Lowering a 456GT

from koni 's site:
This ratio is easily measured: assuming the car is without its wheels, springs and anti-roll bars:

1. Lower the suspension to its maximum droop position.
2. Measure the distance between the damper mounting points.
3. Raise the suspension to the minimum ride height position as found earlier and repeat step 2.
4. The mean motion ratio can now be calculated using the formula stated above

the motion ratio is damper movement/wheel movement.
that is the definition i have always worked with; i have yet to hear of it used to determine the amount of ride height reduction/lowering per turn.

yes, roll centers are something different entirely; however, they relate more to ride height and CofG than motion ratios - that's why i brough them up.

i had a general ride height in mind, sure - but the jist of my point was that min. ride height isn't critical on our cars, and that usually attaining balanced cross weights and maintaining suspension travel are the most important factors once you're aesthetically satisfied with the height you've selected.
did you guys cornerweight the car, too?

 

thoughts on crossweights in general? well, you'll need scales - that's for sure, and you want to be absoloutly certain that they are, or have been recently, calibrated. moreover, you want the right front and left front to be within % points of one another - same with the rear. you also want the right front and the left rear to be proportionate; same with the left front and the right rear. (i have my sheet at home, with my cross weights and cornerweight results, but from what i recall they were with a couple % points - which is pretty good for a street car, on a limited adjustability suspension). furthermore, the more evenly distributed the weight is right to left, and left to right, the more balanced the car will be in all corners, and the more predictable.
as far as rake is concerned (front ride height v. rear) that depends on how you like your car to rotate, what your shock/spring setup is, and whether or not you can adjust static camber independantly of ride height (with camber plates, for example).
it all becomes a compromise between optimal handling, street drivability and tire wear. the most important question(s) are: how do you wnat your car to handle?; which tire are you going to be using (what are they're reccomendations on camber/toe, etc); and what are the limits of your shocks with respect to min. ride height and allowable travel?

 

camber doesn't eat tires, toe does.
i don't really know what camber ranges are effective on 456s or the like, but i'd suppose that right around 2 degrees of negative camber, or there abouts, should be plenty.
toe settings you'll want to keep conservative as well. again, just making suggestions, but you'll maybe want slight toe out up front, and either very, very little toe-in on the rear or zero toe. or, maybe what'll work best is zero toe up front (if you like the crispness of the steering and turn-in) and just a little toe-in on the rear.
the cross weights are empirically determined. so, you have to get your car on scales, cornerweight it and setup up the weights by actually doing it; there's no formula (that i know of) that does this - its something you have to fine tune by hand.

 

toe-in in the rear provides high speed stability, as well as added stability under braking.
where are you going to have it aligned?

 

i'd reccomend my guy to you. if you want his # lemme know.

 

Good discussion Gentlemen.

You're all on the same page, with just a couple errors, mostly in semantics (which is always a challenge in engineering discussions: standardizing a lexicon.)

Byron, in response to your email, stick with Factory alignment specifications for camber, castor and toe to minimize tire wear. Depending on the camber gain of the 456, your alignment shop will be removing all or most of the adjusting shims to remove some negative camber gained from lowering. Not a big deal.

Hubert's right on about toe killing tires quickly. Stick with Factory toe settings. (Rear toe-in is mandatory to aid platform stability in cornering! Front toe-out is a racer's trick to encourage crisp corner entry while sacrificing some stability, compromising the geometry somewhat, not for the street.)

Front Camber: -1 deg +/- 10' (that's degrees and minutes, 30 minutes is 0.5 degrees)
Rear Camber: - 1 deg 30' +/- 10'
Toe-in F: 3 +/- 0.5 mm
Toe-in R: 3.5 +/- 0.5 mm
Castor 5 deg 30' +/-10'

The Koni site is correct about determining motion ratio, they just state the procedure with different terminology.

To the suspension lexicon: "camber plates" typically relate to a McPherson strut suspension, where the shock absorber performs dual duty as an upper control arm. Therefore, camber may be adjusted on this type of suspension via lateral movement (referenced from the longitudinal centerline of the car) of the upper strut mount.

One may argue that on a Ferrari, the shims located between the control arm inboard mounting forks and the frame do indeed adjust camber (and toe), and look like plates. To avoid confusion, let's call these adjusting "shims" instead.

Cross weight:

Hubert is right here in that there is no weight specification per se. There is a standard, typical expressed in units of percent. Hubert's a little confused here though.

On a production based chassis, or large GT type race car, you're typically only able to affect cross weight, and minimize it. The goal is 50/50 % cross weight with driver on board, half tank of fuel, anti-roll bars disconnected.

Little may be done if the cross weight (RF + LR) vs (LF + RR) is correct but the weight on an axle is off.

For example:

Starting specifications:
LF 550 lb RF 550 lb
LR 700 lb RR 850 lb

Here you have even front axle loads, which in theory looks good, but since the cross weight is way off (1250 lb vs 1400 lb, 3% cross weight), the platform is not quite balanced, and may exhibit great turn-in for rights and a push for left turns. Assuming the chassis is level already, and rake is where you want it, adjust LF and RR spring collars up using motion ratio formula to keep the platform stable, and RF and LR spring collars down. This will move cross weight closer to 50/50.

So you may end with something like:
LF 540 RF 570
LR 720 RR 820
The result is (540 + 820) vs. (570 + 720), only 1% cross weight, which is excellent for a GT type road car.

Now, with the car remaining on the corner weight scales, reconnect the anti-roll bars to ensure zero pre-load. Most Ferrari's do not have adjustable drop links for the anti-roll bar, so you'll have to live with the result.

Again, Hubert is right in that one may itterate without knowledge of motion ratio geometry and have perfect corner weights, cross weight, ride height and rake. It just takes a bit longer.

Roll center of course is related to motion ratio in a geometric sence. But strictly for chassis alignment tasks, let's just ignore it for now. Yes, it's important in vehicle dynamics, and it's possible that one may lower "too much", but for Ferraris like the 348, 355, F40, get the rear low as practicable and keep it there. Lowering the mass is more important than roll center concerns for these cars and this type of driving. For 550 and 456, maintain factory rake while lowering.


Best regards,

Rob Schermerhorn
www.deltavee.net
DeltaVee Motorsports
1661 Quail Run Drive
Kalamazoo, MI 49009
847.638.4226
309.415.4378 FAX

 

Can anyone repost the step-by-step writeup for lowering? I saw it a month or so ago, but it has been lost from the following site:

http://www.ferraridrivingclub.com/d...ing a 456GT.doc

Many TIA

Ben

 

This is the document without the pictures. If PM me with an EMAIL address I can send you the complete file.

This is my 456, lowered 1" in the rear and .75" in the front.

MB
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@F456 V12 car looks amazing, can I ask what size rims and tyres you have on them if you still have car ?

also what year is the car and is it a manual ? would you say its been worth it considering all the quirks people are talking about the 456 in general ?

im looking at a 2002 manual

cheers

 

17 year old thread and he sold the car, a 456 GT 6 speed, which appears to have 18" 575M OEM wheels. The one you are looking at is a 456M GT. Look in the 456/550/575 forum for enough information on the 456M to choke a horse.

 

You are correct, 18" 575M OEM wheels. What I don't recall is if I used spacers to make minor changes in offsets.

MB

 

Christian- Looks like she has rear spacers around 25 mm. Fronts look like no spacers. Distance from wheel to brake caliper is the usual clue.

 

Very cool thread. I just added 19” wheels off a caifornia to my car. Requires wheel adapters to adjust for the bolt pattern. Not done yet so will update all later on what was required and the resulting wheel/tire fit. I’ll want to lower it next