Ackerman Steering

Rudolph Ackerman invented Ackerman Steering back in the days of horse drawn carriages. Monty Ackerman is my neighbor and an excellent basketball coach of 10 year old kids. While we can give Rudolph credit for the Ackerman Steering theory, Monty can help us to illustrate how the theory is applied.

When my kids were 10ish - my neighbor Monty was kind enough to volunteer to coach basketball. Monty had figured out the right way to teach kids and was a perfect role model for the little ones. He set a fine example for us bigger kids too. As a parent, I wanted my kids to work hard in hopes that they would become the next Michael Jordon. It seems in my enthusiasm, I would take youth basketball too seriously and applied my cheers in a less than perfect manner. I still remember today the glare from Monty when I vocally displayed displeasure with the teenage referees. Oh, Monty is a mild mannered man and while very rare, I know I had his glare coming. It is funny to look back and vividly see how too much of a good thing was a detriment. It is a bit embarrassing to me now but my support for my kids clearly went over the line. I wonder how many other parents go a little too far at the quarter midget track.

My goal in the basketball gym was to be supportive of my kids but, in implementation, I went way too far. Live and learn - sorry Monty! While Monty has nothing to do with the Ackerman Steering theory, he has everything to do with doing things in a balanced manner. His wonderful family exemplifies balance. When using Rudolf Ackerman’s principal, it pays to understand that everything has a time and place and using the “right” amount of steering encouragement will help your car go faster. Knowing when to use the Ackerman principle is even better.

Ackerman Steering as applied to stock cars is simply using geometry to make the LF tire turn farther and faster than the RF tire as the car is turned to the left which is known as Pro-Ackerman. The simple idea is that since the radius at the inside of the track is shorter than the outside it follows that the LF will follow a sharper radius than the RF. The sharper inside radius can create the need for more degrees of steering at the LF - that is the idea anyway. If you imagine a car with the steering wheel locked fully to the left it would drive in a perfect circle under power. The circle created by the LF would be smaller than that of the RF. Thus, more degrees of LF steering can make sense. The idea is similar to how rear stagger uses the LR tire and a smaller LR diameter to match the smaller arc found on the inside radius of the track.

  • Stagger, Rear Steer, and Ackerman Stagger, Rear Steer, and Ackerman

    You can think of stagger, rear steer and Ackerman in the same chassis category If you match up the Ackerman Steering theory and rear steer you could overcome handling characteristics at a given track. But - excessive stagger, Pro Ackerman and rear steer could be a recipe for disaster so moderation applies.

    Anti-Ackerman can sometimes be used to your advantage as well. With Anti-Ackerman the LF turns less than the RF through a left hand turn. At times, we can use this geometry to make our cars faster.

    The question is when does more LF steering (Pro-Ackerman) make sense? My answer is on smaller low speed track. If your track has a sharp steering transition in the center you might find a speed gain by using Pro-Ackerman. If your track is large with smooth sweeping corners then Pro-Ackerman will produce more negatives than it is worth. Remember our pal Monty – we want to avoid too much of a good thing. With Ackerman it is our goal to not go overboard. Under using Ackerman is better than using too much nearly every time. I wish I could go back in history and use a little less “enthusiasm” at the gym.

  • Match the LF arc to the smaller radius found at the inside of the track Match the LF arc to the smaller radius found at the inside of the track

    Pro Ackerman is shown in the drawing as the LF tire turns more than the RF. The idea is to match the LF arc to the smaller radius found at the inside of the track. Be sure to keep in mind the geometry changes as the car turns left while remembering to consider the steering changes as the wheel unwinds back to the right. Ackerman should be used in moderation but it can be the chassis seasoning tha makes your set up "just right".

    On a stock car Ackerman is adjusted by using the slot on the LF spindle. With a rack and pinion steering system the tie rods run slightly forward from the rack out to the mounting point on the spindles. As you move the tie rod mounting point closer to the ball joints at the LF you speed up how fast the LF turns and you increase how much it turns. The concept is the same with a drag link and steering box.

    A standard Pro-Ackerman amount is 2 degrees in 10 degrees of steering. In other words, if you turn the RF 10 degrees the LF would move 12 degrees. It pays to think about how the LF turns when using Pro-Ackerman. As you turn left, the LF turns more than the RF. As all things have an equal and opposite reaction you should understand that the LF turns back faster at corner exit as well. You can use the Ackerman effect to your advantage in the middle while turning left and on exit as you unwind the steering wheel.

  • Slotted adjustment on the Left Front for Ackerman Adjustment Slotted adjustment on the Left Front for Ackerman Adjustment

    Typical stock cars have a slotted adjustment on the Left Front for Ackerman Adjustment. The fixed bolt on the right shown here is planned out by your car builder in conjunction with the rack forward and aft mounting location. With the slotted LF adjustment moved back the tie rod end moves closer to the ball join center line the steering geometry speeds up how rar the left front spindle turns. Adjusting is simple yet chassis engineers should utilize "just enough".

    In the northwest there are two tracks of similar quarter mile size yet, my thoughts on applying Ackerman are completely different. Wenatchee Valley Speedway was rebuilt by racing legend Garrett Evans. Garret is a racer and he rebuilt Wenatchee into a personal shrine to include new pavement and high banked sweeping turns. The playground for the kids and awesome viewing areas are added bonuses. The other track for comparison is South Sound Speedway which was revamped by the Behn Family. Butch Behn is an old school promoter and took a worn out old speedway and made it very cool. The million dollar stainless steel self cleaning toilets purchased from the city of Seattle for a few hundred bucks are a comical yet clean example of Butch’s wisdom. Both Wenatchee and South Sound are unique tracks. Similar size - but, completely different. These two tracks make good examples for describing when and how to utilize just enough Ackerman Steering geometry.

    At Wenatchee, I was not a fan of Pro-Ackerman. In fact, I would prefer Anti-Ackerman when racing at the Wenatchee quarter mile. Wenatchee has a smooth entry into the corners and the car rolls through the middle if you have the car right. But, even with a fast car, the dynamics of turn 4 at Wenatchee could create a loose condition on exit. Pro-Ackerman would exemplify the problem. On exit and under power the rear tires would effectively push against the toe out created by Pro-Ackerman on exit. The scrub of front tires resists the power of the rear wheels causing the car to break loose late in the Wenatchee corners. At Wenatchee – if you could turn the car in the middle and get a straight shot off the car would hook up and be really fast. Pro-Ackerman could and does make the car loose at late exit as the LF front tire is turned too much under hard acceleration. For this reason Anti-Ackerman is a better plan at this particular track. Anti-Ackerman would slightly toe in the LF on exit. The small amount of Anti-Ackerman induced toe in would help the driver to unwind the steering wheel at late exit point. The right place at the right time applies here and the Anti-Ackerman affect would help the driver be smooth and hooked up on exit.

    South Sound presented unique challenges and I would look at Ackerman in a different way. It is interesting to think about how tracks that look similar from the grandstands invoke a chassis set up mindset that is completely different. The South Sound challenge is that the driver needs to turn the wheel aggressively and quickly in the center. At Wenatchee you can drive through the center with a comfortable amount of steering input. At South Sound, drivers have to get after turning the wheel in the middle. The corners are not quite as rounded and the transitions are more abrupt. The groove relies on a big time pivot in the middle. I think the chassis challenges are that at Wenatchee hooking the car up at late exit was my goal.

    At South Sound a strong pivot in the middle was comparatively more important. If the car pivoted in the middle it would take a nice set and be hooked up on exit. All tracks need a good pivot in the middle but at Wenatchee a good pivot can lead to late exit looseness. At South Sound a good pivot makes for a longer straight away and more over all speed.

    The result is that Pro-Ackerman can help in the middle but might come at the expense of the exit. The trick is to use the Ackerman theory without creating the drawback or condition inherent in a given track. At the end of the day – zero Ackerman is better than too much. That said – the right amount can help cure a corner condition if the amount and timing are right. Ackerman has no affect on the straights and the geometry change increases with steering input. This idea can help you to have a stable entry as Ackerman change increases the more you turn the wheel. At entry the affect is minimal.

    Depending on the track you can add extra Pro-Ackerman for qualifying. The thought is that you may be able to add “too much” Pro-Ackerman for 2 laps. The added LF toe out can build heat quickly in the LF for a qualifying run. Trial and error apply here but you could make the car loose on exit if you get to aggressive. If LF temperature is a problem at your track or if you run a high amount of wedge then a quick addition of Pro-Ackerman for qualifying can sometimes find you more speed.

  • Turn plates can be used to measure your Ackerman Turn plates can be used to measure your Ackerman

    Turn plates can be used to measure your Ackerman. Turn the RF tire 10 degrees and note how many degrees you have on the Left Front. IF the Left Front ends up with more than 10 degrees you have Pro-Ackerman. If the LF ends up with less than 10 degrees you have Anti-Ackerman.

    Ackerman can be classified in your mental adjustment section with rear steer and stagger. The concept is that you are matching up the roll out of the left and right side tires by using one of these three adjustments. If you combine rear steer, stagger and Ackerman you can build a chassis package that line up the best benefits of each. You should guard against using too much of any one of these adjustment types and if you are being aggressive with all three you could be asking for trouble late in a run. If you time the dynamic movements of Ackerman and rear steer could find you a rocket ship set up. Go too far and your rocket will become an evil boat anchor.

    Stagger is felt all the way around the track as the tire size is the same on the straight and in the turns. Rear steer occurs as the car rolls and Ackerman changes as depending on the degrees of steering input. You can imagine matching up the geometric change created by rear steer and Ackerman. Again – these options are best on shorter low speed tracks but they do have their place anywhere.

    Thought about the Ackerman affect is usually confined to when the car turns left. In practice, it is equally if not more important to think out what happens to the car as the steering wheel unwinds. Often, Pro-Ackerman is used has a crutch to help the car turn through the center. Many times racers would be better off if they used other adjustments to help the car turn through the center coupled with using Anti-Ackerman to help keep the car hooked up on exit. I will take a car that is a touch snug in the center with a solid exit every time.

    To achieve the most speed I think of stagger, rear steer and Ackerman as chassis seasoning. Just like a touch of salt on a good steak you can make your car feel better by adding a touch of seasoning to an already fabulous steak. Add too much salt and you are bound to upset the meal. While Rudolf invented Ackerman – we can learn from Monty and apply the benefits of Ackerman in a calculated, moderated and balanced fashion.

Go Forward – Move Ahead
Jeff Butcher
JOES Racing Products
4/28/10