Hi-steer acheman

[RANUKI]

I am looking for a hi-steer kit for the new toy (puslux) and everything I seem to find has no acheman (spelling) on them.

Is anyone aware of any arms that have the correct acheman angle, this thing will also be a daily driver so I need correct geometry?

Benn

[Gribble]

I am looking for a hi-steer kit for the new toy (puslux) and everything I seem to find has no acheman (spelling) on them.

Is anyone aware of any arms that have the correct acheman angle, this thing will also be a daily driver so I need correct geometry?

Benn

Yes, choas's arms have the correct ackerman angle built into their arms, but if your after true high-steer then i dont know. But i would imagine the manufacturer would have designed this into their product or they risk them failing engineering inspections and cornering like shit.

Why is that important that you need it anyway, all solid axle hiluxs' share the same wheelbase.

[RANUKI]

Irrespective of the wheel base, the arms I have and ones I have seen are dead straight. whilst this may be fine for low speed stuff, this is no good for on road use.

Most Hi-steer arm I have seen are for 'off road only' for this reason. I want correct (well as correct as it can be with the lenghtened WB) syeering geometry and I am tipping the ENG will too.

I shall check out the Chaos ones, cheers.

[Gribble]

Irrespective of the wheel base, the arms I have and ones I have seen are dead straight. whilst this may be fine for low speed stuff, this is no good for on road use.

Most Hi-steer arm I have seen are for 'off road only' for this reason. I want correct (well as correct as it can be with the lenghtened WB) syeering geometry and I am tipping the ENG will too.

I shall check out the Chaos ones, cheers.

Ok, im asuming you know how to figure akerman angle?

Even at crawling speeds all your wheel alignment conditions are still critical. Especially akermans angle.

The arms may be straight but i think you will find that the hole for the joint on the steering arm is offset.

Take some pics of the arms.

[RANUKI]

Yes I do, and no the hole is not offset. If i drew a line down the centre of the 4 knuckle mounting holes then i would end up in the middle of the hole for the track rod (maybe these ones were samples hence the price).

Not to worry, we have spoken to our machinest and we are going to make our own. CAD drawings have been sent, now just waiting for the quote.

The arms are in bright at the moment with my truck, i will be back there in 2 weeks, I will post a pic then to show you what I am talking about. It does amaze me as these are a well known product.

[whiteknight]

What brand of arms have you got that dont have the correct angle?

[RANUKI]

I didn't get them from a supplier but from someone else. On all acounts they appear to be M&M ones.

[spazbot]

u tried the snake ones, i know they are cut at angles etc,
afaik the m&m ones were made straight

[RANUKI]

Spaz, mate I haven't, I will just wait and see what the machinest has to say. If the price is right I might get a few sets done.

Thanks for the conformation the the M&M ones are straight, I thought I had a dud set. Why do they do that, it renders them useless??

[RoldIT]

Probably because most people have no idea what ackerman (sp?) even means so they figure they can sell em to the majority with them being none the wiser.

A mechanic/fabricator doing the dodgy? What a surprise ...

[RANUKI]

Probably because most people have no idea what ackerman (sp?) even means so they figure they can sell em to the majority with them being none the wiser.

A mechanic/fabricator doing the dodgy? What a surprise ...

Yes it is disappointing, still the world is full of suckers.

[Bush65]

You do not need Ackermann steering.

Ackermann steering only has an affect at low speeds.

A vehicle with Ackermann steering arms, will not exhibit Akerman steering at higher speeds.

Reverse Ackermann can be an advantage offroad.

See section 19.2 in Race Car Vehicle Dynamics by Milliken and Milliken.

[Gribble]

You do not need Ackermann steering.

Ackermann steering only has an affect at low speeds.

A vehicle with Ackermann steering arms, will not exhibit Akerman steering at higher speeds.

Reverse Ackermann can be an advantage offroad.

See section 19.2 in Race Car Vehicle Dynamics by Milliken and Milliken.

Akerman is a critical alignment in steering, it allowes the front wheels to travel two completely different radius's to one another.

I would like to see the Quote of 19.2 Race Car Vehicle Dynamics by Milliken and the other Milleken if you can get it to see why they think it is not important.

[dumbdunce]

You do not need Ackermann steering.

Ackermann steering only has an affect at low speeds.

A vehicle with Ackermann steering arms, will not exhibit Akerman steering at higher speeds.

Reverse Ackermann can be an advantage offroad.

See section 19.2 in Race Car Vehicle Dynamics by Milliken and Milliken.

Akerman is a critical alignment in steering, it allowes the front wheels to travel two completely different radius's to one another.

I would like to see the Quote of 19.2 Race Car Vehicle Dynamics by Milliken and the other Milleken if you can get it to see why they think it is not important.

I'll have a stab - at higher speeds, due to cornering weight transfer, the grip of the inside tyre becomes less significant and therefore contributes less and less to actual steering, also at higher speeds there is more and more slip even on the tyres with grip. most race cars also have spooled rear ends so ackerman would become less significant as large amounts of slip at all wheels are required to make a turn in any case.

...however...

In the case in point (hilux), I would say that Akerman is an absolute necessity - not so much for off road, as a 4WD with no centre differential has masses of slip when cornering anyway, but for slow-to-moderate speeds on-road, when in 2WD mode - without correct Akerman, regular (sub-60km/h suburban) handling will be completely galloping up diareah drive without a saddle - especially in the wet, it will tend to understeer/push, and where there is a significant difference in traction between front wheels, the wheel with the best grip will dominate the steering, causing significant, potentially dangerous, instantaneous changes in cornering radius.

therefore - for an off-road ONLY vehicle - heaps of slip all the time - not required. For a roaded vehicle, where driving conditions vary from driveway to freeway, absolute necessity.

[RANUKI]

You do not need Ackermann steering.

Ackermann steering only has an affect at low speeds.

A vehicle with Ackermann steering arms, will not exhibit Akerman steering at higher speeds.

Reverse Ackermann can be an advantage offroad.

See section 19.2 in Race Car Vehicle Dynamics by Milliken and Milliken.

If you have a negative or for that matter non existant Ackerman you are destined for a 6 sided box with plenty of nails, not to mention a stack of busted axles you could play on (4wd situation), especially in an off road locked diff situation where it become even more critical.

Dumbdunce is right in the fact that it is not as critical in a spooled rear diff racing situation (due to front end push and weight transfer) however lock the front axle and you will be in a world of pain. Can you imagine the axle wind up you would get if the wheel with the lessor radi had to cover a greater distance than the leading wheel?

Hope you don't work by Milliken and his right hand 'Milliken', cause even with my limited knowledge I have a very hard time believing that someone could publish such belony. I dont know of a single vehicle from a go-kart to an F1 car without Ackerman, if you can by any chance find one please show me a photo.

Ackerman is a very critical factor in correct steering geometry, both front wheels turn a different radi therefor to maximise traction and to reduce driveline ware it is imperitive, not to mention reduce under/over steer.

[Bush65]

I haven't had anything to do with Hiluxes and maybe there is something there!

At low speeds Ackermann steering makes up for the different turning radius between the 4 wheels. With Ackermann steering, the turning radii of 4 wheels have a common centre.

At higher cornering speeds, centripital force is necessary to make the vehicle turn (Newtons Law - otherwise you will go straight ahead). The tyres generate the centripital force by running at an angle to the tangent of the turning radius (called slip angle).

Also the front wheels are only turned a small angle at higher speeds and Ackermann steering is negligable at small steering angles.

In the Milliken book, there is a lot of info on steering.

Section 19.2 starts on page 713 and finishes on page 716 and I will not type it all here. There is good info about this in other sections but much of it involves mathermatics that can't easily be typed in here.

On page 714, after discussing Ackermann steering at low lateral acceleration, which we know about, they say:

High lateral accelerations change the picture considerably. Now the tires all operate at significant slip angles and the loads on the inside track are much less than on the outside track. Looking back at the tire performance curves, it is seen that less slip angle is required at lighter loads to reach the peak of the cornering force curve. If the car has low speed geometry (Ackermann), the inside front tire is forced to a higher slip angle than required for maximum side force. Dragging the inside tire along at high slip angles (above the peak lateral force) raises the tire temperature and slows the car down due to slip angle (induced) drag. For racing, it is common to use parallel steering or even reverse Ackermann as shown on the center and right side of Figure 19.2.

It is possible to calculate the correct amount of reverse Ackermann if the tire properties and loads are known. In most cases the resulting geometry is found to be too extreme because the car must also be driven (or pushed) at low speeds, for example in the pits.

Another point to remember is that most turns in racing have a fairly large radius and the Ackermann effect is very small. In fact, unless the steering system and suspension are very stiff, compliance (deflection) under cornering loads may steer the wheels more than any Ackermann (or reverse Ackermann) built into the geometry.

And the last paragraph of section 19.2 on page 716:

With the conflicting requirements mentioned above, the authors feel that parallel steer or a bit of reverse Ackermann is a reasonable compromise. With parallel steer, the car will be somewhat difficult to push through the pits because the front wheels will be fighting each other. At racing speeds, on large-radius turns, the front wheels are steered very little, thus any Ackermann effects will not have a large effect on the individual wheel slip angles, relative to a reference steer angle, measured at the centerline of the car.

[Bush65]

Irrespective of the wheel base, the arms I have and ones I have seen are dead straight. whilst this may be fine for low speed stuff, this is no good for on road use.

Most Hi-steer arm I have seen are for 'off road only' for this reason. I want correct (well as correct as it can be with the lenghtened WB) syeering geometry and I am tipping the ENG will too.

I shall check out the Chaos ones, cheers.

...If you have a negative or for that matter non existant Ackerman you are destined for a 6 sided box with plenty of nails, not to mention a stack of busted axles you could play on (4wd situation), especially in an off road locked diff situation where it become even more critical.

Dumbdunce is right in the fact that it is not as critical in a spooled rear diff racing situation (due to front end push and weight transfer) however lock the front axle and you will be in a world of pain. Can you imagine the axle wind up you would get if the wheel with the lessor radi had to cover a greater distance than the leading wheel?

Hope you don't work by Milliken and his right hand 'Milliken', cause even with my limited knowledge I have a very hard time believing that someone could publish such belony. I dont know of a single vehicle from a go-kart to an F1 car without Ackerman, if you can by any chance find one please show me a photo.

Ackerman is a very critical factor in correct steering geometry, both front wheels turn a different radi therefor to maximise traction and to reduce driveline ware it is imperitive, not to mention reduce under/over steer.

So how many do you know of, that have used the arms like in your 1st quote ended up in boxes as per your 2nd quote?

With most steering geometry, where the tie-rod is in front of the axle, it is not practical to have Ackermann steering geometry and have the tierod ends clear wheels with offset for the correct scrub radius.

[Pauwolf]

If 'ackerman steering' is so not nesecary why do car manufacturers spend BILLIONS of dollars engineering it into cars in the first place. We may as well go back 50 years and adopt model t suspension. Practices adopted by race cars have NOTHING to offer road cars, and here are the reasons why
1 race cars are designed to be driven very fast 95% of the time
2 race cars are adjustable to suit various surfaces
3 race cars have very stiff suspension with little travel
4 race cars drive very poorly through the pits etc till they get up to speed
5 race cars spend little of their time (in reallity) actually driving

Road cars on the other hand
1 road cars spend 95% of the time under 60 kph
2 road cars encounter different road conditions continually
3 road cars especially 4wd have soft suspension with lots of travel
4 road cars have to be parked and driven slowly regularly
5 road cars spend much more time in use

If the steering origonally had ackerman I would leave it the way it was designed

Paul

[Bush65]

...Hope you don't work by Milliken and his right hand 'Milliken', cause even with my limited knowledge I have a very hard time believing that someone could publish such belony...

Bill and Doug Milliken have impeccable credentials. Their book is published by the Society of Automotive Engineers.

...I dont know of a single vehicle from a go-kart to an F1 car without Ackerman, if you can by any chance find one please show me a photo...

Sorry dont have photos but here are some quotes from page 106 of Allan Staniforth's book Compettition Car Suspension Design, Construction, Tuning. In discussing the postion of steering rack and pinion and Ackermann

From the dayswhen it had an intermediate location somewhere between the top and bottom suspension arms, and was ahead of the driver's feet, it has finished up level with the top links, its rack-end pivots aligned exactly with the inboard pivots of the top wishbone. The only variation on this theme is that some designers put it ahead of the top suspension (Ferrari, Arrows) where it is clear of just about everything, while some place it behind (Benetton, Ligier, McLaren) where it tends to be perilously near the driver's shins.

...Should Ackermann angle be one of the aims, which in many cases it is not, the rearward location offers a much better chance of the steering arm avoiding a caliper, brake disc or wheel itself...

Opinion is so divided that while John Barnard chose a high reaward rack with visible Ackermann for all his highly successful McLaren cars, it was instantly junked in favour of a forward mounting with little if any detectable angle by his successors when he left.

[Pauwolf]

I agree that the books are excellent, in fact I have Milliken and Milliken, but the book is written about race cars and clearly states this, even in the title RACE CAR DYNAMICS. I dont belive that the theories presented in the books mentioned automatically carry over to road registered cars

Paul

[Bush65]

Some more info from Fundamentals of Vehicle Dynamics by Thomas D. Gillespie.

Gillespie is a research scientist at University of Michigan Transportation Research Institute. He also teaches vehicle dynamics courses at Ford Motor Company and others. In 1987-88 he served on the White House staff as a Senior Policy Analyst in the Office of Science and Technology Policy.

This book is not about race cars, but vehicles in general, including trucks. From Chapter 8 - The Steering System at the bottom of page 277 and on page 278 and 279:

Perfect Ackerman is difficult to achieve with practical linkage designs, but is closely approximated by a trapezoidal arrangement as shown in Figure 8.3. When the wheels steer right or left, the asymmetry in the geometry causes the inside wheel to steer to a greater angle than the outside wheel. When the tie rods are located behind the wheel centers, as shown, the steering arm ball joints are located inboard of the steer axis and provide good wheel clearances. If the steering is designed with the tie rods forward of the wheel centers, the steering arm ball joints must be outboard of the steer rotation axis at the wheels in order to get close to Ackerman geometry. Interference with the wheel usually prevents design for good Ackerman in this case. Proper design of the Ackeman geometry is a function of the vehicle wheelbase and front axle tread. Design methods are straightforward and are available in the literature [1]. The degree to which the Ackeman geometry is achieved on a vehicle has little influence on high-speed directional response behavior, but does have an influence on the self-centering torque during low-speed maneuvers [4]. With Ackerman, the steer resisting torque will grow consistently with steer angle. However, with parallel steer (zero Ackerman), the torque will initially grow with angle, but may then diminish (and even become negative) at sufficiently large angles.

[RANUKI]

John, all that you have posted from Millliken has its merits but I think you will also find that, and as you stated (race cars) is relivent to vehicles that have independant front ends be it macphersons or otherwise. As these front ends react in a different way due to weight transfer thus effecting the castor angles and therefor the steering geometry is true.

As I am talking about a solid axle the behaviour is far more static and not effected by an adjustment in castor angle (per say). For this reason it is a different set of rules.

You wont find any (modern race cars) with a soild front axle other than a go-kart, and that is a fight the whole way around the corner.

As for Gillespie well if you read that again, it only supports what I have said previously about the necessity of having correct ackerman..


Further more anyone driving on the road with straight steering arms from any manufacturer is
A: Breaking the law, hiluxs do have an achkermen angle of about 4deg from memory. Therefore you would never get an ADR on such an arm.
B: Suffering very bad steering characteristics, like vibrations and under/oversteer.

At the end of the day this post was not to get into who knows more about steering however the fact that there is no way I will be running a 0 ackerman for a daily driven or off road for that matter, in my vehicle.

The great thing about engeneering is that there is no set rule of play for all situations, each has its own set of rules. For that matter there is always an exception. There are 1000's of books out there many by people highly respected in there field about steering and it's geometry. and also many differing opinions on what is right and what is wrong.

As I said in my very first post, 'I want correct steering geometry'.

[planb]

this is good,

i have also wondered why no one makes a high steer arm to mimic factory ackerman.

[RANUKI]

We are currently in the process, the design is already at the machinists. They will eventually go through some destructive testing and hopefully be ADR'd. But first the manufacturing no promises on the rest.

[Webbie]

So has anyone found out as to wheather or not the angled high steer arms such as SNAKE or ABT or any others ,for that matter ratain the ackerman angle and behave on road as they should.

[65Mog]

I thought it was impossible to get the Ackerman angle 100% right with the drag link in front of the diff, the Tie Rod ends would have to be almost in the middle of the tyres.

[MissDrew]

Mine steers just fine on the highway, even at 150km/hr yep my hilux goes that fast now

It also steers just fine offroad with the front lock on.


One thing I will say about high steer arms is I don`t think you will ever find one that EVERYBODY is happy with. People will allways find something about them to bitch about, no matter who makes em

[Gribble]

I thought it was impossible to get the Ackerman angle 100% right with the drag link in front of the diff, the Tie Rod ends would have to be almost in the middle of the tyres.

You would think so, but it depends on where the steering axis is on the axle. The clearance between the tie-rod end and a hilux's wheel is the best part of a bees penis apart, but its akerman angles are all good.

[professor]

So has anyone found out as to wheather or not the angled high steer arms such as SNAKE or ABT or any others ,for that matter ratain the ackerman angle and behave on road as they should.

NUP they don't

The wheels stay parallel (or very close to)all the time from left to right.

and if the people selling these arm tell you any different, they are FOS!

Ask them to prove it on a wheel aligner.

[CHILLI 2]

I'm going to my 2 cents worth in say that out of all the vehicles on the road in Australia i can assure you that you wouldn't find many if any that have been correctly set up for our roads ,ever wonder why all the imported vehicles pull left or wear the edge off the LH front side of the tyre (except ones with fully adjustable suspension) i'm sure the factory did go to a lot of expense to get it right for the country they were designed to drive in!!!!!