||Strain Gauge Installation Service
( for any data system)
- Dynamic Corner Weights
- Load Transfer
- Aero Loads
Data Analysis: Strain gauges on the push rods (or pull
rods) of a race car enable you to log dynamic
corner weights. The CDS Track Master software turns this corner weight raw data
into many useful answers such as:
The Front Load, Rear Load, and Total Load are calculated (from the individual wheel
loads) and from those signals we calculate
the Load Bias and Aero Bias. The Load Bias is the percent of total load that is acting
on the front of the car, which includes weight
transfer due to acceleration, deceleration,
and change in pitch of the road (hills).
If you take those effects out you are left
with just the aero loads.
Aero Bias (shown in dark green in the above plot)
is the percent of total downforce that is
acting on the front of the car. The Aero
Bias formula has built-in conditions to ignore
the times when the car is under hard acceleration,
braking, or turning so that front/rear load
transfer does not factor into the calculation.
If your system has a vertical G sensor then
you can also factor out road pitch. The map
in the lower left shows the parts of the
track that are used to determine the Aero
Bias. Since there is always some acceleration,
deceleration, and road pitch in actual track
data, the Aero Bias calculation is not perfect but is close
and is very good for comparing aero changes
on the same car at the same track. It can
also be used in coastdown testing where the
results are very close to wind tunnel results.
The Aero Bias data is plotted as a function of Speed to determine the change in aero balance
with speed. As seen in this plot, the
of total downforce that is acting on
front increases from about 33% at 127
to about 38% at 153 MPH. Aero Bias
increasing as speed increases is desirable
Generally speaking it is best to limit the
variation in Aero Bias with speed.
The minor deviations from a perfect curve
reflect the "real world actual track
data" limitations discussed above.
Plotting the individual loads vs. wheel movements
give a picture of the effective Wheel Rates
at all 4 corners. The slight curve up at
higher loads shows the effect of bump rubbers
or "packers" on the actual wheel
These plots can also help identify mechanical
problems such as excessive friction, binding
or other hysterisis in the suspension. Notice
the wider distribution of data points in
the lower right plot (for the Right Rear).
There are also numerous "outlier"
data points in the Right Rear plot. These
are due to a mechanical problems such as
a loose joint, binding, sticking shock, etc.
Zooming in on these data points and seeing
where they occur can help to isolate handling
issues that are being caused by mechanical
The Front & Rear Lateral Load Transfer are calculated and plotted here in green
and red respectively. The Roll Couple, which is the percentage of lateral load transfer
that occurs at the front of the car, is also
shown (in blue at the bottom). The roll couple
illustrates how the load transfer distribution
changes as the car goes through the various
phases of cornering. Notice the high initial
values of the roll couple at the turn in
point of some of the corners as compared
to others. Since the higher values of Roll
Couple correspond to more weight transfer
occurring at the front, these points could
indicate high damper forces or bump rubbers
engaged at these points.
Other calculated signals that can be generated
from the load data include Percent Inside Wheel Load at each end of the car. This is the percentage
of total load at each end of the car that
is carried by the inside wheel. In the top
1/2 of plot above, the Front Inner Percent
is shown in green and the Rear is shown in
red. The load on the rear is more evenly
distributed in the corners
The rear inner percent minus the front inner
percent is called the Dynamic Wedge (shown in blue in the above plot). Usually
the greater the dynamic wedge, the
car will tend to understeer, since
of the car is working better than the
(from a weight distribution perspective).
Having actual load data can be huge advantage
to the Race Engineer who knows how to use
and analyze it. All of the above formulas
(and much more) are included in the latest
release of the CDS Track Master software.
||Can Your Data System Do That?
Complete kit for measuring loads on any push
rod or pull rod car, includes installation
of strain gauges on 4 push rods, 4 of our
SEN-12S amplifiers, and connectors (see note
List Price: $3000 for complete kit.
Email SARA to order!
- This price includes CDS style connectors
installed. Connectors for Pi, Stack Aim,
and other systems also available.
- Amplifiers require unregulated 12 volts.
Current draw is minimal (about 3 milliamps