"John McCoy" <igop…@ix.netcom.com> wrote in message

news:Xns9837CB80319C6pogosupernews@216.168.3.30…

- Hide quoted text — Show quoted text -

> "Phil Rhodes" <p.rho…@NOSPAMcomcast.net> wrote in
> news:k5OdnZLUAvQzAJ3YnZ2dnUVZ_uqdnZ2d@comcast.com:

>> During the Busch Race at Fontana, they asked Kyle Petty to explain
>> coil bind, but I didn’t listen to him, thinkin’ I knew what it was. I
>> did hear ‘em say it was hard on tires.

> Coil bind is when the spring is compressed so far that adjacent
> coils touch.  At that point, it doesn’t act like a spring any more,
> it acts like a solid piece of metal.  When that happens, all the
> dynamic loads of the suspension have to be absorbed by the tire,
> which as you say is very hard on the tire (unless we’re talking
> valve springs, which can also coil bind, which is very hard on both
> the spring and the valve).

>> Anyone have a handle on this? Does a spring rubber in the rear coil
>> make the car tighter by pushing the spoiler up in the air? During
>> post-race ride height inspection, do they get to put the spring rubber
>> back in (since presumably it was originally measured that way?

> What the spring rubber does is make the spring stiffer.  Whether
> that makes the car tighter or looser depends on which spring you
> put it in, of course.  It has an insignificant effect on static
> ride height (about the same as you’d get from one turn on the
> jacking bolt, altho a full spring rubber is very rarely used,
> most often it’s either a half or a quarter, which would have
> proportionally less effect).  Putting a rubber in a rear spring
> would tend to hold the spoiler up more, since the spring won’t
> compress as much due to body roll or acceleration.  But that’s
> not usually the goal of putting the rubber in, what’s desired is
> to change the way the car rolls over, especially in the middle
> of the corner, to get a better distribution of weight between
> the four tires.

> John

> Nice post, thanks.
> In tonights (Friday) Busch Race, they had a TV camera in Cousin Carl’s
> right front wheelwell, showing how hot the brake rotor gets. What it
> also showed was how close the spring comes to binding on the right
> side, as the car rolls over in the turns. Good stuff!

If you were looking closely at that shot, you’ll have noticed a
small black ring around the shaft of the shock absorber.  That
ring gets pushed down the shaft as the shock moves, and shows
the crew how far the shock has compressed.  In testing and
practice they’ll look at that, and if necessary select a
different spring.

(in testing they might also use a "linear actuator" connected
to a telemetry unit or data recorder, so they can get an exact
measure of shock movement.  Since NASCAR doesn’t allow that
stuff on race day, they use the low-tech method

John

> During the Busch Race at Fontana, they asked Kyle Petty to explain
> coil bind, but I didn’t listen to him, thinkin’ I knew what it was. I
> did hear ‘em say it was hard on tires.

Coil bind is when the spring is compressed so far that adjacent
coils touch.  At that point, it doesn’t act like a spring any more,
it acts like a solid piece of metal.  When that happens, all the
dynamic loads of the suspension have to be absorbed by the tire,
which as you say is very hard on the tire (unless we’re talking
valve springs, which can also coil bind, which is very hard on both
the spring and the valve).

> Anyone have a handle on this? Does a spring rubber in the rear coil
> make the car tighter by pushing the spoiler up in the air? During
> post-race ride height inspection, do they get to put the spring rubber
> back in (since presumably it was originally measured that way?

What the spring rubber does is make the spring stiffer.  Whether
that makes the car tighter or looser depends on which spring you
put it in, of course.  It has an insignificant effect on static
ride height (about the same as you’d get from one turn on the
jacking bolt, altho a full spring rubber is very rarely used,
most often it’s either a half or a quarter, which would have
proportionally less effect).  Putting a rubber in a rear spring
would tend to hold the spoiler up more, since the spring won’t
compress as much due to body roll or acceleration.  But that’s
not usually the goal of putting the rubber in, what’s desired is
to change the way the car rolls over, especially in the middle
of the corner, to get a better distribution of weight between
the four tires.

John