Ackerman Angle?

Tubsport · 12-01-12, 09:24 PM

I'm sure I read a post somewhere bout correcting the ackermann angle that seems to be missing from the Type85q, and im sure many other early Audis, does anyone have the info on how to do this, I cant remember the angle that needed altering, and was also wondering about effect on bump-steer, and the possibility of lowering the steering arm to allow for adjustable coil-over platforms, loads I know, but what can I say!

Thanks in advance!
John.

TeXerv · 13-01-12, 01:26 PM

Normally the Ackermann angle is fixed by the position of the tie rod levers at the wheel bearing housings. It is only alterable as there are two adjustable tie rods and that's how it is on the type 85.
As you fix proper wheel track on each side, the Ackermann angle should be even fixed.
Regardez the following link, you can switch to English language.
http://www.kfz-tech.de/Engl/Spur.htm
And here you can find helpful pics.
http://upload.wikimedia.org/wikipedi...kellenkung.jpg
The picture at the bottom shows the Ackermann angle.

SteveT63 · 13-01-12, 01:53 PM

I agree. For road use, It's fixed and is adjustable only within the limits of the steering track rod ends. Adjust the tracking on your vehicle to the correct settings relating to toe and Rudolfs Geometry principle with be set for your specific vehicle.

Groundhog · 13-01-12, 04:29 PM

As the others have pointed out for road use there is no point or gain in altering the Ackerman angles. To alter the angle one needs to adjust the castor angle and I can only think of a handful of cars where this is possible. For general motorsport use there is no need or gain in altering the angle the only time its generally done is circuit cars where they are, by-and-large, going round the same handed corners every lap and then a car set up this way is a handful to drive on normal roads.

On top of that, and this is personal conjecture, rear wheel drive cars benefit from altered angles more than front wheel drive which on a track handle like a barrow full of water at best.

If one did want to modify the simplest way would be to use a generic aluminium top mount that is adjustable for castor / camber but the set up on a type 85 it would mean a lot of work.

You don’t say what you are ultimately chasing, is it a slammed road car or a race car, either way Ackerman angles are the least of your worries if you don’t get the rest of the set up right.

A_N_Other · 13-01-12, 05:11 PM

I think (if I remember correctly) Ackerman is the difference in the wheel angles in a turn:
You don't want parallel wheel in a turn, and the theoretical difference in wheels is "full ackerman"

It's controlled by the relative position of the steering rack front/back.
If the rack is behind the wheels (like in Audi) then moving the rack back I think gives more ackerman (like London Taxi)

Bump steer is controlled by the position of the rack up and down.
And toe-out on bump for example can improve ackerman angles in roll.

Pretty big topic though - I don't really remember all the ins and outs, but there are a few good books out there too.

TeXerv · 13-01-12, 05:56 PM

Quote:

Originally Posted by A_N_Other

I think (if I remember correctly) Ackerman is the difference in the wheel angles in a turn:

Yes! Edit-No

Quote:

You don't want parallel wheel in a turn, and the theoretical difference in wheels is "full ackerman"
It's controlled by the relative position of the steering rack front/back.
If the rack is behind the wheels (like in Audi) then moving the rack back I think gives more ackerman (like London Taxi)

Sorry no, but (for me) it's complicated to explain.
You need a different wheel turn angel in every turn, because the inner wheel has to roll a shorter way than the outer one. This doesn't depend on the ratio of turn. London taxis are able to drive very small turns - Alfa Romeo cars are know for very limited turn ratio. But the principle is the same:
All of (the four) wheels of a car need to have the same midpoint of (a thought) line of their knuckles, as the front wheels are turning. Sometimes an image says more than a thousand words, so take a look at this picture:
http://upload.wikimedia.org/wikipedi...kellenkung.jpg

Tim C · 13-01-12, 10:00 PM

John (tubsport) hillclimbs and sprints his 80 quattro. It has a potent 10V turbo motor in it.

Tubsport · 13-01-12, 11:39 PM

Right, as Tim points out, I hillclimb the 80, it is a bit of a handful on the 'fast road' suspension set-up I have tho, so, Koni struts are to be re-valved for stiffer damping, and H&R springs ditched in favour of fixed rate coil over type with adjustable platforms (found a useful post about this on here)
Also going to add adjustable castor and camber via eccentric top mounts in addition to rose jointed adjustable lower arms on the front, rear prob staying std geometry, as this end works quite well just getting made stiffer,.

Adjustment of the track rods would change the toe setting, the Ackerman angle is changed by cutting the steering arm from the damper rod, and re welding after rotating a few degrees, I read somewhere once how many degrees and which way to rotate to give theoretical correct Ackerman angle, but cannot remember where or how i found it!
As a second part I was considering lowering the steering arm on the damper tube (subject to tyre clearance) and relocating the outer track rod end on top of the steering arm (from underneath) so as the pivot height remaining unchanged therefore not affecting bump steer, which seems real good due to the length and angle of the track rods.

Any input much appreciated! - More than welcome to publicise my findings from this, in case it helps all you motorsport ppl out there!

murran · 13-01-12, 11:40 PM

^^^ that 80 looks awesome!!

without the op stating what he wants to gain/overcome i dont think we can provide advice further.

Tubsport · 13-01-12, 11:47 PM

Just a quick addition, but TeXerv, the picture you pasted of Ackerman angle suggests that if the line drawn from the track rod end, through the centre of the damper rod should meet the centre point of the car on the rear axle line - when the front wheels are in the straight ahead position, if i am reading this correctly, a little trigonometry - maths 101, and i can calculate the steering arm position required for 'mathematically correct' Ackerman?

13-01-12, 01:53 PM	#3
SteveT63 Senior Member Classic Audi Club Member Join Date: Sep 2008 Posts: 3,045	I agree. For road use, It's fixed and is adjustable only within the limits of the steering track rod ends. Adjust the tracking on your vehicle to the correct settings relating to toe and Rudolfs Geometry principle with be set for your specific vehicle. __________________ Peace...........through superior acceleration! T85 1985 90quattro I5 20vT T81 1983 80 Sport Red T81 1983 80 Sport Silver

13-01-12, 10:00 PM	#7
Tim C Senior Member Classic Audi Club Member Join Date: Aug 2009 Location: Poole, Dorset, England Posts: 1,729	John (tubsport) hillclimbs and sprints his 80 quattro. It has a potent 10V turbo motor in it. __________________ quattro RR - crystal silver quattro WR - 1981 Lombard RAC rally recreation (50% share) Nissan Navara - tow car / service vehicle for above A4 2.0T quattro s-line special edition - wife's http://www.flickr.com/photos/37654549@N06/sets/

13-01-12, 01:26 PM	#2
TeXerv Grown up member Join Date: Oct 2011 Location: Northern Krautland Posts: 241	Normally the Ackermann angle is fixed by the position of the tie rod levers at the wheel bearing housings. It is only alterable as there are two adjustable tie rods and that's how it is on the type 85. As you fix proper wheel track on each side, the Ackermann angle should be even fixed. Regardez the following link, you can switch to English language. http://www.kfz-tech.de/Engl/Spur.htm And here you can find helpful pics. http://upload.wikimedia.org/wikipedi...kellenkung.jpg The picture at the bottom shows the Ackermann angle.

13-01-12, 04:29 PM	#4
Groundhog Grown up member Join Date: Nov 2009 Posts: 143	As the others have pointed out for road use there is no point or gain in altering the Ackerman angles. To alter the angle one needs to adjust the castor angle and I can only think of a handful of cars where this is possible. For general motorsport use there is no need or gain in altering the angle the only time its generally done is circuit cars where they are, by-and-large, going round the same handed corners every lap and then a car set up this way is a handful to drive on normal roads. On top of that, and this is personal conjecture, rear wheel drive cars benefit from altered angles more than front wheel drive which on a track handle like a barrow full of water at best. If one did want to modify the simplest way would be to use a generic aluminium top mount that is adjustable for castor / camber but the set up on a type 85 it would mean a lot of work. You don’t say what you are ultimately chasing, is it a slammed road car or a race car, either way Ackerman angles are the least of your worries if you don’t get the rest of the set up right.

13-01-12, 05:11 PM	#5
A_N_Other Grown up member Join Date: Jun 2010 Posts: 116	I think (if I remember correctly) Ackerman is the difference in the wheel angles in a turn: You don't want parallel wheel in a turn, and the theoretical difference in wheels is "full ackerman" It's controlled by the relative position of the steering rack front/back. If the rack is behind the wheels (like in Audi) then moving the rack back I think gives more ackerman (like London Taxi) Bump steer is controlled by the position of the rack up and down. And toe-out on bump for example can improve ackerman angles in roll. Pretty big topic though - I don't really remember all the ins and outs, but there are a few good books out there too.

13-01-12, 11:39 PM	#8
Tubsport Grown up member Classic Audi Club Member Join Date: May 2010 Location: Haywards Heath, West Sussex Posts: 69	Right, as Tim points out, I hillclimb the 80, it is a bit of a handful on the 'fast road' suspension set-up I have tho, so, Koni struts are to be re-valved for stiffer damping, and H&R springs ditched in favour of fixed rate coil over type with adjustable platforms (found a useful post about this on here) Also going to add adjustable castor and camber via eccentric top mounts in addition to rose jointed adjustable lower arms on the front, rear prob staying std geometry, as this end works quite well just getting made stiffer,. Adjustment of the track rods would change the toe setting, the Ackerman angle is changed by cutting the steering arm from the damper rod, and re welding after rotating a few degrees, I read somewhere once how many degrees and which way to rotate to give theoretical correct Ackerman angle, but cannot remember where or how i found it! As a second part I was considering lowering the steering arm on the damper tube (subject to tyre clearance) and relocating the outer track rod end on top of the steering arm (from underneath) so as the pivot height remaining unchanged therefore not affecting bump steer, which seems real good due to the length and angle of the track rods. Any input much appreciated! - More than welcome to publicise my findings from this, in case it helps all you motorsport ppl out there!

13-01-12, 11:40 PM	#9
murran Grown up member Join Date: Nov 2011 Posts: 359	^^^ that 80 looks awesome!! without the op stating what he wants to gain/overcome i dont think we can provide advice further.

13-01-12, 11:47 PM	#10
Tubsport Grown up member Classic Audi Club Member Join Date: May 2010 Location: Haywards Heath, West Sussex Posts: 69	Just a quick addition, but TeXerv, the picture you pasted of Ackerman angle suggests that if the line drawn from the track rod end, through the centre of the damper rod should meet the centre point of the car on the rear axle line - when the front wheels are in the straight ahead position, if i am reading this correctly, a little trigonometry - maths 101, and i can calculate the steering arm position required for 'mathematically correct' Ackerman?