I have a 99 em1 civic si.
I do abit of track work.
I have currently swapped my springs over to ITR springs as they provide a 250/250 lbs spring rate..

My back currently sits alittle higher than the front. (i am running koni yellows)

Would a higher back be good for track work, providing more front end grip and when accelerating sit the car at a flat stance for corner entry...

Or should the back be abit lower/even to front... which would increase back weight providing a better centeral body roll but less traction..


what do people suggest??

 

The height of the front/rear has almost no effect on weight distribution.

 

Check yer CSI post. But to clear it up, roll center is not altered by ride height.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Noob4life &raquo;</TD></TR><TR><TD CLASS="quote">Check yer CSI post. But to clear it up, roll center is not altered by ride height.</TD></TR></TABLE>

WTF? Roll center is very much affected by ride height.

 

My mistake, I forgot that instant center can be moved.

 

What would be the optimum for race

 

Brownies dude, my bad

 

I'm also curious what the optimum ride height is to reduce the distance between the roll centre and centre of gravity on an EK civic. Right now I'm lowered 0.75".

 

A question for people who actually figure this stuff out. How do you do it? I am guessing you have to get a tape measure, a protractor and a level and then you have to draw the **** out on a huge piece of carbord to measure where the points meet and ****? Espicially measuring a RC that is below ground, you must have some system of drawing it out.

 

It's relatively easy to calculate (or draw) once you have taken a few measurements. You need to know the angle and vertical distance above ground plane and horizontal distance from your cars center plane of inner pivot for both UCA and LCA at the ride height you plan to run. If you do a sketch, use properly scaled drawing of the above points (pivots).

On right side of car for front suspension:

For each CA, draw a straight line through the inner pivot at the angle of the arm until each line meets at a point. This point is called the instant center of the suspension (Its the point that the suspension effectively rotates about relative to the sprung mass (i.e. chassis). From the instant center, draw a line to the center of the tire's contact patch.

On left side for front suspension:

Repeat the same procedure used for left side only now use the right side measurements.

Note, at static ride height, the left and right suspensions can be considered symmetrical and then only one side of the above measurements needs to be done. The roll center would then be the point where the line connecting from the instant center to the tire contact patch crosses the lateral center plane of the car.

If you want to calculate the roll center migration of the suspension, you need to do the above analysis assuming the symmetry is no longer present and as a result you would need to compute the angles and inner pivot points for both side of the car at small changes to roll angle.

 

(lurker here. Howdy.)

To add to this post, I did the same calculations for my Celica to figure out what kind of springs I wanted to purchase. I took some measurements and then used Solidworks to figure out the rest as shown here:





The beauty of Solidworks is that I can manipulate the sketch to see what happens to the geometry when I lower the car or change the static camber. It's great! For instance, if I lower the car 1" in the front the roll center drops below the ground and the roll couple increases by 1.5".

Adrian

 

Thanks johhny mac, I understand the IC and RC and everything. But i just couldnt see how you would draw it out in real size. But i guess taking your measurements and drawing it out an like 1/16 scale would let you fit it on a normal sheet of paper. although the smaller you make your drawing the more perfect you have to be, the thickness of the pencil lines is probably like a half inch once you scale it up.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ohjolt2 &raquo;</TD></TR><TR><TD CLASS="quote">Thanks johhny mac, I understand the IC and RC and everything. But i just couldnt see how you would draw it out in real size. But i guess taking your measurements and drawing it out an like 1/16 scale would let you fit it on a normal sheet of paper. although the smaller you make your drawing the more perfect you have to be, the thickness of the pencil lines is probably like a half inch once you scale it up.</TD></TR></TABLE>

It's much easier using a drafting program, even a cheap CAD program can help you find the roll center migration. Hand drawings are only as good as the artist.

 

Vaguely on topic, i was looking at a indy/formula type open wheel suspensions and i noticed that the upper and lower control arms seem to be damn near parallel. I am guessing the instant center has to be like 100 fet away from the car, you would have to use a PC to figure that one out.

 

If the CA's are truly parallel, the instant center will be infinitely far away from the car. The RC is on the ground, though in that situation.

 

does anybody know where the gravity center of the civic si hatch lay in the vertical plane?
i will use a balance to take the weight values beneath each wheel, thus i can calculate the longitudinal position of the center of gravity, but im not able to calculate its vertical position.
thanks a lot.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ohjolt2 &raquo;</TD></TR><TR><TD CLASS="quote">Vaguely on topic, i was looking at a indy/formula type open wheel suspensions and i noticed that the upper and lower control arms seem to be damn near parallel. I am guessing the instant center has to be like 100 fet away from the car, you would have to use a PC to figure that one out.</TD></TR></TABLE>having paralel control arms isnt the best otugh since ur not really gaining enough camber troughout the travel. it might workin some instances tough

 

On an open wheel car the suspension travel is so short that camber gain in nothing anyway. They just set it how they want it.

 

They have computers in the desert?

 

yea but i am not in iraq anymore

 

is there anywhere to read about this stuff more for beginners? Im not familiar with auto suspension setups. I have just dealt with quads that only go as far as rim offset, + sized a-arms, axles, swingarms, camber, caster, toe, steering axis inclination, shock leverage ratio ect... and most of those setting dont have to be anywhere near perfect considering your riding in soft dirt as opposed to pavement. My knowledge is more towards a dual control arm setup which im guessing is very different then a civic that has one control arm?

Anyway anywhere to start reading about this? Thanks

 

http://www.howstuffworks.com has a good starter article. Read that and pm me if you want more i have a list of links some where on specific things.

 

the back end of my car is very much higher than the front end of my car.

with that in mind(front-lowered about 2.5 inches, rear-lowered about 1 inch)... the back basically has very little camber and toe changes, while the front has good toe and aggresive camber. from racing in the hills and tight cornering... i find my suspension to be very good. the back helps to swing the car around a bit.

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btw... with this sort of set-up, in-line(drag) traction is so much better

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ohjolt2 &raquo;</TD></TR><TR><TD CLASS="quote">http://www.howstuffworks.com has a good starter article. Read that and pm me if you want more i have a list of links some where on specific things.</TD></TR></TABLE>

Yea I've read all that. Im looking for something more advanced but explained.

 

Anyone done this on a 4th gen prelude?

I'm lazy.