Toe-in or Toe-out "darty" ??

[JEFFTATE]

I'm using Falken Azenis RT615 tires at 40psi all the way around.
I lowered them to 36psi Front and 32psi Rear when autocrossing to get some bite on the rear.
If I run the tires at anything below 40psi on the street , I loose steering feel.

[a67]

The offset caster to compensate for road crown doesn't always work out. When I did it I found that the car either went straight or pulled hard to the one side.

And the pulling was more often then the going straight.

So I squared up the caster with much better results. The car now either goes straight or has a slight pull to one side or the other.

The most likely reason for these results is that the road crown varies. Different roads, different crown. On concrete roads I don't believe there is a crown at all.

Then on some interstates, the right lane slopes to the right while the left lane slopes to the left.

Bob

[BonzoHansen]

^^I find that too and prefer close to 0 cross-caster, maybe .25 tops.

And yes toe-out makes a vehicle darty. Good for autocross, not so much driving a honda pilot down the interstate (I had to make honda realign our pilot when we got it for this very reason, and the service writer fought me on it).

[6spdmalibu]

So is there such a thing as too much caster?
And does that depend on the height of the rear roll center?

[Norm Peterson]

So is there such a thing as too much caster?

Probably. If nothing else, bumpsteer will be affected. In a few cases - the OE G-body may be one - more caster actually helps this situation out (up to some point, anyway).

You probably aren't thinking about strut suspensions here, but with those arrangement changing the caster also changes the anti-dive/anti-rise.

And does that depend on the height of the rear roll center?

No.


Norm

[chicane67]

Stability of this specific setting is going to be effected by both the caster setting and suspension ride height.

So basically... if you are running an OEM subframe without geometrical changes to the control arm location points and all that has been done is simply lowering the suspension... you will have bumpsteer induced toe-out... which can be reduced (but not eliminated) by adding more caster. The reason it can not be eliminated, is that you are limited on the amount of caster that you can add to the suspension without going to geometrical changes in the control arms, their respective mounting locations or the spindles themselves.

The control arms available offer you 5*+ caster right out of the box... whereas the OEM components will only allow you about 4-4.25* caster without effecting other attributes in a negative way. So the/a control arm change can net you better available caster which will combat bumpsteer on a lowered chassis. But you are still limited on camber gain with any control arm... unless you use something like Global West control arms and use an variation of the 'Guldstrand' modification.

I set up a clients chassis, which was a OEM subframe - control arms - suspension mounting points - wheel size - etc, etc... at pretty much the OEM ride height with the maximum available caster, -0.5* camber and 0.250" total toe-out and if drove straight, it didn't tramline and had excellent stability at low and high speeds. In fact... I was amazed that it did as well as it did with an all OEM set-up... so much that I had to re-verify what was actually there because it did so well.

Now... that was excellent... but as soon as I would have changed any one of those components, it would have changed everything about how the chassis reacted. That is why I believe that most of this will be effected by the smallest attribute being changed.

I commonly use toe-out (between 0.03125 to 0.250" total depending on application of course) without the chassis becoming to twitchy and/or darty. It really depends on the variables.

I say... get yourself two 2x2" aluminum parallels (either 2x2 "U" channel or 2x2" I beam) about 12' in length, four 4x4's about 18" in length, two precision tape measures (that measure in 64ths out to 10 feet)... and start playing with your toe adjustment yourself. You don't need to take it to an alignment shop to do this... in fact this suspension system is so simple... you might just want to purchase a "Longacre" bubble camber caster gage and do your alignments yourself.

Before the modifications to my current '67 subframe, and the fact that I dont care about 'road crown'... I had the '67 set up like this:

-1.75* camber left and right
+3.90* caster left and right
0.1875 total toe out

Mind you that the chassis is set up to "designed ride height", it had a 16" wheel and tire package on it and no geometrical changes done to the OEM components and mounting location. I still had some 'outside' tire wear (due to the aggressive driving, not the alignment) but it drove killer. Then it was one modification at a time, retune the alignment to the singular change... and then go to the next.

That's why I say go get some new tools... you can do the work yourself and learn... not to mention save moola in the long run by doing it yourself. It's a win win...

[JRouche]

Before the modifications to my current '67 subframe, and the fact that I dont care about 'road crown'... I had the '67 set up like this:

-1.75* camber left and right
+3.90* caster left and right
0.1875 total toe out

Mind you that the chassis is set up to "designed ride height", it had a 16" wheel and tire package on it and no geometrical changes done to the OEM components and mounting location. I still had some 'outside' tire wear (due to the aggressive driving, not the alignment) but it drove killer.

Wow, thats alot of static camber, no inside tire wear issues? But now it sounds like a racing car? Not a street car right?

Great info you posted by the way. I agree, folks should do their own alignments, its too easy not too and then you know for sure what the numbers are. And if you notice a lil bad behavior you can get in there and change some settings. Small adjustments make for some major control feel.

I love suspension systems. And they are systems, really important to remember that. One change in an area will affect another part of the system. But if you can get your head wrapped around the entire system, how one variable affects another variable then its all fun at that point. It can be frustrating if you dont realize the interaction of the settings though. Complex systems are fun for me, a suspension system is fairly simple though. Baby steps, not giant steps. I love it!!! JR

[Norm Peterson]

Wow, thats alot of static camber, no inside tire wear issues? But now it sounds like a racing car? Not a street car right?

It's definitely an "enthusiastic" setting, but not all that far beyond the street setting for the car in my avatar (or what other folks who autocross their daily-driver will set). That car sits at just short of -1.5° street, which I would swap to a bit past -2.5° for competition as in the pic. I don't offhand recall the toe settings, other than they went from slightly 'in' for street to about equally 'out'. Wear can be kept very close to even though - if you consistently take corners hard enough you'll still be beating up on the outside shoulders.


Norm

[chicane67]

Wow, thats alot of static camber, no inside tire wear issues? But now it sounds like a racing car? Not a street car right?

Great info you posted by the way. I agree, folks should do their own alignments, its too easy not too and then you know for sure what the numbers are. And if you notice a lil bad behavior you can get in there and change some settings. Small adjustments make for some major control feel.

I love suspension systems. And they are systems, really important to remember that. One change in an area will affect another part of the system. But if you can get your head wrapped around the entire system, how one variable affects another variable then its all fun at that point. It can be frustrating if you dont realize the interaction of the settings though. Complex systems are fun for me, a suspension system is fairly simple though. Baby steps, not giant steps. I love it!!! JR

What was stated... was actually my dailly driver street alignment.

Even though it sounds "enthusiastic" (thanks Norm, I like that term) it had no signs of adverse tire wear... in fact, I had to run that as a minimum to combat outer shoulder tire wear... and still had some slight issue with outer should tire wear. It also helped with fitting the tire in the wheelwell at reduced (designed) ride height. I had even run it out to -2.5*, but I didnt load the chassis enough at low speed on the street to really make a difference and the reduced tire patch started to show signs of adverse tire wear on the inner shoulder if run that way without rotating the wheel/tire(s) often.

The peticular alignment was used with a 720# front and a 320# rear spring on a 16x8, 245/50/16 on all four corners. (Man that was a long time ago)...

[David Pozzi]

The more neg camber you use, the less toe in or you can even run toe out. On the One Lap Camaro I set 1 deg neg camber, then reduced toe to zero, James ran the Silver State that way at 105mph for 90miles and said the car tracked well. Millikan and Millikan Race Car Vehicle Dynamics states that toe should be reduced by .1 deg per 1 deg of neg camber, this is for one wheel.

When you think about the factory specs for toe, the camber is 1/4 to 1/5 deg positive. They spec 1/8" to 1/4" toe in.

Bumpsteer can be pretty bad on a first gen and cause instability and toe variations when cornering, as the car leans more or less, the steering changes direction slightly.
David

[JRouche]

Thats interesting. Im trying to see it in my own lil brain on how the added neg camber can give the high speed "straight steering" stability.

I can kinda see how toe in will give stability. Each tire is fighting the other for control, each one wants to steer in, so when the left tire is trying to turn the car right, right is fighting just as hard and equally to steer it left. Stable high speed runs.

And even when you go into a turn steering left the loaded tire will take control. So the right tire that is already wanting to take you left will agree with your steering input and go with you and continue to steer left, it has a positive toe.

So you have a balance. Yeah, with some scrub in the process, and slow turn in response. Thats why toe setting are so small, it doesnt take much.

Now if you go on the other side of control, and are looking for speed, and a lil over sensitive steering you go a lil toe out, or straight up. So toe out has the tires still fighting. But on the other end of it.

Now in a straight, and there is no such thing as straight, always lil corrections on the steering wheel, when you correct left the left tire is already turning left, so before the car changes load to the outside right tire the inside left tire gets control. And it hooks up, its already in a left hand turn. BINGO, she goes left NOW!! The right tire is still trying to counteract this movement but doesnt have the load change yet....

Thats just at turn in, but that contributes to the feeling of the car. And it is toed out so it wants to steer right in yer left hand turn. So when the load transfer happens, and if its quick, the right tire is gonna pull right and overcome the now unladened left tire that got you into the left turn, and fast. So what happens, a wallowing.

She quickly pulls right on yer left turn so you correct, unload the right tire a lil and the left hooks up a lil and pulls strong left so you correct to the right, load the right tire more and she hooks up with more right turn, you correct again, and again.. This cycle happens till you get outta the turn and say crap, this car is all over the place.

Some folks wanna blame the roll bar on it cause the sensation is the car is flopping all through the turn and think its loose and needs more bar. They dont realize its them flopping the car though the turn with steering corrections. They say they are correcting for a loose car and it needs more spring. But put a camera on them and you can see they are correcting for steering, not body roll..

Long story short. Thats why we tend to set up the car with 0 or slightly pos toe. Kinda like a freebie in car control at the expense of tire wear, top speed and turn in speed.

And at this point Im not directing this at anyone, Im on my soap box LOL And the suds are rising. Must be all my hot air LOL JR

The more neg camber you use, the less toe in or you can even run toe out. On the One Lap Camaro I set 1 deg neg camber, then reduced toe to zero, James ran the Silver State that way at 105mph for 90miles and said the car tracked well. Millikan and Millikan Race Car Vehicle Dynamics states that toe should be reduced by .1 deg per 1 deg of neg camber, this is for one wheel.

When you think about the factory specs for toe, the camber is 1/4 to 1/5 deg positive. They spec 1/8" to 1/4" toe in.

Bumpsteer can be pretty bad on a first gen and cause instability and toe variations when cornering, as the car leans more or less, the steering changes direction slightly.
David

[MonzaRacer]

whoa whoa whoa,,,,,,,,,,A 1/4 OF AN INCH OF TOE OUT?Thats nuts that tire will scrub off rubber at a ridiculous rate if street driven.
Dont believe me,,,I can sure as heck fed ex tires that were ran that way, 2300 miles and steel hanging out of the edge of the tires. and several of these sets were on several different cars with pro touring type cars.
As for me I only run as much negative camber as is needed for handling(ie to keep tires flat on ground in corners), as much caster as can be dialed in. Toe in depends on driving to be done, AND I setup toe in and adjustable rods that can sit between the wheel lips to reset total toe. I do agree with toe in understeer rule though. After setting up many SCCA ACR Neons I got a reputation for being able to set up cars that ran complete seasons and still having rubber left.
First one I did a husband/wife team dual footed it and ran on one set of tires and only changed tires at end of season for points run off and they hit A LOT of runs, and most of the guys they ran with were into their second and third sets of tires.
The next year I had nearly 50 cars to set up.
I never shared secrets from one team to another but my methods got me a lot of work that year and each car was one to two days work depending on what I had to repair/replace.
And let me tell you these cars ran extreme amounts of toe out and chewed the crap out of harder stock tires, most only making around 3000 miles on stock size/type Goodyears.
Also wider, stiffer tires on tighter suspensions do require less toe in but for stability reasons a little is needed.