"Set-Up
F355 Challenge for Racing"
(Conversation with Peter from Australia)
By Rob Schermerhorn
The
Inquiry
Hi
Rob,
Since everyone is giving you such a good rap, I was wondering if
you have basic setup information for a 355CH. No one in Australia
knows a damn thing about them, and I'd LOVE to have a basic starting
point for spring rates, ride height and suspension settings. It's
a pre wing model, and is used on the road as well. Any help would
be very appreciated...I've been trying to get to the bottom of this
for years! It doesn't handle badly, as such, but it would be good
to know that it's in the ballpark.
-Peter
Dear
Peter,
I need
additional information on your set-up, experiences, and expectations.
Is there a benchmark you're shooting for (lap time or specific car
you want to out handle on the track)? What's your own personal driving
CV? What are your current ride heights, toe, camber, and castor?
What tires and pressures? Do you have tire temperature data? How
much street driving as a percent of time or mileage? How important
is street comfort and street tire wear? Is your chassis a factory
built car or conversion? What year chassis? Do you know if all updates
have been installed and do you have the spare optional springs,
set of suspension packers, anti-roll bars, oil cooler update?
All
of this information helps me with recommendations tailored to you
and your car.
I can
supply a baseline, but it assumes all existing Challenge equipment
and Pirelli slicks, which may be different from what you have. Finally,
the chassis can be tuned to the driver's preferences to a certain
extent.
Best regards,
Rob
Schermerhorn
More
Information
Hi Robert,
Well,
I'll try and answer these questions as best I can...I'm not that
mechanically minded. Driving wise, I just go to club days. I usually
win outright unless there's a much faster car there, and sometimes
even then. I started in 1985 when I bought my 3rd Ferrari and have
done plenty of practice and courses over the years. I'm not a great
driver, but most of the others are much worse. I use the car mainly
on the road and track it 4 or 5 times a year. Current ride height
is 160mm rear and 135mm front at the lower suspension arm bolt.
I usually use Hoosiers on the track and aim for about 40psi hot,
which is generally the accepted figure. Comfort and tire wear is
not of PRIMARY concern, but nevertheless the car will always have
to be a compromise...I realize that.
It's
a factory challenge. 1996 and hasn't had any of the 1998 upgrades.
I have 1050lb springs in the front and 700lb in the back. The standard
1800lb springs just felt far too hard compared to the back. I also
have the 900lb/2200lb combination, but would consider that they
would
be an abomination considering what the 1800lb was like! I have no
suspension packers.
Baseline
recommendation is all I'm looking for. I realize that different
conditions, tires, driving styles etc ALL make a difference, but
I'd LOVE to know that I'm in the ballpark, as I said, and would
be happy enough with that. Shockers are another issue, but I don't
now HOW we'd ever get around that subject, unless there's a simple
bump and rebound "number" or something.
Thanks
in advance,
Peter
Now, the Set-up Specifications
Dear
Peter,
I understand
your reasons for compromise. The set up I'd recommend won't be suitable
for your comfort.
Ride Height and Chassis Rake
I run the ride height as low as practicable, 90 mm front, 95 mm
rear, typically, measured from the bottom of the chassis, just behind
the front wheel centerline, and just ahead of the rear wheel centerline,
not including the undertray. Go as low as possible, and balance
high-speed turn in and stability via chassis rake adjustments. You
can vary rake at either the front or rear. Keeping the front as
low as possible gives best aero, keeping the rear as low as possible
aids in rear stability in medium and high speed corners. Most important
is the highest speed corner and sacrifice the slowest (even if it
leads to a long straight). More rake improves turn in, but tends
to destabilize (makes the car feel nervous) at higher speeds. Some
guys prefer to "kill" the front by raising it to balance
the chassis and give more stability.
Toe-in
Increasing rear toe-in will get the rear back under control, I've
run as much as 45 minutes of total toe-in. Toe in or out at the
front is up to you, but usually no more than 10 minutes either way
total. Out promotes turn-initiation, but may 'bird-dog' or increase
high-speed straight-line directional instability, which novice drivers
may find disconcerting.
Springs,
Dampers, and Anti-roll Bars
Typically, I always ran the big front springs, the updated larger
front ARB, larger rear ARB, and the 700 lb/in rear springs. I manually
locked the rear dampers full stiff (CCW) and estimated the front
at 15 degrees off full stiff. The adjuster only rotates 90o from
full soft clockwise to full stiff CCW, so the adjustment is very
sensitive. You must secure these settings or the damper fluid tends
to push the adjuster to full soft (CW). I used RTV gasket silicone
because I had time to let it set up.
Packers
The idea with the 355 Challenge is to lower the chassis as much
as possible which benefits aero and CG, add camber appropriate for
the tires, and offset the increased camber gain by reducing roll
via the stiff (2200 lb/in) springs and adjusting the packers. On
a smooth track, you end up riding the bump rubbers in high 'g' corners.
When done properly, the car is sensitive to 1mm change in packers
and 2 psi tire pressure changes with Pirelli slicks.
Wing
The fastest drivers ran the wing at zero, or +2 at a slow track.
Remember to compensate wing angle for rake changes.
Changing
ride height changes camber and toe, though I'd always do quick changes
in ride height during practice and then just reset and verify all
settings in the evening to save valuable track time. Corner weighting
is mandatory here too.
Running
the soft front springs, as you have found, increases road comfort,
but you're losing ultimate grip and balance here. As you said, set
up is always a compromise.
The
Hoosiers are a great DOT race tire. Do you take pyrometer readings,
three per tire, outside, center and inside? If not, this is the
best way to determine camber. Sounds like your pressures are in
the right range. If you don't do temperatures, you can default to
judging tire wear and feel from your a**-o-meter.
Trying
a set of slicks will drop lap times 3 to 6 seconds per lap at a
twisty 2 mile track, driver skill dependent.
Fun.
Best
regards,
Rob
Schermerhorn
The
Reply
Hi again Robert,
wow...that
is really incredible information. Thank you so much. Now I'm going
to go out and play with it. I finally understand why they supply
those HUGE front springs. I'm going to have to try this. I'm not
sure that I'll be able to lower is quite as much as you've recommended
as I drive it to the track and might not get out of my driveway.
I'll also have to check and see what size roll bars I have. I know
they're bigger than the road car, but I'm pretty sure they're not
the ones you're referring to. Do you have diameters of them, by
any chance?
Peter
Peter,
Search
the Fchat archives for 355 Challenge information, I've posted quite
a bit, including ARB sizes and equivalent wheel rates.
Rob
Other
F355 Challenge Information
1995
Challenge cars were imported as road legal though all did at one
time have the complete kit installed. These are not converted street
cars. If you find an original Challenge manual, it will show the
differences between the factory Challenge and "how to"
convert a normal road car. All factory Challenge have structural
reinforcements to the front suspension, the spring rate in front
is 2200 lb/in, the normal road cars require removal of the upper
spring/shock mount and welding in a beefier component. I believe
there may only be a couple documented truly converted from normal
street production 1995 Challenge in the USA. BTW, the 1995 Challenge
came with the AC compressor, hoses and condenser in a box, not installed.
There
are no 1996 Factory Challenge in the US as the 1995's did not all
sell until 1996. I managed the last 1995 sold, a red/tan, originally
campaigned by Tom Murphy in Challenge, then in SCCA T1 (Runoffs
podium in 1998), then sold to a gentleman on the west coast and
converted back to Challenge roll cage.
The front and rear bumper covers are Kevlar, not carbon fiber, though
carbon ones were/are available, though technically were illegal
for Challenge.
The
undertrays are fiberglass originally, which is good because they
are torn up with an agricultural excursion.
There
is an upgrade to the oil cooling system in 1997. It eliminates the
oil-to-water heat exchanger and uses a conventional oil-to-air heat
exchanger. Before the authorized kit was released, teams could fabricate
their own version, though it was to be replaced in '97 to remain
legal.
Manual
control of cooling fans is standard and recommend you run at all
times on track. They also remain thermostatically controlled.
There
is an upgrade to the ABS ECU in 1998, very important. Upgrade to
quick ratio steering and pump matched to this rack. Larger front
ARB, too. This was part of one large update kit mandatory for 1997
that included the wing.
Brake
rotors are available from any Brembo dealer, I recommend running
slotted only, not drilled, unless rules prohibit otherwise.
I have
run Performance Friction and Pagid pads. I like the PFC's best,
but this is more driver preference for pedal feel than outright
performance improvement. The Pagid R4-2 (blue) is the OEM Challenge
pad.
In
the US, SCCA homologated the complete Challenge specification with
the exception of tires. They may have adjusted the weight, though
I ran the Challenge weight in 1998.
Anti-Roll Bar Changes
This was a front and rear upgrade. The old front bar is approx 0.875
inch diameter, 35" length, 7" arm, 0.5 motion ratio, yielding
a WHEEL RATE (the only spec that really matters) of 96.5 lb/in.
The
old rear bar is 0.669" diameter, 39" long, 7.75"
arm length, 0.6 motion ratio, yielding a wheel rate of 35 lb/in.
New
front bar is 0.945 inch diameter, wheel rate of 131 lb/in.
New
rear bar is 0.748 inch diameter, wheel rate of 54 lb/in.
The
0.945 front bar is the only way to go, the car needs front roll
stiffness.
Wheel
rates with the big front spring and soft rear (2200 and 700 lb/in,
respectively) is 1078 lb/in front and 506 lb/in rear. So, you see
that relative to wheel rate of the springs, front bar does contribute
some, rear bar relatively much less. To put all these numbers into
perspective, the stock wheel rates on a 308 series are around 100
lb/in. comparatively very soft.
Wheel
Rate Primer
The difference between wheel rate and spring rate is the wheel rate
(also in lb/in) is what the driver feels and the tires deal with
while driving. Wheel rate takes the geometry of the suspension into
the equation and makes it easy to compare different cars. A better
comparison is ride frequency, but I'll present one thing at a time.
Motion
ratio is simple to find. Jack the spindle up one inch and measure
how far the lower spring perch has moved relative to the upper spring
perch. On a 348 rear suspension, the spring perch will move an average
of 0.85 inches for every one inch the wheel moves. So, the motion
ratio for 348 rear is 0.85 (you may see equations that use the inverse
of this number, Carroll Smith's equations would come up with 1.18
for the ratio).
With
this knowledge, one discovers that many Ferrari's are designed with
wheel rates as low as 100 LBf/in, which is the TR rear double shock
suspension. So your 200 LBf/in spring in the 308 drops with the
motion ratio to 98 LBf/in. approximately. The equation is WR = SR(MR)2,WR
is wheel rate in LBf/in, SR is the spring constant in LBf/in, and
MR is motion ratio where MR is stated as Dshock position Dwheel
position.
Why
are Ferrari's so "soft"? This term is relative, IMO, Ferrari's
are no softer than most other road going cars, even other sporting
automobiles. Suspension design is all about compromise with a road
car. The environments change, the market is world wide. Ferrari
determined that this is the best solution, and I agree. Most Ferrari's
are comfortable, even on long drives (and I've driven them cross-country),
and sporting enough to be better in many ways than the competition.
Ferrari improves on the average sporting car with a bit more suspension
damping. As an owner, overall you are satisfied. But this compromise
in design opens the door for improvements if you (the owner/driver)
have interests outside Ferrari's average design parameters, like
track events or actual competition on the racetrack.
For
reference, the front wheel rate of a F355 Challenge car is 1,078
LBf/in with a 2200 LBf/in spring! This is very uncomfortable on
the street, plus this system utilizes a tender spring to take up
slack when the suspension goes full droop, and comes crashing down
on this tender spring with every slight roadway undulation.
Questions?
Please email me right here: Info@DeltaVee.net
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