground. I've been studying and discussing over a picture of a repsol honda with 17" front. It looked much worse than the picture i attached.
<div class='quotetop'>QUOTE <div class='quotemain'>Is that bike at maximum lean? How ineffective is the suspension in that photo? Throw me a freakin' brick here!
No, in fact it’s the complete opposite of that. That’s what spring rate/air gap does.
So at least we agree that spring rate are dialed in there.
<div class='quotetop'>QUOTE <div class='quotemain'>I mentioned before about guys in the seventies playing around with two or three different springs in the fork, the heaviest of those only being used for the last 10-15mm of the fork stroke to allow an extra amount of travel to soak up any bumps under extreme braking. A rising rate fork spring is basically three springs engineered into one and it’s what stops bottoming out.
As far as I know rising rate springs and rising rate links are now history in racing, isn't it?
<div class='quotetop'>QUOTE <div class='quotemain'>The damping is critical for what happens as you move out of a situation of maximum breaking and get into the turn. Spring rate or spring preload combined with whatever air gap you want to run will control suspension travel under breaking. If you’re trying to control that by dialling in more and more damping you’re going to get in big trouble when you hit one of your 1cm bumps mid turn because then your suspension will definitely be ineffective. Or is that where you've been going wrong?
Think not. Dampening does play an important role when braking.
But if the adjustment of dampening for all other purposes put limits on the adjustment that are more important then you don't adjust the dampening based on braking and certainly never for braking alone, that's not what I ment.
Besides I guess this is where high and low speed dampenig might come into play. This is realy a side-track. We agree on the main thing, that the spring rate are adjusted for maximum braking and that braking hard and good are impossible without good dampening.

<div class='quotetop'>QUOTE <div class='quotemain'>So before you go telling me to calm down and take it easy can you help straighten these few things out?

Skid said:
"I can't stress this enough, you do not want a tyre to flex in it's sidewall at full lean angle. "
Michelin says:
"Usually, qualifying tires use a softer carcass because <u>our aim is always to create the biggest contact patch possible</u>, <u>and you’ll get a bigger footprint if the carcass flexes more</u>."

To me it's quite clear that michelin want as much flex as possible. That is limited by durability for race tires, but they still get as much flex as possible. Another point: Higher sidewall give the possibility to flex more because:
- You have more cooling surface
- To achive the same total flex each square cm flex less, or more total flex for the same flex pr square cm.

<div class='quotetop'>QUOTE (skidmark @ Apr 4 2007, 07:25 PM) <{POST_SNAPBACK}><div class='quotemain'>Before you guys all gang up on me...It wasn't flex in itself, it was the idea of a flexing sidewall as a more important factor in suspension that the fork itself and it's tunability that I was arguing against. I did make that clear and restated my questions several times, there for all to see.
No wonder you get frustrated as no one has claimed that sidewall flex is more important than the fork itself, but if it take away chatter and add feel and contact patch size I'm all for it.
Besides, as lean angle increase the fork problem increase. The same vertical forces influence the bike in bumps while the fork have more and more trouble handeling them and step by step other components and the bending flex in the fork play a larger role.
<div class='quotetop'>QUOTE <div class='quotemain'>After this point in the thread we were arguing two different points despite my attempts to reslove exactly what it was we were discussing hence my apparent frustration.
When I threw that in it was not to come with a controversial statement, but rather the obvious, just remind you all about (what I thought was) the obvious. Right now I find that point rather fruitless to discuss, but at the same time, if you don't agree, then of course you don't agree in the need for tire flex, fork flex, frame flex the whole dammed complicated thing we call chassis. It all flexes and all those parts influence on the behavior of the bike.