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To increase the caster by 3 °, you have to move the upper ball joint back by about 13 mm (approximately because I don't have the courage to go to my garage to precisely measure the distance between the two ball joints), which will move the wheel * / - 6.5 mm in the wheel arch; I don't think that's really a big problem.
I read I don't remember where that the European Pantera had more roulette and that Ford asked that there be less on the US models because in the 1970s, unlike the Europeans, you Americans were already very accustomed to power steering, therefore light, on the one hand and were already subject to speed limits on motorways which made great stability at high speed unnecessary on the other hand.

@rene4406 posted:

To increase the caster by 3 °, you have to move the upper ball joint back by about 13 mm (approximately because I don't have the courage to go to my garage to precisely measure the distance between the two ball joints), which will move the wheel * / - 6.5 mm in the wheel arch; I don't think that's really a big problem.
I read I don't remember where that the European Pantera had more roulette and that Ford asked that there be less on the US models because in the 1970s, unlike the Europeans, you Americans were already very accustomed to power steering, therefore light, on the one hand and were already subject to speed limits on motorways which made great stability at high speed unnecessary on the other hand.

The recentering doesn't sound like much but consider that the original tire size was a 185-78-15 and was mounted on a 7" wide rim.

Presuming that one stays with a 15" rim and 8" wide, you can mount a tire of 245-50-15. The entire nature of the clearance on the tires turning arc is altered.



Even so, that concerns me less then what exactly happens to the bump steer?

It is possible that there will be several here that will laugh and say, "Doug doesn't know what he is talking about. I have the +6° and I have NO bump steer".





Well I'd LIKE TO take that as an accurate statement but let me just make a point here. I have personal hands on experience with the '65 Shelby GT350.

That car had a suspension modification done post Ford, by Shelby. That modification introduced a nasty amount of violent bump steer to the car.

Was that even mentioned in magazine road tests of the time? Answer: rarely.

Did owner ever complain about it? Almost never.



So what's my point. Until sometime in the mid to late '70s, owners didn't even realize that there was an issue. They didn't know what the term bump steer even meant.

They thought that the tires were over inflated and/or the Koni shocks were set just to high on rebound?



Now I really don't INTEND to ruffle feathers and call current Pantera owners names inferring that they are stupid, but there are many GLARING examples in posts right here on this forum that would indicate to me that the general knowledge base amongst them is embarrassing low.

In fact, it makes me wonder how the vast lot even would up with these cars at all? Did you go out to buy a pickup truck and saw the rear decklid and thought you could carry hay back to the farm on it?

I don't get it?



I'm wonder how many here even would know WTF anyone is talking about when the subject of bump steer comes up? I'll bet they think it is some kind of a now obsolete "disco dance move"?

Amazing! ABSOLUTELY AMAZING! LOL FOREVER!

Last edited by panteradoug

The Bump steer depends on several parameters, the main ones, far ahead of all the others, are the position of the steering rack, in height and lengthwise, and on the position of the articulation point of the steering rods which must be located in the shot of the four triangle joints on the frame. What is true on one car, your '65 Shelby GT 350 for example, is therefore not necessarily true on another.
It is generally possible to reduce the bump steer by adjusting the position of the steering rack with shims.

@rene4406 posted:

The Bump steer depends on several parameters, the main ones, far ahead of all the others, are the position of the steering rack, in height and lengthwise, and on the position of the articulation point of the steering rods which must be located in the shot of the four triangle joints on the frame. What is true on one car, your '65 Shelby GT 350 for example, is therefore not necessarily true on another.
It is generally possible to reduce the bump steer by adjusting the position of the steering rack with shims.

I am aware that there are differences. I used the 65 GT350 only as an example of owners not even knowing that they had it or what it is.



What are your measured bump steer changes before the castor changes and after?

All cars are going to have some since the joint center lines move in arcs, not strait lines. You can only retain what exists, increase the change or reduce the change.



Bump steer is going to occur with toe changes due to suspension moves up and down.

It is always difficult to explain in writing how a set of moving parts works in relation to each other and when in addition it is necessary to translate into a language that we know as little as I know English, it is almost impossible. . A drawing would be more meaningful and I will try to make one.
But I can still explain that the modification of the caster is obtained by moving the upper ball joint in a direction perpendicular to the axis of the steering linkage. The ball joint actually moves in an arc of a circle but, for an angle of 3 ° the vertical displacement of the ball joint is only about 1mm, or about 0.5mm at the level of the steering rod, which can be easily compensated with shims under the steering rack

@rene4406 posted:

It is always difficult to explain in writing how a set of moving parts works in relation to each other and when in addition it is necessary to translate into a language that we know as little as I know English, it is almost impossible. . A drawing would be more meaningful and I will try to make one.
But I can still explain that the modification of the caster is obtained by moving the upper ball joint in a direction perpendicular to the axis of the steering linkage. The ball joint actually moves in an arc of a circle but, for an angle of 3 ° the vertical displacement of the ball joint is only about 1mm, or about 0.5mm at the level of the steering rod, which can be easily compensated with shims under the steering rack

You don't need to explain it.

You just need to state that the castor change resulted in no toe change.



Probably a better question would be, what is the toe change before the castor change to +6° and  an even better one would be, what is an acceptable or unacceptable toe change.



Rene. Thank you for your patience I think that your English comprehension is excellent.

Good thing too. My French is non-existant!

Wow - I guess I brought up a touchy topic!  It is good reading though - not sure anyone is aligned on the settings but it is a good debate. Lots of knowlege/experience on this site!!!

I was just trying to get a feel for who you trust to do the alignment. As there are so many variables with this, I will have the shop use the factory settings as a baseline and go from there.

I am coming out of an '08 Porsche 911 turbo with AWD and lots of nannies so it was easy to drive at crazy/illegal speeds on the twisties.

I will be taking it slow on the Pantera for some time until I get comfortable with the handling so I don't need a bunch of caster at this point.

Thanks!

Current Porsches like all modern fast cars have multi-link suspension systems (I had a 996 turbo 4 WD) and it's a lot more complicated because everything move in all directions. We are not trying to eliminate the induced micro steering but on the contrary we use them to improve the behavior of the car, for example to increase the toe-in of the outer rear wheel in bends to control oversteer. It is so complicated that the different angles at the different positions cannot be calculated without a computer.

@Panteradoug: Google Translate is very useful

Rene4406 - the Porsches are so well developed. The handling is superb, yet with 19" low profile tires, the ride is actually pretty decent on our Michigan (USA) pothole infested roads, even in Sport mode.

I have only driven my Pantera about 25 miles to get it home from the seller's location, so I haven't gotten a chance to see how it handles the curves (winter is here). It did have a reasonably comfortable ride over the bumps.

Rob: This has been an interesting thread. However, let me go back and try to actually answer your initial question.

1. Any good alignment shop can handle a Pantera. It is not rocket science. You need to make sure they understand you are willing to pay for whatever time it takes to do the job correctly. It is not a 30 minute job. Find a shop with a late model Hunter computer alignment system. The things these systems can do are amazing. They are super accurate and more importantly, they give repeatable numbers, as you will probably have the wheels on and off the car more than once during the process.

2. Here is how we set up my 1973 Pantera L, stock arms and sway bars with polyurethane bushings, Hall lowered suspension about 1-1.5", Koni Shocks, stock wheels and Pirelli tires.



Front:

Caster: 2.70 degrees Positive

Camber: 0.50 degrees Negative

Toe: 0.22 degrees IN total (0.11 per wheel)

Rear:

Camber: 1.55 degrees Negative

Toe: 0.40 degrees IN total (0.20 per wheel)



These numbers are based upon the factory specs, but with some changes due to my 30 years running a vintage sports car race team, and the additional engineering knowledge about chassis alignment known today. Rear toe is enough to give stable braking, buy not wear the tires excessively.



Results: The car drives AMAZING. Super pleasant and responsive steering. Tracks well and brakes in a straight line. Could not be happier. The driving dynamics are one of the most surprising things I have discovered about the Pantera.  I have been around Italian GT cars for almost 60 years, and the Pantera amazed me. Feel free to PM me with any questions.

At risk of inflaming any one, it’s not obvious to me how a caster change would result in toe-in or bump steer changes, especially when we are talking about caster changes of 3-5*.

I guess I’ll have to break out my “Engineer to Win”, and “Tune to Win” books, and the included suspension models!

I am familiar with the bump steer, as I have been setting up & swinging the suspension on my TVR.  It can be pretty wicked at the limits of suspension travel.

I guess think a key design goal is minimizing it in the 80% of the range the suspension typically operates in.

Rocky

Last edited by rocky
@petematus posted:

Rocky,

Any change in caster setting will result in a "toe-in" change in a Pantera front suspension.

Having owned a Griffith 200, I can understand your frustration with your 1971 TVR front suspension issues!

Pete M.

That was my point, that the castor re-setting creates a change in toe change.

The issue is that no one can state what that change is nor what the original toe change is.

Therefore by arbitrarily changing to +6°, you are going in blind and stuck with whatever the geometry change results.





Considering that castor increase is beyond what the original Dallara design provided for, why would I arbitrarily presume that is a good change?

That additional castor is also beyond what the original considerations were on the car. So there are stability  improvements with it, but what are the trade offs?





I wound up also with just about the same positive caster of 2.7. I could get a little more on one side but I couldn't match them so it was limited to the lesser value.

I have similar camber values as well. -.50° was about what worked. The front doesn't seem to need any more but this is on P7's so I don't know what racing tires would need. Probably another -.5° or so but that's not an issue for me.

Rears are at just about -.75°. I don't want to increase the rear bite more at fear of the rear steering. Larger GTS rear bar. Stock front.

I'm very sure that the car was aimed at drivers expecting to be able to hang the rear out like a live axle car and being able to just back off the throttle if it started to get loose, predictably.



Some of you may like the 911's handling now but my 82 930 still had issues of trailing throttle over steer.  The Pantera is much more manageable even with considerable power added over stock.





I'm still looking for what is considered a desirable limit to bump steer. I suppose the real answer is "as little as possible" and one should just hope that it can be acceptable?

This text uses -2.5°/m as the "target". It doesn't state that is desirable.

https://www.suspensiondesigner...ump-steer-linearity/

Last edited by panteradoug

Over the years, there have been many articles done on resetting the street Pantera suspension for radial tires, not for racing. They are ALL available in the POCA ArchivesUse at your own discretion!  A few highlights:

* 2.5-2.7 degrees is the max caster one can get from a stock front suspension. Offset upper a-arm bushings will increase it to about 4.2-4.5 degrees. Milling 0.100" off one side of the upper ball joint holders will further increase that to about 5 degrees. If you add power steering, also adding offset bushings in the lower a-arms (along with the uppers) will give 7+ degrees. Custom shims allow trimming to your preferences. No need to cut & weld anything.

* UPPER offset bushings should be installed to push the spindle top toward the cabin, while offset LOWER bushings pull the spindle bottom towards the front bumper. The effect is the same: tilting the spindle for better self-centering and more steering stability. Poly bushings only; rubber bushings are not made in offset configurations because being flexible, they are too imprecise.

* '70s Corvettes use 7 degrees on far larger front tires but they also have stock power steering. My little wife could tolerate 4.5 degrees of caster in our street Pantera with only a bit of puffing and grunting when parking. Above 25 mph one does not notice the steering effort increase from increased caster. She seldom went slow....

* Stock Panteras mid-'72-up got two 5/16" thick factory bump-steer shims between the rack mounts and the chassis. That fixes bump steering and is about the only mistake I've found with Dallara's design (taken from his '69 DeTomaso F-2 open-wheel race car). Lowering the car by any means makes bump-steer worse unless you readjust everything.

* 7" x 15" Campys have nearly 1" of positive front tire-scrub  while 8" x 15" Campys have zero. So adding wider 8" Campys in front (with appropriately wider tires) actually makes steering easier & improves front tire life. Check this carefully with all aftermarket wheels.

* Old-school alignment of a Pantera rear suspension is done by backing the car onto an alignment rack and reversing the readings. At least that's the way Bear Alignment used to do it in the '70s. Due to the usual rear subframe collapse (fixed with a properly designed adjustable rear camber bar), the avg. Pantera has about 2 degrees of rear camber which cannot normally be adjusted out. Adjustable upper rear a-arms fix this but then reduce max rear tire sizes.

* Be careful in using stock alignment settings AND driving the Pantera anywhere near its capabilities. The stock chassis is set up slightly nose-HIGH (probably due to DOT bumper and headlight height requirements). Without a front spoiler, the nose will begin to lift above 110 mph. Raking the chassis about 2 degrees nose-LOW helps high speed stability.

* Changing components like steering rod lengths without rechecking everything often reduces or even reverses Ackermann-toe settings. This then affects low speed driveability. One really needs to know what they're doing in changing Pantera alignments due to 'unforseen results'!

4460. 9/72 build. No rack shims or evidence of them when I got it.

With the maximum castor change from offset poly bushings, and my own rack shims added, I can't measure any toe change. Zero.

I would need a digital laser device to measure that 100% accurately I'm sure. I'd suspect there is a trace but for my own purposes I'll call it zero.

Also stock spring spacers removed so car is lowered 1".

*- Agree. My #4366 did not have them either but I've heard of a few '72-1/2 L's having them as well as most '73-up cars. Simple flat 8mm/5/16" thick bump-steer spacers have a part number listed in later Illustrated Parts Lists and in the European GTS/Gr-3 Supplemental Parts Lists, but like most Pantera upgrades, there is no hard date for their introduction. I call it an  'L Model Thing' that carried over to '80s wide body cars at least thru the '87 GT5-s cars.

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