|I think it is
possible to draw a distinction between two types of shock adjustments you might
make. The change is either for:
(a) Response, control of the chassis platform, and/or "wheel control"
And we should probably add another.....
(c) Specific insights from dynoing and working with shocks.
We should be aware that some changes we make under (a) can change balance.
There is general agreement amongst racing people
about the aims of shock tuning for response, control of the chassis platform and tyre
compliance. We want quick response, but not too quick for the driver to handle, good
control of the chassis platform, and good tyre compliance. We could consider
adjustments to rebound particularly, but also bump, to improve response in initial turn
in, improve power down, and control the car in roll, dive and squat. These are the
most important shock adjustments. A general procedure for baselining shock settings,
as recommended by most racing shock manufacturers, is shown at the bottom of this page.
Smithees Shock Tuning for
|With shock tuning for
balance, you are choosing a particular transient (corner phase), a movement of the car,
where you can wedge or de-wedge the car, sometimes to increase overall grip and at other
times, to make the car more progressive for the driver. For example, you may want to
improve turn in, or reduce the onset of oversteer on corner exit. Note that
improving one corner phase may influence another corner phase for the better, or worse.
1. Draw a diagram of your corner phase showing where the weight
is going - an arrow from the shock(s) in rebound to the shock(s) in bump.
2. Consider the affect of
weight transfer for the front wheel pair first, and then the rear wheel pair seperately.
Is the weight (as indicated by the arrow on your diagram) moving towards the inside wheel,
or the outside wheel? This will tell you if you are adding to inside percentage, or
decreasing inside percentage, for each of front and rear wheel pairs.
3. Consider whether the
increasing or decreasing inside percentages at front and rear are adding to your aim of
wedging or de-wedging the car, or subtracting from it.
4. If the weight movement is helpfull, stiffen that shock (or
shocks). This will speed up the weight transfer.
(Note added after
Claude Rouelle Seminar, 2004) This a complete error.
shock will slowdown weight transfer)
If the weight movement is in the
wrong direction, soften that shock (or shocks). This will delay the weight transfer.
For road racing, we change both front and/or both rear shocks so that the car
behaves the same for RH & LH corners.
We know it is inside weight
percentage, front vs rear, that affects balance. So for the diagonal weight
transfers, if we soften one corner, we always stiffen the
opposing corner, and vice versa. There are any number movements of the race car
which you could influence using our tuning procedure. As with all suspension tuning,
the chassis must be stiff enough to allow the loads to build, and the shocks need to be in
a tuneable range.
1. With shock tuning for balance,
we are wedging and de-weding the car (or leaving wedge unchanged),
the shocks are only applying loads while they are
moving in bump or re-bound (transients).
Too hard to say what happens.
Weight transfer is slowed, tyre load peak may be reduced but will be spread
over a longer period.
2. The stiffer shock always transfers
weight faster than the softer shock, in both bump and rebound.
If a shock is bound up ie shock stiffness
goes to infinity, weight transfer is almost instantaneous, like hitting a hard bump
stop. If the shocks have failed completely ie shock stiffness is zero, weight
transfer is slow and spongy (and of course the chassis hunts around in an uncontrolled
The effect of a shock hitting full droop
is interesting. Any weight left to go must instantly be transferred to the other
side. At the rear this could cause snap oversteer, and lack of tyre compliance on
the inside rear wheel for acceleration. All bad. So why would we do it on the front - the
so called "zero droop" front suspension? There are a couple of positive effects I can think of. The car would
stay jacked down at the front, helping aerodynamics (less air under the car), and negative
camber in droop would be reduced, helping grip on the inside tyre.
3. The stiffer shocked wheel pair
will always transfer more weight than the softer shocked wheel pair (just as for wheel
pair stiffness from springs, bars and suspension geometry). Each shock adds to wheel
pair stiffness, whether in bump or rebound.
4. A stiffer shock
transfers the same amount of weight as a softer shock. Think of it like
this. As weight is transferred in the car, and the chassis rolls or pitches,
the tyre load builds or reduces depending on the springs and bars.
5. In the last phase of
roll or pitch, the stiff shock in rebound is still be moving, while a softer shock would
have already stopped. The chassis is still moving. Won't the stiff shock still
be transferring weight?
Yes, it will
6. "Less front rebound allows for a greater amount of weight transfer to
the rear under acceleration." The same
amount of weight will transfer for stiff or soft rebound in the front.
Yes, but it will be faster weight
transfer with softer rebound
So why would
drag cars go for very soft rebound in the front? I guess it would be to pitch the car high in the front, so as to overshoot the front
springs in extension. This, along with some pro-lift in the rear suspension, might
lift the centre of gravity, and this will transfer more weight. The
exagerated chassis movement might also create some inertia to help rear tyre loadings.
I think they call all this "wrapping the tyres". None of it
applies, except at the drag strip.
7. Let's very quickly revise
weight transfer in pitch. Most racing people understand weight transfer in roll
well enough. Pitch is the same as roll turned around 90 degrees. So, instead
of front and rear wheel pair stiffness, the amount of weight transfer will be in
proportion to RH and LH wheel pair stiffness. For road racing, RH and LH wheel pair
stiffness will be the same. So weight transfer in pitch is 50-50 each side.
The car is not wedged. For asymetrical speedway set ups, if the car is RH stiff, the
RHS side transfers a greater percentage of the weight transfer. The car is wedged in
forward pitch, and de-wedged in rearward pitch (in relation to LH turns). If the
car is LH stiff, the car is de-wedged in forward pitch and wedged in rearward pitch.
8. We need to work with the
shocks showing the greatest movement, otherwise the effect we are after will be cancelled
out. This might be
determined by driver description, track side observation, or from data acquisition.
Here's one easy tuning adjustment that
always works. Where the whole car unloads over a rise in the track, all 4 corners go
into rebound. For instance, as you come off the dogleg at Oran Park, the car goes
light and you are still turning left. (Too many Konica V8 Lite Supercars have looses
here.) Set your front low speed rebound stiffer at the front than the rear.
The stiffer front end will unload the most. So our car will be momentarily wedged
(tighter). If shock settings were stiffer at the rear, the car would momentarily
de-wedge (or be loose).
If it were possible to work out which end
of the car was moving the most, either by observation or on-board data, you could change
one end only.
More on Shock Tuning:
The shocks must be in sync with your
springs. If you increase your spring rate you probably decrease shock bump, and
increase shock rebound, and vice versa. You need shock dyno graphs to show that your
shock adjusters are working as expected, and matched between shock pairs. You
will probably want a fair bit of "nose" on your graphs, irrespective of whether
you have low speed adjustment or not. This is to give you good low speed control
over the chassis platform. As a result, you may be able to run softer springs to
increase tyre compliance with the road.
Your bump curve on the dyno graph will probably be digressive ie flatten out with
increasing shaft velocity, so the car is not too harsh. Your rebound curve should
show increasing force pretty much in proportion to shaft velocity, and only digress at
higher shaft velocities. You will want as much rebound as you can, short of jacking
the car down excessively, lifting wheels clear of the road, or where too much rebound
affects power down.
Hopefully, your car will work over a
reasonable range of shock settings. Only then could you consider using shock
adjustments for balance, as per (b).
PLEASE READ THIS.....
There is a huge caveat on all of this as it relates to shock tuning - you must
work on the shocks with sufficiently greater movement for it to work. Also the
driver must be consistent with the way he balances the car as he drives, otherwise the
movements of the car may be different.
Speedway teams are at less risk of getting it wrong. They
only need to change one side at either front and/or rear.
Consider the following table from the Carrerra Shocks website:-
2 Issue 1
Page 4 of 4
If you only run
at one track, youve probably got your set-up down pat. However, if you travel to
different tracks getting your car handling well, quickly, is a must if you want to
Here are a few tips to help you get close.
ASPHALT HANDLING TIPS
| Short Tracks:
||Softer all the way around.
| Flat or Tight Turn Tracks:
| High Bank Tracks:
||One step stiffer on RF & RR.
| Push Going In:
||Softer compression on RF or
stiffer rebound on LR.
| Loose Coming Out:
||Softer RR or stiffer rebound on LF.
| Loose Going In:
||Softer rebound on LR or stiffer RF.