[s-cars] alignment Q

Robert Myers bob at chips-ur-s.com
Thu Jan 15 06:35:08 PST 2009 

At 09:15 AM 1/15/2009, pkrasusky at ups.com wrote:

>Thanks again Dave, and sorry all again for the WOB but hey this is fun stuff.
>
>I've got a wheel here with me.  If I camber it up max, it's merely 
>riding on my desk on a razor thin edge of contact.  I'm having 
>trouble (easy for me) envisioning where the scrub is being introduced.

Dredging faint memories from my sophomore physics class ISTR that 
friction forces are the result of coefficient of friction times the 
"normal force".  Normal in this sense means perpendicular to the 
surface.  The surface area has no part in the process.  Whether the 
contact patch is razopr narrow or somewhat wider should have no effect.

>Not that I'm doubting you just trying to understand.  Such camber 
>'appears' to have benefit of nearly zero surface contact aka 
>friction.  Would this negate / outweigh any claimed scrub?
>
>Appreciate any further insight here.
>
>Maybe this is different than 'tires' as it's a hard plastic wheel?

Internal friction (from compression and relaxation of internal forces 
when the rubber tire is flexed should be much lower for the virtually 
rigid plastic "tires".  This should then reduce frictional drag from 
the wheels rubbing on the axles.


>Regarding wobble - these wheels do wobble on the axle some - any 
>suggested remedies?  I'm drawing blanks.

A bushing?  Perhaps machine a slightly larger diameter 
axle?  Elimination of wobble should help significantly by reducing 
the normal forces of the wheel sliding on the axle.

Do the rules permit lubrication of the axle?


>and
>
>Any thoughts as to good way to 'allow' for quick & easy alignment 
>tweaks to the axles while still maintaining a solid axle mount?  I 
>was trying to envision 'adjusters' like a hard staple or something, 
>as glue is going to be cumbersome to try and set unset set unset set.
>
>Jah, 930.  The Boy was insistent.  Hit it with like 10 coats of 
>clear last night - hilarity.
>
>*Tx again* all, mucho appreciatto...
>
>-Paul
>
>________________________________
>From: djdawson2 at aol.com [mailto:djdawson2 at aol.com]
>Sent: Wednesday, January 14, 2009 5:40 PM
>To: Krasusky Paul (WQQ2PXK); s-car-list at audifans.com
>Subject: Re: [s-cars] alignment Q
>
>Toe would cause more scrub than camber.  I think the main goal for 
>you is to minimize lost energy.  There is an energy loss associated 
>with camber... look into motorcycle tire design.  High speeds, 
>combined with a lean angle (essentially camber) generates extreme 
>heat = lost energy.
>
>Normally, derby car wheels are more like a motorcycle tire than a 
>car tire... the contact surface has a radius instead of being flat.
>
>Think of the pinpoint contact with the road surface.  Only at the 
>exact point of contact is where the ideal situation exists.  As soon 
>as the tire moves past that point of contact it is now "scrubbing" 
>perpendicular to the direction of travel.  It's a little like taking 
>a turn in a vehicle with a live axle... something has to scrub.
>
>0 toe and 0 camber should provide the least energy loss.  I think 
>wheels wobbling on axles would be a major concern.
>
>Nice to hear it will be a 930  ;-)
>
>
>-----Original Message-----
>From: pkrasusky at ups.com
>To: djdawson2 at aol.com; s-car-list at audifans.com
>Sent: Wed, 14 Jan 2009 2:20 pm
>Subject: RE: [s-cars] alignment Q
>
>
>I would think toe causes more scrub
>
>if camber scrubs... is it better than the full friction of the wheel 
>surface area created by having zero camber?  Just wondering aloud.
>
>Thanks Dave - good to hear from you btw...
>
>-Paul
>
>________________________________
>From: djdawson2 at aol.com<mailto:djdawson2 at aol.com> 
>[mailto:djdawson2 at aol.com<mailto:djdawson2 at aol.com?>]
>Sent: Wednesday, January 14, 2009 4:19 PM
>To: Krasusky Paul (WQQ2PXK); 
>s-car-list at audifans.com<mailto:s-car-list at audifans.com>
>Subject: Re: [s-cars] alignment Q
>
>I can speak to camber...
>
>Zero camber would be best.  Any camber causes a "scrub."
>
>
>-----Original Message-----
>From: pkrasusky at ups.com<mailto:pkrasusky at ups.com>
>To: s-car-list at audifans.com<mailto:s-car-list at audifans.com>
>Sent: Wed, 14 Jan 2009 1:23 pm
>Subject: [s-cars] alignment Q
>
>
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>NAC, in fact it's a Porsche.
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>So The Boy insisted we make a 930 (of course) for his inaugural Pinewood Derby
>
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>this year - could he pick a more bulbous car?  Oy.  We're nearing 
>completion and
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>ready to mount wheels.
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>Question for the Geekdom here - what is the 'fastest alignment' for a car that
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>only has to go down a straight hill?  I'm thinking maximum negative camber (to
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>decrease wheel surface friction on track) and zero toe - F&R.
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>Am I right?
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>Also - rules state cannot add bearings.  I just got the genius (I 
>think) idea to
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>separate the wheel from its integral hub via a cut, and then glue 
>the 'hub' onto
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>the car, polishing both contacting surfaces of wheel / hub.  Think 
>1) this would
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>be effective and 2) think it's legal?  We're not 'adding' anything and using
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>what's provided.  I do have a note in the Cubmaster on it, I can pretty much
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>guess the reply of course but figured I'd ask anyway.
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>Any other hotrodder tricks appreciated - we're already polishing the axles and
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>wheels and hubs best we can, using graphite lube, etc.
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>Insight appreciated - by Tyler 8-).
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>We pretty darn well nailed the 930 look - esp. the rear flanks and 
>profile, and
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>front nose.  Unfort. rules dictate must use OE axle locations and then they
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>limit max width, result is a 930LWB.  Hindsight would have me 
>approach the front
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>flares different and run them further into the doors - next 
>time.  And the front
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>wheels are so close to the nose our ride height is more Rothman's 959 than 930
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>(maybe I should strip the Guard's Red and go with the Livery heh heh?) as
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>tucking the wheels any more up would hit them into the headlight 
>area.  Ah well.
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>But it came out pretty darn kewl.
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>TIA!
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>-Paul
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