It is all about balancing the rate of the rubber, depending on how it is used, with the motion ratio. It is possible to be too stiff with little travel & too soft with little linear travel. It is complicated & requires a method of measuring the rates & then modeling the geometry & wheel rates. Actually not too complicated if you can measure the rubber rate.
It is VERY important to note that you cannot enclose the rubber in the can too tightly or the rate will go to the moon with a rubber or polyurethane spring. The polyurethane gas entrained elastomer springs use different physics in that they are actually compressible. More on this when I get a chance to write it down. Thanks ... Jay Novak -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Louis A. Schultz Sent: Thursday, July 13, 2006 2:34 PM To: [email protected] Subject: Re: [F500] Bigger Rubbers- cont'd... My original thinking is more centered around this part of your reply: "2. Turn it 90 deg & compress it against the side of the radius. (less sensitive to ratio & setup but the rate curve is shaped differently)". I sort've did get this far before your reply; however, my continued reasoning conjured up the following. With more rubber mass to compress, in a canister, the hardness or compressibility (?) of the rubber needs be less (softer). Not sure if that reasoning is correct. Then if was correct, this would lead to less control of tire movement, i.e. increased wheel bounce. So where am I wrong here? Lou Schultz PS If I'd known way back when I would be thinking/talking about this stuff...I would have never have change my major from Engineering to Accounting! Louie ----- Original Message ----- From: "Jay Novak" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Thursday, July 13, 2006 3:00 AM Subject: RE: [F500] Bigger Rubbers- misc thoughts & questions... > Lou it is really not about more travel it is about a longer linear (nearly) > range of the wheel rates. Every kind of elastomer has a compression rate > curve that has a rather short linear range & then the rates start increasing > very quickly. There are really 2 different types of rubbers that are being > used in F500 they are: > > 1. Rubber of various compounds & polyurethanes of various compounds (there > is really no such thing as natural rubber any more) > > 2. Polyurethane gas entrained foam compounds or various types (foamed types) > > Type 1 can be made in various durometers (hardness that we can use) that > range from the softest at about 50 durometer to the hardest around 75 > durometer (Shore A scale) > > This type of material can have very different levels of damping (hysteresis) > depending on the compounds. This is really not true damping as in a > hydraulic damper but there are different rates in compression & rebound. > The damping can be changed depending on the material & the shape and or > materials used for the compression plates. > > The linear range of this type of material is generally about .25 to .35 of > the thickness & the stiffness really start going up dramatically after about > .5 of the thickness. > > The stiffness are proportional to the compressed area (bigger diameter means > it is stiffer) & inversely proportional to the length (longer means it is > softer). The stiffness can also be changed by the shape & size of the > compression plates. > > This material acts like a constrained liquid in that the total volume does > not change when the material is compressed, if the part has 3 cubic inches > of material when uncompressed it will still have 3 cubic inches of material > when you squeeze it as hard as you can. This means that you must have room > in a can for the material to flow to. > > To use this material effectively you must have very accurate control of your > motion ratios. > > In F500 there are 2 ways to use this type of material: > 1. Compress it on it's axis (along the 1" direction (very sensitive to > ratio & setup) > 2. Turn it 90 deg & compress it against the side of the radius. (less > sensitive to ratio & setup but the rate curve is shaped differently) > > Both methods can be made to work very effectively. > > As you can see this can get to be an extremely complicated subject & this > discussion BARELY scratches the surface. > > More on type 2 material tomorrow. > > Thanks ... Jay Novak > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Louis > A. Schultz > Sent: Wednesday, July 12, 2006 7:21 PM > To: [email protected] > Subject: Re: [F500] Bigger Rubbers- misc thoughts & questions... > > Don't have the original wording on the "why" for longer pucks but didn't it > have something to do suspension repeatability or better set up. > > Seems to me if we're expecting more travel (softer ride) without a rebound > mechanism more wheel bouncie, bouncie follows...and that isn't a good > thing. > > I guess I don't understand "how" the longer rubbers will impact/change > suspension movement...like make the car handle better. > > Jay can you throw out some engineering on this subject? > > Also (for Jay) not all cars use the same kind of rubber material. Will > Jay's testing results be applicable to us natural rubber racers? > > As far as increasing class size by telling people we have longer rubbers. > Ahhh, I'm not so sure that's really a good selling point. > > Lou Schultz > Philly Region > ----- Original Message ----- > From: "Dave Phaneuf" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Wednesday, July 12, 2006 9:35 AM > Subject: [F500] Bigger Rubbers- misc thoughts & questions... > > > > Chuck > > That's were I've been coming from...is there a type of rubber that > > will dampen the rebound enough to actually want more travel? > > Stu Phipps had a comment during an event at Peru ( kinda bumpy ) > > about pogo sticks having plenty of travel.......... > > Dave Phaneuf > > > > _______________________________________________ > > F500 mailing list - [email protected] > > To unsubscribe or change options please visit: > > http://f500.org/mailman/listinfo/f500 > > *** Please, DO NOT send unsubscribe requests to the mailing list! *** > > _______________________________________________ > F500 mailing list - [email protected] > To unsubscribe or change options please visit: > http://f500.org/mailman/listinfo/f500 > *** Please, DO NOT send unsubscribe requests to the mailing list! *** > > > _______________________________________________ > F500 mailing list - [email protected] > To unsubscribe or change options please visit: > http://f500.org/mailman/listinfo/f500 > *** Please, DO NOT send unsubscribe requests to the mailing list! *** _______________________________________________ F500 mailing list - [email protected] To unsubscribe or change options please visit: http://f500.org/mailman/listinfo/f500 *** Please, DO NOT send unsubscribe requests to the mailing list! *** _______________________________________________ F500 mailing list - [email protected] To unsubscribe or change options please visit: http://f500.org/mailman/listinfo/f500 *** Please, DO NOT send unsubscribe requests to the mailing list! ***
