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View Full Version : Suspension geometry & cornering/handling


sheekeebut
07-18-2014, 09:26 PM
This is for all you engineering specialists and track goers.

I've just lowered my sedan on Tein Street Basis coilovers, with what measures out to a 1.5" (38 mm) drop. Last week I checked under the car, and my front lower control arm height measures .70" (20 mm) lower at the inner bushing than at the ball joint. Therefore the arm points slightly upwards.

I know that this lengthens roll couple and lowers roll center, especially if the strut is straight up in terms of lateral angle. At the same time, I'm a little worried about it fudging up my camber movement(?) at spirited road twists.

So the questions:

1) Is the Yaris front strut angled laterally (logically inwards?) in any way? How much?
2) What ride height do you track goers tend to go for your overall cornering performance? Calculated and numerical data gathered for tuning, or just seat of your pants tuning?
3) What does a low or even below-ground roll center "feel" like at corners and bumps?
4) Short of getting adjustable ball joints and steering linkages, do I have to raise the ride height a bit (18 mm if struts straight up?) to get back to a lower-control-arm-to-strut angle of 90° or less to optimize performance? As in, does going over 90° mean having already gone beyond good camber and roll center characteristics?
5) Am I overthinking this?

sheekeebut
07-27-2014, 02:05 PM
A week and a half, and no one's interested in answering any of the questions? Feels worse than just getting full-on flamed..

eablola69
07-28-2014, 03:31 AM
A week and a half, and no one's interested in answering any of the questions? Feels worse than just getting full-on flamed..

#5, yes you might be over thinking it. :smile:

Flipper_1938
07-28-2014, 09:42 AM
As flimsy as the lower control arm is, if you trow it into a corner too hard....the lower arm is probably going to deflect and your alignment settings are for refernce only.

Bluevitz-rs
07-29-2014, 10:10 AM
yes, over lowering the car will have negative impact on the camber geometry to a certain extant. But at 1.5" you shouldn't have much issues. The angle between the control arm and the strut is still probably less than 90°.

Rigaud
07-29-2014, 07:38 PM
yes, over lowering the car will have negative impact on the camber geometry to a certain extant. But at 1.5" you shouldn't have much issues. The angle between the control arm and the strut is still probably less than 90°.

What about dropped say 2" or 2.5"?

Bluevitz-rs
07-29-2014, 07:39 PM
I don't know. I don't have a Yaris.

malibuguy
07-29-2014, 09:22 PM
Mines lowered 1.75~ and it handles awesome...however the ride is not so great

sheekeebut
07-30-2014, 04:13 PM
Thanks for the feedback!

Mittelklasse
08-09-2014, 06:17 PM
(1) Did you mean Steering Axis Inclination angle?
If so, then it is 11.30 degrees.

sheekeebut
08-10-2014, 03:49 AM
Thank YOU Troll-Face-Avatar. You good sir (madame?) have just given me my next topic of research... And in comprehensively answering 1), you have given me the means to answer question 4) objectively.

After soon trying out a slammed-silly civic sedan, I may find my own answer to 3).

All that remains is 2). I think only two practical ways to get this:

Find people who race with coilovers.
Or
Start going to the track.

Hmm..

ilikerice
08-10-2014, 09:22 AM
I race with coil overs. I have -2.5 camber up front. I lowered mine I believe 2.5-3 inches. I do not know exactly. I run megan coil overs witha 15x7 rim with 225-45 Hankook RS3 tires.

All my adjusting I have done has been how the car feels to me. I like my rear very loose. My tire pressures are 40psi in front and 55psi. This is for autocross. On track days, I drop it to 28psi front and 45psi in the back because the tires get A LOT hotter for longer periods of time.

If you look at my times here:
http://www.buccaneerregion.com/ce-7-14.html
This was my last event. It was a pretty fast event. I do not own a gopro, so I don't have any video of the course. If you are really wanna see how the course was layed out I can link a video for you. I killed the RAW time and Took 1st in Pax.

Each driver is different though. You need to play around with your settings on how you drive. What works for one person on the same car, may not work for another person.

sheekeebut
08-10-2014, 08:27 PM
And with ilikerice's answer, thread has been concluded. Thanks all. If I remember, I'll add to this thread by describing my crazy low driving experience.

cali yaris
08-12-2014, 02:38 AM
^ Oh?

ok, I won't post then. :rolleyes:

sheekeebut
08-12-2014, 04:16 AM
Oh, Garm over here holding out on me! Please, share some racing knowledge with the poor folk.