OMG Rob,

Those wheels are really nice looking. Light too. :D

It's about time you got back!!!!:warning: Hope you had a good trip

We did. We had fun hanging with my Formula car buddy Neil Porter as he ran 4 cars at Sears Point.

Then my girls & I went camping for 5 days. Fun stuff.

Thanks for the race video. Good stuff.

Yes way light for wheels that size.

Welcome back Glad to hear the trip was good.

And I incorrectly stated the difference in TW was 1.75" but it is 2.75" I didn't measure these but calculated them based on the hub to hub distance and the wheel offsets.

The Panhard bar is 8" off the ground and level.

Welcome back Ron! I vote 'C' plus phone number, website and personal preferences....unless you're related lol.

welcome back
 

Ron,

I think I speak for many when I say we're all glad you're back to create a diversion from the incessant trash talking. :D

And since we have the famous Ron in Socal and the infamous Rob in Socal, would you please do us a favor and add to your sig "Ron in Norcal"?

That is all, thanks. :lol:

No reason to avoid

a. ?

Plenty of people would want to hear that.

For sure let's go with the hard one.

b. ?

You're funny Ron.

She's a slightly famous model friend we have used for promos for several years. The answers are: 25, BR-549, no website ...but she should, likes & has a Dodge 4x4 truck that she works on herself.

Ron Sorry about the bad numbers. I think a few to many long days at work:underchair: . I wanted to catch you on the PM before you used my bad number. We are basically at a 2" difference.

Maybe it's the Elephant.:lmao:

Front End Geometry
 

Rob,

I tell most everyone, "we can go no faster through the corner than the front end has grip" ... and since we have 285's on the front of a big car ... we need to optimize them to their fullest potential, within the limitations you have put on the car yourself: no fender mods, 2" of front wheel lip, etc.

Here are the keys:

1. Your KPI/Caster Split should favor the caster by 0.5 to 0.75 degrees. Your C6 spindles have 9.15 degrees of KPI. Which would mean you want 9.65 to 10 degrees of static caster. That "seems like" a lot of caster, but just what the doctor ordered. GM runs this spindle at 7.7-8.3 degrees of caster in the stock Z51 & all the fast Corvette track guys run 10.0-10.5 degrees of caster.

2. You will want the A-arms installed to achieve "anti-dive." That means the LCA angles down in front & the UCA angles up in front. This will compliment the suspension set-up I'm going to recommend. And it will provide you with dynamic "caster gain" as the suspension compresses. You need about 0.5 degrees of caster gain. If you end up with more ... which would be good ... you need to reduce your static caster by the amount above 0.5 degrees.

3. How much camber gain you can end up with will also affect your roll center. Since your priorities are road course track days, Silver State high speed runs & Optima type "all around" performance events, you'll want a slightly higher front RC than you would for AutoX. I'd say 4" at ride height & 1.25"-1.5" in dive. That is easy to get by increasing the UCA angle (taller spindle or ball joint) ... which will also increase camber gain.

4. If you end up with 2.0 degrees of camber gain, I'd suggest a "starting point" of .75 degrees of static camber, for a total of 2.75 degrees of camber in dive (suspension compressed). If you end up with less camber gain ... add more static camber ... and keep the 2.75 degrees total. Other tuners may tell you need way more camber, but they're not used to working with a KPI/Caster Split favoring the caster.

5. Run .060" total toe-out. Yes ... out. Then play with the Ackerman & bump steer ... so you end up with .140"-.150" toe out ... in dive ... with the wheels turned 20 degrees.

6. You need to transfer a high amount of weight off the rear tires & onto the front tires for optimum cornering.

7. You need to achieve & maintain a low roll angle to optimize the front tire contact patches.

8. Therefore the optimum suspension set-up for your ride would be a high travel front end ... to achieve high pitch change & low roll angle ... also known as soft spring big bar.

I'll hop back on here tomorrow & outline the suspension set-up to achieve this ... along with tuning tools to balance the car at the track.

I corrected post #1212 after getting a PM from Rob with his spindle info.

I did not correct earlier posts to reflect his correct track width difference of 2" wider in the rear, but we'll use that number from here on out.

Hey Rob,

I've calculated the wheel spring rate we need, but to tell you what spring rates to get, I'll need "True Spring Motion Ratios" that include spring angle from your chassis builder ... so get front & rear ... and post them.

We may be able to work with your existing rear sway bar, if the effective rate is high enough. Typically AME's have 3 positions. Get the effective rate in all 3 positions & post.

Might as well get & post the effective rates for the front sway bar too, but I doubt it will be high enough for the SS/BB set-up I'm going to recommend.

Rob,

What I have outlined below is a soft spring/big bar … high travel, low roll suspension setup that you & I discussed … to optimize the handling of your long wheelbase car with tires 21% larger in the rear.

It is just a baseline to start from ... and it assumes a lot of things for us to discuss & get clear on. Most of these assumptions can be tuned around, if my assumption is wrong. Some can not.

Assumptions:
3500# car
116" Wheelbase
51.5% front weight
19” CG height
2.5”-3” front shock travel in dive
Front track width 56” & rear 58” / 2” wider in rear
285 front tires & 345 rear tires / Same compound front & rear

Readers … do not run with this set-up for your car. That would be like taking someone else’s medicine when you have no idea what health issues they have. I can not say this strongly enough. This is not a universal set-up or even a universal concept. I have outlined this for Rob’s long wheelbase Torino with tires 21% larger in the rear & a 2” wider rear track width.

Baseline Starting Point to Tune From:

Springs & ARB's:
Front Wheel Rate: 275#
Front Spring Motion Ratio: _________?
Front Spring Rate: _________?
Front ARB Effective Rate: 1050#
Rear Wheel Rate: 350#
Rear Spring Motion Ratio: _________?
Rear Spring Rate: _________?
Rear ARB Effective Rate: 400#

ARB (Anti Roll Bar) Arms:
Front: Short, strong (4130 chromoly)
Rear: Steel, no aluminum

Front Roll Center: 4" at ride height & 1.25"-1.5" in dive
Rear Roll Center: 11” with level Panhard Bar at ride height

4-link Specs:
Lower Bars: 0.0 degrees / Level at ride height
Upper Bars: 9-10 degrees down in front
Instant Center: Same height as lower bars … 50-60” ahead of rear axle CL
Pinion angle: 2-3 degrees negative from the driveshaft*

Front Shocks:
I’m not willing to share my proprietary valving info on a Forum. In general, you will need moderate compression valving in the front, to slow the rate of compression on braking & corner entry & substantial rebound valving to hold the front end down through the corner.

Rear Shocks:
Again, I’m not willing to share my proprietary valving info on a Forum. In general, you will need moderate compression valving in the rear, to slow the rate of compression on & corner entry & moderate rebound valving to keep the rear tires planted on corner exit.

Adjustable Shocks:
Triple adjustable shocks ... low-speed rebound, hi-speed rebound & hi-speed compression ... are a key to dialing in a bad ass race car on track day ... and dialing it back to a drivable Pro Touring car at the end of the day. There are poor shocks, good shocks & great shocks available. I choose not to talk brands on a forum.

Wheel width:
Your 285’s need to be on wheels 1” wider than the tread width & put the rear tires on wheels with the same width at the tread width. You want the front tires “stable” and you want the rear tires to “move around” a little.

Tire pressures:
Optimized for full contact patch & even temps.

Rob, as with all cars that get pushed to their limits ... when you find the limits, you WILL NEED TO TUNE on this set-up. I’ve got you close … except for shock valving … which we’ll need to discuss.

In my next post, I’ll outline some tuning strategies after you run it on a road course. And if you want, we can discuss some changes for better AutoX performance.

Hey Ron. I just got home from running errands and goofing around at a buddys house. I'll take some measurements tomorrow and get some specs.:headscratch:

I went down to Speedway Engineering today to grab the proper drive plates, inner seals and dust caps.:D

I continue to be impressed with the Machine work done by Travis and crew at Formula 43. The drive hubs in the last pic are being held in place by the perfect interference fit of the hub to the wheel center. Hub centric magic at its best:thankyou: Travis.

http://i291.photobucket.com/albums/l...ps50c59a40.jpghttp://i291.photobucket.com/albums/l...ps64433c71.jpghttp://i291.photobucket.com/albums/l...ps3e54d430.jpg

:cheers:

Real technical advice, clear pictures of high $$$ race parts...... WHAT THE HELL IS GOING ON IN HERE?? :warning: :snapout: :wrongforum: :badidea: :bang:

Man Rob your thread is just dripping with tech now, this is great!! It kinda drowns out all the BS :lol: although I'm sure once you slow down on the tech and progress it will be full steam ahead!!

Fun little road trip yesterday. Rob and I stopped at Speedway and we're like two kids in a candy store. Their finished parts warehouse was just so cool. Snouts, drive plates, dust covers, housings, crowned axles you name it.

I couldn't help but pick up and admire at least one of everything and you can see above the quality of finished products. And the people there are just great too.

I think Rob bought an extra drive plate to be made into a hip hop/car guy necklace :lol:

Dust cover and fit looks killer Rob. :cheers:

Wow, you are sure not cutting corners anywhere! I don't know how you sleep much at night, as all of this all comes together.

What is your projected completion date?

Rob,
And anyone reading along with us …

The following helps explain each suspension set-up or tuning item in more detail.

The “Soft Front Spring/Big Sway Bar - High Travel/Low Roll” set-up loads the front tires more on corner entry & braking … and therefore unloads the rear tires more … than “Conventional Stiff Front Spring/Small Sway Bar – Low Travel/High Roll” set-ups.

An additional benefit of the front end compressing more & is it acts like stored energy on exit … allowing more front end lift travel under throttle, for increased load & grip on the rear tires.

Utilizing this strategy for this application is based on the need to:
a. Assist this long 116" wheelbase car to turn better.
b. Overcome a 21% larger rear tire bias.

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

Here are the keys to this modern suspension strategy & a few other tuning suggestions, all designed to take a car that would otherwise push … due to the long WB & 21% bigger rear tires … into a good turning road course track car.

1. The KPI/Caster Split favoring the caster … combined with a small amount of caster gain in dive … corrects the angle of both inside & outside wheels … to achieve a full contact patch with both front tires for optimum cornering ability … without running excessive static camber.

2. The “anti-dive” built into the A-arms helps prevent the soft front suspension from compressing too fast under braking. Plus provides the desired caster gain.

3. Achieving camber gain with the A-arm/spindle/ball joint geometry means we don’t need as much static camber. You want some static camber, as it loads the outside front tire instantly on turn-in … improving responsiveness. Just don’t get greedy, and run more camber & less caster. Caster helps both tires achieve the correct tire contact patch… and is progressive. Camber helps the outside tire angle & hurts the inside tire angle & is always doing it. I see some AutoX guys with 5-6 degrees of camber and during corners the inside front tire is using half the contact patch or less.

4. You want a little toe-out. Like static camber, static toe-out improves initial turn in responsiveness.

5. Get the rest of the “dynamic toe out” with Ackerman or bump steer. In race cars, it almost doesn’t matter which we use, because the suspension is always compressed in the corner when we’re turning. Ackerman is the preferred method in a PT car, so you get the benefit on the street too, when the suspension is not compressed. Regardless, you need the inside front tire turning at a tighter radius than the outside tire for optimum front tire grip. Otherwise, you’re dragging the inside tire, instead of the inside tire helping the car to turn.

6. The softer front springs allow the front end to travel farther on corner entry & braking. This varies by application, but the goal is 2”+ instead of ¾”-1” of a conventional set-up. This loads the front tires more, giving them more grip & providing better turning ability.

7. The huge front ARB, plus stiffer rear springs & stiffer than most rear ARB … all work together to keep the car at a low roll angle. This keeps the inside front tire engaged more than a high roll set-up. It also unloads the rear tires more evenly.

8. The stiffer, stronger (and shorter if possible) ARB Arms … load the tires quicker … and make the car more responsive. You will need this in a big, wide, 116” wb car.

9. The front roll center at 1.25"-1.5" “in dive” seems low, but is actually a little high … which is best for loading the front tires on road courses. If you were AutoXing, we would run it around 0” in dive.

10. The rear panhard bar at 11” is high … only to free up the load & grip on the 345 rear tires … and to help the suspension keep the inside front tire loaded during cornering. This will be one of the first things you should tune on at the road course track. If the car is loose, you will lower it. If yours is not infinitely tunable … correct this. Having a non-adjustable panhard bar in a handling car is ridiculous.

11. The 4-link specs I provided will provide more traction on exit and frankly assist with weight transfer from the rear tires to front tires on corner entry. This needs to be tuned to find the happy balance. If you increase the downward angle of the top link, you will add “initial” grip to the rear tires on corner exit as you pick up the throttle … AND it will transfer more weight from the rear end to the front end, as the rear lifts under braking. If you go too far … in search of exit grip … you will make the car loose on entry.

12. The lower bars of the 4-link (3-links too) control “rear steer” or “roll steer”. If you run the bars level at ride height … or 0.0 degrees … as the car rolls over in a corner … both bars pull the rear end forward the same amount, so the rear end stays “true” to the chassis. If you raise the front of the bars (at the chassis mount) or lower the rear (at the rear end housing) you get rear steer … meaning the outside tire is pushed back & the inside tire is pulled forward. This helps steer the car from the rear a little like the fork lift concept.

More angle is more rear steer. Going down in the front or up in the rear, acts in the opposite way, pushing the outside tire forward & the inside tire is pushed back, which does the opposite, causing the car to “tighten” as it is being steering to the outside of the corner. Rear steer affects the exit too, because the car is still rolled over to a degree. So I use rear steer as a tuning tool to free up the car when it is tight or pushy mid-corner & exit.

13. Again, I’m not willing to share my proprietary valving info on a Forum, but you need front shocks valved to have the front end compress at a nice, controlled, smooth rate … and keep the front end down through the middle of the corner, after you have lifted off the brakes … and release & let the front lift as you roll on the throttle.

14. Having front wheels wider than the tread width will improve both initial turn-in responsiveness & front tire grip. Having the rear wheels equal to the tread width will help free up the car on entry & middle & help grip up the car on exit.

Make sense? Got questions?
Everyone feel free to chime in if you have relevant conversation.

...

:lol: :lol: :lol:


Wow Rob, there is sooo much going on here! It is great to see this big girl coming together. It is also great that Ron is passing along his info for us to read. I keep having to go back over it to absorb it. :thankyou:
I have a feeling when the car is ready you will be :king:

And then the fight broke out:warning: If I put it in print it will come back to haunt me. It will hit the road and track in shakedown mode. No new paint no finished interior just bare bones first to sort some things out. I will say that will happen within six months.:wacko:

Yes they are a pleasure to deal with. No need to go anywhere else if you are looking for real, usable, durable and beautifully made parts.
I have a car I wanted to build and knew in building it I had to overcome some obstacles. The biggest is my desire for the car to still be a Torino and not some hacked up rendition of one. Nobody take that wrong. Even the pedigreed race Torino dale posted is hacked up. Look at the wheel wells they just cut a big opening to clear the big wide tire for the front. A car can look very cool hacked if hacked properly that just wasn't my goal for this car. So the technical discussion of how to fit 10lbs of suspension in a 5lbs box is a great one that I am really enjoying, and learning, from.

Ron I am digesting. I sent you some more info and some more thoughts.

Your point on rim width was one I was getting at when this stared. I felt first I needed to determine the widest wheel I could fit on the front and then size the tire. I came up with the 18x10.5" wheel within my body, frame, suspension limitations. My feeling was the 285 35 18 on that wheel was a better fit than a 295 or 305 because of the slight stretch. I believe I was thinking along the lines you are stating. Correct me if I'm wrong.

• The stretched tire would actually have as big or larger effective contact patch due to teh treads flatter profile at the same pressure.
• The stretched tire would allow me to run more tire pressure allowing for more laod capacity while still maintaing the contact patch over a larger tire on teh same width wheel.
• The stretched tire would stiffen the sidewall (screwing up my ride) but improving the tires turn in and holding power.

To maintain my aesthetic goal of no flares the 10.5" wheel was my max. I can run a larger tire on that wheel but my feeling was the one I chose was the best fit for my car.:wacko:

Rob & I calculated the motion ratios for the coil overs, so here are the final spring & ARB numbers ...

Springs & ARB's:
Front Spring Rate: 470# *
Front ARB Effective Rate: 1050#
Rear Spring Rate: 318# **
Rear ARB Effective Rate: 400#

*I would err on the stiffer side & go with 500# front springs ... and if during testing you are not getting the car to travel the front end enough ... and the car is tight or pushy in the middle ... then you can step down in front spring rate to 475# or 450#. This stiffer front spring will also give you a bit more confidence on corner entry until you get used to the high travel.

** I would err on the slightly stiffer side & go with 325# rear springs ... and if during testing the car turns well but needs more grip on exit ... you can step down in front spring rate to 300# or 275#.

Great stuff here, thanks for sharing Ron (in NorCal). Should this stuff be a sticky somewhere? :headscratch:

Torino's gonna be awesome when its out doing shakedowns in it's birthday suit... I also chose to build the car twice, once to get bugs out and tweak it, then tear down for cleanup and paint. After driving a couple of days, I'll stay that tearing it down will be a hard, hard thing to do.

Keep at it Rob!

I'm loving reading this kind of detail! Thank you Rob and Ron for having most of this discussion 'publicly'. :)

I do have a question about the C6 spindle. I wasn't aware that the C6 ran that much caster. Can you explain a bit about the effect of running that much caster, or perhaps asked different, if you run less caster with the C6 spindle, what would the effect be?

My setup uses that spindle, but I've been told to target 6.5 - 7.0* of caster, and my recent alignment check shows 6.8* and 6.2* (I haven't had it aligned fully yet, but that is with camber dead on at the moment). While I realize my setup is different, it supposedly uses pretty close to C6 geometry points.

Keep the techie stuff coming! I'm learning from all of this too!

Thanks. If I had your patina I wouldn't have paint on my agenda ever.:thumbsup:

I think the oddity of my build is a good thing. It lets me ask Ron his opinion out in the open without giving any edge to the other Torino builders.:lmao:

At the same time if you follow along Ron is giving a good overview of suspension and handling dynamics and things to consider when setting up a car.

I'm sure Ron will weigh in on your caster question and it's relationship to camber.

I'm still confused why there aren't more Torinos:headscratch: They have been going round corners for decades.

http://i291.photobucket.com/albums/l...psf3c4d378.jpghttp://i291.photobucket.com/albums/l...ps311e5a88.jpg

Ron - Here's my track width data:

Measured outer sidewall to sidewall front and rear. Tire width is sidewall to sidewall. Nitto NT-05's IIRCC - Dale's running Nitto NT-01 255/40/17, 275/40/17.

Front: 69.0625" 245/40/18 tire on 8" rim measures 9.5"
Centerline Track = 59.5625"

Rear: 70.875" 275/40/18 tire on 9.5" rim measures 10.875"
Centerline Track = 60.00"

I really need to expand my terminology. I’m behind.

Does “Jiffypop” mean the wheel center is crowned out … or flush with the outer edge of the wheel … or both? :headscratch:

...

:lol: Don't worry about learning a one off term from the Ford guy. :lol:

With the big brakes and calipers everyone want to run on these cars all (most) the centers crown out for clearance. The obvious exception is the concave spoke wheels. So that I'd say is a given.

To me JMO, Just my term, when I see that crowned center with a high offset wheel with no outer lip it reminds me of popcorn about to pop. This really becomes noticeable to me when the outer edge of the center protrudes beyond the inner step on a step lip wheel.

This obviously doesn't apply to flat lip wheels but for me, as nice as they look in some styles, those don't exist.:lmao: :underchair:


:cheers:

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.

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

Part 2 of 3 ... answering Carbuff's question about caster & KPI.

First … think of caster as “dynamic camber” … since caster has no affect on angle of the tires & wheels … until you turn the steering. Then caster is tipping the top of BOTH tires towards the inside of the corner you’re turning into (Good).

KPI angle is important to keep the scrub radius lower. You can look at the illustration in the previous post & imagine how big the scrub radius would be if the KPI was straight up & down through the ball joints.

Think of KPI as “dynamic camber” … since it also has no affect on the angle of the tires & wheels … until you turn the steering. But unlike caster, it is not tipping both tires towards the inside of the corner you’re turning into. KPI is tipping the top of the outside tire out towards the outside of the corner you’re turning into (BAD) and tipping the top of the inside tire in towards the inside of the corner (Good).

When the KPI/Caster Split favors the KPI … the tire & wheel, on the outside of corners, goes into a state of positive camber (BAD) … rolling over on the outside part of the tread and sidewall of the tire … with the inside part of the tread becoming unloaded. Basically, at this point, the actual tread making contact with the pavement (contact patch) gets narrower, making it incapable of maintaining the speed it was capable of an instant earlier, when it had a full contact patch.

Now let’s talk about the tire on the inside of the corner. Some cars roll so much the inside suspension goes into a “droop” or state of extension … and if that car has negative camber gain built in … the droop actually helps the inside tire stand straighter. For cars don’t roll as much … and that compress the suspension on the inside tire & wheel when cornering, the negative camber gain on the tire on the inside of the corner is tilting that inside tire the wrong way. It is rolling over on the inside part of the tread and sidewall of the tire … with the outside part of the tread becoming unloaded. Also making the contact patch narrower, making it incapable of maintaining the speed it was capable of an instant earlier, when it had more contact patch.

So your front tires that were already at their limit of grip … just lost a significant amount of contact patch & essentially got narrower … and lost even more front traction … creating a push or understeer condition.

The amount of dynamic camber loss is minimal with slight amounts of steering input on large sweeping corners, but grows exponentially worse with higher rates of steering input (front wheel steering angle) on tighter corners. More caster would help both situations … creating more dynamic camber the correct way for both tires … keeping the tire contact patches flatter on the track surface. But how much is enough? Read on.

Let’s start with understanding how spindle KPI/SAI works. Let’s use a C6 based spindle with 9.15 degrees of KPI/SAI. If you were to set both the caster & camber at zero … and rotated the spindle 90 degrees each direction … the difference would be 2x the KPI/SAI angle … so in this case 18.3 degrees.

We know the wheels don’t turn anywhere near 90 degrees, but this example makes everything more clear. Please humor me & follow along closely, because I’m about to share something that is one of the most overlooked keys to proper cornering set-up. We will account for the ACTUAL steering turning radius later.

If you rotate the spindle 90 degrees toward the front (like the wheel is turning on an outside corner) the tire & wheel experience 9.15 degrees of camber loss (goes into positive camber). Bad … very bad for the outside tire of a corner. :)

If you rotate the spindle 90 degrees toward the rear (like the wheel is turning on an inside corner) the tire & wheel also experience 9.15 degrees of camber loss (goes into positive camber). But this good for the inside tire of a corner. :)

Reminder, we not turning the wheel 90 degrees in the real world, so don’t lock in on the numbers “too much” … just the concept.

Caster is different. If we set caster at 9.15 degrees positive (top to the rear) & leave KPI/SAI out of the equation, as if we had a spindle with zero KPI/SAI … and you rotate the spindle 90 degrees toward the front (like the wheel is turning on an outside corner) the tire & wheel experience 9.15 degrees of camber gain (goes into negative camber). The right direction for the outside tire in a corner.

If you rotate the spindle 90 degrees toward the rear (like the wheel is turning on an inside corner) the tire & wheel experience 9.15 degrees of camber loss (goes into positive camber). And this is the right direction for the inside tire of a corner.

So … caster helps both the inside & outside wheel & tire. :)

Here’s the most important piece of info to know at this point. It is the first & most important key to getting the front tires to use their full contract patch when cornering … increasing front end grip & turning speed. Drum roll please …

Caster offsets KPI/SAI on the wheel & tire on the outside corner … and compounds (adds to) KPI/SAI on the wheel & tire on the inside corner. :)
Read that again. It’s very important.

This is called KPI/Caster Split. When the Caster & KPI are equal … the caster offsets the negative effects of the spindle KPI on the outside wheel ... and compound the advantages of the KPI on the inside wheel. When the KPI is greater than the caster (unless the car has a TON of Camber) the outside wheel is going to lose camber as the steering is turned & roll over on the outside front tire. Ugly.

The greater the split favoring the KPI, the worse the problem. On the other hand if the KPI/Caster split favors the caster … meaning the caster is slightly greater than the KPI, the outside wheel is going to gain camber as the steering is turned, creating a flatter, better tire contact patch. The inside wheel also gets cambered the correct direction (for the inside wheel) and both front tires stay flatter to the road, have more grip, better turning & higher corner speeds.

Sooo … if we set the car up using spindles with 9.15 degrees of KPI/SAI and 9.15 degrees of caster … and you rotate the spindle 90 degrees toward the front (like the wheel is turning on an outside corner) the tire & wheel experience 0 degrees of camber gain or loss.

Frankly it is zero, no matter what degree you rotate it to the front, because 9.15 degrees of caster counteracts … or neutralizes … the 9.15 degrees of KPI/SAI.

If you rotate the spindle 90 degrees toward the rear (like the wheel is turning on an inside corner) the tire & wheel experience 18.3 degrees of camber loss (goes into positive camber). This is the right direction for the inside tire of a corner … way too much ... but we’re not turning 90 degrees. We’re turning somewhere from 0 to 25 degrees.

What if the wheels were turning 15 degrees? … that’s 1/6 of 90 degrees … times 18.3 … equals 3.05 degrees … the right direction.

So … at this point ... we have:
IF Tire +3.05 degrees (Good)
OF Tire +0.0 degrees (OK)

You’re probably going “Hmmmm” … but we don’t have the whole picture yet.


We have a lot of other geometry to factor in. Remember, we’re peeling this onion a layer at a time, so we’ll get to camber gain, chassis/body roll angle & static camber in steps.

...

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.

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

Part 3 of 3 ... answering Carbuff's question about caster & KPI.

Camber gain & chassis roll angle are next. Chassis roll angle hurts the contact patch of both tires. Camber gain (towards negative) helps the contact patch for your outside tire & hurts the contact patch for the inside tire.

If you worked out your camber gain to be 1.5 degrees negative “in dive” on the outside tire … and add that to the combination of your caster & KPI/SAI angle of zero … and factor in the car has a chassis/body roll angle of 2.0 degrees … you would still end up with 0.5 degrees of positive dynamic camber (Bad).

Assuming you have a modern low roll angle suspension … to achieve this chassis/body roll angle of 2.0 degrees … the inside tire, of this car in the same corner, is compressed, but not as far, so it doesn’t have as much camber gain towards negative (reminder: camber gain towards negative is bad on the inside tire).

Let’s say we end up with 2/3 the travel & end up with 1.0 degrees negative camber gain (the bad direction for the inside tire) … and add in the 2.0 degrees of roll angle … makes the inside tire with 3.0 degrees of negative dynamic camber (Bad). Then we factor in the 3.05 degrees of positive dynamic camber (Good) … provided by the combination of caster & KPI/SAI … and we end up with the inside tire at 0.05 degrees of positive dynamic camber (Good).

So … at this point ... dynamically we have:
IF Tire +0.05 degrees (Good)
OF Tire +0.5 degrees (Bad)
Not optimum yet, but we’re going the right direction & we’re not done yet. :)

The next layer of the onion is static camber. You need SOME static camber … to help with initial steering turn-in responsiveness. Just don’t get greedy. In road racing or AutoX where you’re turning left & right, static camber is like camber gain. It helps the contact patch on the outside tire & hurts on the inside tire. For this example, let’s add 1.0 degrees of static camber.

Now with static camber added … with your car hard in the corner … suspension in dive, wheel turned 15 degrees for a tight corner … we have:
IF Tire -0.95 degrees (Bad)
OF Tire -0.5 degrees (Good)
Not optimum yet, but we’re going the right direction & we’re not done yet. :)

Now, here is another part I love. You simply add caster until the contact patches of both tires are flat & happy. And from this point the math is easy.

Add 1.0 degree of caster and …
IF Tire +0.05 degrees (Good)
OF Tire -1.5 degrees (Good)

Add 1.25 degree of caster and …
IF Tire +0.30 degrees (Good)
OF Tire -1.75 degrees (Good)

Add 1.5 degree of caster and …
IF Tire +0.55 degrees (Good)
OF Tire -2.0 degrees (Good)

There are many factors that will define your optimum set-up, but this creates a baseline that is darn close.

**P.S. I like to end up “around” 1-2 degrees more dynamic camber on the outside tire, since it is loaded so much more.

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There is a little more involved in this, when you involve exact steering angles for specific corners. The good news is … when you run tighter corners requiring more steering angle than 15 degrees … the caster increases the dynamic camber to help the tires maintain flat contact patches. I use a spread sheet I developed to plug in all the info & know exactly what dynamic camber I have at different steering angles & different camber gain & different suspension travels.

The best way I have found to work out a front end setting is to start with KPI/SAI & caster … then bring in camber gain … and finally static camber … to achieve the optimum dynamic camber for BOTH tires. Regardless of how you get there ... all of these geometry pieces need to work together in harmony to achieve full, optimum contact patches for both front tires in hard cornering situations … for optimum cornering grip & speed.

It probably is clearer now why getting advice on one setting that worked for a buddy’s car … without knowing the whole picture … can be misleading. As a tuner, I couldn’t imagine setting the caster without knowing the spindle KPI & the car’s camber gain … and then of course testing on track with tire crayon on the edges every run (plus taking tire temps).

It’s been said a zillion times. It’s the whole package, not one part or one setting.

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Remember the KPI/Caster Split concept ... if the caster is slightly greater than the KPI, the outside wheel is going to gain camber as the steering is turned, creating a flatter, better tire contact patch. The inside wheel also gets cambered the correct direction (for the inside wheel) and both front tires have more grip, better turning & higher corner speeds.

When I'm designing a front suspension for a specific class with rules on what spindle we can run, I pick the best spindle available under the rules and design everything else to either fix or compliment that spindle. Factory spindles usually have a lot of KPI/SAI ranging from 7-10 degrees. When I have to run a factory spindle ... I know I'm going to end up with 1-2 degrees of caster more than the KPI.

I designed & raced NASCAR Modifieds with factory GM #2 spindles with 8.75 KPI. 10-10.25 degrees of caster produced awesome results. We had a crew chief go off the range with set-ups & try 6-7 degrees of caster, but the cars always pushed in mid corner ... and snapped loose on exit. He was used to running less caster, but didn't take into account the KPI of the spindles we had to run.

The whole combination of KPI/SAI, caster, caster gain, camber, camber gain, Ackerman, toe, steering ratio, etc. ... ALL have to be designed together for optimum cornering performance. All of them are important, but the KPI/Caster Split is critical & often not fully understood.

When I'm designing a front suspension with no rules on what spindle we can run, I design the spindles & have them built. Then I'm not trying to fix anything ... and everything else in the front suspension can be designed to compliment that spindle. For a road racing car, I designed the spindle with 3 degrees of KPI/SAI ... and designed the rest of the the front suspension around what is called a "zero scrub" set-up ... & we ended up with 4.0 degrees of caster for optimum handling. This car did NOT require a high caster number, because the spindle KPI was lower. What is optimum for tight cornering is having the KPI/Caster Split slightly favoring the Caster.

Another successful car I designed with 5 degrees of KPI/SAI ... ended up with optimum handling with 6.5-7.0 degrees of caster ... depending on the track. Again, the key was the KPI/Caster Split slightly favoring the Caster.

This higher amount of caster seems odd to most mechanics & street car guys, but when you look at the newer Corvettes you'll see they run a lot more caster than what most think of as "typical" in the 1.5-3 degree range. The Factory GM specs for the C6 ZR1 is 7.7+ degrees of caster, with a 9.15 degree KPI spindle. The KPI/Caster Split is LOW, but still slightly favoring the KPI by 1.45 degrees. But owners that compete & win in the C6's increase the caster to 9.5-10.5 degrees of caster ... with the KPI/Caster Split favoring the Caster.

The common denominator is we are almost always running more caster than KPI/SAI ... if we can. We run spindles with lowerr KPI where we can too ... but it requires running wheels with DEEP back spacing to get the scrub radius low (or sometimes zero). So simply ordering a spindle with smaller KPI is NOT a bolt-on solution.


Make sense?
Got questions? ... chime in.


...

Thanks Ron :thumbsup:

For detail and the sprained brain :sieg:

Hi Sieg,

Your rear TW is 7/16" wider than the front, so that will contribute a very small amount to freeing up your car in the corners.

The 12% wider tires in the rear will contribute a larger amount to tightening up your car in the corners.

Both of those items are just two pieces of the bigger puzzle.

If ... your front geometry is like most PT cars with the KPI/Caster split favoring the KPI significantly ... that would contribute the largest amount to the car's handling being unbalanced & tight/pushy on tight corners ... until the front geometry is corrected or the rear suspension tuned to reduce grip to free the car up.

On the other hand, if you're not running track days with tight corners or AutoX, it may not matter. I surely don't know your car or situation, so I don't want to make any unfounded assumptions.

...

Ron,

:wacko: I meant Rob - as he requested my data in a PM...........:bang:

But Ron, thank you very much :thumbsup:

I have a spare stock subframe sitting in the garage that I plan to do on a budget somewhat "Smokey" style and this information greatly helps the quest.

My current setup is somewhat goofy as I feel it handles much better than it should, but I've yet to get it to the track and exploit the short-comings. FWIW my only road course experience is on two wheels.

Again thank you for sharing this information, it is very much appreciated.

Wow... Ask what I thought was a pretty simple question, and I got an amazingly detailed answer! Thank you for taking the time to explain all of that! I've read it twice, and I'm still absorbing it, but your explanation made sense and was very well presented!

I think the next thing I need to figure out is what scrub radius I actually have now. It sounds like that would be one of the next big factors in the equation...

Thanx again!

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. 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.

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?

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?