Toymods Car Club Inc: Tech & Conversions => removing Ackerman Steering

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oldcorollas
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003

Re: removing Ackerman Steering

Mon, 17 November 2003 06:10

Jonny2TG wrote on Tue, 10 September 2002 03:45

Ok. Lets try the proper spelling "ackermann" and you get quite a bit of info. The very best quote on the internet is this:

"Ackermann Steering
Every area of human interest has its dark corners guarding arcane information, useful to very few but implying vast knowledge when dredged up and injected into a dull conversation. Airplane design, for example, has the infamous Reynolds Number, just the thing to spring on an instructor during a flight review who thinks he/she's got you on the run."

"In automobiles, the trivia winner simply has to be Ackermann steering. The mere mention of it in a room of would-be racers makes the conversational volume level plummet. To prepare you for such a day, here's a tantalizing set of online conversations that came through the Internet's 240 Z car list. You don't have to understand it. Just memorize a few lines, toss them in at the next meeting and watch the fun."

LOL, i remember reading this with much mrth many moons ago,.. where is it from??

as far as ackermann goes.....

it's used because inside and outside tyre have a different radius (form the point that the car is turning around) and so need to be at different angles to follow this line.

on road cars where you actually use full lock, ackermann is good as you don't scrob the tyres at full lock, and will generally reduce tyre wear.. the proviso of this is that you are not actually sliding the tyres at all.... soon as you do, true ackermann is out the window..

what it comes down to is the % of slip that a tyre needs for it to have maximum grip. road tyres are like 10% slip or more, whereas race slicks are only a few percent slip. (this is all on tarmac) you need to design the steering geometry with a few things in mind....
1) how much will the wheels be realistically turned when cornering hard (and design for that).
2) the weight transfer from inside to ouside wheel, or basically the difference in the wheels contact patch load.
3) how much grip will that load impart
4) how much slip gives best traction
5) what angles the tyres need to be (ie ackermann or not) to impart this amount of slip.

race guys often don't take ackermann into consideration because of a few things.
1) there is so much weight transfer the inside wheel is doing virtually nothing, although the angle will affect going turing in, and powering out of corners.
2) the amount of steering input used in tarmac race cars is much smaller than if you are doing a three point turn so you are taking about two tenths of sfa when it comes to altering the steerign angles....

if you really want to get serious about it. find a corner on a track, or skid pan etc etc, that you cna take at a good speed, and has about the most steering input you would want at speed.
take note of the steering wheel position. adjust toe-in and toe-out and keep going round the corner... this way you can measure the wheel angles that work best, and then alter the ackermann angles so you get the right angles at the right time....

it will be different for every car, and every suspension setup., due to spring and shock rates, body roll, and every angle in the suspension..... but it makes for funny drunken discussion with car buddies Wink

and lots of impromptu diagrams made of snakes and pretzel sticks and such......

Cya, Stewart

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