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 Post subject: rear toe and oversteer
PostPosted: Tue Feb 28, 2012 11:10 am 
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The good news:

Even though it was only my third day ever, the last time out autocrossing I won the street tire class on cheap Chinese all-season touring tires.

The bad news:

I should have rotated my tires sooner, definitely before autocrossing, because I found that some minor cupping I noticed on the right rear tire before the runs was bad enough afterwards to cause a distinct vibration at 65 mph all the way home. The diagonal wear pattern suggests a problem with toe out in the rear

The questions:

Most people seem to advise running about 2mm toe in on the rear, but this is coming from people that already have installed larger rear sway bars, stiffer springs, and stiffer shocks. In theory, I believe toe in will "tighten" (shift balance towards understeer) and toe out will "loosen" (shift balance towards oversteer) the car. When I checked how the adjustment bolts were set on my car however, they were set for toe out, the right side a little more than the left, which probably accounts for my tire wear problem.

I was very pleased with the way the car handled on the autocross course though, with the back end of the car starting to come around nicely (if rather quickly!) once the tires warmed up (and three pounds less pressure in the front). So maybe one of the car's previous owners already new the relationship and messed with the toe at the expense of the tires? I immediately turned the adjusters for a small amount of toe-in instead to save them, but I wonder if I shouldn't put some toe out back into the car before I auto cross again. For now I am stock but in the long term I have poly bushings and an Addco sway bar coming and plan to cut some Mk4 springs to stock ride height in the back, so then maybe I'll have to switch back to toe in?

Knowing that pretty much everything on suspension set up is a compromise of some sort, why stiffen the back end so much to balance the car when you could just run a small amount of toe out instead? Stiff cars are also definitely easier to drive in general, but given that the Swift is so good in transitions already, is all of the work to stiffen them up really that helpful in terms of absolute traction, or does it just help with laptimes by smothing transitions and not so much at the skidpad (given the logic that softer-sprung cars should grip better?) I.E. could a softer sprung car be much more difficult to drive quickly, but be capable of faster times when driven by a hypothetical badass driver capable of dealing with the difficult (less progressive) changes in vehicle composure without losing control?

Another example of this is the rear toe-bars, which everyone complains are flimsy and bend under hard cornering. Given that this would tend to balance the car by increasing toe out, why is this such a bad thing? I am planning on replacing mine with tractor supply pieces as posted elsehwere, but I am wondering whether increasing the stiffness might be more about tire wear when pushing the car hard than handling?

I assume that all of this work to stiffen the suspension and reduce body roll really does increase grip or no one would spend all the time and effort doing it, but it would be fantastic to get a better description of why this really makes the car faster. For example, is this more of a question of when the car begins to rotate (turn in vs. YIKES just before corner exit?) and not just balance?

Basically I am just looking for some answers to the logical conundrum that stiffening the suspension improves handling, but a softer car will have better grip, especially as it relates to toe links and toe settings on the Swift GT.

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PostPosted: Tue Feb 28, 2012 1:47 pm 
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Dude this has been covered dozens of times, for competition the short answer is solid toebars and 1-2mm of toe out, I appreciate the answers don't always leap out when looking for them but maybe spend a week reading thru this forum and you'll find a lot of other people have already been there and done that so to speak, (again not being rude just giving you a gentle nudge in the right direction)


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PostPosted: Tue Feb 28, 2012 2:46 pm 
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Dattman,

Your answer for everything is that anyone who asks a question or posts information hasn't spent enough time searching the forum or is posting information that somebody else has already covered.

I've done a good bit of research in the forum, particularly in the track talk section, but it is true that there might be a thread that has exactly what I'm looking for--and it's not a simple response like "run solid toe bars and 1-2mm toe out" without any explanation of why or what the rest of the set up is. Why don't you post a link to the thread that you think has the definitive answer? Otherwise you're just being a jerk.

FYI, you are the first to recommned toe OUT of any of the threads I have been sorting through, none of the good information is under the suspension set up sticky, and there's no one good thread on alignment parameters. I suspect your recommendation is spot on for a stock set up, but it doesn't explain why it is better to spend so much money to stiffen up the rear of the car vs. stock only to work against that by running toe IN like most posters seem to do afterwards, unless it's a matter of backing off the effect of the thicker rear bar and/or stiffer springs/ damping just a little bit to get it just right, or being able to run higher pressures in the front tires in order to keep the car balanced without rolling them over, or causing the car to begin rotating at a different point during turning, a little bit of all of these or something else I am not grasping.

If I am on the right track, let me know. If you have something to add, please do. If it's all been hashed out already somewhere else in the forum why do you bother to post?

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PostPosted: Tue Feb 28, 2012 3:03 pm 
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I tell people to search because the reality is 99% of noobs don't search, they spent 30mins looking and give up, I spent a whole week and read every single post in the transmission section, before I asked a single question (granted theres 3 x as many posts now)

Unfortunately a lot of the old racers aren't on here any more, Murr, BDgracia, Lander etc, guys with a lot of knowledge that have moved onto newer cars, their posts are about 5 server moves old so a lot of the links are broken and well before the track section was ever created.

I don't always provide links as it takes time, why waste my time?, if I don't answer then a lot of the time people chip in with 2nd or 3rd hand experience and we get mis-information making it even harder for the next guy to find answers, I pretty much usually stick to gearboxes, chassis and suspension, things I have first hand experience in, I'm not an engine guy, there are others who are way more knowledgeable than I.

Have you read Dennis Grants ebook, Autocross to win? google 'Far north racing' I think, good read.


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PostPosted: Tue Feb 28, 2012 5:42 pm 
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Thanks Dattman,

You are exonerated. Your reading recommendation comes up everywhere as I sift through information here and elsewhere, and as a lot of what I am trying to wrap my head around is not even Swift specific I need to do my homework and start there first.

Right now my plan is to run 0 rear toe on the street in the hopes that I will stop cupping tires, then tweak it slightly out to your recommendation next autocross day when I get there. When I have poly bushings, koni yellows, a caster kit, cut Mk4 springs and strut braces for the rear and bottom front, I will re-evaluate.

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http://www.teamswift.net/viewtopic.php?f=17&t=57216


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PostPosted: Tue Feb 28, 2012 6:37 pm 
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Teeth wrote:
Thanks Dattman,
a lot of what I am trying to wrap my head around is not even Swift specific I need to do my homework and start there first.


Thank you...yes not specifically swift but definitely fwd related, as for Toe, on a swift road car I would go zero toe all around but for a competition car, especially autocross I would start with 2mm toe out all round, here's why

1) having toe out increases the slip angle of the tyre generating more grip earlier.
2) with fwd you only get one chance to change the stance of a car thru the corner, thats at the start of the corner, so a little toe out on the rear helps turn in, slower the course then more toe out, faster courses you want less as it reduces stability. (rather over simplified explaination I'm afraid)

Of course toe settings all turn to custard with standard toe bars, they and the rubber on them stretches on corner entry giving understeer and then past the apex they compress giving oversteer, EXACTLY the opposite of what you actually want.
If the rules allow then get something lighter than tractor links, they are heavy and some of that weight is actually unsprung weight.

I would recommend just playing with toe for the next event, take notes on speed, track, weather, don't change too much or else you won't be able to determine what each change does and how it effects the car.
Don't get sucked into buy flash tires yet, you'll rip them to bits until you get the handling sorted and just mask the handling flaws.


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PostPosted: Wed Feb 29, 2012 12:18 pm 
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I am going to put any further questions/musings in my Spanish Inquisition thread in the track talk section (please follow if you are interested) but I wanted to thank you again for pointing me to Autocross to Win, which I digested pretty thoroughly over yesterday. I also appreciate your explanation on why the toe links need to be more rigid--I was not thinking about what stretching the bushings would cause vs. the timing of when the links would deform during cornering. I just had the thought that they can only get shorter with deformation, which is sloppy but it's at least moving the geometry in the right direction--in some ways even better because it is temporary. From your explanation it sounds like the issue is the affect on the timing of oversteer and the uncontrolled nature of the transition. The tractor links are 3lbs apiece, which is heavy, but not that heavy for $10 vs. $200. They won't fit well with SCCA rules, but I can see that the rulebook and I aren't going to get along well anyway. They'll just have to let me run in an X class or something and beat everybody on raw times (not likely, but maybe at least they will consistently improve).

There were several important points in the article that will change my course a little bit, though much of the reading helped to validate realizations I was coming to already--the section on FWD and macpherson struts was particularly helpful.

My favorite quote from the article was:

"The very best [drivers] can make use of a car's bad habits and will minimize their effects - and will do so without even thinking about it.

Paradoxically, this can make discussing car setup with the truly talented somewhat counterproductive."

I can only assume that this is why I believe Swifts and Metros to be the best handling cars ever made.

One of the things I think I am doing right is collecting as much data as I can. I use my android phone and a bluetooth GPS to capture velocity, heading and acceleration at 1 s intervals using the Trackmaster app. This isn't realy fine enough resolution and it doesn't tell me what the throttle or steering angles are, but it still helps me to baseline how much grip I am getting in terms of lateral acceleration, how well I am stopping, how well the power is getting to the ground, where I am running the fastest on the course, and where the brake points are, which is not bad for a simple tool.

If I get some other stuff done I will post some of the Trackmaster outputs to my track talk thread and pick apart how my required reading assignment will affect my next decisions.

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http://www.teamswift.net/viewtopic.php?f=17&t=57216


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