removing grip

[Paul Kish]

quote:

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Originally posted by Dave Embry:
Hi Paul,

No, I don't think you're being picky. I've enjoyed this forum(& of course the former forum) very much ....especially during the off season. I appreciate all who post and leave their opinions. Anyone who reads them can put together everyone's thoughts and try and form their own opinions as compared to their experiences on the track. I've always read what people write here but only use it as a basis of a test myself!! The only way my mind is made up on any subject is the results on the track. ("The proof is in the puddin'"??)

I think maybe you have misunderstood me as I think we are really saying basically the same thing. I've said twice I think....that I don't believe raising the VCG changes the "amount" of weight transferred in any direction...it just changes how that wt. acts upon the contact patches. I think where I'm loosing you is "where" that VCG acts the way I explained it. I agree with you that the wt. "wants" to continue in the same direction that the kart is going which would be straight ahead and downward (the "force" of gravity) when the kart is traveling straight with either the brakes applied or with release of the throttle.

Then, as a turn is initiated....that wt. then wants to continue straight except that the kart is beginning to turn so the wt. transfer begins to change where it is pointing at on the kart from straight ahead to the OF, then on towards the OR and finally straight back as the kart accelerates out of the corner.

BUT....the other force that is always acting upon the wt. ....equally....and at all times "downward".... is gravity. That wt. is always wanting to go "down" no matter how it's acting dynamically or statically. You can take away the "forward" motion of the CG but you can't take away the "downward" motion (unless you strap on a rocket pointing up!)

The main part of the turn I referred to in my example was more in the center of the turn or where the wt. wants to go towards the outside of the kart where the most grip is needed (with the exception possibly of the shifters where you may need more grip on exit due to the power that needs to be transferred to the ground through the tires). The contact patches give resistance to the the wt. wanting to contine to go forward (or to the outside of the kart at this point in the turn) but gravity will continue to "pull" the wt. downwards. In my example, the wt. being "pulled downwards" by gravity would be applied differently (more "downwards" instead of "sideways" on the tires) the higher it is due to the angle.

If a pole vaulter (which is the opposite of the CG in relation to the pole or axle in a kart....right John??) is running towards the point where he will stick the pole into the ground.....his VCG is low to the ground. His whole point is to raise the CG (or at least the majority of it.....his body) over the horizontal pole. Imagine that the pole is the axle on the kart, his hands are where the bearings mount to the chassis and his body is the CG and the end of the pole is a tire. (If this were a kart, the pole vaulter would have to have the pole [or axle in our example] behind him since the CG would be on top of the axle).

As the vaulter runs towards the horizontal pole and sticks the end of his vaulting pole into the ground (the outside rear tire in a turn), where would it have the most grip? When the vaulter's (CG) feet were still touching the ground or when it was at the top of the vault? The higher the CG goes (the vaulter's body), the less likely that the end of the pole on the ground will "slip out" (more OR tire grip). So even though the wt. has remained the same amount, and even though that wt. wants to continue straight...the force of the resistance of the cg moving forward has caused the angle of the gravity pulling downward on the CG to give more grip because the wt. is now more "downward" on the end of the pole the higher the wt. goes whereas it's more "sideways" the lower the wt. is.

To go further, (and this is where I used to really get confused with chassis handling) imagine that if the end of the pole didn't have sufficient grip to "hold", then it would just slip out and the vaulter (CG) would remain basically unchanged. What if the pole vaulter was trying to vault on an asphalt surface with no hole to plant the end of his vault into? Nothing would change right? The vaulter would just keep running without any change as the end of the pole "slid" along the asphalt.

The VCG in this case would continue to move in the same direction it was traveling dynamincally which was straight and downward (gravity). If the running vaulter were to lift his feet up suddenly, his butt would hit the ground and slide along if there were not sufficient grip at the end of the pole. This shows that the "Downward" force of gravity is still going to pull that wt. down regardless.

What if he then added a hard rubber grip to the end of the pole? More grip...more resistance to the forward motion of the CG ..however...no change in the gravitational downward force on the CG.

Now if the vaulter has enough "grip" on the end of his pole to cause sufficient forward resistance to the wt of the pole vaulter...do you think it would provide "more grip" if the pole vaulter himself were a 2 foot midget or an 8 foot giant (imagine the "angle" between the point where the end of the pole vault plants into the ground and the vaulter himself). I think the taller the vaulter (the higher the VCG), then the more grip the end of that pole would have.....and the higher the VCG gets (as the end of that vault remains planted on the ground and the vaulters body rises off the ground further and further), the more grip the end of the pole has (or maybe the "less grip" is required).

So if this were your chassis, if you aren't getting enough grip in the tires to force the CG to move...your chassis isn't doing much of anything for you. So, you have to first establish that you have enough grip to make the wt. transfer before considering what chassis/axle adjustments should be made to make it work better.

You can do all kinds of "thinking" about the relationship between this vaulter and a kart's rear end, like "what if the same vaulter used a short or longer pole (distance between bearing hangers and contact patches [narrower rear track]) or used a more flexible pole (axle), or held his arms further away from his body (making the CG further away from the axle....raising the VCG), etc. etc. etc.

If we go to an asphalt sprint track where we have a tire rule and can't go to a softer compound and aren't getting the grip we need....the fix that I usually use first is to raise the VCG (which in our case is easy since we have so much added wt....I just move wts. up on the seat backs). This has ALWAYS given us more grip. Once I have the grip to let the wt. transfer, I start tuning the chassis to make the wt. "work" the way I need it to based upon what the chassis is doing once it has sufficient grip to resist the forward movement of the CG. Until that grip is found, the chassis is just a chunk of tubes gliding across the surface. (the pole vaulter pole won't "bend" and would make no difference to the vaulter what it was made of or where he held his hands, etc. if there was first insufficient grip to hold the end of the pole and let the wt. tranfer to the pole).

Whew......all this "thinking out loud" gets tiring and long. This is all just my thinking and the way I "see" it and I assure you....it could all be total balony!!! (but it sure is fun to try and figure it all out!)

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I just thought it would be fun to quote what you wrote so you would have to read it again.

I agree you have a pivot point, a lever and a vcg.

We can debate the pivot point or points that vary and never come to agreement.

We can debate where the rear roll center is and never come to agreement.

And probably debating what the actual lever is will never be decided.

I also understand and see how you have never experienced anything other than an increase in grip when you moved the 35# weight up.
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But:
"The contact patches give resistance to the the wt. wanting to contine to go forward (or to the outside of the kart at this point in the turn) but gravity will continue to "pull" the wt. downwards. In my example, the wt. being "pulled downwards" by gravity would be applied differently (more "downwards" instead of "sideways" on the tires) the higher it is due to the angle."

Only if the vcg is stationary and not being propelled forward.
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"The higher the CG goes (the vaulter's body), the less likely that the end of the pole on the ground will "slip out" (more OR tire grip)."

But:
Isn't it also true that the end of the pole will be less likely to slip because as the vcg gets higher more of the weight will be projected above, beyond and past the pivot point because the weight is also being projected laterally? And if less lateral weight is then available to be applied to the pivot point because more of it is being aimed elsewhere the pole at the pivot point would also be less likely to slip?
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I think that if your driver happens to grow alot and becomes a very large and strong top heavy young man you may experience a loose kart. Because too high of a percentage of the kart and drivers weight is projected laterallty above the contact patch. That can result in reducing the weight available for grip at the contact patch and a loose kart.
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This is and karting is fun.

[ December 02, 2001: Message edited by: Paul Kish ]

[Dave Embry]

quote:

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Originally posted by Paul Kish:

_________________________________________
I just thought it would be fun to quote what you wrote so you would have to read it again.

But:
Isn't it also true that the end of the pole will be less likely to slip because as the vcg gets higher more of the weight will be projected above, beyond and past the pivot point because the weight is also being projected laterally? And if less lateral weight is then available to be applied to the pivot point because more of it is being aimed elsewhere the pole at the pivot point would also be less likely to slip?
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I think that if your driver happens to grow alot and becomes a very large and strong top heavy young man you may experience a loose kart. Because too high of a percentage of the kart and drivers weight is projected laterallty above the contact patch. That can result in reducing the weight available for grip at the contact patch and a loose kart.
________________________
This is and karting is fun.

[ December 02, 2001: Message edited by: Paul Kish ]

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WHAT! You want me to actually READ all that stuff I was thinking out loud!! It was hard enought to WRITE IT!! haha!

I agree that more wt. will be "trying" to be projected more above the contact patches "IF" that wt. were not attached to something (like a kart)....but....since that wt. IS attached to the kart then I think the old saying of "the bigger they are...the harder they fall" applies.

The wt. is attached to the kart...when the centripetal forces apply to the kart in the corner, the wt. tries to "fly away" and continue in the same direction BUT since it is attached to the chassis (the driver being the heaviest component of the kart, the wt of the body presses against the seat, etc.), as the wt. tries to continue on..it pulls the chassis with it from the inside of the turn and presses downward on the outside of the kart through the seat mounts/struts, etc. The wt. is trying to go but it can't (I guess if the driver was sitting on a flat seat and not holding onto the steering wheel, etc. then he would just fly out of the kart but since he is retained and made a part of the wt. of the overall chassis by the seat, etc.....then the movement of the wt. is restrained).

My FINAL example .......take 2 twenty pound sled hammers. 1 has a 1' handle and the other a 6' handle. Stand each hammer up on the end of it's handle so that the heavy part is standing straight up in the air. Now put your toe under the one that you think will hurt the least when you tip it over onto your foot! (I'd pick the "shorter" handle ...ie lower VCG....because it won't hit with as much force)

Now imagine putting that hammer in motion and then pulling it down abruptly. Which hammer would you rather smack your toe and would you rather the hammer be sitting still or moving horizontally about 30 mph when it falls on that toe? The lower the VCG, the less the downward force. The higher the eccentrical force via g-force/speed through the corner the more the downward force when it gets "pulled" down by gravity and by the contact patches offering resistance.

If I had a bullet with a very strong string attached through it that was so 20' long and I had you stand exactly 20' from me...would you rather I "throw" that bullet at you from 10' up in the air or "shoot" it at you from a rifle (higher velocity)? The bullet would fly along straight until it hits the end of the string, then come very quickly and hard down to earth. It would "like" to continue on flying forever at the 10' level BUT gravity pulls it down....and then there's that darn string!! It's going to bring it down really fast (the string is the resistance....or the tires contact patches....) to the wt.) The wt. is moving along but when it reaches the end of the string....down it comes ....hard and fast....and the faster it's moving (shot from the rifle), the harder it's going to come down WHEN it does come down.

(I'm really not trying to smash your toes or hit you with bullets Paul...just seems like good examples!!)

I hope many engineers aren't reading this and thank goodness Learmonth is out camping in the outback with the kids this weekend!!

[ December 06, 2001: Message edited by: Dave Embry ]

[Paul Kish]

The wt. is moving along but when it reaches the end of the string....down it comes ....hard and fast....and the faster it's moving (shot from the rifle), the harder it's going to come down WHEN it does come down.
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But:

The bullet only came down because it was no longer traveling forward.

Or.... I guess maby it was leveraged down buy a string.
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I too hope there ain't no engineers reading this because I too don't know for sure. But it's fun to debate it.

[ December 02, 2001: Message edited by: Paul Kish ]

[John Learmonth]

quote:

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Originally posted by Dave Embry:



Hint...."Vertical Center of Gravity"? It's the same as raising the seat or weight on kart. The higher the VCG, the more downward the wt. on the tires = more grip. So....higher chassis = higher VCG = more grip. IMO

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Dave, I don't think its quite that simple (I never do!). Raising /lowering the chassis will raise / lower the CG in the same manner as raising / lowering the seat, but won't have exactly the same effect because changing chassis height also raises or lowers the effective 'suspension' members, which raising lowering the seat only doesn't do.

Changing chassis height has an effect on roll stiffness because it affects roll centre locations, and simply changing seat height won't. Of course you do have to accept that roll centres exist on karts in the first place for this to make any sense!

[Dave Embry]

quote:

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Originally posted by John Learmonth:


Dave, I don't think its quite that simple (I never do!). Raising /lowering the chassis will raise / lower the CG in the same manner as raising / lowering the seat, but won't have exactly the same effect because changing chassis height also raises or lowers the effective 'suspension' members, which raising lowering the seat only doesn't do.

Changing chassis height has an effect on roll stiffness because it affects roll centre locations, and simply changing seat height won't. Of course you do have to accept that roll centres exist on karts in the first place for this to make any sense!

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Oh no!! I was afraid you would return and read all this junk!!

[John Learmonth]

Dave said:
“...when the eccentrical forces (neat word huh? Learmonth taught me that word)”

Dave, it is a neat new word (the English language continues to evolve!), but I didn’t teach it to you! The first time I ever heard it was from you in a recent email. I knew what you meant so didn’t correct it. The word you’re thinking of is ‘centripetal’, which is what most people mean when they say ‘centrifical’ (which isn’t a real word), or ‘centrifugal’ (which I don’t think is a real word, but is probably acceptable in Scrabble!)

“I hope many engineers aren't reading this and thank goodness Learmonth is out camping in the outback with the kids this weekend!!“

Australia is a big place, and the ‘outback’ is a long way from the school camp!

PS,its good to see some posts at least as long as I write on occasion!

[Paul Kish]

quote:

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Originally posted by Mike Goebel:
Lets say you were to put Pauls head under the right rear tire with the kart level. Attach a 1 foot rod to the bottom of the seat, push at the top of the rod so that Pauls head has to resist the moment you are applying. Now take a 10 foot rod attach to the seat and push in the direction that is resisted by Pauls head. Which will hurt Pauls head more. Most likey just thinking about it will hurt the most. Just messing with ya.

Mike G.

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I suspose Mike you never even considered what might happen if the the rod were to flex.

[Dave Embry]

quote:

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Originally posted by John Learmonth:
Dave said:
“...when the eccentrical forces (neat word huh? Learmonth taught me that word)”

Dave, it is a neat new word (the English language continues to evolve!), but I didn’t teach it to you! The first time I ever heard it was from you in a recent email. I knew what you meant so didn’t correct it. The word you’re thinking of is ‘centripetal’, which is what most people mean when they say ‘centrifical’ (which isn’t a real word), or ‘centrifugal’ (which I don’t think is a real word, but is probably acceptable in Scrabble!)

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dadgum.....give an old man who has no memory left a break huh! Just call me Archie Bunker!

Can't get me upset today though....#1 son won his first SKUSA Regional race yesterday! Go Team Interkart!

[Paul Kish]

quote:

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Originally posted by Dave Embry:


Can't get me upset today though....#1 son won his first SKUSA Regional race yesterday! Go Team Interkart!

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CONGRADULATIONS !

"The first one it tough the rest get easier."

[Steve Moore]

quote:

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Originally posted by Mike Goebel:
Which will hurt Pauls head more.
Mike G.

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My head hurts now, and I'm not Paul.

[Bob Evans]

Centrifugal force is what makes you slide off the track.
Centripetal force is the amount of grip required to keep you from sliding off the track. (loose interpretation)

You could try grinding the shoulders of the rear tires round and/or mounting the rear tires on wider rims. Works on dirt, however (on asphalt) it could backfire.

[Paul Kish]

Per Webster

Centrifugal forcr- the force tending to pull a thing outward when it is rotating rapidly around a center.

centripetal force- the force tending to pull a thing inward when it is rotating rapidly around a center.
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Now I'm really confused and don't understand it.

[Mike Goebel]

Lets say you were to put Pauls head under the right rear tire with the kart level. Attach a 1 foot rod to the bottom of the seat, push at the top of the rod so that Pauls head has to resist the moment you are applying. Now take a 10 foot rod attach to the seat and push in the direction that is resisted by Pauls head. Which will hurt Pauls head more. Most likey just thinking about it will hurt the most. Just messing with ya.

Mike G.

[Dave Embry]

quote:

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Originally posted by Bob Evans:

Centrifugal force is what makes you slide off the track.
Centripetal force is the amount of grip required to keep you from sliding off the track. (loose interpretation)

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aha.....so the string attached to the bullet is what gives it the "centripetal force" and brings it down to the ground faster than the forces of gravity alone.... and the contact patches providing the resistance to the wt's outward movement in a turn and bringing it "down" on the contact patches is also the "centripetal force".


My bullet example assumed you either threw the bullet or shot it from a rifle at 10' above the ground. If you shot it from a rifle at that 10' level...and the barrel was perfectly level with the ground with no string attached to the bullet....it would immediately begin to fall to earth as soon as it left the barrel and continue to fall in an arch ("trajectory") until it hit the earth. How far and the degree of the arch/trajectory would depend on the amount of force propelling it forward (amount of "powder" used in the shell or the wt. fo the bullet itself).

If the string were attached, it would travel along in it's natural trajectory caused by the forces of gravity until it hit the end of the string somewhere just under the 10' height that it started at (depending on the length of this really strong string!). If the other end of the string were attached at the ground level just under the rifle, then when it hits the end of the string (or the string is pulled tight) then it will be pulled downward towards the ground rapidly in a much smaller arc than it's natural trajectory would be.

If the string were attached up at the rifle (at 10' off the ground), then when the bullet hit the end of the string.....it would just stop in it's tracks and fall straight down to earth (unless it was a very stretch string where it might slingshot back at you!). (Actually, it would drop down only if it were at exactly the same ht. above the ground that the string was when it hit the end but close enough)

So as the VCG in the kart is moved up by raising let's say....either the driver via a higher seat or by moving ballast wt. up higher on the seat back....it would depend on "where" that wt. was attached to the kart (this would represent where the bullet string was attached at the rifle end above the ground) but since the seats are attached to the chassis down low via the seat mounts/seat struts....the wt.will always be "attached" to the kart below the VCG on the kart.

Let's just assume for example sake that the VCG on our kart is at 11" above the ground. In the turn as the wt. (bullet) wants to continue going straight at the same level it started at (11 inches), it can't because it is attached to the kart rigidly (as represented by the wt. of the chassis, tires, engine, etc.) and more fluidly (as represented by a driver's body that more or less can move about in a turn). As the wt. tries to go straight ahead at the 11" level it is immediately "out of string" since it's attached to the kart with virtually no slack and the "centripetal force" of the resistance of the contact patches pulls that wt. downward onto the outside contact patches (or at least moreso in that direction). If the wt. were not attached to the kart (say the driver was sitting on a flat board...not tied into the kart)....and went around the turn, he/she would bounce their keister in the grass as the kart went on around the turn. In that case...if the wt. is not restrained by being attached to the kart, the wt. would actually continue on in the same direction and at the same height above the contact patches with only the forces of gravity forcing it downward in an arc towards the ground with the higher the speed in the corner (the more "powder" in the bullet) the further your bum would go before hitting the ground! But of course this doesn't happen since the driver (which usually comprises the majority of the wt. of a kart) is more or less attached to the kart.

The higher the VCG...so long as it is attached at the same low spot on the chassis like it is now (to the chassis frame via seat mounts/struts) then the more energy is directed downward onto the outside contact patches. (assuming that their is sufficient grip at the contact patches to provide enough resistance ....uh..or..."centripetal force")

If you mounted a seat onto 6 foot long seat mounts so that the driver was sitting over 6' above the chassis and went around a corner what would happen? El Flippo! (unless you were turning the corner at the ice skating rink and the contact patches had zero grip or no "centripetal" force)

If you lowered the seat so that the VCG was virtually "On" the chassis rails....the more likely the kart would "slide"...or 4 wheel slide/drift through the corner instead of flipping because much less force is directed downward on the outside contact patches resulting in less grip. I can't imagine how you would ever get a kart "loose" by raising the VCG (assuming "loose" means less grip overall on the chassis). That would be true only if that wt. were not attached to the chassis.

When we lower the wt. (VCG) on our chassis too much, the kart just "drifts/4 wheel slides) through the corners with much less overall grip. If that happens, I raise the VCG until enough grip is found for the chassis to begin to "work" so I can then determine where the chassis needs to be balanced. The more grip, the more effect chassis adjustments have on the handling of the kart and only then does chassis adjustment really have any effect. If I keep raising it, it's possible to eventually get the kart to bicycle through the turn (or keep on and it would flip).

Again...I'm just rambling on here .....NOT being an engineer "type"....I have to "visualize" these things in terms/examples I already understand and try to apply them to the karting principles....and since it's deer hunting season here now....I guess bullets are on my mind!

[ December 04, 2001: Message edited by: Dave Embry ]

[Paul Harraka]

The term you're looking for and the effect you are describeing is call the " Polar Moment of Inertia ". When you raise the weight in relationship to the roll axis of the kart, it has a polar moment of inertia, which mutiplies the effect of the weight. This doesn't only effect cornering grip, it also effects foward bite when you are going straight.