Tamago's guide to ultimate yaris handling

[mikenacarato]

good thread! :)

[Loren]

Originally Posted by PK198105

don't forget however that changing your camber, toe in/out will affect the lifetime of your tires. Tamago you wrote so much im not sure you mentioned this (my fault probably i fat read your post)

Done properly, it won't necessarily affect the wear of your tires. In fact, depending on your driving style, it could IMPROVE your tire wear.

I'm running factory alignment in the rear (-0.9 camber, slight toe-in), and -2.5 camber in the front with very slight toe-in. My tire wear is very event all around. If I DIDN'T have all that front camber, my front tires would be wearing on the outside edges.

Excessive toe, especially when coupled with agressive camber will cause tire wear issues. But, with neutral toe settings, up to 3 degrees of camber is not a problem even on a daily-driven vehicle.

(trivia: The factory alignment on the rear of my Triumph is 3 degrees negative camber)

[Loren]

Originally Posted by ddongbap

Damn Loren.

You talking about how changing the toe just a little bit would get it to rotate better got me wet.

Yeah, I'm sexy like that. You should hear me talk about rev-matching and heel-toe downshifting.

[SEVEN]

Originally Posted by Tamago

basic "autocross setup" springs... if you're gonna autocross, and you've installed lowering springs, please get a set of shocks that were built to be coupled with a lowering spring. stock struts and "lower" springs just don't fit into autocross land.[/size]

will tein s.techs and trd shocks work???

[Loren]

Originally Posted by SEVEN

will tein s.techs and trd shocks work???

What you'll eventually conclude with that setup and really think about it is that a) you don't have enough suspension travel so you bottom out both in hard turns and over bumps and b) the shocks don't sufficiently control the motion of the springs on rebound.

Will it "work"? Yes, but not if you want the car to handle as good as it could.

[SEVEN]

Are there TEIN shocks for yaris??? I can't find any ...

[cleong]

Cusco does make a front anti sway bar (part no. 900 311 A26). So its available for a price should you feel the need for it. As I cannot read Japanese I cannot say if it is stiffer than stock or not.

I found that running too much negative camber on skinny street tires reduces its off-the-line traction. It might not really hurt acceleration that much but it seems easier to get the tires to break loose.

[ChinoCharles]

Bravo Tamago.

[Loren]

Originally Posted by PK198105

thanks for clarifying Loren. I just though since you're changing the vertical angle (camber) the contact patch will be offset to either side.

Well, it does, but it's just not enough to be a problem unless you combine it with too much toe.

Running 2 degrees of camber with mild toe settings and doing strictly highway miles might result in 2mm more wear on the inside of the tire vs the outside. Of course, if you do strictly highway driving, you don't NEED that much camber! If you have that much camber, it's probably because you do some mountain driving, or autocross, or track driving... and that performance driving is going to largely equalize the wear. You might still see maybe 1mm more wear on the inside vs. the outside... but who cares? That's close enough.

[Loren]

Originally Posted by cleong

Cusco does make a front anti sway bar (part no. 900 311 A26). So its available for a price should you feel the need for it. As I cannot read Japanese I cannot say if it is stiffer than stock or not.

The last thing you want on a FWD car is a larger front swaybar. It would just require you to stiffen the rear that much more to reach something close to "neutral" rather than "obscene understeer".

The only reason Cusco makes it is because people who don't know any better WILL buy it... not because anyone really needs it.

[Tamago]

Originally Posted by eTiMaGo

I'll take it that is a rhetorical question

talk to Russell teh Pirate, i helped set up their yaris :)

[cleong]

We can't be certain of that fact which is why I stated the bar was available but can't speak for its effects. If it would make the car understeer worse like you say it would, then if you took the front anti roll bar off, would it cure the understeer without having to fit a rear anti roll bar?

I think it is possible that a correct front anti roll bar would reduce front roll, and optimize the tire contact patch in the corners, because too much roll unloads the inside tires. I'm not saying the Cusco would do it, because I've never tried it, but it is a tuning option that should be tried before being written off.

[Tamago]

Originally Posted by PK198105

don't forget however that changing your camber, toe in/out will affect the lifetime of your tires. Tamago you wrote so much im not sure you mentioned this (my fault probably i fat read your post)

yes, it will.. absolutely.

this guide is to help those who are interested in handling, before tire longevity, etc etc.

[Tamago]

Originally Posted by turboyaris

i gotta interject, .

stolen word for word and added to the guide.

keep the good info coming guys!

[Loren]

Originally Posted by cleong

We can't be certain of that fact which is why I stated the bar was available but can't speak for its effects. If it would make the car understeer worse like you say it would, then if you took the front anti roll bar off, would it cure the understeer without having to fit a rear anti roll bar?

Yes, we can be certain that fitting a stiffer front swaybar (with no other changes) will make the car understeer more. That's just simple suspension physics at work. That's just the way it is.

And, yes, removing the front swaybar would probably make the car understeer less (it's been done on some FWD cars with success), but while it might have higher cornering limits, the steering would feel very "sloppy" and it wouldn't be enjoyable to drive. One absolute truth about suspension tuning: It's always a compromise.

I think it is possible that a correct front anti roll bar would reduce front roll, and optimize the tire contact patch in the corners, because too much roll unloads the inside tires.

Body roll is not the "evil" that so many people think it is. Look at some of the best handling cars in the world... a Lotus Elise, for example... lots of body roll. Even purpose built race cars have some body roll in as much as their suspension moves. (look at an F1 car full-on in a corner, the outside is compressed visibly more than the outside) Body roll isn't bad. It's a by-product of weight transfer. What you want is control of that roll (good damping), and balance of the weight transfer (spring rates and sway bar rates).

If eliminating all body roll was the answer, every race car and high-end performance car would have NO body roll. Eliminating more body roll (with a larger front swaybar) at the expense of moving the handling balance of the car further in the wrong direction is no solution.

This whole discussion is much like arguing about lowering springs with ricers. They think that "lower is better" no matter what... and "stiffer and flatter" is better no matter what. It's simply not true.

I'm not saying the Cusco would do it, because I've never tried it, but it is a tuning option that should be tried before being written off.

I've not tried it on a Yaris, but most of my suspension tuning knowledge does come from experience. One of the first suspension mods I did to my Saturn when I started autocrossing was to put a bigger front swaybar on it. Same reason everyone else wants to: to get rid of the body roll. I then spent the next 3 years finding ways to eliminate the understeer that it caused. I was stubborn and refused to remove the front bar that I'd spent good money on, which would have solved the problem instantly. (as a side note, the Saturn S-Series cars had two swaybar options, the twin cam front bar was larger than the single cam bar... and the twin cam had a rear bar whereas the single cam had none... the hot ticket is simply putting the smaller front bar onto a twin cam car!) To balance the larger front bar, I ended up having to put a rear bar on that was so stiff that it actually BENT the stock rear end link mounts.

Wanna play with what removing the front swaybar would do? It's easy, just remove an end link on one side. The other side will hold the bar in place and keep it from flopping around, but with one side disconnected, the bar will have no effect. Very simple experiment. Somebody do it and report back. (maybe I'll do it when I have time)

If you have a stiff coilover suspension, you might get away without the front swaybar. I tuned the suspension on my old Miata with really stiff springs and NO swaybars. People thought I was nuts, but I wanted to prove that it could be done. It took really stiff front springs to get it to feel right, of course.

[cleong]

But similarly with tire pressures, generally softer yields better traction. Yet you could go too soft and cause tire contact deformity, or too hard, which causes lack of tread compliance. Hence optimizing is the key, what you have called compromises. But I respect your experience, which I do not have. If I manage to get my hands on this Cusco bar, I'll report back with what I found, at least it'll help others make a more informed decision.

[Loren]

Adjusting tire pressures does two things: adjusts the shape of the tire's contact patch, and adjusts the effective "spring rate" of the tire.

Today's high-end performance tires have SO much reinforcement of the tread area that tire pressure has little effect on the shape of the contact patch. It stays flat no matter what. If you're on craptastic all-season tires, you might see some change in the contact patch with pressure. (but this thread isn't for those people!)

The change in effective spring rate of the tire, as long as you don't distort the contact patch too much, is primarily what we feel with our tire pressure changes when we're tuning a car. We work within the "window" of pressures that the contact patch stays flat in. (with a good performance tire, that can be a big window... like the Azenis... easily 30-50 psi!) Within that window, you're simply fine-tuning a spring rate that has the same effects as changing any other "spring rate" in the suspension.

So, whether you're adjusting tire pressure, spring rate, sway bar rate or shock damping, the general effects are the same:
Stiffen the front = create more understeer or less oversteer
Soften the front = create less understeer or more oversteer
Stiffen the rear = create more oversteer or less understeer
Soften the rear = create less oversteer or more understeer

Those are the facts. You can look them up in any suspension tuning book or even on one of a thousand different suspension tuning guides that you might find on the internet.

Knowing that, if you NEED to fit that larger front swaybar to prove it to yourself, go for it. There really is no substitute for experience. I'm all for experimentation that will help people learn and quantify what suspension changes really do. I just hate to see people waste money on parts that aren't going to help them. Do the cheap or free experiments first... like playing with tire pressures... disconnecting the front swaybar... stuff like that.

Those cheap rubber donut spring spacers that you can get from JC Whitney for like $20 a set are a GREAT experimentation tool. Toss a set of those on your springs... take some measurements and figure out what you've changed the spring rate to, and document the results. (I tried a pair on the rear of my Yaris, my calcs said it raised the spring rate from about 2.0 kg to 2.5 kg... it was a happy understeer-reducing change, just like it was supposed to be, and it's why I never wanted to fit the 2.2 kg rear springs that came with my K-Sport kit)

[id3379]

Originally Posted by eTiMaGo

great writeup, thanks!