No, one look at the spindle and steering knuckle and you will see if it has ackermans or not. Ours does not have ackermans steering. With the wheels straight ahead you can't measure ackermans because there is no ackermans effect. You CAN see what kind of toe control it has but it only applies if you have ackermans, we don't have it.

The ackermans effect is only possible with angled steering knuckles and a drag link. With an ETO rack you can have ckermans effect but not true ackermans since it lacks the center link (that has to move and change angle rel. to car axis to complete the ackerman effect) the CTO racks don't have this either, that whole setup is fixed with the complte rack center moving.

 

You don't want a Commodore Rack (sounding like OBiWan Kenobe)
The Commodore Rack is for A RIGHT HAND DRIVE car. I have my steering wheel on the Right side of my Vette. I have given you the dimensions you need to search for a rack suitable for use in the US with the original LHD.
We no longer have to convert old cars from LHD to RHD but when I did the original conversion back in '85 (now I'm talking like Grampa Simpson) It was LAW.
Pictures of my car at http://www.chevcarclubvic.org.au/vic_vettes/feature_car[/URL]



[Modified by RHD '68 L89, 11:31 AM 5/15/2003]

 

Norval,Try my exercise at calculating the theoretical Acherman Angles.
It is only the theoretical calculation to have Zero scrub on the inside tyre as you go around a corner. The factory setting may be zero acherman and I am still trying to find someone to measure what the '63-'82 chassis had as acherman angle from the factory. (silly me, I never actually measured what the factory put in!) I know for a fact that my car used to have a lot less acherman angle before I put the rack in it because I had a soooo much smaller turning circle.(the inside tyre hits the chassis a lot sooner with the rack).
The chassis was designed back in '60 or earlier for skinny tyres and I think it was yourself who revealed all the positive camber in the suspension to allow for the tyres rolling off the rims(at least you participated in the thread)
The steering settup was designed with slide rules and blackboard chalk. There are so many arcs in the front suspension and steering they must have used black magic as well to get our cars handling as well as they did back then. By using a rack I removed some of the arcs and made it simpler to do the RHD conversion. I did originally have a mirror image conversion with a steering box but I had to move the BB over 2 inches to make room.

Skinny tyres can get away with no acherman as the contact patch is narrow. If you put a wide sticky tyre on there is a lot more tread to scrub. This also puts more stress on the chassis because the inside tyre wants to go straighter than the outside tyre. Sure there is a lot less force on the inside tyre because of the weight transfer during cornering but it is still scrubbing the tyre. Basically, with no Acherman the inside tyre is sliding diagonally across the road.
The amount of Acherman angle is related to the Acherman point. This is the point where a line extending from all the axles point when going through a corner.

When I calculated (and measured on a bare chassis) my theoretical acherman angles I only had to move the holes in the steering arms 4mm to give the theoretical perfect acherman angles. I Calculated that if the inside wheel turns 30 degrees the outside wheel only has to turn 24 degrees.
To get the theoretical acherman into practice you have to take into account the position of the rack, the length of the rack, the length of the tierods, the length of the steering arms and the position of the holes for the tierods in the steering arms(with relation to the centre of the axle rotation ie a line between the balljoints). You cannot simply say if the rack is behind the centreline of the ball joints you have acherman.
You may be describing "Akerman effect" but it is not related to the Acherman point which is designed in.
For steering with Acherman designed in, the inside wheel has a massive change in toe from a fraction of a degree "in" to several degrees "out "compared to the outside wheel. This only describes what happens. It is not related to the actual static Toe settings.
regards,
James
:rant:

 

Actually the new Pontiac GTO is based on the Australian Monaro which is a Commodore Coupe. Hey guys, I think I found you a Rack!
:party:


[Modified by RHD '68 L89, 12:12 PM 5/15/2003]

 

RHD, OK, to the net effect is what?? where did you set up your rack relative to say the engine mounts?? or the centerline of the steering knuckles...are the innter tie rod ends further back than the outer tie rod ends?? or you using an ETO rack?? if it's ETO, I guess my questions are moot...but maybe not, still interesting where the rack centerline is relative to knuckles....
my rack is CTO, and it's mounted with the center tie rods about 2 inches behind the tie rod outer ends..steering knuckles....I still have to get my inner tie rod ends up in the air more...next project....

GENE

 

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Wrong! Wrong! Wrong! I believe this describes the Acherman point for a centre steer arrangement similar to a C1
Toe is set by the adjusting the tierods to have the wheels pointing slightly in (toe In) You don't want Toe out as it will be impossible to hold in a straight line. Think of a skier doing the snow plough. If he points the tips of his skis out he will fall over!
Toe in is partly to allow for the flex in the front end during actual driving conditions. The road "pushes " against the tyre and wants to move the wheel back causing toe out. With toe in already there the end result is "0" toe or just a little toe in.
________________________________________ ________________________

That is ackerman steering for a setup w/ center link and 1 pitman or one idler. OR for a setup w/ idler and pitman that are NOT angled straight forward (when steering is centered). If the pitman and idler are under an oxx center angle then you will have ackermans again since the center link will be angled too (again, because of the angles of the idler and pitman, steering to one side will set one of the arms straighter whereas the other will be angled to the side) It's a bit difficult to explain in words though.
Refer to the topic about a arms some time ago, there's a drawing there.
This means that we don't have ackermans since we have a pitman and idler arm.

The ackermans has nothing to do with setting toe, it's a design feature and it's in the spindle and steering knuckle. If the stereing knuckle is in line with the ball joint then it has no ackerman, simple as that. This because the position of the knuckle in relation to the ball joints makes for the fact that the steering arm becomes "longer" or "shorter" when you turn the wheel. Because the angle of the knuckle changes with steering the knuckle angle is either substracted or added to the steering link length.

________________________________________ ______________
For Zero Bump Steer, the tie rod end has to travel through the same arc as the extension of the suspension. ( the steering arm). If the steering arm hole mounts the tierod ball joint at the same height as the A arm ball joint then the arc is the same as the A arm ball joints arc. The tierod needs to be parallel to the A arm (and the same length) to give zero bump steer.
Now if the tie rod end is mounted at a different height you get the length of the upper arm coming into play as well. So you have to measure or calculate the arc the tierod end joint will go through and duplicate the travel of the arc the tierod end goes through. this is done by adjusting the length of the tierod. Changing the position of the rack up and down or forwards and backwards.
I know all this because I spent many hours out in the garage with my rack, pieces of string and steel, a calculator and not much sleep!
I can tell you there are no straight lines in a corvette front end!
________________________________________ ________________________

IF the steering rod pivots at the points where the green line is and it's parallel to the lower control arm then you can move your suspension in all directions and the 2 will always be perfectly aligned. They will make the same arc.
just like this: (this is the same as my drawing above!)




indeed, the higher you mount it the more the upper arm comes into play.That's why in my drawing there's a green line on the left. That's the line on which the outer steering ball joint must be to maintain proper arc.

There are straight lines, if you have 2 points (upper arm pivot and lower arm pivot) there's ALWAYS a stright line through them. I have yet to find a situation where you can not draw a straight line through 2 points.

 

RHD(Right Hand Drive) rack means the input shaft is on the wrong side of the car for the US.
The rack is set 257mm back from the centre line of the ball joints. This puts it under the engine mounts. I have a plate from the 2 holes in the rear of the cross member and then arms up to the Chassis to mount it. They also help stop Chassis flex. The rack is an End Take Off (I take it this what ETO means)
And is 615mm from joint centre to joint centre. the tierods are 315mm long C2C and are angled forward. the steering arms are also shortened to 140mm (refer previous posts) There was some moving the steering arms up and down to get the bump steer to 0 over the travel but the rack is as close to the sump of the BB as possible.
How much travel does your CTO rack have end to end?
The angle the tie rods are on affects the bump steer as well. (Refer previous post again)
:cheers:

 

I agree with you TT!
And yes there are staight lines but they make everything else move in Arcs!
:hurray:


[Modified by RHD '68 L89, 2:05 PM 5/15/2003]

 

RHD, my rack is about 2.8 turns lock to lock and has a longer travel...Jim Shea said i'ts 158mm or so....it is plenty enough to turn the wheels on MY car to the modified snubbers on the lower A arms...I can still hit the tires on the frame/sway bar a bit....so not too bad....the rack is a Grand Am rack of course LHD since we are on opposite ends of the globe....;-)))

so your setup is ten inches rearward of the ball joints?? I think I can measure that this morning, as I have to jack up the car anyways for something else...mysterious loss of rear brake fluids....I"m SO happy...;-(((

GENE

 

Yes but the arcs are not that hard to draw out. But, you won't even need them. It's all like a big trapezoid that skews, if you maintain parrallel lines and the correct points (like the green lines intersecting w/ the yellow) it will always follow the same arc. It's just a 2d geometry problem in essence.

Those dimensions you gave are pretty damn handy. However, if someone changes the pivot points (like discussed in the other topic) to get neg. camber change w/ suspension up travel and a better location for the instantanious roll center the lines change and with them the dimensions needed for the steering rods of the ETO rack.

I think I will get a rack here and look if I can fab up something w/ front steer. I'd rather have front steer to eliminate the complex angles on the steering shaft. I'd probably have to chop a piece out of a motor mount but it can be reinforced. the only problem is the sway bar is in the way. I was thinking about moving it to the top of the frame and using longer bolts or a custom bar like Monty has (heim links).

There are some "sporty" racks available here, a bunch of them are GM like stuff from Opel, Saab, to name a few. I think they all have saginaw racks. I definitely want an ETO rack. Maybe it's even possible to get one from a Lotus Omega since that's short ratio (it's a lotus version of the old model Opel Omega. The new opel omega is the same as the Cadillac catera. Those Lotus Omega's also have ZF-6 speeds. Exact same case, just longer input shaft (like ZR-1) and a different tail section.

Marck

 

I with Fevre . . . My idea of Camping is a Marriott Suite, if there's a creek nearby, it better be on a golf course. :lolg: :lolg: :lolg: :lolg:

Very good thread though! :yesnod: :yesnod: :yesnod:

 

Don't know about all you other lurkers......but I'm gettin' a headache! :crazy: :crazy: :crazy:

:lurk: