Wednesday, January 1, 2014

RE-Xtreme RC Drift Bible - Ackerman and Angle.

More geometry! Yes indeed. Steering ackerman and steering angle and a lesser extent toe angle. How much is enough and how effective is it all? 

all images from Yokomo Japan with a little modification.

This plastic setup looks old but actually it's the newer IMADOKI front end for the drift package. Why was it upgraded?  The answer is increased steering angle and faster ackerman. The ability to "catch" and "control" a drift chassis is a necessity.

The original Drift package is a 50:50 4wd drift car. As more people use the FCD set and a front one way for CS drift, the chassis simply isn't capable of performing without upgrades. The imadoki solution solves the puzzle in a basic way.

Increased angle comes from the c hub carrier being recessed and the knuckle also being notched so that they can physically move further inward on the type B suspension. The wiper is also thinner so it can move further toward the drift package gearbox.

So basically if you notched the plastic arm with a file, then also filed the c-hub you would end up with a similar capability. I have filed the alloy C hub carriers on my DIB to allow for more than 45 degrees. Every little bit helps, but there are of course things to consider.

Due to the length of the steering wipers the rate of the steering will increase as well as the distance from side to side so the angle the wheels turn will be increased also.

The length of the steering wiper is much longer, the length of the tie rod is much shorter. This means for the same amount of servo throw the wiper is moving further and therefore moving faster also which makes control and drive rate / steering curve on your controller a consideration. You may want to speed it up or slow it down electronically via the servo because the mechanical geometry is faster.

There is another option for angles we will come to soon.

 If you don't want to "hack" there are other newer options. This version from Yokomo offers a solid base but eliminates the steering angle restrictions from the C-hub carrier You basically can set the steering to turn until it binds on the front drive shafts.

So be careful.  Servo end points are not reliable stopping points. On impact and under side load damage can occur even if you think it's safe. 

The final option has been adopted heavily by the Rear Wheel Drive community but similarly works well on the CS 4wd machines.

Some people were not  keen to adopt this setup as the upper and lower ball joints can allow play in the steering and previously adjustability of KPI was not offered. Recently many knuckles are now available with KPI and this "type C" suspension is becoming a norm with reinforced clamped ball designs.

Large steering angle can be accomodated on 4WD machines with newer true universal joints and high angle CVD joints are also available. 60 degree capability is not uncommon.

Spacing the lower ball outward can adjust camber as well as the upper ball. Castor can be accommodated easily from the a-arm position so it's very flexible.

You will notice three positions in the knuckle for the steering arm connection.

Why is this? Ackerman.

 Here you can see the difference between a Type B and Type C Yokomo setup. The pivot point of the suspension also effects the scrub radius and must be taken into account.

So that's angle.

Ackerman is the angle that one wheel has in relation to the other during the sweep of the suspension.

Typically in a race car, the outside wheel must travel further around the corner so the angle of that wheel is important.

In Drift the ackerman component is completely different because when travelling around a corner the steering is not at 5 degrees lock. It is at 45 degrees lock or more. the leading wheel is about 100mm in front of the trailing wheel.

If you have perfectly equal ackerman. the "tram lining" effect can occur and instability can occur so many drifters prefer a wider ackerman for front end stabiltiy and control. 

In this example, the position of ball on the steering knuckle creates a 7 degree change.

If you have a 3.5 degrees of  toe out each side its possible to create a similar situation, however that 3.5 degrees each side occurs from the start to the end of the steering throw where this change occurs over the whole stroke with a zero degree toe starting position.

So if you have a whole stack of holes in your steering knuclkes and wipers, play around and see the changes. you will be very surprised at what happens to the speed and amount of steering as a result.

If you look at this picture, you can get an idea that a drift car is definitely not behaving like a race car. The angle of the front wheels can be used to "Steer" the rear and the importance of ackerman, toe, steering angle and all the other things I've covered about suspension combine to make it a very complex equation.

Beginners need advice, more than I can provide on this blog, but look, stare and imagine what your chassis is doing in this position. Components are there for reasons such as short or long tracks and the amount of grip you have, the amount of CS you are using and more. Changing components can be good or bad. testing is the key.

That 12 degree castor hub may need something else for it to work properly.



  1. Hello,
    I'll have a Dib-2 with Aluminium Type A Arm IB-GC3. I would like to mount 1.5 CS.
    It will be easy to ajust camber and caster.
    Is it enough ? Is this type C on DIB is already optimized for CS ?

    Is there an interest to try to ajust the ackerman and the kingpin angle ? If so, what's parts to use ?

    Thank-you for RC Drift Bible.

    1. DIB-2

      You can adjust castor and camber.
      You will need one of many of the new knuckle types to adjust KPI. Wrap Up, M's, MST or Mikuni etc.

      at CS 1.5, you won't be using much steering angle. once ou get to CS 3.0 then you will find true use of ackerman over the entire corner radius.

  2. Ok, then I'll use the original KPI.
    Thanks a lot.


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