andrewg

anyone know if you get steering arms to give different ackerman angles mine don't seem that good, i know you different hights for the track rod for adjusting bump steer,,?

Chip

iTrader: (3)

Can you not space the existing arms inwards to change the ackerman angle, or are you wanting less not more?

CossieRich

iTrader: (1)

what is an ackerman angle?

Chip

iTrader: (3)

When you turn your steering, the inner wheel turns by more degrees than the outer one, so that they each follow a different size circle, the ackerman angle is essentially the extent to which this happens.

In order to change the ackerman angle you change the angle of the steering arms bolted (or cast) up to the strut, the further they come in towards the centre of the car, the more ackerman you get.

Chip

iTrader: (3)

PS

The "accepted" optimum (obviously in racing its all about fine tuning) is that the two arms, if extneded would meet in the centre of the rear wheels, ie at the diff.

If andrew is using arms designed for a longer wheelbase car then he would need more ackerman to get back to the same settings essentially.

Chip

iTrader: (3)

PPS

In andrews case, he probably wants more ackerman on tighter tracks, and not on looser tracks, as thats how most people tend to run, so a system using shims to space the arms in and out is a good solution.

ian sibbert

Andrew,

There were a few generations of steering arm for the grp 'a' gravel hubs, which steering arms do you have on the car.

The gravel steering arms have alternative tca pin positions and different heights for attachment to the drumsticks....the later steering arm pin is more in-line with the hub, the earlier ones were more inwardly cranked, optimising the ackerman angle isn't generally as important as dialing out the bumpsteer.

How much bumpsteer are you getting, how much castor do you run,

CossieRich

iTrader: (1)

Chippa,

cheers for that mate

any more pps's you would like ot add

Chip

iTrader: (3)

I was trying to think what other questions you would ask Rich, and pre-empt them, lol

The height changes that Ian mentions, are there to change the amount of steering that gets induced when the wheel moves up into the car, ie bump steer.

CossieRich

iTrader: (1)

i didnt mean it sarcasticly either mate. ITs all gfood knowledge to have, not that i will ever use it. Just like learning. Cheers mate

Chip

iTrader: (3)

Rich, I know mate

Suspension is fascinating stuff and something I wish there was a LOT more discussion of on here, Stu style essays on the subject would be awesome, but we have none

alistairolsen

you can help the effect by moving the rack forward and back in the car on the same horizontal plane as the steering arm mounts so Im told, but I havent drawn it out to convince myself yet.

Chip

iTrader: (3)

Well that makes sense as you would effectively be altering one side of a triangle, and not a second, so the third has to change as a result I should think, but like yourself, ive not ever tried it.

We SO need more of this stuff on here!

andrewg

my wheels are near paralel on full lock with around 1 deg extra on inside wheel, been chopping up steering arms and moving the main bj in and out, still messing around with it

Chip

iTrader: (3)

Have you also tried applying weight to see what the angle is when the car is leant into a bend, as the problem with static tests by just turning the rack is that it wont include bumpsteer.
That said, Id have expected more than that, id try shimming the arms in a couple of mm and redoing the test (ie literally just put a washer on each bolt between the arm and the strut to test it, not to drive it of course)

you should then be able to work out a formula for what sort of change in ackerman angle you get based on how much you move the track rod mounting point by.

what was your toe angle when you did that test? as obviously before you see the ackerman angle on full lock it first has to cancel out any toe settings etc

andrewg

always start with 0 toe out/in

Chip

iTrader: (3)

cool, just checking, no offence intended.

as above then, I would try adding washers and see what change that makes, then make some appropriately sized shims up and then obviously just a case of testing a few settings on track from different sized shims to see where it lands you.

andrewg

Chip

iTrader: (3)

They actually fit up different to how I was thinking, so obviously ignore what I was saying about washers.

How much difference did that make, as it looks like you have moved it in the way by about 20mm, so presumabley a fair bit?

CossieRich

iTrader: (1)

Maybe you could offer Mike R a little something and then he could do a tech write up. He knows his stuff on suspension

andrewg

25 mm the best result was from moving the rod end forward but that will reduce the turn ratio reducing steering response

Chip

iTrader: (3)

Well a different number of turns lock to lock on the rack would correct that, but obviously that isnt quite as easy to knock up.

smaller steering wheel maybe?

joffy

iTrader: (1)

slightly different i know but as we are on the subject and you rightly say there isnt enough said about suspension?? ive got a 3dr cossie, with about 320bhp nothing major, its only used on the road and i cant afford a huge engine and if i could id rather it handled and stopped right first so ive been looking into making it handle as best as i can. i have koni adjustables but not coilovers, adjustable tca's and toyo 888r's on standard wheels and pretty close to getting an adrenaline rear beam, was just wondering how much difference things like adjustable top mounts and compression struts would make and would it be worth it on a car that isnt going on a track?? ive heard that you shouldnt do compression struts and lose the anti roll bar etc, im a interested novice so ANY info or suggestions would be good!!!

Chip

iTrader: (3)

Start a new thread mate, and some of us will reply to it (hopefully including MikeR like Rich mentions) not fair on AG to drag this one so far off topic.

alistairolsen

looking at the pictures andrew, you have moved the balljoint in and increased the track, and then you have moved the tie rod end in by the same amount with that plate.

What confuses me is you have drilled 3 holes in a row forward and back int he car? Surely to affect ackerman these need to be accross the car? the important angle is looking downwards, thru the main balljoint and track rod end with relation to the centreline of the car?

since youve already killed the part in th bottom pics, Id be inclined to cut the steering arm off completely and replace it with a piece of plate with a bunch of holes drilled in one end accross the car and mount that to the two front bots on the hub for a mockup. (Id also put the balljoint back where it was if I was gonna do that)

sorry if Im waaay off the mark or teaching granny how to suck eggs!

joffy

iTrader: (1)

fair point, new thread started

andrewg

when i moved the bj i screwed in the tca to compensate with standard rod end hole

alistairolsen

yes, but having a range of holes in line along the length of the car alters arm length and therefore steering ratio, not ackerman angle :S

EDIT: scratch the above, I think Ive got you figured now :P

The plate changes ackerman in one direction, and then you removed it and moved the balljoint instead to try it in the other direction?

andrewg

well it gave around 2.5 deg diff on full lock by just moving rod end forward

Chip

iTrader: (3)

Ali, what AG was doing with the holes, was essentially what you mentined here. (well moving the arm end not the rack, but same effect in terms of moving one relative to the other)

But ALL the holes are spaced in 25mm, so he was doing both at once, well thats how it looks to me, but TBH I have to say AG's build skills are a lot better than his photography ones

andrewg

what i wanted to try was moving the rod end to outside of the car but the
disc was stopping that happening so i tried moving the ball joint in but that seemed to make it worse

markk

iTrader: (2)

how much castor you running andy ?

and WTF have you done to them parts

andrewg

think 5 deg? was going try reduce that and that should increase the AA

andrewg

just measured a standard new shape focus and it has 4 deg diff on full lock

Chip

iTrader: (3)

Well thats a pretty good figure to start from then.

Chip

iTrader: (3)

Have you done the maths to see if that results in a convergence of the arms at the centre of the rear wheels when its toed at zero degrees?

If you cant be arsed, then if you quote the width between the arms at the centreline of the front wheels, and the wheelbase of the car, then im sure one of us with nothing better to do could do so, lol

John Doe

Just done a quick drawing to help explain what Ackerman is and how its achieved on cars ..

Do we need one for bump steer to help those who are new to suspensions ?

andrewg

must of been tripping last night when i moved the ball joints in cause today i couldn't understand why it didn't work so i did it again and now i have 5 deg on full lock!

just need to get a pair of new ones made with that offset!

andrewg

some one must have a formula to work out angles of front wheels on full lock to track/wheelbase?

FXTURE

My first thought was what is ackerman? .With the combination of Chip and retromotorsport's explanation I now understand! It's a Very informative place this community.Thanks

Gary? always appreciate the diagrams and explanations on Turbosport .Any chance you can touch on the subject of bump steer?maybe on turbosport.

Gra