rack n pinion front steer ackerman issues...explain...

-
When you read about the scary ackerman concerns it is referring to a rear steer car made
into a front steer by flipping the arms side to side to make them point forward for a front
steer (front mounted rack) setup.

The Wikipedia article RRR posted explains this well. Notice the different front wheel angles
when turning with a properly set up rear steer (stock) vehicle.

220px-Ackermann_turning.svg.png

Illustration courtesy of Wikipedia

When you flip those arms side-to-side it has the opposite effect, making the outside wheel
turn much more sharply than the inside one. This is very difficult to drive and when backing
up while turning it tries to peel the tires right off of the rims.

The correct geometry can be achieved by designing a steering arm that has the outer tie-rod
end fall on an imaginary line drawn through the lower ball joint to the center of the differential
as illustrated, again excellently, in the Wikipedia article.

Notice that if the arms were pointed forward for a front steer that they would be practically
into the tires. The very best illustration I could find to exaggerate the point is to look at the
photos below of the properly configured steering arms on a front steer Bugeye Sprite.

170px-Ackermann_simple_design.svg.png

Illustration courtesy of Wikipedia

Bugeye%20spindle%20c_zpstnwlly2e.jpg

Bugeye%20spindle_zpsstsgckic.jpg
 
Bugeye%20spindle_zpsstsgckic.jpg


Following along with some interest, that last photo says it all. Notice how the car is making a left turn and the wheels are positioned correctly with the inside one turned at a much sharper angle than the outside one. This is proper Ackerman. If this were a rear steer car with flipped steering arms, the Mopar arms would be pointed to the inside as nearly as severely as the Sprite arms are pointing to the outside. The angles of the wheels would then be reversed with the inside wheel angled at about half of the severity it is in the picture and the outside wheel would be the one with (roughly) twice the angle and you can imagine how terrible it would steer.
 
the problem with attempting to utilize the factory spindle is the ball joint mount in relationship to the spindle....it is right on top of it. That location forces the tie rod end outward even more .....compare it to a front steer spindle where the ball joint mounts on the spindle further inward.

it doesn't cost anymore to build a K for factory spindles than it does to for one with the correct front steer spindles, but the cost of all the related components drives the overall investment up.

schools out.

good luck,
Denny
 
Old man mopar that is what i was saying ackerman was an issue about. May have worded it wrong of course as usual. Good to know it is a simple movement of the balljoint angle. It what i figured it was from day one. Seems many just blow it out of proportion vs get down to the nitty gritty like this thread finally did after several posts of beating around the bush about it. Its like pulling teeth around here. Ive looked but always found the same ol "it just doesnt work" answers repeatedly. Never a why. Thank you guys very much for helping me under stand why after all this time it is why it is in the mopar k member world so expensive.

Seems time for a change doesnt it? Wouldnt it be nice to have an abody k member kit comparable to a mustang or camaro?
 
turbofreek said:
..................... Good to know it is a simple movement of the balljoint angle.
Click to expand...

if ONLY so simple.

keep in mind when the location of a steering component changes, other components must change also, otherwise you get serious bumpsteer. ....... a whole other issue.
 
HemiDenny said:
if ONLY so simple.

keep in mind when the location of a steering component changes, other components must change also, otherwise you get serious bumpsteer. ....... a whole other issue.
Click to expand...

I am not doing it denny. A chassis guy who has done many others is. I trust he knows what he is doing. His cars work and win a lot with different brands and different sports to boot not just drags. I just got spooked by all the ney sayers when i knew nothing about any of it but bits and pieces from threads along the way here and there. This one cleared all of it up quickly. Putting my mind at ease. Nothing like ones safey getting pug into question after dropping money and your car off. Ive been readi g and studying non stop on suspension geometry since and im understanding it quite a bit now. So i know what to look for etc. I ha e a lot to learn i didnt think all to much about and took for granted. Thank you all.
 
All good.....looking forward to see what he comes up with. After all, there is more than one way to skin the cat ( no offense Scruffs)
 
well i learned a lot about mopar front suspension these last few months as did my chassis guy taught me a bunch about it. we seen all you guys talked about and he fixed all the issues without raising costs of a k member for the a bodies that is gonna be available once i get to test it out for any issues etc... cant wait to display it once im done testing out. feather weight and roomy is an understatement. i could run zoomies with it. it will allow corner carving im betting, still keeps the stock spindles, i can run a full sump oil pan and remove the pan in car. so many positives. cant even see any negatives. fully adjustable lower control arms. coil overs, i can run flipped manifolds no issues. the real estate is unbelievable for sure. big tube headers will be able to be tucked up away from the ground finally. no more dragging them on low clearance areas. the cars will be able to sit lower and still have tons of ground clearance. everything the mopar world has been missing and long waiting for in my opinion. say good by the the 4x4 a body mopar community once and for all. pic under my car can be seen in my build thread. you wont see the k member but maybe a tiny tiny idea of what is happening up under the front.

the suspense is gonna kill for sure but when it gets presented. it will be well worth the wait. thank you guys very much for all the q and a of this board.
 
67Dart273 said:
Have you ever posted this, details, photos, what rack you use?

I've thought about a rear rack. In fact, I have a "rear steer" rack. Big problem for me was figuring a good way to deal with the extreme column to U joint angle to get to the rack.

A set up like this, tho "properly done" would not have the issues the OP was talking about.
Click to expand...

I should add that I changed the column to a GM tilt unit '68 Camaro. yes the u-joint angles are close to being too severe but close is not over the limit. I will try to post some photos when I can get the car back on the hoist. to busy to think about it right now.
 
jos51700 said:
Dillinger chassis has you covered.
Click to expand...

i like dillingers stuff. couldnt touch what is on my car not even cost wise. weight, strength, real estate or simplicity. imagine camaro ls1 fbody costs, manufacturer reliability and race car adjustability and weight reduction all in a mopar package. no more ford parts. no more(gulp) mustangII comments about your suspension. no 4500 dollar kits to swallow or get a loan for or save for or just never be able to get. imagine upgrading to a better suspension setup for less than a stock rebuilt one. this is what is going to be coming from this and what is on my dart. there is already another who has seen it and is just as pleases as me. he to has to wait till its tested but he knows it is a bad *****.

my car will be done this summer come hell or high water. i will test it in ways most will never be able to. from power wheelys with 1500hp and pot holes of illinois and missouri. highway cruising across the midwest and i will even throw some wide fronts and try some corners after all that. if anybody can break something. i am that guy. so it will be tried and true once its available to the public.
 
turbofreek said:
i like dillingers stuff. couldnt touch what is on my car not even cost wise. weight, strength, real estate or simplicity. imagine camaro ls1 fbody costs, manufacturer reliability and race car adjustability and weight reduction all in a mopar package. no more ford parts. no more(gulp) mustangII comments about your suspension. no 4500 dollar kits to swallow or get a loan for or save for or just never be able to get. imagine upgrading to a better suspension setup for less than a stock rebuilt one. this is what is going to be coming from this and what is on my dart. there is already another who has seen it and is just as pleases as me. he to has to wait till its tested but he knows it is a bad *****.

my car will be done this summer come hell or high water. i will test it in ways most will never be able to. from power wheelys with 1500hp and pot holes of illinois and missouri. highway cruising across the midwest and i will even throw some wide fronts and try some corners after all that. if anybody can break something. i am that guy. so it will be tried and true once its available to the public.
Click to expand...


Sounds intriguing. Always glad to hear more options for our Mopars. Best of luck!
 
I forgot to add it rolls better than my stock front did with the wheels turned. Ackerman be damned.lol
 
Rolling straight is never the issue with ackerman.....turning is

Even with the factory lowers ball joints/steering arms simply flipped side for side (front steer configuration ), it will roll easily without weight (motor/trans).
 
HemiDenny said:
Rolling straight is never the issue with ackerman.....turning is

Even with the factory lowers ball joints/steering arms simply flipped side for side (front steer configuration ), it will roll easily without weight (motor/trans).
Click to expand...

im talking about turning not strait. it rolls in circles beautifully. almost to easily lol i literally just pull on the steering wheel and move the car around. granted i dont have the pumkin in the rearend and all the wheel axles and bearings etc.. are brand new.
 
Ackerman be important...
 

Attachments

  • image.jpg
    41.9 KB · Views: 369
turbofreek said:
im talking about turning not strait. it rolls in circles beautifully. almost to easily lol i literally just pull on the steering wheel and move the car around. granted i dont have the pumkin in the rearend and all the wheel axles and bearings etc.. are brand new.
Click to expand...

That's great.....is the car a shell?....or does it have a motor /trans in it?

do you support the axles in the center /middle somehow without the punkin in it?
 
HemiDenny said:
That's great.....is the car a shell?....or does it have a motor /trans in it?

do you support the axles in the center /middle somehow without the punkin in it?
Click to expand...

the axles are bolted in at the flange. it does rest on the tires. i only roll the car to move it and then put it back up on stands or lift. it dont sit for more than a few hours on the tires this way. strange said i would be fine with this and wont hurt the axles, bearings or housing etc... cars complete engine trans brakes etc... no plumbing yet but has nearly the full 25.3 spec cage besides the floor and driver head wrap around bars in it yet. wont do those bars till the last moment to ease build of interior/dash/intercooler stuff. im a huge guy so climbing around a jumgle gym isnt my fortey right now. lol

i need to run my line lock and bleed the brake lines as well too.
 
turbofreek said:
....still keeps the stock spindles.
Click to expand...
Now that's funny and I don't care who you are.

It won't work with stock unmodified spindles and steering arms just flipped side-to-side.

You cannot simulate the issues you're facing by just rolling it around on the shop floor with no engine in it.

I'd love to see the look on your face the first you put it in reverse and try to back up with the wheel turned sharp.
 
i posted this over in my build thread on here but nobody looks over there. lol here is a sneek peak.


 
front steer systems using A arms are a bit harder to design from a practical perspective. This is because the steering arms themselves seem to have a need to occupy the same space as the brake rotors [drums also], or the wheels themselves. this is on a factory setup of course. You may also notice that on the vast majority of front steer set-ups the spindle {or the strut for that matter} has a lot more KPI [king pin inclination] as compared to vehicles utilizing rear steer. the KPI is an angle as viewed from the front of the vehicle and it is an imaginary line that goes thrrough the center of the ball joints. On our A body cars the ball joints are almost on top of each other, very little KPI. Now compare this to the typical Mustang II spindle, and you will see that it has lots of KPI and it is a front steer setup. The KPI makes it easier to get the front steer system to fit all together. the steering arm has more room because of the KPI geometry. I say all this but of course there are exceptions.One being the late 60's chevelle and same year camaro's which basically used the same spindle but one was front steer and the other was rear steer but they both used the same spindle with different steering arms of course. the spindle utilized some KPI but not as drastic as some other setups.
 
You must log in or register to reply here.
-

Back
Top