Moparmonster
Well-Known Member
Funny you say that since today is bicep and chest day before I go to work.
Steering Box Ratio
- Thread starter Moparmonster
- Start date
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Funny you say that since today is bicep and chest day before I go to work.
cookiee monster
New Member
did you have to cut down steering shaft and buy there coupler ??
Yes. Took out a minimum amount. Lucky for me the body was on the lift. I used a spare k frame and mocked everything up.
After getting a lot of good info from this thread, I got the 20:1 new manual box from PST (fabo discount is great!).
The performance on my ‘68 Barracuda FB meets my expectations. I don’t find it any harder to turn than the old box, but love the increased turning for less effort. Was able to swap out without moving any anything (my headers were no issue).
I probably could have managed the 16:1 too, but this is a sweet spot for anyone upgrading a worn out box.
Thanks to the fabo community for the good info.
The performance on my ‘68 Barracuda FB meets my expectations. I don’t find it any harder to turn than the old box, but love the increased turning for less effort. Was able to swap out without moving any anything (my headers were no issue).
I probably could have managed the 16:1 too, but this is a sweet spot for anyone upgrading a worn out box.
Thanks to the fabo community for the good info.
Dave999
Well-Known Member
yeah any new or well rebuilt box is a joy and with everything else new, no dead in the middle. just works
tune steering weight with tyre pressure and castor
20:1 was standard fitmnet on most australian, south african and export to europe/UK manualy equipped A body cars. i.e all the right hand drive markets and fully exported RHD baracuda or the belgium assembled CKD kits for LHD Europe
Dave
tune steering weight with tyre pressure and castor
20:1 was standard fitmnet on most australian, south african and export to europe/UK manualy equipped A body cars. i.e all the right hand drive markets and fully exported RHD baracuda or the belgium assembled CKD kits for LHD Europe
Dave
hi @Syleng1 -
Was this from FirmFeel? They seem to stock rebuilt original units such as the "Small Sector Stage 2 (Modern Street)".
Or was this a Borgeson like from Mancini Racing (BRG800126), with a 14:1 ratio?
14:1 sounds tough from other comments here. Was it good for you?
That's what we're looking for!
Thanks!
Firm feel when they rebuilt my unit was a small sector stage 2. I waited about 6 weeks for the rebuild. I loved it but still felt like an old car driving experience. It also kept getting very hot from the headers and over heating my power steering pump causing me grief.
I went recently to the Borgeson unit ( not sure if ratio) that I purchased on line along with the joint kit and power steering line kit. All fit perfectly and works great. Temps dropped dramatically and steers “almost” as good as my wife’s 300S. Lol!
People can do their best to help steer others away from trouble but some people are still driven to do whatever they want.
It has been mentioned that the early A steering components are unique to themselves, that the 1967-72 and 1973-76 A body steering components are different and do not fit the early A chassis. Some individual parts can be used but certainly not all of them. The Fast Ratio Idler and Pitman arms are only made to fit the 1973 and later design so they don't work. They have a tapered mounting stud that points DOWN, not UP. ALL 63-66 and 67-72 models use a design where the idler and pitman studs point UP meaning the center link attaches from above. The center link has a taper where the tie rod ends and idler/pitman attach. That taper in the center link prevents a direct swap to the later parts. One could...in theory, modify the center link to allow the use of non stock parts but in some states, steering modifications like this are not legal for street use.
AutoXcuda was clear on that. He has no reason to lie, mislead or post incorrect information. He is someone that you can trust.
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Dave999
Well-Known Member
the fast ratio pitman arms were designed for cars that were going to be used in specific race series. can't remember which but one presumes it involved going left most of the time.
a sector based steering box is fast in the middle and slower towards the ends of travel. due to the way the pitman arm interacts with the cross link.
the twist of the sector is linear but the movement of the pitman arm stud in the cross link decreases the further away from central it gets (i.e 90*/ perpendicular to the cross link)
this is the opposite of what is built into modern steering which favours slower in the middle, and faster towards each lock. This cuts down no. of turns lock to lock. makes it easy to go straight, harder to veer wildly off course, or roll, if you jerk the wheel...
modern steering is slow in positions that favour going fast, and fast in positions that dictate going slower, like parking
if you extend the pitman arm. you make the system even faster in the middle. something you may not want..
if you never drive straight this is not a problem, its also faster either side of off centre, this is good for circle track racing. i.e the steering is now as fast off centre where you do most circle track driving , as it was in the centre as standard. It is now fast in a position that allows you to traverse a circle or oval race track. and very fast straight on where you spend little or no time when circle track racing.
a steering box that is too fast in the middle makes it much harder to go straight, and adds to a feeling of instability. you can offset this a bit by whacking in loads of positive castor and paying attention to toe in, but that is more expense.
if you have manual steering and you drive it on the street 90%
choose a ratio you want and use standard pitman arm
if power steering you already have 14.5:1 or thereabouts. and you don't feel the weight of it because its power steering...get a smaller steering wheel.
In my view
better to have manual 16:1 and standard pitman
than try to gain the same ratio with 20 or 24:1 and a long pitman arm
there will be cars and people who have balanced ratio and pitman arm length perfectly for what they want to do i'm sure....but for most of us easier to keep it simple
think about it from a leverage point of view
a sack of gravel:- That you can lift with 1 hand close to the body, would be impossible to lift with one hand 2 foot away with your arm out stretched.... leverage too much for you shoulder
longer pitman you make it harder on the steering box internals and easier for the wheels to knock the steering wheel out of your grip
Basically easier to get busted fingers if you hit a hole or curb....
you need your hands to help you get out in a crash...
Dave
a sector based steering box is fast in the middle and slower towards the ends of travel. due to the way the pitman arm interacts with the cross link.
the twist of the sector is linear but the movement of the pitman arm stud in the cross link decreases the further away from central it gets (i.e 90*/ perpendicular to the cross link)
this is the opposite of what is built into modern steering which favours slower in the middle, and faster towards each lock. This cuts down no. of turns lock to lock. makes it easy to go straight, harder to veer wildly off course, or roll, if you jerk the wheel...
modern steering is slow in positions that favour going fast, and fast in positions that dictate going slower, like parking
if you extend the pitman arm. you make the system even faster in the middle. something you may not want..
if you never drive straight this is not a problem, its also faster either side of off centre, this is good for circle track racing. i.e the steering is now as fast off centre where you do most circle track driving , as it was in the centre as standard. It is now fast in a position that allows you to traverse a circle or oval race track. and very fast straight on where you spend little or no time when circle track racing.
a steering box that is too fast in the middle makes it much harder to go straight, and adds to a feeling of instability. you can offset this a bit by whacking in loads of positive castor and paying attention to toe in, but that is more expense.
if you have manual steering and you drive it on the street 90%
choose a ratio you want and use standard pitman arm
if power steering you already have 14.5:1 or thereabouts. and you don't feel the weight of it because its power steering...get a smaller steering wheel.
In my view
better to have manual 16:1 and standard pitman
than try to gain the same ratio with 20 or 24:1 and a long pitman arm
there will be cars and people who have balanced ratio and pitman arm length perfectly for what they want to do i'm sure....but for most of us easier to keep it simple
think about it from a leverage point of view
a sack of gravel:- That you can lift with 1 hand close to the body, would be impossible to lift with one hand 2 foot away with your arm out stretched.... leverage too much for you shoulder
longer pitman you make it harder on the steering box internals and easier for the wheels to knock the steering wheel out of your grip
Basically easier to get busted fingers if you hit a hole or curb....
you need your hands to help you get out in a crash...
Dave
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Wow, that was well-written. It makes sense.
Nope, totally wrong. The fast ratio pitman arms were designed for the TA and AAR cars. They raced on road courses, not ovals.
Nope. Someone needs to watch what happens to the center link when the pitman and idler move. I'll give you a hint, it doesn't just move linearly.
Nope. The steering ratio determines the lock to lock number of turns, that's true of rack and pinion and worm and ball and has nothing at all to do with the type of steering.
The self centering effect you're talking about is caster, which is higher on modern cars. But that has everything to do with modern tires, and can be adjusted on older cars with the right suspension components.
Nope. Some modern cars change the amount of assist based on your speed or settings, but that doesn't change the steering ratio or how fast/slow the steering is. Changing the assist doesn't change the ratio.
Literally none of this is accurate.
I mean, that's one way. But the better way would be to just reduce the amount of pressure produced by the steering pump, lowering the amount of assist. This has been covered lots with Mopar power steering because of its "over boosted" feel. Check out the article "pump it down". Small spacer change in the power steering pump, lower pressure output, heavier steering.
this is actually mostly true. But mostly because a longer pitman arm creates header and frame clearance issues, and if you can just buy a box with the right ratio and use a standard pitman the clearances all work. And standard pitmans and idlers are cheaper. Otherwise, final ratio is final ratio.
Completely irrelevant example. The way your muscles work and the number and size of the muscles used by each lift have more of an effect on this than the actual leverage.
Ugh, no, again. If the final steering ratio is the same the force at the steering wheel is the same. Doesn't matter if the steering box is 16:1 with a standard pitman arm or if it's 20:1 with a fast ratio arm that makes the final ratio 16:1. Same ratio, same force at the steering wheel.
Dave999
Well-Known Member
oh i think you have been a bit harsh and too quick to dismiss
Point 1 OK i said i didn't know, now i do... more corners than your average city street or stretch of freeway though...i'd guess. they were designed for a job in a car prepped for racing.
linear. as in "not varying" nice straight line on a graph not a curve etc
Point 2
I didn't say the cross link movement was linear. the sector turns by the same number of degrees near center, and off center i.e its movement is linear, as in not varying.
The pitman arm is perpendicular to the cross link at the mid point. At this point any movement of the pitman causes maximum movement of the cross link. As the pitman turns away from the center point, less of the movement at the cross link is side to side and more of it is front to back or indeed back to front, of the car, depending on if it is LHD or RHD ( which way pitman arm faces differs between the two). For a distance turned at the steering wheel, you get a smaller distance moved at the cross link the closer to lock you get. The sector turning is linear, the movement of the cross link across the car decreases the further from centre you go. NOT linear. The sector turns around a point, the pitman arm connected to it scribes an arc.
However so do the levers at the ball joints. If they are the same length pivot to pivot as the pitman arm length, there is some compensation for the arc, the pitman follows. how effective that is, is really dependent on if your pitman faces front or back, the length of the track rods, how parallel they are with the cross link and the compromises in the design. But we are talking here about lengthening one (pitman) and not the other (balljoint). The cross link movement is not linear... and i never said it was. i personally don't think i'm as daft as you think i am..
but hey, that can be proved wrong, as i find everyday...
3) OK not my best use of terms but "what is built into modern steering" covers my sins.
ratio doesn't change... But variable rate racks exist..... maybe i should have said a combination of modern technology conspires to keep us safe. when talking about modern steering. we don't have that in a 50 year old mopar
The modern set up is designed so that the lock to lock turns are low, and the steering is "less lively" in the middle, and nicely tuned to make driving through winding narrow streets and parking at slow speed easier on the arms, less input for a tighter turn to help close quarters maneuvering . You don't get much of that with a steering box and you will make its " dead" point, in the middle smaller when you extend the pitman arm.
4) We are saying the same thing i think... i didn't mention ratio
5) by extending the pitman arm, the distance from centre of sector, to centre of pitman arm stud is now longer. so the arc it scribes is longer for the same no. of degrees turned by the sector, and the cross link needs to move fore/aft more as the steering approaches the locks. but no change to the length of the balljoint levers. so i still say faster in the middle and faster off centre than it was with the original. Each degree at the sector now scribes a longer arc at the cross link. like a sector of a bigger circle
6) well aware of "pump it down".. must have been 20 year ago now, Mr Ebergs killer tech and all that. Find a slant 6 pump or shim the valve, easy with saginaw pumps.... yes I read that...
There were questions in this thread that hinted that 14:1 power steering must be really hard work if 16:1 manual is hard work.. obviously not the case, not comparing like with like.
Shim the valve, change the wheel size add more + castor yeah you can do stuff to alter the feel of power steering, some things easier to do than others.
7) Ok, thanks... would be hard to disagree with keeping it nearly standard...
8) we all have an arm and a shoulder, but fine, ok, just a way to illustrate, and i'll agree perhaps not the best one, that you can make things easier or harder for a system where you use a pivot point, and a lever, to apply a force, when altering the length of the lever.
9)you have just put a longer lever on the end of the sector... a longer lever results in a mechanical advantage at the point farthest from the pivot. So feed back from the wheels into the box can apply greater force to the box internals and then from there to the steering wheel. looking at it the other way the forces seen at the sector tooth/ballnut interface will be greater, because from the pivot point at the sector you are now trying to swing a longer pitman arm/lever. the mechanical advantage works against the steering box in this case. The point where you change the direction of the force applied to steer the wheels now see's the end of, and has to try to swing, a longer lever. the steering box is at the "wrong" end of the lever.
The steering box comes off worst. In a system with no steering damper in theory it will wear out faster.
if it takes x ftlb to shove the cross link left 2 inches with a 4 inch pitman arm
it will take 2x ftlb to shove it 2 inches left with an 8 inch pitman. but the distance turned by the sector will be less, half.... its probably 1/2 the degrees.... i'm not gonna work it out, for a made up deliberately simple example, it is less.... and the distance you turn the steering wheel is less.
Work Done, and force are different things. the energy expended by you turning the steering wheel = force x distance
the Work Done at the steering wheel will be the same for both pitman arms.
With the longer one, the steering wheel is harder to turn, but you don't need to turn it as far.
Short one easier to turn, but you turn the wheel much further.
same energy used, but different ratio of "force to turn" and "distance turned" at the steering wheel.
The forces seen in the steering gear will be greater for the long one, covering a smaller rotation of the sector that results in the same 2 inches movement at the cross link.
Doesn't matter how you achieve a ratio, if the ratio stays the same with 2 different configurations the "force" you use to turn the wheel is the same, but the forces across the components of the system between you and the tyres are distributed differently. id rather be a tooth on a sector shaft in a shorter pitman arm equipped box.
granted some of the things i said, or the way i said it, are open to interpretation
but i tried to give a layman's terms explanation to illustrate why i think achieving steering ratio with the steering box is better than with a long pitman arm. the long arm seems like a bit of a "hack" for a specific racing purpose.
I feel in some areas you may have been a bit quick to dismiss as wrong, things that are not actually wrong. Not liking the way i put it, is different from it being wrong.
Dave
Point 1 OK i said i didn't know, now i do... more corners than your average city street or stretch of freeway though...i'd guess. they were designed for a job in a car prepped for racing.
linear. as in "not varying" nice straight line on a graph not a curve etc
Point 2
I didn't say the cross link movement was linear. the sector turns by the same number of degrees near center, and off center i.e its movement is linear, as in not varying.
The pitman arm is perpendicular to the cross link at the mid point. At this point any movement of the pitman causes maximum movement of the cross link. As the pitman turns away from the center point, less of the movement at the cross link is side to side and more of it is front to back or indeed back to front, of the car, depending on if it is LHD or RHD ( which way pitman arm faces differs between the two). For a distance turned at the steering wheel, you get a smaller distance moved at the cross link the closer to lock you get. The sector turning is linear, the movement of the cross link across the car decreases the further from centre you go. NOT linear. The sector turns around a point, the pitman arm connected to it scribes an arc.
However so do the levers at the ball joints. If they are the same length pivot to pivot as the pitman arm length, there is some compensation for the arc, the pitman follows. how effective that is, is really dependent on if your pitman faces front or back, the length of the track rods, how parallel they are with the cross link and the compromises in the design. But we are talking here about lengthening one (pitman) and not the other (balljoint). The cross link movement is not linear... and i never said it was. i personally don't think i'm as daft as you think i am..
but hey, that can be proved wrong, as i find everyday...3) OK not my best use of terms but "what is built into modern steering" covers my sins.
ratio doesn't change... But variable rate racks exist..... maybe i should have said a combination of modern technology conspires to keep us safe. when talking about modern steering. we don't have that in a 50 year old mopar
The modern set up is designed so that the lock to lock turns are low, and the steering is "less lively" in the middle, and nicely tuned to make driving through winding narrow streets and parking at slow speed easier on the arms, less input for a tighter turn to help close quarters maneuvering . You don't get much of that with a steering box and you will make its " dead" point, in the middle smaller when you extend the pitman arm.
4) We are saying the same thing i think... i didn't mention ratio
5) by extending the pitman arm, the distance from centre of sector, to centre of pitman arm stud is now longer. so the arc it scribes is longer for the same no. of degrees turned by the sector, and the cross link needs to move fore/aft more as the steering approaches the locks. but no change to the length of the balljoint levers. so i still say faster in the middle and faster off centre than it was with the original. Each degree at the sector now scribes a longer arc at the cross link. like a sector of a bigger circle
6) well aware of "pump it down".. must have been 20 year ago now, Mr Ebergs killer tech and all that. Find a slant 6 pump or shim the valve, easy with saginaw pumps.... yes I read that...
There were questions in this thread that hinted that 14:1 power steering must be really hard work if 16:1 manual is hard work.. obviously not the case, not comparing like with like.
Shim the valve, change the wheel size add more + castor yeah you can do stuff to alter the feel of power steering, some things easier to do than others.
7) Ok, thanks... would be hard to disagree with keeping it nearly standard...
8) we all have an arm and a shoulder, but fine, ok, just a way to illustrate, and i'll agree perhaps not the best one, that you can make things easier or harder for a system where you use a pivot point, and a lever, to apply a force, when altering the length of the lever.
9)you have just put a longer lever on the end of the sector... a longer lever results in a mechanical advantage at the point farthest from the pivot. So feed back from the wheels into the box can apply greater force to the box internals and then from there to the steering wheel. looking at it the other way the forces seen at the sector tooth/ballnut interface will be greater, because from the pivot point at the sector you are now trying to swing a longer pitman arm/lever. the mechanical advantage works against the steering box in this case. The point where you change the direction of the force applied to steer the wheels now see's the end of, and has to try to swing, a longer lever. the steering box is at the "wrong" end of the lever.
The steering box comes off worst. In a system with no steering damper in theory it will wear out faster.
if it takes x ftlb to shove the cross link left 2 inches with a 4 inch pitman arm
it will take 2x ftlb to shove it 2 inches left with an 8 inch pitman. but the distance turned by the sector will be less, half.... its probably 1/2 the degrees.... i'm not gonna work it out, for a made up deliberately simple example, it is less.... and the distance you turn the steering wheel is less.
Work Done, and force are different things. the energy expended by you turning the steering wheel = force x distance
the Work Done at the steering wheel will be the same for both pitman arms.
With the longer one, the steering wheel is harder to turn, but you don't need to turn it as far.
Short one easier to turn, but you turn the wheel much further.
same energy used, but different ratio of "force to turn" and "distance turned" at the steering wheel.
The forces seen in the steering gear will be greater for the long one, covering a smaller rotation of the sector that results in the same 2 inches movement at the cross link.
Doesn't matter how you achieve a ratio, if the ratio stays the same with 2 different configurations the "force" you use to turn the wheel is the same, but the forces across the components of the system between you and the tyres are distributed differently. id rather be a tooth on a sector shaft in a shorter pitman arm equipped box.
granted some of the things i said, or the way i said it, are open to interpretation
but i tried to give a layman's terms explanation to illustrate why i think achieving steering ratio with the steering box is better than with a long pitman arm. the long arm seems like a bit of a "hack" for a specific racing purpose.
I feel in some areas you may have been a bit quick to dismiss as wrong, things that are not actually wrong. Not liking the way i put it, is different from it being wrong.
Dave
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oh i think you have been a bit harsh and too quick to dismiss
Point 1 OK i said i didn't know, now i do... more corners than your average city street or stretch of freeway though...i'd guess. they were designed for a job in a car prepped for racing.
linear. as in "not varying" nice straight line on a graph not a curve etc
Point 2
I didn't say the cross link movement was linear. the sector turns by the same number of degrees near center, and off center i.e its movement is linear, as in not varying.
The pitman arm is perpendicular to the cross link at the mid point. At this point any movement of the pitman causes maximum movement of the cross link. As the pitman turns away from the center point, less of the movement at the cross link is side to side and more of it is front to back or indeed back to front, of the car, depending on if it is LHD or RHD ( which way pitman arm faces differs between the two). For a distance turned at the steering wheel, you get a smaller distance moved at the cross link the closer to lock you get. The sector turning is linear, the movement of the cross link across the car decreases the further from centre you go. NOT linear. The sector turns around a point, the pitman arm connected to it scribes an arc.
However so do the levers at the ball joints. If they are the same length pivot to pivot as the pitman arm length, there is some compensation for the arc, the pitman follows. how effective that is, is really dependent on if your pitman faces front or back, the length of the track rods, how parallel they are with the cross link and the compromises in the design. But we are talking here about lengthening one (pitman) and not the other (balljoint). The cross link movement is not linear... and i never said it was. i personally don't think i'm as daft as you think i am..
Nope. Let me be very clear about this, you are 100% wrong about sector steering. This is basic geometry.
The ends of the pitman, idler, and both steering arms all travel in circular arcs. They are all connected by solid rods that do not change length (excepting bump steer, not what we're talking about here).
Because everything is moving in an arc, there is no "center" or "ends" where the geometry changes between the pitman, center link, and tie rods. It's all uniform motion along the arc. Any length difference between the pitman and steering arms is a ratio split evenly over the arc.
That makes everything you said above completely false. There is no "faster" or "slower" depending on how far the wheels have been turned- the center of the box doesn't mean anything to the geometry relationship between the pitman and center link. Not for standard pitmans, not for fast ratio pitmans, none of it.
Rack and pinions are just a gear and a bunch of teeth. There do not get "less lively" in the middle. That is again 100% false. The stability in the steering on center is an effect of the alignment geometry, not the racks, which are uniform throughout.
If you know of a variable steering ratio rack that's commonly installed in any automotive application, I'd love to see it. Every system in wide production I'm aware of varies the amount of boost or power assist, not the steering ratio. Not saying on doesn't exist, but again, lets see it.
You're right, how you achieve the ratio is irrelevant. The force multiplier in the steering system is always the combination of the steering box and the pitman arm, the "standard" pitman arm is included in the ratio calculation for the steering box. If the ratio is the same, the force is the same. Now, a longer pitman arm might put more force on the bottom bearing of the box instead of entirely within the worm and ball? Sure. But the input and output remains the same. The force multiplication always occurs within the box and pitman arm, changing the ratio or length of the arm just changes slightly the components within the box that see the most force.
If a 16:1 box is going to snap your fingers off, then so will a 20:1 box with a fast ratio steering arm resulting in a final 16:1 ratio. Same force, same number of rotations lock to lock.
Everything we're discussing is basic physics and geometry. It's really not up for "interpretation", it happens the way that it happens. It was all designed to work a certain way, and it DOES work in that way. Whether or not you or I understand it correctly doesn't change how it actually works.
Dave999
Well-Known Member
OK variable rate racks and solutions for steering
AutoZine Technical School
https://www.brakeandfrontend.com/variable-ratio-steering-systems/
i belive the cars that GM Holden sold in the US under the chevy and pontiac brands, rear wheel drive v8 saloons had this, can't find anything to show that. but the above illustrates some of the history. You can get a modified K frame in Australia to facilitate fitment to a Mopar
AutoZine Technical School
https://www.brakeandfrontend.com/variable-ratio-steering-systems/
i belive the cars that GM Holden sold in the US under the chevy and pontiac brands, rear wheel drive v8 saloons had this, can't find anything to show that. but the above illustrates some of the history. You can get a modified K frame in Australia to facilitate fitment to a Mopar
Dave999
Well-Known Member
It is basic geometry and i shouldn't have tried to respond to a range of NOs and Ughs without asking why I just succeeded in trying to dispute things that took us away from the original point..
and yes i shouldn't use flippant throw away comments like busted fingers.
I won't use quick steering to mean fewer turns of the wheel or greater turn in of the road wheel, in respect to the same input at the steering wheel or slow to mean more turns, it seems to drag us off into other things
But do me one last service and give me your view. if i'm wrong i wanna know how wrong
V
if this represents the position of a LONG pitman arm at left lock and right lock, Pitman length and the 2 positions represented by the arms of the v, the arc between the tips of the V is long, It took 4.5 turns of the wheel to swing from left lock position to right lock position.
v if this represents the position of a short pitman arm that has been swung through the same angle. The arc between the tips of the V is much shorter and the wheels didn't reach left or right lock
so in the second case i've changed the ratio of my steering by going long pitman arm to short. If i want to turn the driving wheels as far to the left, and as far to the right as i did previously its going to take more than 4.5 turns of the steering wheel to swing from 1 lock to the other, as you would expect. its probably going to be 5.5 or 6.5 turns of the wheel. i've basically gone from say 16:1 steering to 20: or 24:1 and my v is not splayed wide enough to represent lock to lock
as i approach the fullest extent of travel of the centre link in either direction the angle between the pitman arm and the cross link gets more extreme and my V angle would need to get wider if it has to represent left lock and right lock with the shorter pitman
angle swept by long pitman when viewed from the sector shaft is say 30* angle swept by smaller pitman is 45*
the full travel from lock to lock with the long pitman takes place whilst the angle between it and the cross link is still favoring predominantly sideways motion of the cross link
The full travel lock to lock with the shorter pitman arm tends towards a situation near each lock where the angle between the pitman and cross link is veering towards a situation where the biggest component of the movement of the cross link will be fore or aft rather than side to side
this has to have an impact on delivery of turn in/ out at the wheels in respect to input at the steering wheel.
you explained it away with "Its all arcs and simple geometry" and said no impact.
i'm interested in why no impact? I can't see how there couldn't be an impact
if i made the pitman much longer , Long enough to get a ratio of 4:1 steering much like a Kart
1 full turn of the steering wheel now gives me a steering from one lock to the other.
My V in this case is very very narrow. The sector turns only a few degrees to make a big ark with my long pitman and the movement at the cross link was all created by a pitman arm that was a damn sight closer to perpendicular to the cross link for the whole of its travel than either of the previous two
i can't see how this change in interaction between cross link and pitman in respect to the angles between, can be dismissed as irrelevant.
the delivery of the steering request that the driver makes has to change its "profile" as far as i can see
how am i wrong here? i just can't see it.
the cross link is constrained by the arc it follows at the idler, otherwise long pitman arms in extreme cases would have tyres or brake calipers hitting inner fenders i'd guess. but how is that relevant to a situation that plays out only in terms of the angle scribed between pitman arm and cross link
this relationship changes as you extend the pitman arm
this was my only point, i made it in a bad way and ive tried to make it in a good way but either way if its wrong thats not good and i'd like to understand why.
if you change ratio in the steering box from 20:1 to 16:1 you have to turn the wheel fewer turns, but the delivery of you steering request is the same, the turn-in of the car into a hard right will be the same, apart from the fact that you moved the steering wheel a shorter distance. the effect should be much the same at the wheels
if you change ratio to 16:1 by adding longer pitman to a 20:1 steering box you have to turn the wheel fewer turns in this area its the same as the 16:1 box. but delivery of your steering requests out side of straight on will be different. for the same steering wheel input the turn in of the car will be different.
the long arm stays closer to perpendicular with the cross link throughout its travel than the short arm, therefore the reaction of cross link to steering input has to change in all areas that are not straight ahead.
in seat of the pants terms i guess you might not notice but in simple geometry terms all i can see.... is a difference
Dave
I just succeeded in trying to dispute things that took us away from the original point..and yes i shouldn't use flippant throw away comments like busted fingers.
I won't use quick steering to mean fewer turns of the wheel or greater turn in of the road wheel, in respect to the same input at the steering wheel or slow to mean more turns, it seems to drag us off into other things
But do me one last service and give me your view. if i'm wrong i wanna know how wrong
V
if this represents the position of a LONG pitman arm at left lock and right lock, Pitman length and the 2 positions represented by the arms of the v, the arc between the tips of the V is long, It took 4.5 turns of the wheel to swing from left lock position to right lock position.
v if this represents the position of a short pitman arm that has been swung through the same angle. The arc between the tips of the V is much shorter and the wheels didn't reach left or right lock
so in the second case i've changed the ratio of my steering by going long pitman arm to short. If i want to turn the driving wheels as far to the left, and as far to the right as i did previously its going to take more than 4.5 turns of the steering wheel to swing from 1 lock to the other, as you would expect. its probably going to be 5.5 or 6.5 turns of the wheel. i've basically gone from say 16:1 steering to 20: or 24:1 and my v is not splayed wide enough to represent lock to lock
as i approach the fullest extent of travel of the centre link in either direction the angle between the pitman arm and the cross link gets more extreme and my V angle would need to get wider if it has to represent left lock and right lock with the shorter pitman
angle swept by long pitman when viewed from the sector shaft is say 30* angle swept by smaller pitman is 45*
the full travel from lock to lock with the long pitman takes place whilst the angle between it and the cross link is still favoring predominantly sideways motion of the cross link
The full travel lock to lock with the shorter pitman arm tends towards a situation near each lock where the angle between the pitman and cross link is veering towards a situation where the biggest component of the movement of the cross link will be fore or aft rather than side to side
this has to have an impact on delivery of turn in/ out at the wheels in respect to input at the steering wheel.
you explained it away with "Its all arcs and simple geometry" and said no impact.
i'm interested in why no impact? I can't see how there couldn't be an impact
if i made the pitman much longer , Long enough to get a ratio of 4:1 steering much like a Kart
1 full turn of the steering wheel now gives me a steering from one lock to the other.
My V in this case is very very narrow. The sector turns only a few degrees to make a big ark with my long pitman and the movement at the cross link was all created by a pitman arm that was a damn sight closer to perpendicular to the cross link for the whole of its travel than either of the previous two
i can't see how this change in interaction between cross link and pitman in respect to the angles between, can be dismissed as irrelevant.
the delivery of the steering request that the driver makes has to change its "profile" as far as i can see
how am i wrong here? i just can't see it.
the cross link is constrained by the arc it follows at the idler, otherwise long pitman arms in extreme cases would have tyres or brake calipers hitting inner fenders i'd guess. but how is that relevant to a situation that plays out only in terms of the angle scribed between pitman arm and cross link
this relationship changes as you extend the pitman arm
this was my only point, i made it in a bad way and ive tried to make it in a good way but either way if its wrong thats not good and i'd like to understand why.
if you change ratio in the steering box from 20:1 to 16:1 you have to turn the wheel fewer turns, but the delivery of you steering request is the same, the turn-in of the car into a hard right will be the same, apart from the fact that you moved the steering wheel a shorter distance. the effect should be much the same at the wheels
if you change ratio to 16:1 by adding longer pitman to a 20:1 steering box you have to turn the wheel fewer turns in this area its the same as the 16:1 box. but delivery of your steering requests out side of straight on will be different. for the same steering wheel input the turn in of the car will be different.
the long arm stays closer to perpendicular with the cross link throughout its travel than the short arm, therefore the reaction of cross link to steering input has to change in all areas that are not straight ahead.
in seat of the pants terms i guess you might not notice but in simple geometry terms all i can see.... is a difference
Dave
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Kirby-Bishop made variable ratio steering boxes & racks for Fords & Holden's in Australia and later for Mercedes and a few others aswell.
I have one of their variable ratio power steering boxes to go in my valiant - 2.5 turns lock to lock, 17.5 - 11.5 ratio. I couldn't find much info on them but apparently "the variable ratio is provided by a variable pitch hourglass worm". The variable ratio rack they made for Mercedes is a similar design to the Honda rack posted above.
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