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

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, 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.