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hey zach - edit: some good racing info at the end

This is a discussion on hey zach - edit: some good racing info at the end within the Vintage Motorcycle Racing forums, part of the Caferacer.net Forums category; JohnnyB. Not to throw more mud into the murky waters of rear suspension, but we have these same discussions in dirttrack. One of the critical ...

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  1. #31
    FR
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    JohnnyB.
    Not to throw more mud into the murky waters of rear suspension, but we have these same discussions in dirttrack. One of the critical measurements/dimensions that changes under load is the swingarm angle.
    When you have the ability to lengthen the wheelbase, either because of a change in rear sprocket, or a longer swingarm, you can effectively reduce the "chain bite", the load on the suspension from the engine (presumably). All I know is that when your suspension is near full compression, and you're adding something close to max torque, you're going to load both the tire and suspension at a time when both may be at or near their limit, possibly causing the oscillation you refer to.

    Also, I found that grooving the shoes, and periodically renewing the chamfer on the leading edge of the shoe helps quite a bit with brake feel.

    FR


  2. #32
    Moderator joe c's Avatar
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    jb, ive had my lever to the bar several times, especially at summit. what i notice is after a certain point, there is now more. you grab that thing, it slows you, you grab a little more, slower again, then really squeeze, and hold on, youre going for a ride. and my bike really stops nicely too. ive thought about going to a hotter compound, but at a place like summit, or louden, youre not on the brakes that hard. and what ive also noticed is the tap em and preheat them helps, but its so damned hard to do while youre trying to fight someone off. i much more prefer the "see who'll reach first" scenario then the touch early and try to get em hot move. although, ive never been duped into running off the track going too fast since i started. (unless of course you call what i did in t3 with phinney after me at summit) but that doesnt count, cause i was trying to lose his ass.

    jc








  3. #33
    Moderator imslow's Avatar
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    jb, you brought up a subject that NOONE has talked about. I suspected it years ago, riding vintage. I really think that "snapping" the throttle open is good on modern bikes, but on things like 175s, the response is actaully smoother and faster if it is controlled, so the engine responds accordingly, smoothly, to fuel/air ratios on a curve that suits the engine dynamics.

    My first try at Penguin, I had been used to opening the throttle slowly. Then I asked the guys there, how do YOU do it. They all said crack it open. But I was on one of the rented EX500s. and then I started racing. Now if you are on a RD 350, I think you wanna go wide open. But on the 175 (oops--are we up to 210 yet?) it likes a slow gradual opening ( take that not literally s l o w, but you know if its gettin gas/air and things are moving, then all is good. But if you snap it open and you go nowhere, what's the use?).

    Zach, whaddya think? You snap open the 350 duc? Or roll it on?

    Evil



    Edited by - imslow on Feb 04 2005 8:29:06 PM

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  5. #34
    Moderator jbranson's Avatar
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    I guess a lot depends on the traction available on a modern bike as to how fast you can get away with opening the throttle. In general I wouldn't think whacking it open is a good idea on anything with more than about 50hp. I know from expeirence that snapping open the throttle on an RD350 is NOT a good idea.

    But on our 175's it's a different deal...it's like you say..not a hp deal, it's a compromise with the characteristics of the engine which just tends to fall on it's face if it's whipped open too fast. We run large carbs to facilitate running very high rpms...so we are basically over carbed at lower rpms...which leads to falling on it's face when you dump both 24mm carbs wide open on a 200cc engine at 7,000 rpm.

    It's really very relative...what is a fast opening of the throttle on one bike might be slower than necessary on another. I know on my RC, or any liter class sport bike...if you come out of three, or 12 in second gear and decide you want to snap the throttle open you'll very rapidly find yourself on the ground or climbing up the tank to keep the front end down.

    The EX500 is like an electic motor and it's got a real soft hit, you could get away with a lot of stuff on that bike that you couldn't even get away with on a hot vintage bike.

    I'd be willing to bet that Zack will say that even on his RS125 that coming out of three and 12 he has to give the bike a second to hook up before he goes WOT.

    Our 175's work in a different realm...we feather the throttle to get it up on the pipe smoothly....big hp bikes feather the throttle to prevent wheelspin and inconvenient wheelies.

    FR.
    You comments about swingarm length are right on the money...but on our 175's the hp is just not there to have an appreciable effect on rear suspension geometry. I like about 1.5" of down angle on the SA but it's much more for chain tension and ground clearance issues....I wish I had the hp to worry about torque effects on the rear suspension . Of course...if one was right on the limit...like you suggest...even our tiny 20hp could produce bad behaviour.

    JohnnyB


  6. #35
    paced_haste's Avatar
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    damn, this thread rocks...i want to respond real bad but i'm going to a bike show, so i assume you guys understand. i've got some good stuff to say...after.

    Z


  7. #36
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    k i'm back...whadda we got? WOT, yea, wicked.
    my personal preference in turn 12 is to have the throttle wide open before i even hit the left apex. this definitely depends on the bike, and it's just coincidence that both bikes i race i can do this. the only reason i get away with it on the 125 is that on a fast lap i try to roll through there in 2nd gear. power hits at 9-9,500 so trying to get the powerband in 2nd means rolling on the throttle in the right half, and then by the time i'm turning left have it turned all the way. if you watch the video you can see, the motor is at maybe 8, and then as the bike leans onto the smaller diameter side of the tire, revs come up just enough to push me out of the corner.
    the duc is similar, but since potential traction is lower it makes the process less nerve-racking. so i do the same thing with the vintage bike, roll on through the right, and have it wide open by the time i'm turning left, and the bike's not really fast enough to push out to the wall. it's a pretty long corner if you think about it, and there's a lot of room.
    johnnyB - you're right on about throttle delivery on vintage bikes. in addition to what you said, i think anyone who snaps the throttle open might find that they could open the throttle sooner if they use a gentler 'roll-on' technique. not to mention taking up slack in the drivetrain and allowing the bike's suspension to work properly, hence giving a smoother ride over bumps and allowing...what? that's right, more corner speed which means opening the throttle even sooner. ahhh, and the circle is complete. thank me later...

    Z


  8. #37
    Moderator jbranson's Avatar
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    For us small bike riders it's all easier...we are trying to operate the throttle to get hp sooner out of our engines....rather than trying to control an excess of hp.

    Now that you mention it, turn 12 is just the way you describe...typically I'm acclerating already out of the right turn, towards the left....I just notice the hit as I come out of 12 and the rpms climb quickly. Our 175's don't make a bunch of power...but for Aaron and I at least...we are making about 14hp at 8,000 rpm and then 22-23 hp at 11,000 rpm. Not a big hp jump...but a HUGE percentage power jump. And in second gear they spin up from 8 to 11k in about 3 seconds.
    It's easy to confuse WHEN you open the throttle with when the power actually hits...I tend to remember and calculate where I open the throttle on where the power actually comes in. Meaning I open the thottle "here" but it feels like I opened it "there" (which is 30 feet father down the track)...make sense? So you have to plan ahead...keeping your powerband and rpm in the back of your mind.
    JohnnyB

    PS. Not to beat a dead horse...but at Frontier Land in the 250 race where I kept passing Roper in the very tight downhill left, he asked me where I was getting on the gas...before the little transition bump or after. I was getting on it before the bump...cause I knew it would take a second or two for my little twin to come on strong....his 250 single has way more torque...he was having to wait until AFTER the transition bump to get on the throttle to keep from upsetting his bike...that tiny 2 second area where I could start winding up my engine and he couldn't was enough to get me ahead of him for the next 500 feet, then his hp would take over and he could motor by. A prime example of exploiting the capabilities of your particular bike/engine compared to another. For a couple of seconds I had hp I could USE, while he had to hold off a bit. Of course he was having to hold off because his rear tire was old and going off on him, but a race is a race...doesn't really matter WHY the other guy does what he does..you just take advantage of what you and your bike CAN do at the moment.
    JohnnyB



    Edited by - jbranson on Feb 06 2005 5:16:58 PM

  9. #38
    bfd
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    Thanks guys, this is very helpful
    bfd


  10. #39
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    i know it's not a big thing in vintage racing, but a lot can be done with movement on the bike too. especially with this whole corner exit thing. you can lean off and pick the bike up more to stay on powerband, or lean off the other way to keep the bike on the smaller diameter of the tire to get on powerband. this is all greg nichols stuff, i don't want to take credit for it.

    i forgot to talk about braking before. FR is right about shoes. pete takes the sharp edge off the leading edge of the shoes to reduce the initial bite. it seems to help. i've said this before but i think what people don't realize about initial bite is what it means for the end of your braking. the lack of modulation initially turns into lack of modulation as you release the lever too, which is tough for trail braking. when i was trying to keep up with Dave on that G50 i could feel the front tire smear into turn 3 at the very end of braking. and as i released the lever all the way it would hook up. difficult to control, i credit tire technology.
    as for lever pressure johnnyB, i think pulling harder means you stop harder, even if it's hard to tell. i think the only time you should have mercy on the front brake cables is if the track is wet or the rear tire is up in the air. and i don't think you should worry about locking up the front, except initially. i think that is when you're most likely to do it, before the front tire is loaded up. once it has dug in, i think it's unlikely that it will lock. i've never had it happen anyway, but i don't have that much experience. also, sometimes i cook the front brake on the warm-up lap a little bit, just so i know what to expect in turn 1. i HAVE locked up the front in the first turn, and it was far more suspense than i was interested in with that many bikes right behind me. how well are your brakes vented? do you think they cool well enough?

    Z


  11. #40
    Moderator imslow's Avatar
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    best forum info yet.


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