Yet More on Chassis Stiffening

[RonHorowitz <RonHorowitz@xxxxxxxxxxxxxx>]

>I had a half formed idea of using a laser pointer as a straight edge..

At Harbor Frieght, or at least when they're on sale, they aren't very
expensive. This isn't a bad way to go.

> lift the front wheel at that side.

If you can seperate the effects of chassis flex and body roll, great, but
do check to make sure it's repeatable. Also, I think the method would
probably be pretty tedious for taking more than a few data points.

>Why not just take a Spider with a chassis stiffener to a track?  Time
>some laps with, some without.

An interesting thought, yes, but unfortunately, the relation of chassis
stiffness to lap times would probably be an unsolvable system of equations.
It's likely the effects of improved stiffness would be small compared to
the noise of driver inputs,  tire wear, various temperatures, atmospheric
conditions, etc. Also, I'd say for 95% of the people out there, shaking and
rattling on normal roads are probably more of an issue than lap times. You
could fit the chassis with accelerometers and data loggers and derive a
curve via data aquisition and analysis, but it's not a super-direct method.
You wouldn't have to go to the track to do that, of course, just drive down
a bumpy road.

>I don't know why people are so hung up on measuring the effects of a
>stiffener.  What are you going to do with the results?

Well, two things:

1) Quantify the performance of the existing design options (i.e., stock vs.
stock+bolt-on)
2) Develop a brace design that's better than the existing options

>If somebody says
>it increases the torsional stiffness of your Spider by x%, then does
>that number really mean anything to anybody on this list?

Um,... well, ... as a relative unit of merit, of _course_.

This is done with horsepower figures routinely, right? Within any
reasonable limits, horsepower is a _much_ more non-linear curve vs RPM than
stiffness is vs. load. In other words, the torsional stiffness of the
chassis can probably be summed up pretty well by a single number
characterizing the slope of the curve near the zero crossing, whereas peak
horsepower says virtually nothing about the power integral over the range
of RPM, and we use it for comparisons all the time. Well, anyway, I'd have
to say that a single number for chassis stiffness has got to be a whole lot
more meaningful to people than no numbers at all, right?

>Isn't it enough that everybody on the list who has installed one has
>noticed a significant improvement?

Well, um, ah,... to be _perfectly_ honest with you, ...  no and no.

I've recieved a number of emails from people who've said they didn't think
the bolt-on brace did very much, or that they didn't think it was was worth
the money, or it wasn't worth the added hassles, or they took it back off,
or whatever, so I'm not seeing a lot of real agreement out there.

Second, and I have a fair amount of experience with this one, without an
objective measure, or at least without double-blind testing, when doing
subjective testing, you simply _must_ account for cognitive dissonance,
placebo effect, emperors new clothes, and all of that. After spending a lot
of money, time, and effort installing a shiny new widget, there just aren't
too many people who are capable of giving a totally objective assesment.

Whereas, our capacity for self-dellusion is truly amazing, the new
convertibles by BMW, Honda, etc. really don't shake like our old Alfas do.
I'd have to say, getting our Alfas to stop shaking is a matter of
engineering, and for that, we'll need objective data.

Does that make sense?

RON
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