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quote:
That sounds like Gary Jedniak (sp). Super nice guy...but not very fast.
JohnnyB

i second that, super nice guy. sounds like him too, 350 harley. my dad rode that bike, says it's kind of a handful. it looked like it had kind of a long wheelbase, is that an aermacchi thing?

Z
 

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Discussion Starter #22
ok, next question. if the harley seems to have a long wheel base, and it not be good, why would you want to put an extended swing arm on things?? for example, people say to use an sl swingarm on the cb becasue its an inch longer. jb m,ade a longer swingarm for his 175, right?? or is that to adjust for the front end geometry?? seems to me, if the front is undesirable, a longer swing arm wont help it. also seems like you want the most compact package you can get without letting it get handling poorly. anyone?? bueller?

jc
 

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zach,

it wasn't a track day. it was a racing school that they held on a uscra race day at loudon. we were done after lunch.

i think you would really enjoy riding/racing a properly prepared 350 aermacchi. frank giannini has two of them, both 350 cc, but i don't know if he has them back together. lots of midrange, and some say it handles much better than a ducati. maybe if you see him you could get a ride.

o.k., back to my spanish lessons.

caio,

tex
 

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i like joe's question. most of these bikes that we race were street bikes at one point (or still are). and street bikes tend to be heavy in the rear, so doesn't a longer swingarm put more weight on the front end? lord knows it's not to prevent wheelies under acceleration. but you probably sacrifice a little bit of agility doing that. i don't know the answers to any of these questions but i like my guesses.
and tex - i've got a ride on a nice 350 that handles just fine. but tell giannini to get his bikes together and we'll race. y'know, just for a laugh.

Z
 

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Longer swingarms are done for various reasons...on a superbike it makes the rear suspension behave much better on hard accleration out of corners. On bikes that are light in the front it transfers more weight to the front. On bikes that are short wheel base and squirrely it makes them more stable in the sweepers.

I want a longer swingarm on my 175 to get more weight in the front...cause of my size and because they are ass heavy to begin with. It won't hurt to increase the wheelbase a tad to make it behave a little better under power out of corners either.

JohnnyB
 

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think it would work to pitch the bike forward too johnnyB? raise rear ride height and slide the forks up in the triple clamps a little? i'm not even sure if you can do that on vintage bike, but that might help too.
the swingarm thing - the superbike effect of instablity under acceleration is probably present for us too, we just don't notice it because it's so mild. so lengthening the swingarm will probably help with that too, though it might not be noticable.

Z
 

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Raising rear ride height/dropping the forks is common on late model bikes to quicken the steering. On vintage bikes it's typically just dropping the forks (cause rear shocks are a fixed length)...problem is if you just drop the forks you can start to have ground clearance problems. I had to fabricate some taller rear shock mounts on Mary's bike to get the back up some....would have been better to just get shocks the right length I guess.

I'm hoping a longer swingarm calms my bike down out of the corners...like you say, not very noticable on vintage bikes...but combine steep lean angles with skinny tires and a short wheel base and even vintage bikes can dance around a bit under power out of corners...I know mine does. Probably an issue of excessive weight on the rear than actual hp. I guess pretty much regardless of bike and hp, if you are pushing your traction limit and then add the component of hp to the mix you can make anything break loose.

Last year coming out of the hair pin at the bottom of the hill at Frontier Land, every single lap the back end of the bike would slip a couple inches, grab, slip a couple inches, grab..about four times in about a second and a half, then it would settle down. It wasn't scary just because of the way the track is there I didn't have any worries about losing it...but it was unnerving and made me think about backing it off a hair there. Which is not something you want your bike telling you if you can do something to fix it.
JohnnyB



Edited by - jbranson on Feb 04 2005 12:21:44 PM
 

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yea i found the place with the least traction at frontierland was the dirt on the outside of the corner. doesn't take much HP to spool it up out there...it's weird.
i agree with your ideas about rear traction too. i definitely think that most of the rear traction issues come from too much weight back there. we get rear chatter every now and then with pete's bike. that's what he shoots for, if both ends of the bike break loose, then he figures it's pretty much at the end of potential traction. it sucks though, because it so depends on how the corner is built. downhill always equals front chatter, uphill equals rear chatter. the flat ones are the only times that i can feel like i'm getting the most out of the bike. ever get loss of rear traction out of the last turn at NHIS?

Z
 

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I think the pavement at Frontier has a lot to do with that. Check the difference between there and the main track. Frontier has much larger agregate (rocks)...the rocks polish up nice with use. Get a little sand on them and it's like sand on a concrete floor, pretty slippery. The main track has very small rocks and lots of rubber....course to you the "outside of the corner" sometimes means off the track so yeah...traction would be limited out there.

I don't think our little bikes get much chatter because A: the wheels and tires are quite light..B: they don't go that fast. From what I understand chatter is the inability of the suspension to react fast enough to the surface of the track. Less unsprung weight helps...but a faster bike is hitting all the little bumps faster...which raises the frequency that the suspension must be able to respond to. So coming down the hill in the back of the main track, if you are carrying an additional 5-10mph of speed, plus have more unsprung weight I can see it causing chatter that I'd never see on my bike.

I've broken the back loose out of 12 once on my bike going inside someone on a larger bike and getting on the gas real hard in a lower gear to try to get the jump on them down the straight. I also had it happen a couple of times on Marhan's RD350 during an edurance race in the wet. It usually doesn't bother me much in small doses. Even on small bikes throttle control is really important. Riding a high hp, late model sport bike even on the street helps....you just don't go whooping the throttle wide open if you want to stay upright.

It's amazing watching a race how many people come out of a corner and snap the throttle open like they are going to tear it off the bars, it looks almost comical, like they are trying to kill something. You can get away with it on vintage bikes most of the time. But when you get close to limit of traction it sure doesn't help things. Also most of these little engines don't respond well to that kind of throttle hand...they don't have acclerator pumps, and have narrow powerbands..a person would probably actually go a bit faster rolling the throttle on smoothly. It's all relative I guess...by rolling on smoothly I mean taking one second to roll it on rather than snaping it open as fast as you can. Probably the more hp the longer the "roll" would be.

Braking is what bothers me the most, and where I could use some pointers....I'm just not sure how hard to pull that lever. I'm used to bikes with giant twin disks up front where it's pretty obvious when you are reaching the limit of the brakes. With drums I always wonder if I should just pull that lever as hard as I can to see what happens. And over bumps if you get a drum air borne for a fraction of a second it can lock up and stay that way when it touches back down, disks seem much more forgiving in that respect. Disks feel very linear to me, drums have that initial grab...then an exponential increase in power...then....nothing more it seems no matter how hard you pull the lever. But I guess different compounds work different ways.
JohnnyB
 

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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
 

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Discussion Starter #32
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
 

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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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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
 

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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
 

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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
 

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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
 

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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
 
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