rog

iTrader: (2)

Today i've decided I'm going to learn what an Akerman angle is, heard that term being mentioned before and don't know what it is, so thought i'd put this question out there for someone to explain to me, and others if they're interested????

Brian

iTrader: (2)

Google it mate laods comes up about it


Brian

mikelomax

it is to do with the way the tracking on the front wheels when turned. od viously tracking is parrallel when the wheels are straight but when turned one wheels will turn a bit more than the other therefore creating the akerman angle.

on my race car we adjust the front axle so that no akerman is created when turning therefore creating 2 perfect parrallel wheels when on opposite lock.

correct me if im wrong

regards
mike

Chip

iTrader: (3)

As mike has mentioned its all to do with the fact that when you are turning a tight corner the inside and outside wheels are going in quite dramatically different sized circles, so need to be pointing in different directions (the inside wheel turns in more)
However that is for a perfect theoretical ackerman angle and there is a lot more to it than that in practice in terms of how the g forces pull the rim around relative to the tyre etc, in some instances its even desirable to deliberately have the opposite effect!

AlexF

Its now refered to as "toe on turn" if you want to google it

rog

iTrader: (2)

Cheers for the explanation, i know i could've googled it but i prefer to ask stuff like that on here where i know i will get a clear answer. Hopefully other people can read this and benefit, especially if they're bored at work!

markk

iTrader: (2)

i cant think of any reason why i would want my wheels parrallel when turning ?


just doesnt make sense- that would handle terribly, unless your just turning very small angles ?

JEEMO

I've never even heard of the term before, interesting.

dojj

iTrader: (3)

your rear wheels have a line through the centre of them that goes out at 90 degrees to the rest of the body along the ground if viewd from above

when you turn your front wheels, the centre line from one wheel will eventually make a triangle with the rear wheel line
the wheel on the other side will also make a triangle when you draw a line
the points at which these triangles meet the rear wheel centre line should be the same point as you turn the wheel

i hope that makes sense without diagrams

dojj

iTrader: (3)

this should make this easy

burnzy

i'm guessing this is what makes your front wheel squeel on full lock in car parks and stuff but i have to ask the question why would making them parallel through full lock make the handling worse, taking into account chips comment of allowing for tyre movement cornering force and so on, having 1 wheel scrub isn't that basically lowering traction?

Ade

Why would you want no ackerman?

Dan1281

i just drew this, the ackerman angle is the angle of the arms off the hubs that connect to the steering rack, the red is the angle of the arms that come off the hubs, the blue is the rack, i just means that bcause of the ackerman angle due to the length of the vehicle the wheels will be at the optimal angle for turning and limiting tyre wear

mikelomax

Because i race stockcars and we spend a good half the oval lap on opposite lock with the arse end at the side of you so having the wheels parrallel at this point is a MASSIVE advantage.


Mike

Chip

iTrader: (3)

Because if you are turning in with reverse ackerman it can cause understeer, and if you are going onto opposite lock with postivie ackerman it can cause understeer too.

So by having it parellel although its neither ideal for turning in, nor ideal for reverse lock, its actually "ok" for both, which overall makes it the best setup in some scanarios like that.

Ackerman angle more than anything else on a car's geometry IMHO is where there really are no hard and fast rules and its massively application specific as to what works best.

B19 JUB

im sure london cabs have ackerman steering hence why they are known to turn on a sixpence

Chip

iTrader: (3)

Yes they have near perfect ackerman angles which is awesome for low speed manouvreing, they also have enormous steering angle as well.

rog

iTrader: (2)

Glad i asked now!

markk

iTrader: (2)

yes, ok the exception really

Chip

iTrader: (3)

One of many.

Offroaders commonly use anti ackerman because of tyre movement on the rim.

And even in circuit racing it can have a home, its not uncommon to set a car up with static toe out, and then anti ackerman steering.

Nascar is the most significant example that springs to mind.

markk

iTrader: (2)

all cars where multi directional handling is not really required.

Ade

So how would you go about removing or at least reducing the Ackerman effect?

Chip

iTrader: (3)

Kind of, but anyway im sure the point you are trying to make is that for the sort of things poeple on this forum do, you wouldnt typically want reverse ackerman, like on your road cossie etc, and I totally agree with that.

Chip

iTrader: (3)

You simply change the steering arm angles and or locations.

But I cant see that being of any use to you on a road going cossie/RST etc, if that is what you are thinking?

Ade

I thought maybe the two cars going sideways in my sig would be a clue