Motorcycle Geometry ? - Chicagoland Sportbikes
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post #1 of 27 (permalink) Old 03-24-2004, 02:05 PM
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Motorcycle Geometry ?

This is about my SV I'm setting up for the track.

Front end Geometry ?


The SVS comes stock with a 120/60/17 front tire.

Every SV I've seen out at the track is running a 120/70/17 front tire. Which is a taller tire.

Wouldn't this make the bike turn in with more effort? Making handling worse because the front end is higher.

I'm thinking about moving my forks up in the trees ever so slightly to see how handling is effected with the 120/70 I'm running.

Anyone ever mess with this?

Comments/Suggestions?
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post #2 of 27 (permalink) Old 03-24-2004, 02:58 PM
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At the risk of reviving last season's agonizing tire-profile thread (complete with MS Paint visuals!). I "think" the taller, more pointed tires are being used to provide a larger contact patch when cornering. This benefit outweighs any added front-end height. I could be WAY off here. But that's my suspicion.

Then again, they could just be cheaper/easier to get. What the hell do I know?

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post #3 of 27 (permalink) Old 03-24-2004, 03:07 PM
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Then again, they could just be cheaper/easier to get. What the hell do I know? [/B][/QUOTE]

I called 4&6 and he said most people use the 120/70 because the tire is more readily available.

Makes sense. Most modern new sportbikes are running that tire size.

When I asked him about moving the forks up in the trees to compensate for the taller tire he kind of shyed away from the question. He said something about liablity and he'd have to see the bike.

But he did say that moving the forks up in the trees will make the bike lean in or turn in easier. I'm going to try a ever so slight raising of the fork tubes to see how it feals.

Thanks for the reply underdog, I'm bored at work, I need to keep my mind occupied, all I think of is the bike in the garage.

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post #4 of 27 (permalink) Old 03-24-2004, 03:14 PM
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I know that feeling (on both counts). If you want to know about moving the forks around, talk to Sticky. The clip-ons on his race bike are barely above the brake rotors...and his forks stick up like goal posts! I haven't seen it yet, but I think he props his head up in there after a few laps to conserve energy!

(then again, he could lap me repeatedly on a Fizzer 400...so maybe he's on to something?)

Good luck with all your adjustments. Try stuff, then try other stuff. Rinse and repeat until you're faster than I am!

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post #5 of 27 (permalink) Old 03-24-2004, 03:17 PM
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No, this is an excellent question. There are differences in tire height between different sizes and even between tires of the same size from different manufacturers.

You're right that you need to adjust the tubes in the triples to compensate for different tire height to have the same geometry you had with a different tire. Don't forget the rear tire changes between manufacturers as well.

Last edited by Jack; 03-24-2004 at 03:20 PM.
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post #6 of 27 (permalink) Old 03-24-2004, 03:17 PM
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Quote:
Originally posted by Underdog
I know that feeling (on both counts). If you want to know about moving the forks around, talk to Sticky. The clip-ons on his race bike are barely above the brake rotors...and his forks stick up like goal posts! I haven't seen it yet, but I think he props his head up in there after a few laps to conserve energy!

(then again, he could lap me repeatedly on a Fizzer 400...so maybe he's on to something?)

Good luck with all your adjustments. Try stuff, then try other stuff. Rinse and repeat until you're faster than I am!

Who says my slow ass isn't faster then you already


No, this is an excellent question. There are differences in tire height between different sizes and event between tires of the same size from different manufacturers.

You're right that you need to adjust the tubes in the triples to compensate for different tire height to have the same geometry you had with a different tire. Don't forget the rear tire changes between manufacturers as well.





It's all new to me. Just when I think I'm starting to learn something, I realize I know Jack Shit. No offense Jack

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post #7 of 27 (permalink) Old 03-24-2004, 03:17 PM
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grass hopper try this


hey I went to the seminar they did on computrack and he talked about the issue you are raising it is not as simple as just raising the triples and boom its done. the other issue he talked about was that if the bike is used and you go to set it up that it will be bent and it will not perform the way it is supposed to. He charges a hundred bucks to check it out and then charges for the work to be done if you decide to do it. I think knowing whether or not the bike is strait first will help as much as anything on set up and I am know expert on it. But i do know about alignment and how it effects the ability to track strait.
Just my two cents
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post #8 of 27 (permalink) Old 03-24-2004, 03:18 PM
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The R6 is the same comes with a 120/60. Most all race tires only come in a 120/70. Most people drop the front 10mm to make up for the tire size change. This will get you back to your stock geometry. There is a fancy equation for figuring this out exactly but I can't remember it right now.
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post #9 of 27 (permalink) Old 03-24-2004, 03:21 PM
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Originally posted by zeus-9R
The R6 is the same comes with a 120/60. Most all race tires only come in a 120/70. Most people drop the front 10mm to make up for the tire size change. This will get you back to your stock geometry. There is a fancy equation for figuring this out exactly but I can't remember it right now.

10mm eh
post #10 of 27 (permalink) Old 03-24-2004, 03:26 PM
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Grasshopper,
You could also raise the rear end and get to a similar geometry. By only dropping the forks, you change more than just the front ride height. I think that you are also beginning to mess with your trail, rake and swing arm angle as well.

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post #11 of 27 (permalink) Old 03-24-2004, 03:29 PM
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I know you're already faster than me. I'm just hoping that you'll get so caught up making adjustments that you'll forget how to ride!

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post #12 of 27 (permalink) Old 03-24-2004, 03:36 PM
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Originally posted by bmoney
Grasshopper,
You could also raise the rear end and get to a similar geometry. By only dropping the forks, you change more than just the front ride height. I think that you are also beginning to mess with your trail, rake and swing arm angle as well.

I think I'm in over my head here.
post #13 of 27 (permalink) Old 03-24-2004, 03:37 PM
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Front end height adjustments should be made in very small increments. I only raised mine about 5mm, they look tall because my clip-ons were originally mounted above the triple. I lowered the clips for more mid-corner control. You also shorten you wheel base when you make that adjustment, yes it will turn in more quickly which is what you're looking for right? Friday is practice day at the track on a race weekend, that when you try this.

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post #14 of 27 (permalink) Old 03-24-2004, 03:41 PM
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Most F3 racers I've read use a 120/70 tire, too. I heard a good rule of thumb is to raise the tubes up the height of a nickle.

I'm gonna run this tire for the hell of it next time I buy a set just to see if makes any difference in cornering.
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post #15 of 27 (permalink) Old 03-24-2004, 03:41 PM
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Is there some good reading material out there with up to date literature about setting the suspension up on Race Bike?

Anyone know a good book to buy, I think thats my best bet.


Sticky, I'm just trying to confuse myself as much as I can. I was originally thinking about the tire size change and that made me think of the geometry question.
post #16 of 27 (permalink) Old 03-24-2004, 03:50 PM
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Quote:
Sticky, I'm just trying to confuse myself as much as I can. I was originally thinking about the tire size change and that made me think of the geometry question.
Not at all, you're right on. You're trying to maintain a certain level of feel, when you change a variable you need to compensate. Check out Max McAllister's site Here

He's that man for suspension.

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post #17 of 27 (permalink) Old 03-24-2004, 03:56 PM
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I don't know Nick, this place is as good as any. I've seen a couple places on the Net that have some good writeups. I've got a suspension book or two but they get deep quick.

I try to learn a bit more each year. You pick things up, try to put them to use. Suspension to me is a mix between learning the basics and feeling it for yourself. I was hoping I could just read a book or just ask questions, but it doesn't seem anyone has all the answers. It doesn't really work that way, or at least it doesn't for me. It seems you learn the basics and the more you try to put it to use the more it makes sense. I've just scratched the surface but I hope to learn a bit more this year, and the next...
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post #18 of 27 (permalink) Old 03-24-2004, 03:56 PM
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Originally posted by Sticky
Not at all, you're right on. You're trying to maintain a certain level of feel, when you change a variable you need to compensate. Check out Max McAllister's site Here

He's that man for suspension.

Sweet,

I just printed out a whole shit load of info on suspension theory and set-up.

Thanks for the replies, greatly appreciated. See you guys out at the track.

post #19 of 27 (permalink) Old 03-24-2004, 03:58 PM
 
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Quote:
Originally posted by Grasshopper
Is there some good reading material out there with up to date literature about setting the suspension up on Race Bike?

Anyone know a good book to buy, I think thats my best bet.
Motorcycle Handling and Chassis Design - the art and science by Tony Foale
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post #20 of 27 (permalink) Old 03-24-2004, 03:59 PM
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post #21 of 27 (permalink) Old 03-24-2004, 04:01 PM
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Originally posted by vtr996
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Got it Mark,


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post #22 of 27 (permalink) Old 03-24-2004, 04:02 PM
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Traxxion is going to have a support vehicle at the NESBA 17th and 18th dates at Blackhawk.

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post #23 of 27 (permalink) Old 03-24-2004, 04:27 PM
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Nick, I have my SV set up with 120/70 tire, 15mm showing on the fork tubes and back raised about an inch. It handles much better, turns in quick and is stable enough for me. I don't run a steering stabilizer (yet) and she never shakes her head, well maybe a wiggle now and again but I'm sure thats from me moving my body around using the bars. Rule of thumb would be to raise the fork tubes up in the clamp 5mm at a time and go for a ride, see how it feels and add 5mm more until it starts to feel unstable then back up a few mm. If you are using the GSXR shock that will add about an inch of ride height in the back so that about makes up for the height of a 70 series tire. I've seen very raced out SV with much more extreme geometry, but they all have run steering dampers. My $.02, for what it's worth.

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post #24 of 27 (permalink) Old 03-24-2004, 04:46 PM
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Have Ed take care of it at the track. Trackside Engineering guy knows his stuff and is really reasonable on price too. If you are thinking of doing anything as far as ride height, moving forks up or down my personal opinion is consult someone who knows.

When you talk about bike geomotry there are so many variables that it really doesn't seem worth all the trouble, especially when there are people that can help for not too much $$$. Just my personal opinion though.
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post #25 of 27 (permalink) Old 03-24-2004, 08:20 PM
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For what it's worth, here's my take, my rambling...

Suspension is KEY. Having a properly sorted bike with good suspension can make a huge difference in how easy it is to go fast. Now that doesn't mean that my suspension is going to make me fast, there still will be other riders faster, even on worse bikes, with worse suspension. They ride around the problems. I will always be my biggest limiting factor. I choose to ride the way I do and which chances I take.

It was a few years ago when I was contemplating getting a new shock. I asked people why I would spend $850, or whatever, on a shock. What would it do? What benefits would I get? All I ever got were responses like, "man, you wonít believe the difference. It will totally transform the bike." But when pushed for more details, I never got any.

It wasn't until I took a ride on an MV Agusta F4 that I got it. I finally felt what suspension could feel like, ďThe difference.Ē I hardly road the thing for a few miles and not hard, but I could feel it. I had that feeling again when I road a friends RC51 on the track. He had done a lot to the bike and damn if it didn't feel like that F4.

So how would I describe it? Planted. So planted it was confidence inspiring. Going through a long sweeper it just felt like I could get lower and lower each pass. Lower than I had ever been before, and on someone elseís bike on a track I had never been to before. The bike did exactly what I asked, it didn't shuffle, twitch, just bam and you were at lean and in control. I could feel everything on the track, yet nothing upset it. It was just so predictable, not spongy, not springy, just totally damped. It made it easy to concentrate on other aspects of my riding. It was how I wanted my bike to feel.

The great thing about our sport is that it is challenging. There's always something to learn, practice, and try and get better at. Suspension is no different. I think there are two paths, or maybe two levels to suspension. One is getting someone to set the bike up for you. This is great, and what I did. A good tuner will set you up with a shock with the appropriate spring, and forks configured for your riding. And theyíll be able to give you basic setup settings, rebound, compression, ride height, tube placement, etc. for you and your tires. Depending on your tuner you could be there, the almost perfect setup.

But what do you do next? Do you know what the knobs and screws do? What about different tires, can you adapt? What about different tracks? What about tire wear? This is where it gets tough and there are no shortcuts. You have to ride, learn what the settings do, get ideas of what to try and try them. To have such a sense of feel for your bike and what it is doing that you know what settings to tweak, what to change or try. That is experience and the challenge.

I donít want to give anyone the wrong impression. Iím not a great rider by any means. I enjoy the sport and I enjoy trying to get better. If anything, Iím a student, at best.
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post #26 of 27 (permalink) Old 03-24-2004, 08:31 PM
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Well put Jack

By the way, what do all those knobs and screws do anyways

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post #27 of 27 (permalink) Old 03-25-2004, 08:47 AM
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Experience Experience Experience, thats the only way for me to get better at this sport. And just when I think I have some experience, I realize I don't have much at all.

Well, with suspension set up.

Thanks for taking the time to write your thoughts on this subject guys. . If there's anything I can help you guys out with, you bet your ass I'll try.

I moved the forks up about 5mm last night and made sure everything was straight then torqued it all down and went for a ride. She feals stable, but the few backroads around my place don't come close to the race track.

Dave, I'm going to set aside a little extra cash for that NESBA day and have the guys take a look at the suspension on my bike.

I know my sag is set correctly, or at least within "rule of thumb spec" So I have a good start.

Thanks again,

see you at the track, they'll be a cooler of brewskies at my pit area for after we're done riding on the 17th.

Nick

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