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Ride height for track car, some help needed!

 
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Cédric  



Joined: 27 Aug 2004
Posts: 2023
Location: Sweden

PostPosted: Thu Jul 25, 2013 8:14 pm    Post subject: Ride height for track car, some help needed! Reply with quote

Hi !

I have been running with current setup for a while, obvisluy its fast if I look at lap times, and incredibly fun, but on bumpy parts I has been a little bouncy, and not responding to adjustments as I wanted to.

So yesterday I checked out available bump travel and its really limited, I know ca ca how much I would want to have, but I was so sursprised to se that it was almost in the bottom. I never bothered keeping track of it (car has been adjusted several times) since I thought the ride height looked pretty safe compared to the race cars. A little embarrassed since me if anyone should keep track of these things, but what a hell, sometimes you miss stuff...

Since my car isnt that low I cant understand how the racecars run that low, shorter front struts? Chopped bumpstops at the rear?


So what I would want from you guys is to measure the distance between the center of the wheel and the wheel arch.

I add a pic so you can see the height..




aa, wtf, a will add better pics later on, the upload is f**** with me..

Thankful for some help !
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11396
Location: PacNW

PostPosted: Fri Jul 26, 2013 6:41 am    Post subject: Reply with quote

The only real restriction with the factory setup is not to lower the car so far that the front control arms are beyond perpendicular to the ground. If you want to go lower, you can buy special long pin ball joints that allow you to drop it without passing the perpendicular mark.

If your car is feeling "bouncy," and this is a change from how it used to be, it would suggest that your shocks are starting to fail.

For reference, Spec944 rules specify a minimum height of five inches, measured from the ground to the bottom of the rocker panel.
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morghen  



Joined: 21 Jan 2005
Posts: 8232
Location: Romania

PostPosted: Fri Jul 26, 2013 7:10 am    Post subject: Reply with quote

Rasta, i think he would know if the shocks are going, instead i think he means that he feels like the suspension is not absorbing enough energy.
That happens to a buddy of mine with his TA Technix coilovers on his MK3 golf...but not to me in my MK3 golf...because i have KW V3s on it.
His springs are too hard and the shocks too. My KW V3 have decent springs but soft shocks.

Get a decent side picture, i think i'm as low as you are...i dont track the car but its not bouncy...there is enough suspension travel for how i drive the car.
What shocks are you using? i'm using the OEM shocks with my setup and the ride is quite smooth. I think this is the best overall solution, soft shocks and stiff springs.

I'll get some measurements tomorrow.

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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Fri Jul 26, 2013 7:35 am    Post subject: Reply with quote

Bouncy/choppy suspension tends to be due to a lack of proper control of the springs. If the shocks are worn or improperly adjusted or valved for the springs in use, then you can get issues. Most people just look at ride height as the ultimate goal for suspension changes along with the "rubber ducky" syndrome of what looks good, so and so is faster and uses X product, etc.

There's a reason there are such things as shock dyno's and the smarter folks determine the effective wheel rates and the amount of weight on each wheel to choose spring and shock rates. The rest of us have to piece this information together from various vendor's dribbles of information and other's experiences. There's still a certain amount of fine tuning needed to tailor the handling to the driver's preference and that can be a bit of a black art as well.

Reading anything written by Carroll Smith, Fred Puhn and Herb Adams will help (some of the info may be out of date now, but it does provide a decent background to work from) will help greatly understand what is happening and what changes will generally do to the handling of the vehicle.

If you're running out of travel and running into the bump stops then you'll have near infinite spring rates and the car will be nearly impossible to drive. Some people have gone so far as to alter their types of bump stops to reduce this issue.

A simple zip tie on the strut/shock shaft can give you an idea of the amount of travel you're using.

As a piece of information, I found that the Mookeh strut mounts I was using reduced the shock travel by about an inch, so I can understand why people were breaking them as running as low as most racers tend to run will result in very little suspension travel and when the suspension compressed completely the forces had to go someplace and the weakest link failed. I'll redesign them to maintain the stock mounting locations and allow caster and camber adjustment.
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Cédric  



Joined: 27 Aug 2004
Posts: 2023
Location: Sweden

PostPosted: Fri Jul 26, 2013 8:15 am    Post subject: Reply with quote

Suspension kinetamic and vehicle dynamic wise I am pretty confident where I have the car atm and how stuff works. I´ve been doing this for a while (And have a Msc in vehicle dynamics ). Carrol smith and fred puhn books are actually where I started my car interest once upon a time !

I am though not overly conviced with the GAZ damper curve (GAZ GAI2008 with 350lbs/inch springs on stock struts converted to "race springs and adjustable spring seat). I think i would have probably do a better guess with some pretty simple quarter car simulations, (and dampers adjustable in high and low speed range), but I cant afford anyone to produce those curves. Thats why I am running cheaper stuff. But high speed damping have always been a problem with these dampers, I would rather like more low speed to keep body control, but thats kind of hard when I cant ajdust them individually. Theres where most of the bumpiness comes from. But running the dampers close to the end of the travel is never good performance wise. Although the bump stop is quite long and soft.

BUT, they do feel quite good on track though, running with stiff springs and soft dampers is not any fun though, car gets really hard to control when you start upping the speed, but great for the street.

Running beyond perpendicular arms can be handeled, its just a matter of dealing with compromises. Horizontal arms are per se not the goal, going faster is The reduced dynamic camber you get can sometimes be compensated by more static camber and a stiffer car, but strange stuff can happen when the roll centras starts to run away, and the car could behave tricky. So If you start streching the boundaries of ride height you have to think one or two times. But there are seldom black and white, most of the time its a fine tuning art, and a tricky such

Would be interesting if you guys had some pics of your dampers at ride height, or had a feeling on how much bounce travel you run with (depending on springs of course).

Here is a pic on 205/50 15".


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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2053
Location: Somerset, UK

PostPosted: Fri Jul 26, 2013 8:57 am    Post subject: Reply with quote

Measured from the lowest part of the monocoque sill seam, but not the wing seam.

Front 95mm rear 110mm


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931 twinturbo  



Joined: 20 Jun 2007
Posts: 117
Location: Norway

PostPosted: Fri Jul 26, 2013 7:59 pm    Post subject: Reply with quote

On my old 944S i just had a set of lowering springs in front, don`t remember how much. But around 40mm in the back it was lowered 3 knep (tooth) on the innerside off the torsion and had yellow koni`s.
It became very low, but i had no problems over speed bumps if i drove slow an tacle them from the side...
For me it felt Perfect for an Budget setup and it was glued into the road... Could have much bigger speed in and out of corners that a friend of me With his 911....

But to be honest, didn`t try it on a track, sold it before i had the chance....



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