Take care.

...

Scrub Radius is important, but again, it's just one of many factors that all need to work together.

...

I'm located in Springfield, OR.......near nothing. :D

Hey I grew up in Eugene. I remember when Springfield really had nothing but a Pulp mill!

Hi Bryan,

On the subject of caster, I do have another question...

I've heard that changing the amount of caster has an impact on the 'feel' of the steering.
More caster increases the feel of the track in the steering wheel ... communicating to the driver what the front end is doing. Less caster decrease this feel.

More scrub radius increases the feel of the track in the steering wheel ... communicating to the driver what the front end is doing. Less scrub radius decrease this feel.

Since reducing scrub radius is good for turning ability ... but takes away the feel ... and adding caster also helps the turning ability ... and returns the feel ... these are two good tuning changes to do together. . :)

I've also heard that caster is often used in a street alignment to offset the irregularities that we may experience when driving down the road.
What your referring to is factory passenger car settings to help the car drive straight on roads that are crowned. Some mechanics like to put a little more caster in the RF wheel to offset this ... others prefer to add a little static camber in the RF to achieve this.

I'm a race car designer & crew chief, focused on track cars, so we don't do this on road course or AutoX cars ... just oval track cars.

Can you touch on either or both of those, particular how either would relate to the KPI / SAI as you explained them above? Is there a crossover point, for example, on how increasing / decreasing the caster will affect the steering 'feel'? I ask partly because if that's true, I wonder if you can hit a point where we might 'overwork' the steering rack we are using? In other words, I would guess that if we make a change to the caster that causes us to have to use more force to turn the wheels, are we possibly putting more pressure on the rack, and risk damaging it?
That question reminds me of a guy one time buying a large duration, high lift, "mean" aggressive inverted flank ramp roller cam to build optimum power in his 434" SBC ... and then asking how the fuel mileage would be? :omg:

Yes, almost anything you do to make your front end grip more & turn better, is going to put more load on the steering box. Wider tires, grippier tires, wheels with the width wider than the tread width, low profile tires, faster steering ratios, more caster, more camber, bigger sway bars, springs & shocks to provide grip, etc, etc, etc.

About the only thing that will help the car turn better & not increase the load on the steering box is reducing scrub radius.

I'm thinking out loud with that question, so perhaps it's irrelevant... But in my case, since I'm using a Ford rack that was likely never built to take much abuse, I wonder if that can become a problem?[/QUOTE]
That's smart thinking. If you build a mean handling machine & utilize a small, moderate duty steering box, you could have issues.

What R&P do you have ?

.

I've been through Eugene before ... on my way to Portland. We're about 500 miles apart which makes it impractical, but I'm confident there are some low buck ... cut & weld mods ... that would make the stock clip work good.

You'd still need some aftermarket parts, but wouldn't need to spend a fortune.

Let me know if you move forward on it & we'll see if we can figure something out.

.

I am assuming you (and I) have the same rack that Jake used (and still is being used by Vinny in AIX) ?

Ron

It is enlightening to see the full discussion of KPI/SAI & caster and it's relationship to camber laid out in an easy to digest discussion.:thumbsup:

I'm tempted to cut and paste your roll center discussion on here also but maybe I should leave that to you.

Reading this reminds me of why I reached out to you. A statement made by Carroll Smith in Tune to Win. c.1978. He was speaking of purpose built race chassis. More narrowly focused than the quality pices of engineering available to the PT market.

"What you can buy is a starting point. In a really competitive class of racing it is unlikely to be capable of winning races out of the box. Development is up to you. You will do it by tuning"

Even with a Camaro:mock: there are many variables introduced by the owner that a suspension designer cannot account for. And every design brought to mass market is a compromise that will work for the whole market.

What most of us have from the vendors is a good or great starting point. But if you really want it to work, to the nth degree, you have to invest some time to understand what you really have and how to tune it.:superhack:

With nothing more than a proper install, most, if not all, of these systems would produce a more than competent street car with good manners and ride. But then some people just have to really beat on their stuff.

Instead of race class rules there exists another set of limitations dictated by style and some minimal rules such as tire compounds.

I really enjoy your willingness to post some of the thought process of how to squeeze more blood out of the Turnip or in this case the Torino.:thumbsup:

I have plenty left to do on this build and plan on continuing to post all of tweaks that I hope in the end will result in a very competent big boned girl.


:cheers:

Thanks for getting this started Rob!
Ron, I greatly appraciate the information. Roll center please!

Hi Rob,

Thanks for the kind words.

Your points are all spot on. If you want to optimize performance, you need to tune & test. I have always found the people that do that most, are the ones to beat.

P.S. Love Carroll Smith's books. I read them in 1980 & it set me on the path to design, build & tune race cars the way I do.

.

Guys,

I'm getting conflicting information on the C6 spindle KPI angle. So take that into account when reading #1234 & #1235.

If the KPI #'s I have been given are incorrect, I will correct the KPI # & the equation in these posts and let everyone know.

.

And now all that is there is Pulp fiction

Ron, one more question on KPI/SAI: is the angle relative to ground plane? In other words, does the KPI change when static camber is changed? Or is it a hard angle directly from the manufacturing geometry of the spindle? So with a particular spindle, the KPI angle would always be the same for that spindle? Just wondering as I am trying to visualize all this. I like your analogy of the wheel turning 90 degrees, it's easier to see whats happening.

What an awesome discussion, thank you.

Oh, more Torino pics Rob!

http://assets.diylol.com/hfs/8c7/f25...ead-d0d8ee.jpg

Me so sorry :lol:

KPI is spindle dependent not camber dependent.

Ron,

Since you've entered Rob's world I think some people might actually be scared of this big boned girl. :peepwall:

:thumbsup:

Oh ... I think he was "committed" to making it a mean track car regardless. Maybe I can help him get it there quicker.

.

Fords do need all the help they can get :snapout: :secret:

Again...Fords do need all the help they can get AND CLASS IS IN SESSION WITH Mr RON :y0!:

HI ROB!!!!!!! :underchair:

You're funny.

I really enjoy & relate to your signature line ...
"And people who don't know the game ask me why we race. I always reply that it has nothing to do with the racing, what we do is a people thing. The cars are just what we use to measure skills from one day to the next".


It reminds me of when Neil Bonnet was reflecting on his career after he came back from a bad crash & said, "I used to think I was racing against all these people ... until I got perspective & realized I was racing WITH all these people. It's the relationships I value most."

That struck a cord for me after I broke my back in a high speed Kart wreck in 1991 at Sears Point & has been one of my guiding principles since. I want to win ... and I'll work as hard as necessary until I do ... but I value enjoyable relationships more. When I look back on all my racing exploits, it's the great people & the good times I remember & enjoy most.

.

100% agree'd!! There is nothing like the racing family/car community (yes Sieg motorcycles too). When I'm inside those race track gates... the rest of the world doesn't exist.. It's in your blood or it's NOT :patriot: Neil was one of my favorites, And sorry you broke your back.

I believe that to be true. And if I remember correctly, it's the Ford rack from the 88-94 Mustang. One of us would have to confirm that with Jake, although I probably have it in an old email somewhere. :)

Ah, a quick search of my email turned this up:

"its late 80's through mid 90's ford rack"

So I was close. :)

:thankyou: again for such a detailed answer on KPI. Can't wait for roll center lessons :popcorn2:

It's all part of the discussion on tuning a car. In this case it applies to my car so no hijack on your part.

By "some people" I would think you mean a certain SB2 owner. :mock:

JerDog

You know you have a soft spot in that Bowtie heart for my Ford. :snapout: Glad to see you back from your vacation from my thread.:welcome3:

All this suspension discussion is just an attempt to tame the Tunnelport.


http://i291.photobucket.com/albums/l...ps757fba27.jpg
Click Below

http://i291.photobucket.com/albums/l...GOPR0564-1.jpg[/QUOTE]

I am purrty sure you can and you will!


Um. I'd say you nailed it. :D

I might be on that list now.... it's all Norcal Ron's fault.... :buttkick:

Oh.. I almost forgot. :bigun2:

http://i236.photobucket.com/albums/f...ps6a533df1.jpg

Glad to be back. I don't think you can tame the beastport. And BTW with Mr Ron helping, you've lost your "amateur status" :hello:

Click Below

http://i291.photobucket.com/albums/l...GOPR0564-1.jpg
Nice video sounds good.

:stirthepot: :confused59:
:catfight: I agree.

[QUOTE=Flash68;493499] Oh.. I almost forgot. :bigun2:

http://i2.photobucket.com/albums/y3/...ps932328b9.jpg

BMF BMF BMF :king:

[QUOTE=intocarss;493563]BMF needs Ford stripes over the roof.

[quote=intocarss;493563]


:lol:


Nice one Jerdog. :D


That being said, sure are a lot of Shivee guys paying attention to yer FErd Rob.

I come from a mixed family (owned a bunch of FErds/GM's) so I don't care who beats whose brains out. :hitaxeonthehead:


:lol:

[QUOTE=Matt.A;493570]Fact!

And Dodge paint. :sieg:

Rob, so are you gonna redo your wheels and run something like a 285 on a 13 inch wide wheel? :wacko:

http://i236.photobucket.com/albums/f...ps9a88ac6e.jpg

I figured before we move on to discuss Roll Centers, we should wrap up our conversation on steering geometry.

All of us know that each front suspension geometry setting affects the overall picture ... and to a degree ... each other. As a race car Designer & Crew Chief, I can't look at just one individual setting. I have to look at the spindle KPI/SAI, Caster, Caster Gain/Loss, Camber, Camber Gain/Loss as a team ... a team of geometry devices that I need to work together in harmony to improve how the tires contact the road dynamically.

Having done this for years, designing, building, tuning & racing a lot of cars, in just about every type of racing, has given me some firsthand insight into how all these things work. So now it's a little easier & quicker for me to "get a set-up there" to the sweet spot. I have a process that gets me there quickest ... with the least back-n-forth.

First … some guidelines:
Zero scrub radius with long control arms & deep backspaced wheels is optimum, but many race series rules prevent us from achieving this, with rules on the LCA. If the rules allow, we're running long control arms & a low KPI spindle on deep backspaced wheels & achieving low to zero scrub radius.

But when the rules restricting our LCA choices prevent us getting the ball joints "out there" … making us choose between track width & scrub radius … we are “usually” going with wheels with less backspacing to achieve the maximum track width allowed by rules … then running higher KPI spindles to reduce the scrub radius as much as we can.

I've had people ask me why don't we give up track width to achieve a lower or zero scrub radius ... but in the big picture ... track width trumps scrub radius, up to a point. Everything has its limits & there are exceptions for everything. Tight AutoX courses sometimes favor narrower cars with narrower track widths. But most anything faster than that favors a wider track width. When you have no rules or limitations, you making everything optimum. When rules prevent that, you’re shooting for the best overall compromise.

My process:

A. I have to work out the Spindle KPI/SAI with the length of the A-arms, tire width & wheel backspacing ... to end up with maximum track width & a desirable scrub radius.

B. Once I know the spindle KPI/SAI … that guides me on how much caster I need to build in to achieve a KPI/Caster Split favoring the caster.

C. I need to figure out if we want caster gain* … and if so, how much … or for the caster to stay the same, as the front suspension compresses fully under braking & turning (called "Dive"). I have seen poorly set-up cars with caster loss in their set-up, but it is not desirable.

D. If I can get the caster I want ... statically and/or with gain ... so the KPI/Caster Split favors the caster ... I can run less total Camber, which is the goal. If I can NOT get the the KPI/Caster Split favoring the caster … we will need more total camber. Once I know how much total camber I need for that combo, I work out how much of it is going to be static camber & how much is going to be camber gain. I like to get 50%-60% of the total camber desired … through camber gain.**

E. If I can get the camber gain I want ... I can run less static Camber, which is the goal. We're always going to run some static negative camber … because it improves initial turn-in response***. Depending on the application, I like -0.75 up to -2.0 … again, as long as I can get the camber gain AND the KPI/Caster Split favoring the caster. But if I can not … I will need more static camber.**

F. How we get the camber gain, & how much, affects the car's static & dynamic roll center ... so they have to work as a team too.

All of this is to optimize both front tires’ contact patch with the asphalt ... In the car's dynamic states when it's driven HARD ... meaning turning, braking, rolling, unwinding & accelerating to the limits of the car, tires & driver ... sometimes beyond. :)

-----------------------------------------------------------------------------------------------------------

*Caster gain is achieved when the front A-arm geometry is set for anti-dive. Zero caster loss or gain is achieved with zero anti-dive. Caster loss is achieved when the front A-arm geometry is set for the opposite of anti-dive … called “pro-dive.”

** The more static camber you have to run to optimize the outside tire, the more you’re hurting the inside tire. I like to get 50%-60% of the total camber desired … through camber gain. Here is why: The suspension on the inside of the corner is not compressed as far as the suspension on the outside corner. So effectively … the inside tire is not getting as much negative camber gain to fight & overcome.

*** Don’t get greedy with static camber. Yes it improves initial turn-in steering response, which is good. But two things:
1. Camber helps the outside tire & hurts the inside tire. If you run too much static camber, you can’t get the inside tire to work optimum.
2. There are a LOT of other things that help turn-in response … so use some of those … & don’t get greedy with static camber.

-----------------------------------------------------------------------------------------------------------

You know how people say a little information can be dangerous? This is one of those times.

If your car has a large-ish scrub radius … you have to be careful with how much caster you can put in the car … because caster combined with a high scrub radius creates a “jacking effect” when you turn the wheels. Dynamically, this jacking effect “de-wedges” the car … loading the inside front & outside rear tires more … while also unloading the inside rear tire & increasing the degree the car diagonally rocks & loads the outside front tire.

All of this helps the car to turn better. But go too far … and the car will get loose on entry. This is where track tuning comes into play. If you have a large-ish scrub radius … sneek up on the caster you put in the car … until you get the car “free” on entry … then reduce the caster a tick … or tune something else to allow you to keep that amount of caster, so the car turns well in the middle. But don’t keep a set-up that makes the rear step out on corner entry.

Make sense?

.

[QUOTE=Matt.A;493570] Sorry i don't like Ford or Dodge roof stripes..IT'S A FRICKEN CHEBY!!!:snapout: :warning:

DG I sent you that picture in confidence.:secret:

Ron

What would you consider Large-ish scrub radius in the case of these 275-315 range of tires?

I have heard that an inch or under can be thought of as zero.

Maybe a little more detail on scrub would be good. :idea:

I was having a conversation stating there is a nominal effect on scrub due to height differences in tires. That difference in scrub between a 30 and 35 series tire of the same section width on the same wheel would be pretty minimal and in real world probably insignificant. But with all things it is best not to assume and really dig into what amount of scrub becomes noticeable or detrimental.:headscratch:

:cheers:

Hey mods....How about moving this great suspension technology stuff over to where it might be more appropriate for others to ask questions about their own cars? :idea:

Seriously? This thread finally has substance! :sieg:

No kidding....maybe we should transfer it over to the Bad Funny Finger thread :lol:

Now that gentlemen, is how you HiJack a thread.:trophy-1302: