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Positive Ackerman theory


Tony
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Snow has melted, our new project 300zx is finished, its cold, but dry, just done suggested setups. Time to take it for a spin and get some feels of new setup :cowboy:

 

Without giving to much away, what areas are you looking to improve?

 

Modified steering as suggested here, want to see if it does any good. Mechanic spent half day to give this a try, i will post some pictures later of work done!

 

We will look forward to that :rambo:

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right idea wrong tree, or right tree wrong idea, the reason behind more steering angle for the "drift" is to achieve greater drift angle, and be able to hold it, a low steering angle means when pushing for greater drift angle the car tends to go into a spin situation, as the angle of the car overtakes the angle of the steering.......

 

im sure it has posh names, but ill be dammed if i know them.....lol

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right idea wrong tree, or right tree wrong idea, the reason behind more steering angle for the "drift" is to achieve greater drift angle, and be able to hold it, a low steering angle means when pushing for greater drift angle the car tends to go into a spin situation, as the angle of the car overtakes the angle of the steering.......

 

im sure it has posh names, but ill be dammed if i know them.....lol

 

I understood that mat.... There are some serious mechanical issues to overcome if the lock angles are to be increased by a high amount..... I have seem some impressive examples in DW but no clues were given to how this was achieved.

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right idea wrong tree, or right tree wrong idea, the reason behind more steering angle for the "drift" is to achieve greater drift angle, and be able to hold it, a low steering angle means when pushing for greater drift angle the car tends to go into a spin situation, as the angle of the car overtakes the angle of the steering.......

 

im sure it has posh names, but ill be dammed if i know them.....lol

 

I understood that mat.... There are some serious mechanical issues to overcome if the lock angles are to be increased by a high amount..... I have seem some impressive examples in DW but no clues were given to how this was achieved.

 

they achieve the increased lock, by...shimming the end of the rack where the steering arms screw in, this then allows the amount the rack can move increase....the shims/shims MUST be of the same diameter as the original part of the rod so that it passes into the rack

 

DSC00245copy.jpg

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Basically extending the mechanical reach of the lock angles...... Ok i am going to ask a logical question others may wonder.

 

The addition of the spacer will displace the toe... If the toe is corrected then wouldn't this belay the modification....

 

Also if the modification is allowed it's pull potential then would this explain why some Drift cars have such extreme front toe positions?

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putting washers in makes the distance between the two (rack) stops greater, giving more lock side to side, The washers are sized to fit INSIDE the steering rack, so you can physically turn the wheel a little bit further before the track rod end hits the outside of the rack (THE RACK STOPS)

 

Obviously when the spacers are installed the settings are re-done..

 

i say this as though i have done it, but i haven't, but this is the method that is widely used.....

 

if, however there is another way...we have the platform to experiment

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another option is....and i quote from one of the other drivers with an s14a

 

rather than just putting the washers in though, only gives one wheel at a time more lock, I.e, if you have a 3mm washer in and you turn it hard onto left lock the right hand rod moves out an extra 3mm but the left hand rod still sits at the same place as before the washers.

How ever if you have it with 4mm machined of the rod and a 3mm washer each side, now on left lock the right rod is pushed out an extra 7mm over standard and the left rod comes in an extra 4mm over standard, basically giving some sick amounts of lock!!

 

here is the method as used on the Toyota AE86....

 

steeringextension1.jpg

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putting washers in makes the distance between the two (rack) stops greater, giving more lock side to side, The washers are sized to fit INSIDE the steering rack, so you can physically turn the wheel a little bit further before the track rod end hits the outside of the rack (THE RACK STOPS)

 

Obviously when the spacers are installed the settings are re-done..

 

i say this as though i have done it, but i haven't, but this is the method that is widely used.....

 

if, however there is another way...we have the platform to experiment

 

It's the 're-done" bit that bothers me..... Lock+Toot have a real relationship... As we know even F1 have only recently introduced positive Ackerman.

 

I feel we can implement some low cost, high value Geometric gains solely aimed at Drift with some testing.

 

Do you have and turn/toot data from the TDi Visualiner calibration rig you can pm me?....... And before you say "but Tony you set the car" yes i did but my target was within a different field of the calibration :cowboy:

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putting washers in makes the distance between the two (rack) stops greater, giving more lock side to side, The washers are sized to fit INSIDE the steering rack, so you can physically turn the wheel a little bit further before the track rod end hits the outside of the rack (THE RACK STOPS)

 

Obviously when the spacers are installed the settings are re-done..

 

i say this as though i have done it, but i haven't, but this is the method that is widely used.....

 

if, however there is another way...we have the platform to experiment

 

It's the 're-done" bit that bothers me..... Lock+Toot have a real relationship... As we know even F1 have only recently introduced positive Ackerman.

 

I feel we can implement some low cost, high value Geometric gains solely aimed at Drift with some testing.

 

Do you have and turn/toot data from the TDi Visualiner calibration rig you can pm me?....... And before you say "but Tony you set the car" yes i did but my target was within a different field of the calibration :lol:

 

re-done is my technical slap dash term for it...... :rambo:

 

i dont have any of the Data, im sure Sam has, if not i am there on the 15th....and the car is going back onto the machine for some publicity stuff :cowboy:

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another option is....and i quote from one of the other drivers with an s14a

 

rather than just putting the washers in though, only gives one wheel at a time more lock, I.e, if you have a 3mm washer in and you turn it hard onto left lock the right hand rod moves out an extra 3mm but the left hand rod still sits at the same place as before the washers.

How ever if you have it with 4mm machined of the rod and a 3mm washer each side, now on left lock the right rod is pushed out an extra 7mm over standard and the left rod comes in an extra 4mm over standard, basically giving some sick amounts of lock!!

 

here is the method as used on the Toyota AE86....

 

steeringextension1.jpg

 

My point exactly.... I can give you an additional 10 degrees lock but only on one lock left or right "you decide"... Obviously this is no good unless the track is all left or all right orbits.

 

The spacer mod allows a more divided value but the L+R is hardly consistent for the serious Drifter.

 

I will ask TDi for some secondary data from your Drifty if you don't mind mat...... Obviously any actual data will be out of sight but it will contribute toward our end goal.

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it doesn't really need to be out of sight.....i think we should be the pioneers, of being open, and transparent in the development....

 

the base line can be very open, its the finite development that ultimately will be the crux of the development, and its these fine data acquisitions that are specific to my needs, may or may not be the same benefit to all the other lex drifters out there........wherever they are :cowboy:

 

if anything, its the finite data that should be kept close to our chests

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it doesn't really need to be out of sight.....i think we should be the pioneers, of being open, and transparent in the development....

 

the base line can be very open, its the finite development that ultimately will be the crux of the development, and its these fine data acquisitions that are specific to my needs, may or may not be the same benefit to all the other lex drifters out there........wherever they are :cowboy:

 

if anything, its the finite data that should be kept close to our chests

 

Assuming the wim centre opens early 08 then our machine will be the Hunter DSP... It's software enables theoretical corrections and displays them in real time...... Maybe you can leave the Drifty with us for a few days so we can explore the possibilities :rambo:

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One of these is are JIC adjustable tie rods. And the other are pillowball erm...bla bla (dont know in english, but pink bits :unsure: ) Kazama, also adjustable in height with special spacers. With these thingies i believe i will be able to fight bigger steering angle as tie rods are longer and the other pilowballs if installed upwards and even if not can help fighting ackerman :) At least i believe so ;) Well, i got these bits inspired by this topic

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I would love to know more..... As i see things the longer steering arm will indeed increase the lock angle.... You can adjust the perpendicular position of the track-rod-end and the height relative to the radii of the wishbone..... This belays bump-steer or bump loses.

 

What bothers me is since the steering arm is longer than OEM then the toe will be displaced.... Surly once the toe is corrected then the benefits are lost?

 

As i said before i can change the lock angle of any OEM car by reducing then length of one steering arm and increasing the length of the other... The overall toe is the same but since the arms are different lengths the lock angle has changed, but only for one lock?

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  • 5 months later...

Hi Chaps

Forgive me butting in and without introducing myself but I've just been reading this thread and it made me think about your problem.

I'm not sure whether you've reached a successful solution to this yet but it isn't posted here.

If I understand correctly you want a greater amount of turn in on the outside wheel relative to the inside one compared to the standard setup.

 

It's a few years (20+) since I read anything to do with Acherman principle so be prepared for me to be wrong here, but iirc the relationship between the steering control arms fixed to the hub and the centre of steering pivot is that the steering control arms follow a line to the centre of the rear wheels with respect to the steering pivot for straight ahead travel, thus are inboard of the steering pivot if the rack is mounted behind the wheel centre.

 

This causes the inner wheel to transcribe a tighter arc when turning.

 

If you want the wheels to transcribe a similar arc to each other the steering arms must follow a line directly back from the steering pivots.

Does that make sense so far.?

 

Therefore if you want the outside wheel to transcribe a tighter path than at present than the inside wheel comparatively you need to create a setup of the steering arms being similar to a longer wheelbase vehicle.

 

This could be achieved either with bespoke hub carrier/steering arms or by mounting the track rod joint end outside the steering arms by use of a special coupling to effectively push the angle outward.

 

If you need the outer wheel to transcribe a tighter arc then either be more extreme with the steering control arms or mount the rack in front of the steering pivot and then mount the arms inboard of the pivots again.

 

There may be clearance issues on tight lock but this could be overcome by moving the steering knuckle forwards or by a bespoke steering control rod.

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Hi Chaps

Forgive me butting in and without introducing myself but I've just been reading this thread and it made me think about your problem.

I'm not sure whether you've reached a successful solution to this yet but it isn't posted here.

If I understand correctly you want a greater amount of turn in on the outside wheel relative to the inside one compared to the standard setup.

 

It's a few years (20+) since I read anything to do with Acherman principle so be prepared for me to be wrong here, but iirc the relationship between the steering control arms fixed to the hub and the centre of steering pivot is that the steering control arms follow a line to the centre of the rear wheels with respect to the steering pivot for straight ahead travel, thus are inboard of the steering pivot if the rack is mounted behind the wheel centre.

 

This causes the inner wheel to transcribe a tighter arc when turning.

 

If you want the wheels to transcribe a similar arc to each other the steering arms must follow a line directly back from the steering pivots.

Does that make sense so far.?

 

Therefore if you want the outside wheel to transcribe a tighter path than at present than the inside wheel comparatively you need to create a setup of the steering arms being similar to a longer wheelbase vehicle.

 

This could be achieved either with bespoke hub carrier/steering arms or by mounting the track rod joint end outside the steering arms by use of a special coupling to effectively push the angle outward.

 

If you need the outer wheel to transcribe a tighter arc then either be more extreme with the steering control arms or mount the rack in front of the steering pivot and then mount the arms inboard of the pivots again.

 

There may be clearance issues on tight lock but this could be overcome by moving the steering knuckle forwards or by a bespoke steering control rod.

 

Hello

I agree with your analogy for the steering pivotal points and the conclusion by degrees to the steering positions radii at the thrust angle but none of your examples will evolve a positive Ackerman...... Accentuate a negative yes.

 

The project in question is on this>

post-2-1212950322.jpg

 

Where i want the outer wheel on (transition) to hold a positive Ackerman.

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Oh, Ok. I said I was prepared to be wrong.

So if they will accentuate a negative acherman principle would the opposite create a positive one? You've got me curious now.

 

I read the whole thread regarding drifting the IS. Helpful to have a ready supply of tyres I guess..

 

I remember a collegue having IS bad inner shoulder wear. Not alone I see.

 

I am indeedy from MBclub, Tony's posts got me interested in popping over here. Nice avatar scorps. B)

 

Nice technical site.

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Oh, Ok. I said I was prepared to be wrong.

So if they will accentuate a negative acherman principle would the opposite create a positive one? You've got me curious now.

 

I read the whole thread regarding drifting the IS. Helpful to have a ready supply of tyres I guess..

 

I remember a collegue having IS bad inner shoulder wear. Not alone I see.

 

I am indeedy from MBclub, Tony's posts got me interested in popping over here. Nice avatar scorps. :huh:

 

Nice technical site.

 

Scorps Avatar is indeed delicious B)

 

As you may have read wim re-wrote the Geometry for the Lexus IS200/300/sc so we are not scared to go that extra mile.

 

I have the Drifty on site for a few weeks so i hope to evolve a cheap, effective modification to the toot.... Don't be mistaken from the similarity of the toot and turn angles..... They are completely different babies.

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A few seem to be quite negative on MB forum as Tony was offering helpful advise, but were glad your here as you can relay Tonys best interests as WIM sorts out peoples problems on many a car club forum..i mean you dont open a million pound centre knowing nothing.

 

If you keep staring at my avatar all your problems will go away and everything in the world will be put right. :)

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A few seem to be quite negative on MB forum as Tony was offering helpful advise, but were glad your here as you can relay Tonys best interests as WIM sorts out peoples problems on many a car club forum..i mean you dont open a million pound centre knowing nothing.

 

If you keep staring at my avatar all your problems will go away and everything in the world will be put right. :)

 

 

he is right , been staring at them for hours, ........no problem !

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A few seem to be quite negative on MB forum as Tony was offering helpful advise, but were glad your here as you can relay Tonys best interests as WIM sorts out peoples problems on many a car club forum..i mean you dont open a million pound centre knowing nothing.

 

If you keep staring at my avatar all your problems will go away and everything in the world will be put right. :)

 

 

I'm feeling better already, thanks..

 

I did notice Tony's welcoming commitee.

Not sure we rolled the red carpet out properly there.:)

 

There are loads of Mercedes with pulling, tyre wear and stability problems, well only about 99% of them so you never know we might be able to find you some 'punters' cars to get your hands dirty on...

It would be interesting to see what you can do to a problematic car.

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A few seem to be quite negative on MB forum as Tony was offering helpful advise, but were glad your here as you can relay Tonys best interests as WIM sorts out peoples problems on many a car club forum..i mean you dont open a million pound centre knowing nothing.

 

If you keep staring at my avatar all your problems will go away and everything in the world will be put right. :)

 

 

I'm feeling better already, thanks..

 

I did notice Tony's welcoming commitee.

Not sure we rolled the red carpet out properly there.:)

 

There are loads of Mercedes with pulling, tyre wear and stability problems, well only about 99% of them so you never know we might be able to find you some 'punters' cars to get your hands dirty on...

It would be interesting to see what you can do to a problematic car.

 

I agree we (the forums) did get off on the wrong foot.... The poster who slagged me off needs to remember someone posting a technical reply is volunteering help and it's not my fault he doesn't understand the content!

 

Whatever!..... Back on topic.

+Y2000 we have corrective restrictions with MB, nevertheless the pulling issues and tyre wear issues are correctable.

 

MB set a president for drift as "eventual" but has never disclosed the distance?....

 

To explain, most manufacturers disclose the car will have an "eventual drift" after (lets say 30yds) this drift is a resistant result of the road crown.... If the car drifts before 30yds a complaint is recognized, after 30yds then happy days.

 

The MB's long castor angle is aggravated by the road crown, in the past this agitation was smothered pneumatically but with today's ever lower aspect ratio tyres this is no longer the case.

 

I'm all up for a "problematic" test car... send it down. It may help everyone understand the data offered by Mercedes is a "suggestion" not law"!!

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