Tamago's guide to ultimate yaris handling

[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)

[Loren]

Hmmm... in SCCA stock class, you can't change the springs or alter the ride height. Dampers are otherwise unlimited... Hmmm...

Seems to me that you could get a generic race shock to replace the rear shocks on the Yaris pretty easily. It's just an eye at the bottom and pin at the top, very common configuration. Get something that you can dial in really some really stiff compression damping for autocrossing and it should do a world of good for reducing understeer.

That, plus maxing out the front camber, and the tires mentioned above... that should do a pretty good job of challenging the competition.

footnote: One of the caveats of the "shocks are free" rule is that you can't alter the spring perch height. Since the spring perches aren't part of the Yaris rear shocks... you should be free to replace those rear shocks with ANYTHING.

[markitect]

Originally Posted by Loren

Seems to me that you could get a generic race shock to replace the rear shocks on the Yaris pretty easily.

I hadn't thought about that, sounds like I have some measuring to do before May.

[2006fronty]

Originally Posted by Loren

Seems to me that you could get a generic race shock to replace the rear shocks on the Yaris pretty easily.

Originally Posted by markitect

I hadn't thought about that, sounds like I have some measuring to do before May.

I've looked at the rear shocks and it does seem pretty easy get a shock that fits, Radflo makes a GREAT race shock and they'll make shocks to your dimensions (collapsed and extended lengths) I've ran several sets of their shocks on my previous trucks. The front would be more of a task considering the mount from the strut to the knuckle would have to be figured out. 2.5 inch diameter race shocks on all 4 corners of a Yaris would be fun (well maybe 2.0's would be more reasonable haha)An External reservoir or internal floating piston shock would be nice.

[rob323]

Originally Posted by 2006fronty

An External reservoir or internal floating piston shock would be nice.

Very nice infact .



Now I just have to save up to get the same on the fronts

[2006fronty]

Ohlins right^^^^^^^??? I'm pretty sure that's how they set up their external reservoirs.

[d1nzfe]

Originally Posted by rob323

Very nice infact .



Now I just have to save up to get the same on the fronts

whats so different when its invented?


ooops.... just saw the canister! its remoted and camouflaged!

[Tamago]

..... and getting the yaris to rotate is by far the most important thing in stock class :D

it's a shame you won't get any real camber out of the front though :(

[tk-421]

Question: How would 10mm rear hub spacers affect handling?

[kngrsll]

Originally Posted by tk-421

Question: How would 10mm rear hub spacers affect handling?

i have been meaning to look this up as well.

[Loren]

Wider track usually means more grip (for various reasons). So, widening the track in the rear would make the rear stick better. Not really what most of us are fighting for, with a FWD car, you want more grip in the front.

The rear hub spacers are purely a cosmetic mod. (not to be confused with alignment shims)

[kngrsll]

Originally Posted by Loren

Wider track usually means more grip (for various reasons). So, widening the track in the rear would make the rear stick better. Not really what most of us are fighting for, with a FWD car, you want more grip in the front.

The rear hub spacers are purely a cosmetic mod. (not to be confused with alignment shims)

ah, thats right... i remember a friend of mine use to use them on the front when he would autox (SE-R, fwd).

im still working on this shocks thing, i have to turn in a research proposal this week and its consuming all my time! :(

[Tamago]

Originally Posted by Loren

Wider track usually means more grip (for various reasons). So, widening the track in the rear would make the rear stick better. Not really what most of us are fighting for, with a FWD car, you want more grip in the front.

The rear hub spacers are purely a cosmetic mod. (not to be confused with alignment shims)

Originally Posted by kngrsll

so we ran a track day with the spacers installed. although there was rubbing on the streets, with the spare and other junk removed, there was no longer any rubbing. If you remove a little weight, you can get away with the 15x7 +10.

The really important thing is how the car drove. My co-driver and i did 2 sessions a piece. He has driven the car at ever event that i have, so his feed back is just as valuable. The spacers had a noticeable increase in rear stability. It made it a little easier to carry speed into the corner without the rear wanting to chase you, so turn-in speeds may have been a little faster. What was more important was stability increased the "trust" in the car in the corner. As you may know, if you feel confident about the car, you will be able to drive it well.

Since I needed to remove the spacers for street use, i pulled them off before the last session. The rear end felt a little more unstable (duh) and if you gave the same inputs as before, the back end would tend to slide a little more. That may be good for autox, but not for the track. As easy as the are to take on and off, i may swap them on depending on the type of course. Tight courses may favor the spacers out, while the more open courses (like the one we were one) would be better with the rear spacers in.

All in all, i think they helped with the stability of the car. If i were not running such low offsets, i would continue to use them. If you have anthing more than a 35 mm offset, they are a no brainer, they easily fit and increase rear stability. The 10 mm should put the track in the front and rear dead even, while the 13 mm spacers may make the rear track greater than the front.

Great mod, track approved :)

taken from : http://www.yarisworld.com/forums/sho...71&postcount=6

[tropicalsuckerpunch]

Post #1 of this thread doesn't show me yaris handling information?

[CtrlAltDefeat]

Originally Posted by Tamago

the information given in this post is here merely to provide a starting point for your future autocross or road racing endeavors. this is not the end-all-be-all of information on the yaris. as i come across exact situations related directly to the yaris i will add them to this post

uhh... where did the info go?

[Tamago]

fortunately i kept a backup. PM me and i'll email it to you. until i know it won't get deleted again without explanation i'm not going to post it in the original post.

edit: lol look! it magically re-appeared.

[fmicle]

I am looking for a little advice. So the wheels I have now on the Yaris were the very first mod I did and I must say, I didn't do my homework before buying. So I ended up getting 16x7" with 195/50-16 tires. After finding this kick-ass thread and doing more reading on the subject, I'm thinking about going back to 15x6.5" with 195/55-15, as recommended here

Now, I also have lowering springs (NF210) and shocks on my list, which is the next thing I had in mind, but I was wondering, would it make more sense to replace the wheels first and then get the springs and shocks or get the springs/shocks first?