Now we move into some of the more complex chassis adjustments. Most racers will benefit by using the
more basic adjustments, because it is easy to dial yourself out with some of the adjustments we are
going to cover from this point on.
Wheelbase
What is Wheelbase?
Wheelbase is the distance between the center of the front axle and the center of the rear axle.
How do you determine what your wheelbase is?
Typically one would use a ruler, calipers, or any measuring tool that can measure the distance between
center of front and rear axles.
How do you adjust wheelbase?
Wheelbase can be adjusted several ways. The most common adjustment is by moving shims on the rear
outer hinge pin to move your rear hub carriers forward or back. Some cars are designed and built with
multiple holes in the chassis to run long or short wheelbase, and some cars are designed to use shims on
the inner rear hinge pins to allow movement of the rear arms forward and back as well. No one way is
right or wrong, and all have similar effects on handling.
How does Wheelbase affect the handling of my chassis?
In General, the shorter your wheelbase, the more your car will want to rotate in the corner. Likewise a
longer wheelbase will tend to rotate less in the corner. Shorter wheelbase chassis tend to be more
aggressive and harder to drive, while longer wheelbase chassis tend to numb down the steering and
make the car more forgiving.
Wheelbase and How It Affects Weight Transfer
Adjusting wheelbase changes the location of your static weight relative to the front and rear axle. In
simple terms, one must take note of how their wheelbase adjustments change location of the weight
fore and aft.
Off Power:
If you lengthen the wheelbase, you reduce chassis rotation because the static weight is further ahead of
the rear axle. The further your weight is to the rear of the chassis, the more weight can and will be
transferred to the front upon corner entry (off power). Lengthening the wheelbase reduces Off Power
Steering by reducing weight transfer to the front of the chassis. Shortening the wheelbase moves the
weight more toward the rear, allowing more weight transfer, which increases off power rotation.
On Power:
Just like with Off Power weight transfer, lengthening the wheelbase reduces on throttle rotation,
however to a lesser extent, and not because of weight transfer, but because of the nature of a longer
wheelbase chassis resisting rotation. Likewise, if you are tight on throttle, shortening your wheelbase
can help your chassis rotate on power because a shorter wheelbase promotes more rotation.
Wheelbase Quick Notes:
- Longer Wheelbase is ALWAYS more stable and easier to drive
- Shorter wheelbase is ALWAYS more aggressive and rotates easier
- On tight tracks, Short Wheelbase may be the answer to get the chassis to rotate like you want
- On tracks with wide flowing corners, Long Wheelbase can be much smoother and consistent
Kickup
What is Kickup?
Kickup is the front inner hinge pin angle, as measured in relation to the chassis plate. Almost ALL chassis
used in RC Dirt Oval have a kickup angle. Typical angles range between 10-35 degrees. If your chassis
had its front inner hinge pins parallel to the chassis you would have zero kickup. Positive Kickup is found
on all chassis, and means that the front of the hinge pin is higher than the rear of the hinge pin.
What does Kickup do?
Kickup controls how much the chassis will squat during braking and/or deceleration during corner entry.
Kickup also sets the plane for which your caster blocks will be measured to figure total caster. For
example, if you have 25 degrees of kickup, your total caster will be dependent on the degrees built in
the block relative to your kickup angle. So with a 25 degree kickup, and a 10 degree caster block, you
will have 35 degrees of total caster. If you have a 25 degree kickup and a -5 caster block, you will have
20 degrees of total caster.
How Do We Use Kickup to Control Weight Transfer?
- Running more kickup affectively puts more bind into the front end reducing how much the chassis will
dive, also reducing weight transfer. The more positive kickup you run, the more resistance to weight
transfer you will have, resulting in less initial turn in steering. - Running less kickup affectively reduces the chassis’ resistance to dive, which increases weight transfer.
The less kickup you run, the more easily the weight will transfer, which will increase initial turn in
steering.
No Free Lunch:
One of the downsides to tuning with Kickup is that your kickup directly affects your total caster. - Adding kickup reduces weight transfer, but increases caster. The more caster you run, the more
camber gain you will have, which can actually increase the grip level of the front tires creating more
weight transfer to the front. - Taking away kickup increases weight transfer, but reduces caster. The less caster you run, the less
camber gain you will have, which can actually reduce the grip level of the front tires creating less weight
transfer to the front.
SQUAT
What is Squat?
Squat is the angle of the rear inner hinge pin, as measured in relation to the chassis plate. The squat
angle controls the rear end of the chassis’ ability to “Squat” under acceleration, thus controlling weight
transfer.
How is Squat Adjusted?
Some cars have independent front and rear suspension mounts that use various pills or spacers to raise
or lower the front or rear of the hinge pin. Other chassis use tapered shims under the rear suspension
mounts to raise or lower one end of the hinge pin relative to the chassis. Either method you use, the
effects are the same.
There are three types of squat. Pro-Squat, Anti-Squat, and Zero-Squat.
Anti-Squat:
Anti-Squat is achieved by elevating the front of the Rear Inner hinge pin, or dropping the rear of the
inner rear hinge pin. The angle created in doing so becomes your amount of anti-squat. Typical amounts
of anti-squat are 1 to 5 degrees. Anti-Squat will reduce the amount the rear of the chassis squats down,
thus reducing weight transfer to the rear, which means the chassis will have more on and off power
steering. Anti-Squat is typically used ONLY on higher bite surfaces.
Pro-Squat:
Pro-Squat is achieved by elevating the rear of the Rear Inner hinge pin, or dropping the front of the
inner rear hinge pin. The angle created in doing so becomes your amount of pro-squat. Typical amounts
of pro-squat are 1 to 3 degrees. Pro-Squat will increase the amount the rear of the chassis squats down,
thus increasing weight transfer to the rear, which means the chassis will have less on and off power
steering. Pro-Squat is typically ONLY used on lower bite surfaces.
Zero-Squat:
Zero-Squat is the most typical setting and is achieved by adjusting your rear inner hinge pin to be
parallel to the chassis plate. It is called Zero-Squat, because you are not using Pro-Squat or Anti-Squat to
manipulate the weight transfer to the rear of the chassis. Zero-Squat will usually be the best balance of
rear traction and steering, and give the racer a nice balanced feel. Zero-Squat is ideal for use in most
conditions.
Racer’s Tip:
Squat is a fine tuning adjustment, and larger gains can be had by adjusting springs first. Squat, when
used properly can help fine tune a chassis and improve lap times, however, do not expect massive gains
by tuning with Squat. Squat adjustments will not turn a chassis that is a 6 out of 10 in to a 9 out of 10;
but it can help a chassis that is 8.5 out of 10 become a 9 out of 10.
Chassis Tuning 101
Matt Murphy’s Dirt Oval Chassis Tuning Guide