Marcus RWD RC Drift Blog

RWD RC Drifting - Front Alignment UPDATE

RWD RC Drifting - Front Alignment

How does your tire look when counter steering? Steering does not have to be at full lock, but how your leading tire, and trailing tire contacts the surface is dictated by your front alignment. This is a combination of Camber, Caster, and KPI alignment.

In this setup, Camber is set at Negative 10 at neutral.

Leading tire is between 7-8 deg POSITIVE Camber

Trailing tire is at 7 deg NEGATIVE Camber

CAMBER

Camber angle is the vertical alignment of the wheel relative to the driving surface. Top of the tire should be leaning into the body at the neutral steering position, which is negative camber. The key element for front alignment in RWD RC Drift is the front tire contact patch that is primarily dictated by camber. Contact patch is how the tires contacts the surface which are using the edge with less contact, or using a larger surface with more contact. This applies to both the leading and trailing tires. As you steer, the camber will change relative to how the other alignment is set in combination with camber.

CASTER

Caster is the angle created by the steering pivot point of top and bottom arms, or the king pin in the front to back direction of the chassis. This angle should be leaning towards the back of the chassis. Caster is same as the steering fork of a bicycle, more lean = more stable it is, but also makes the steering less responsive. Caster is closely related to camber. As you turn your steering, the camber throughout the steering will change relative to the caster.

Leading tire = Negative camber will be cancelled out by Caster. Going zero camber, then positive camber depending on camber/caster setup

Trailing tire = Camber will increase by Caster.

KPI (KING PIN INCLINATION)

Caster is the steering pivot point or the king pin angle in the front to back direction of the chassis. KPI is king pin angle in the left to right direction of the chassis, leaning in to the chassis at the top, but NOT to be confused with camber.

KPI will change the ‘progression’ of the Camber in combination with the Caster throughout the steering stroke. This is a compound element of Camber, Caster and KPI.

Leading tire = KPI will add the amount of positive Camber gain. Depending on the setting, negative Camber at neutral will progress to zero, then to positive Camber

Trailing tire = KPI will cancel out the amount of negative Camber gain.

KPI can be utilized to adjust the Camber progression throughout the steering stroke, both negative and positive.

These are simple simulation of how Caster will add Camber from Neutrail to full lock on Leading and Trailing tires. To simplify the test, Camber is set to ZERO.

With Camber at ZERO and Caster at ZERO, there is no change in Camber for leading and trailing tires.

With Camber at ZERO and ADDING Caster, the amount of Caster adds/subtracts to the Camber.

In the next simulation, KPI has been added. Again, Camber is set at ZERO.

With Camber at ZERO and Caster at ZERO, the amount of KPI affect the change in Camber for leading and trailing tires.

With Camber at ZERO and ADDING Caster, the amount of Caster adds/subtracts to the Camber.

On the Leading tire, you can see the KPI added more positive Camber to the Caster. On the trailing, the KPI cancels out the camber change from the Caster.

TUNING CAMBER / CASTER / KPI

The total tune between these 3 elements will dictate how the Camber progresses, how the tires contacts the surface, and also at what point in the steering stroke.

>Negative Camber at full lock = Tuning the leading tire to stay negative Camber throughout the entire steering stroke up to full lock.

>Zero Camber point = Tuning the point where the leading tire goes to zero Camber at a certain angle of the steering stroke

>Positive Camber at full lock = Tuning the positive Camber at full lock to be opposite of the trailing tire for both leading and trailing to look parallel in Camber

FURTHER TUNING CONSIDERATION

There are few more elements in setting the front alignment, in addition to the Camber/Caster/KPI to further dial in the steering characteristic.

TRAIL

If you have a front Knuckle that has the ability to adjust Trail, then it may be worth trying. Trail is the offset of the axle or tire rotation center relative to the steering pivot point or king pin. The axle behind the king pin is negative trail, axle being in front of the king pin is positive trail.

Positive trail = Will increase stability steering less responsive

Negative Trail = Will reduce stability, steering more responsive

Trail has a similar effect as adding caster, but adding caster also affects camber, therefore adjusting trail in combination to camber and caster as is another way to tune for stability and responsiveness.

SCRUB

Scrub is the distance or radius of the steering pivot point or king pin to the center of the tire. What scrub does is it dictates how much the front tires move relative to the steering radius. Scrub can affect steering responsiveness and more scrub will drag the tire as you steer.

However, in RWD Drifting, more scrub allows for more clearance for steering linkage to achieve more lock, so it will be a balance to tune the scrub with the amount of lock.

More Scrub - Less steering responsiveness, more drag, more clearance for steering linkage

Less Scrub - More steering responsiveness, less drag, less clearance for steering linkage

SUMMARY

This write up covered the basic tuning aspects of front alignment. Hopefully was a good reference to understand how these elements come together and help you tune to your liking. There are other elements such as bump steer, upper and lower arm settings, and the most obvious being Ackerman.

This is the OVERDOSE Adjustable Knuckle Type-2 which is one of the most versatile Front Knuckles that has been around for a few years. Adjustments for KPI of 0, 3, 5 and 8 deg, as well as spacer adjustments for Trail. The linkage position adjust-ability is very useful in dialing the desired Ackerman.

The most recent discovery for me was the Shibata GRK light weight front knuckle Ver Y designed by the GRK driver Mr Yoshiba. I have always loved the adjustability of OD Front Knuckles, and this one was an eye opener for the balance of stability and responsiveness, as well as a full parallel Ackerman throughout. KPI is set around 3 deg, positive trail of 0.5mm, with slightly higher scrub even with 5mm hex and 6-7mm offset wheels, and a steering linkage point strategically set to achieve a full parallel Ackerman.