Anyone driven a 348 without the rear anti-roll bar?

It will give the car considerable understeer. This comes because the front end is performing more of the roll stiffness, and this overloads the outside front tire.

If you dislike how the car currently feels, you can adjust the oversteer/understeer relationship by raising (more oversteer) or lowering (more understeer) the rear end by turning the nuts on the shock towers with a spanner wrench.

 

I never did understand suspensions. So Mitch help me out. This is an interesting question that i could only answer if I drove the car to see what happened. A bar is just a spring and removing the rear bar just decrease the relative wheel rate front to rear right? We know 348/55 handle better with more in the front than the rear due to the extra front rollstiffness. So i could see how deleting the rear bar could make you faster on paper just like generally putting more front spring does. The 355c used some giant front springs and I used some pretty big numbers on the front of the 348 racecar and that totally made for a faster car.

 

My challenge car had it removed. It had big springs all around. Handled fine.

 

I would go with the beefy 355C springs as a base. It is a proven package and tune from there with double adjustable shocks and adjustable bars are gravy. Problem is 348 is a wet noodle. You have to stiffen the chassis especially for the 355C front springs or you will wipe out the chassis. The 355C has an extra stiffener plate welded around the coilover box. When I first tracked my 348 I got the stiffest springs I could run before destruction. Later I got more serious and welded my cage all the way to the front shock tower tops and WOW! the chassis got so rigid I had to learn to drive it all over again. I actually think a hot racecar could be made from the 355 spyder which has beefier sill plate/tube than the normal 355's with roofs. Then weld a cage in there and weld on a roof and you would have a pretty awesome chassis. Around here in socal 355 spyders are a dime a dozen and prices are down to the high $40's!

 

Yup. To create oversteer (sliding the tail) in drifting, we frequently remove the front anti-roll bar of the lower-hp cars.

Remove the rear anti-roll bar and you get understeer (front wheels are pushing, not turning the car enough to make the corner).



It's counter-intuitive, but that's how it seems to play out. The front anti-roll bar effects the rear handling, and the rear anti-roll bar effects the front.

 

When one removes an anti-roll bar at the rear, the front has to do more of the roll stiffness. The rear still does a significant amount because the regular springs do much of the work, and the anti-roll bars are there to balance the car.

In (very) general, the softer the suspension the more grip one has--right up to the point where the suspension cambers over too much and the tires quit gripping. {Consider an infinitly stiff suspension. Any lateral acceleration would transfer all the weight to the outside tire leaving the inside tire nothing to do. Now consider an infinitely soft suspension. The car can roll back and forth and both inner and outer tires are left on the road with the same weight they started with.} It is only when the suspension geometry allows the tire to present a less optimal tire footprint on the road that grip goes down. So springs and bar need to be just hard enough to support the car, and keep the suspension geometry inside a certain window.

This is due to the spring and shocks on the cars currently. The rear is a little under-tired so by moving a lot of the roll stiffness to the front a nice balance of understeer/oversteer is found.

But let us go back to fundamentals: Why does a car even have anti-roll bars?

If a car had a track that was equal to its wheelbase there would be NO NEED for anti-roll bars at all! So the anti-roll bars are present because the wheel base is longer than the track! Then the springs are chosen (road car) for a certain amount of dive under brakes, and a certain amount of squat under power (say about 1/2 the static ground clearance). Then anti-roll bars are fitted such that one can have a smooth transition from heavy brakes to high G cornering in such a way that the outside front tire has the same amount of weight through the whole transition. That is, the front end compresses under brakes, and then as one rolls into the turn while reducing the brake force and the outside front tire remains at the same compressed height throughout. A suspension that is not moving is holding its tire well to the pavement.

More fundamentals: Why do we use more (heavier) bars at the front than at the rear?

The rear tire is not just along for the ride. It provides all the forward thrust (while all 4 tires provide backwards thrust under brakes). So the rear tire not only has to carry the latteral loads of the weight on this end of the car, it also has to carry the perpendicular thrust loads from the engine power. This combination can overload the rear tire.

So, by transfering some of the latteral roll stiffness from the rear to the front (and assuming good chassis rigidity) the outside front tire carries excess latteral load, allowing the rear tire to carry the thrust loads along with its reduced lateral loads. By choosing anti-roll bars properly, one ends up with a car, well balanced in cornering under power.

Last fundamental: Why are the rear tires bigger than the front tires?

In a Mid engined Ferrari, there is a lot of weight in the rear end. While one is tuddling down the road, you want each tire to have the same load per unit footprint. So with 40/60 weight distribution, one wants the rear tire 50% bigger than the front tire. With each tire holding the same vertical load per unit footprint, long tire life and balanced tire life can be achieved. In addition, with each tire holding a same load per footprint, external inputs to the cars body (winds) disturb the car in a neutral maner. With a little natural low speed understeer dialed in, the car handles these events all by itself and the driver hardly notices.

So, overall, the tires are the size they are for weight distribution of the car, the springs are chosen for braking and acceleration, and the roll bars are chosen for balance in the transitionir from braking to cornering to accelerating out of the corners. Its a small box to operate within.

It really has nothing to with speed directly, it has to do with balance.

One last item: Roll couple distribution.

The car reacts to lateral acceleration as if it rolls around an axis defined by the front and read roll centers. These points can be found geometrically. In the F348/F355 at standard ride heights, the front roll center is 0.5 inches BELOW the road surface and the rear roll center is about 4.2" above the road surface (F348 espciale and forward and all F355s). This axis is noticibly forward sloping, and influences how much weight transfers from the rear t0 the front under cornering.

The front roll center hardly moves as the front is raised or lowered, while the rear roll center moves rapidly. The instant center at the front is some 300 inches outside the centerline of the car, wth the instant center at the rear is only 60 inches from the centerline of the car. With the especiale, Ferrari shortened the instant center at the rear (from about 72 inches to 60 inches) and thus made the rear more sensitive to ride height adustments.

As the rear of the car is raised more weight is transfered to the outside front tires under lateral acceleration. This gives that front tire more grip, and thus is seen as oversteer to the driver. Conversely, lowering the rear can induce understeer. Thus, one can use rear ride height to tune the car for the springs, bars, and tires; and even to a bigger motor.

Now, if one were to setup a (near race) car for streetable operations, but be highly raceble at the same time, I would suggest springs about 150% of the road car springs, and then figure out what kind of adjustible links are needs on the existant bars to balance the car; using ride hight as the final adjustments. Of course, shocks are going to have to be matched t the springs. This prescription will not be as fast as a pure challenge setup, but will be a lot nicer on the street and be less than 1/2 second slower on tracks.

 

Wow Mitch, thanks for this write up. This is 348 FAQ material.

 

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