RR98ITR

I've been busy lately...thinking about things...and the things that intrude on my thoughts about the other things...but so often have so much to do with them...

Have you read this one: http://jalopnik.com/5930557/why-you-...-to-drive-fast

Alex makes some good points...but some of them, however good, are still debatable. We have to use words to describe what we're doing, or trying to do in any case, to the best of our understanding, which isn't always that good.

Which is where your higher quality nerd comes in. All of the lesser nerds look to them for guidance. You know some of their names: Puhn, Smith, the other Smith, Aird, Dixon, Haney, Bastow, Olley, Rowley, Zapletal, Nowlan, Van Valkenburg, Adams, Doo, Campbell, Norbye, Milliken's, Kasprzak, Roberts, Staniforth, Daniels, Gillespie, Terry, Holmes, Matschinsky, Reimpell, Gillespie, Ortiz, Wright, Mitchell, Pacejka, and probably some more...including guys who share on the internet like Jersey Tom, DaveW, Cibachrome, Dynatune, Z (I know I already covered him, but he's worth a double mention at the very least), Novak, and SRSVW (Who?)...

Nerds, Engineers, Thinkers...What's the difference to the "Just Shut Up and Get In and Drive" crowd eh? I'll tell you - All The Difference in The World when they're the crucial difference that's kicking your *** in the brain!

So what am I gonna rant about this time? Caster. and the Front Wheel Drive Race Car.

I caught myself not thinking again, and in the midst of That I came across some postings by now retired VW race prep guru/crank Dick Shine (SRSVW) that made me stop and think, and some postings by Cibachrome and Jersey Tom that helped me think about how to think about...this.

Have your thoughts about Caster been limited to negative camber gain and weight jacking in turning and hence guiding you in the direction of "more", subject only to the limit of your upper body strength and endurance? That would put you well within the commonly informed consensus. MAYBE you heard that around 11 or more degrees you're too likely to get oscillation overthrusting and a tendency toward the 8th Dimension.

And MAYBE you even know about Mz and Fy and PT and Magic Formula and BMW and sublime steering feel. And if you know that much maybe you know that Danny Nowlan says flat out that your hands and *** are not going to provide you with coherent and synchronized information, and that it's your job if you're worth a **** to get the job done regardless. Others, more of them, advise the use of geometric caster and trail to align your signal inputs.

Just in case you don't know much about all that stuff, a simple and not wrong picture of it looks like this: the tire doesn't want to turn, by an amount of torque typically referred to as Mz, that you feel in the wheel. At Zero Caster that's what you feel, and it varies with steering and slip angle, and it's a characteristic of the Tire. As you add Caster, you feel a percentage of the tires lateral force Fy thru the wheel. Why you would want to do that (besides wanting to avail yourself of negative camber generation and weight jacking) is because the Mz signal peaks Before Fy and is rapidly heading for Zero as Fy is peaking.

Most of us who got our primary education in the physics of driving from Carroll Smith, think in terms of driving the "top" of a tire curve. We only get such a thing when there's enough caster to give us such a curve. How much is that? Depends on tire, determined experimentally, by YOU. There is ultimately no escape from the responsibility described by Nowlan. There is however something to be said for a car that is More rather than Less nice to drive.

But there's more...Dick Shine, from the VW world of Mac Struts, where you'd Think desire for negative camber gain would be maxed out, was famously outspoken on Caster as EVIL.

Say What! Flip thru all those books...dig and dig...and find no unambiguous description of what Shine could possibly be talking about. So is he just a crank? And a collection of championships and wins coincident only and not contributed to by his philosophy with respect to caster?

Jersey Tom related an epiphany he had about Mz...it's an understeering moment input into the car. That it's converging on zero as the tires lateral force Fy is peaking is nice. The torque about the steering axis created by geometric caster (caster trail) and Fy on the other hand "looks" like the Fy curve itself - ie it's maxed when Fy is maxed.

Did you connect those dots? Caster had a COST...charged to you in additional understeering moment...charged against that same "all the Fy you've got"...by crude calculation 5-8% of the work of getting the front end around the corner at some of the numbers that are commonly quoted. On your front grip challenged front wheel drive race car. You wouldn't do it unless you didn't know better. And near as I can tell almost nobody is telling you any better.

You see it right? It's hiding in plain sight. You can think of the chassis and the wheel as ONE solid body, held as such by your hold on the steering wheel, and the Fy X Trail moment is an understeer moment. Stability, wanting to go straight, is the same as not wanting to turn. Not something you typically want your front wheel drive race car to not want to do.

There are some who know...designers for Honda, Alfa, Lancia, Renault, Peugeot, Citroen, Volkswagen...dig up some factory caster specs...note too that many have power steering...

Scott, who sometimes forgets to think, sometimes doesn't think to think, and sometimes is damn near determined Not to think...but sometimes you gotta...

***EDIT: AND YOU GOTTA KEEP THINKING BECAUSE YOU MIGHT BE WRONG...AND I AM. The attendant forces caused by mechanical trail are resolved thru the steering and do not equate to an understeering moment input to the car. Whatever Shine was onto (or on?) This doesn't appear to be it. I'm gonna keep thinking...despite the risk now so obvious of only having a brain this good to work with.

VTECIntegra9

....drive it

mattbatson

this is pretty interesting, and I always try to learn more...

but I'm also pretty much a guy that just gets in and drives it.

if it isn't handling right...I just drive around it...sometimes not entirely a conscious thing either...

Black R

I went ahead and maxed out caster within factory recommended range - for a grand total of 4deg.

I'm happy with that.

But then other nerds tell me that 2.5 is where it's at - to make the car easier to drive - and easier to drive is faster.

- me, who likes to take the hard road.

Xian

Interesting point about the reduction in caster... I've never tried the opposite end of the spectrum though. I've got some spacers that came with my Kingpin sphericals that would take out a decent amount of the caster. Guess it would be easy enough to give it a try.

As far as the "just race" message... well, yeah. That's important. But knowing what the car is doing, why it's doing it, and then being able to make educated decisions about changes to the setup and driving style is pretty damn important. Especially so when the off-season crops up...

redzcstandardhatch

I think about this stuff too much, yet I basically just drive it. I need to spend more time with prep and adjustments/tuning this year.. Big time

rice_classic

I love knowing! But I hate it too.

Because the more I know, the more I realize I don't know. The well just keeps getting deeper the more I peer into it. It can be like spending all your time analyzing the dots and the composition and merits of each individual dot and eventually you forget to step back and enjoy the damn painting, or worse, forget you ever started looking at a painting in the first place and all you've become is a dot-analyzer. Willful ignorance is not what I'm recommending at all but an understanding of when to take a step back and realize that the whole reason you went down the rabbit hole in the first place was to go play with cars at the race track. Knowing when and how to keep the rabbit hole from sucking you in is a talent in and of itself.

So if the pursuit of the knowledge is going to keep you from getting track time, keep you from practicing, from learning how to actually drive fast, how to develop race craft and strategy then sure, I can see how the nerdy stuff can work against developing the driver.

Kaan

iTrader: (3)

thats something that should be debated over beer... my ADD kicked in trying to read it. /chasethenextshinyobject

VTECIntegra9

Agreed fellas... But some people - example: our paddock-mate, fellow spitfire racer, good friend, hell of a race car brain... but his car makes it out rarely and despite it being beautifully engineered with full independent rear suspension and inboard brakes, etc, etc... I am still 6seconds PER LAP faster than him... on our spare motor...

mattbatson

this here

I remember reading about some up and coming racer back 10 yrs ago...think it was chip herr, cant remember...
but he was getting into some intro pro racing series and he bought a used car that had raced the season before...but had no money to put into it.
He did really well with it for several races before they came up with some money and decided to send the shocks out for mod's.
turns out, the shock guy said three of the shocks were blown.

good racers will find a way to be fast...despite the equipment or level of prep

seat time is so important

VTECIntegra9

Love stories like that and wish we could all be the one in that hot seat. I like to think i've done well in my first season but I'm no driving rookie (10th year of track driving coming up)...
...however track time won't do you much good if you are no making improvements and using that seat time to better yourself and the car (when applicable).

Love this "quote" even if it's not directed at anything in this thread...and the quote is not even from anyone meaningful... it still applies:

"The definition of insanity is doing the same thing over and over and expecting different results."

RR98ITR

I like magical and heroic stories as much as anybody, but...tell me why Galati didn't do better in the Mercedes in 2005? Or why Senna joined Williams for 1994?

Scott, who believes that both driver and car must perform to get...uh...the most fastest...

Xian

My favorite heroic story is about this guy... on the left coast. He has awesome ideas that aren't always "right" but his drive and conviction makes up for any not rightness they may possess. He owns a little piece of Sochiro's history with parts that were lovingly crafted by eunich Kimono Ninja Buddhist Monk's in the heart of the mountains. I don't know that there's any driver out there with jackstands as experienced as this guy...

FWIW and all that, I think I'll go flip the spacers around and see what "less" caster does (or doesn't do). I'm not completely happy with the balance right now and if this will reduce the understeering moment... that would be a good thing.

Black R

Less caster = shorter wheelbase = moar better slalomz

RR98ITR

I was wrong about sway barz...and I paid for it...and I fess'ed to it. The payin' for it was the worst of the two.

Scott, who checked under his Kimono and finds all his junk ("High Five!"), so Christian is talking about some other mutant ninja...

Black R

I missed that thread.

I do remember a pic of an itr on jack stands and an omg gigantor hollow rear bar passing through the chassis...

Off to look for it.

RR98ITR

I was against them before I was for them. In my ignorance I had been mislead by Agent Sigfried's identical twin cousin from Amerika.

Scott, who has a "little" 3/4 inch running thru the spare tire well...with a 1:1 motion ratio...

Xian

LOL! The eunuchs crafted the car... they're not wrenching on it now. That's our Hero.

Interesting... yeah, after playing with a couple different Honda chassis' with several different barz, the setup I liked most is one with a (relatively) big front bar and an even larger rear bar. Granted, I didn't have a pimp "through the chassis" sorta setup with an easier-to-calculate-everything motion ratio. The bad news is that I finally got around to doing the math on the bar that's on the white thing in the garage... and it's woefully inadequate. Maybe I can move it's attachment point to the lower shock fork and get a little more oontz out of it...

PS
It just seeped through my (sometimes thick) skull. 1:1 motion ratio for the rear bar? Where/how did you manage that?

RR98ITR

Rear bar 1:1 (the way I did it) requires brake changes (which I was making anyway) to purchase room. The way the DC fabricators did theirs (not 1:1) is smarter packaging and trouble-wise. The key thing is to note that the offset pickup on the stock LCA twists the LCA on its bushings (as well as along its very being) - something you can't tolerate if you swap them all to spherical. Front done ala a SoCal racers example.

Scott, who DID NOT / IS NOT posting about barz...this was supposed to be about caster, but my subject is apparently a no-brainer of the one kind...or the other...well it was a brainer to me!

Xian

Yep, the offset location of the end link has always troubled me (a little). Since I've always run either rubber or poly in the LCA's though, it's not done more than make me go "well, that's not ideal". I know Brinson has played with (offers?) delrin spacers for the rear LCA to keep it from twisting under load but, in speaking with him, these are a "wear item" and need periodic replacement. Again, not ideal but not terrible either.

Out of the two designs, I'm kinda partial to yours. Just because it has shiny new metal and means that you can run a smaller/lighter bar back there. Just eyeballing the arm length, looks like you're in the ~5" range (horizontally)? That seems potentially a little soft in rate back there but at least it's easily corrected if you find yourself wanting more.

The DC rear solution is no doubt an easier one that offers additional bar options from the existing aftermarket... is that just a stock ITR lower arm that's been boxed in and then had the attachment point for the endlink moved to the middle?

As far as your front bar solution... cool but overkill, IMO. Have you had it on track yet or is this still in the garage-noodling stage?

PS
All this ^^^ does relate to the caster commentary since both ends of the car are tied together by the middle. The better the front works, the less shenanigans the rear needs to undergo...

RR98ITR

"Weight savings" has been for me more of a seductive possibility that gets me started than a beneficial reality realized on completion. Part of that is because I'm afraid to make anything too light, and the rest is because simplicity has advantages.

Re the DC LCA - yes, boxed in the bottom, cut a new hole in the top so that the bar link can be centered, AND space the bar back a corresponding amount, AND because the spring rates are high enough the chassis bar mounts don't tear up/out.

My front bar was intended to make bar changes quick and easy, and to "save weight". It also has the additional benefit of moving the actually Increased weight UP (not that there aren't people who don't think that's a bad thing, apparently there are, though to be fair there are even more who aren't sure).

Scott, whose car is farther along than some of those old pictures suggest, notwithstanding subsequent disassembly of this or that for other purposes including but not limited to starting over again or moving on to the next thing (though I haven't done That just recently)....

ginsu2k

Regarding caster being evil...well if it significantly increases effort to steer, then yes, something is bad about that. So, I think 2-3 degrees is the most for me. Also, if you have some serious anti-roll control then the inside tire is suffering with regards to camber gain. Additionally, going overboard on caster can only add to Mz, giving mucho distortion to the tire carcass which is robbing energy and generating heat, all of which are generally bad...y'know what they say about too much of a good thing!

Sorry, somewhat offtopic regarding caster, but those pics put thoughts in my head.

Regarding the front bar, at least you have a long endlink which will be hardly affected by bar rotation...the stock teeny,tiny endlinks do have this obvious problem compared to the rear's nice mid-length endlinks.

I designed the ARB's and some other suspension pieces on our Formula SAE 3 time world championship race winning OSU car! And I learned a lot about ARB's before I designed them, but nobody, I mean nobody, not Dixon, not Milliken, not Carrol Smith, etc...had the info I needed...mainly an actual Free Body Diagram regarding the ARB's...but, guess who, Fred Puhn, my man....so using his absolutely ancient book from the OSU library I went to work on the design. It's good to see you are using some essential principles that I gleaned from that book. Mainly, super stiff mounts, mounting to frame rails, wide spacing of mount points, long endlinks, and 1:1 motion ratios. Yes, I drool over those bars, maybe I would do something different with the front, but I dunno, those endlinks are trick.

Good on ya, Scott!

Xian

Well, being the only slightly lazy guy that I am, I finally got around to this ^^^.

The immediate seat-of-the-pants results are... interesting. Let's set the stage on the car/setup first:

Street/track/autox EF hatch (B16 powered but full interior, AC, etc.)
I've got no real idea what it weighs since I haven't shoved it on the scales *yet*
It should be corner weighted pretty damn close to a 50% cross as the shocks on it are off my last EF hatch
750/550 spring rates
Stock front bar, 24mm EG/DC fitment rear bar (roughly equal to the "big" ASR hollow bar for EF's).
MCS triples front, doubles rear
15x7.5 wheels with 225/205 staggered R888's

To reduce caster, I moved the little 5mm shim on my Kingpin Radius Rod kit to the "back" side of the spherical. I don't have any way to measure the caster difference in degrees other than to know that it's "less".

Before the caster reduction, I wasn't super thrilled with mid-corner balance. Not that it was terrible but, with a partial throttle lift, it wasn't as quick to tighten the line as I'd have liked. I'd pretty much relegated myself to needing to add more rear rate via spring and/or bar.

After the caster reduction, steering weight is lighter (duh) but still has plenty of feel/weight to it (manual steering). Turn-in is the same or near enough as makes little to no difference. Where I noticed a difference was mid-corner primarily with a little difference on corner exit (likely a result of the mid-corner change carrying over). With the car loaded up, slight reductions in throttle application had a much larger impact on tightening the line (as the rear stepped out) than they did previously. Color me surprised... I didn't expect to see/feel anything different than a reduction in steering effort.

I've got a TnT autoX event coming up so I'll give it a try there and report back... off the cuff though, it looks like the Coyote may be onto something here.

Black R

Doh say it ain't so!

I kinda like 4 degrees of caster!

RR98ITR

It ain't so. I added an edit to the bottom of my first post in the thread.

This is me: