High Speed stability

You car is more than 20 years old and has been sitting on the same springs and loading the same bushings for all that time.
It is time to have the suspension reset to factory ride heights and corner weighted.
It may also be time to replace the suspension bushings.

This kind of maintenance does worlds of good the the feel of these cars.

 

well not sure the similarity between suspension/steering geometry of the 348 vs 355

but I have a 97 355gtb and hit 210kms per hour earlier in summer, so roughly 130mph

and the car was solid and straight.
probably could have gotten higher but ran out of open highway.

maybe have an alignment check ?

 

Do you have stock wheels and tires?
Tire pressure on all 4?
Is the car lowered? How much?
Last time alignment was checked?
I would put it on a lift and THOROUGHLY inspect all ball joints, linkages, and bushings.
Grab the tire/wheel and yank it around in every direction and see if there is any play in any part of the front suspension.

Turn the wheel/tire by hand back and forth and see how the steering wheel responds by turning and if it has any play in it.

 

Cross winds ? I used to drive my 328 at higher speeds way back when you could afford the ticket. I would drive up a river gorge that went on forever, some days at a 100 mph the wind would have the car all over the road. Other days ..... we will just say 1.5 times the above amount and it was solid as a rock.
Also after a year the front tires were still good tread, back were shot so only bought new rears ...... never again, mismatched tires made the thing scary at 80 plus. Replaced all 4 and was good to go. The car was only 10 years old when I bought it.

 

What do you mean by "loose"? The steering wheel gets light? The car wanders, or is darty?

Due to the nature of the 348's steering, it's never going to feel as solid as a Lexus at speed, simply because it transmits every bit of available information, much of which is filtered out in modern transportation appliances. So even when it's in perfect shape the 348 requires more driver involvement at speed than most road cars.

As far as I know, your '94 should have all of the factory updates for the suspension, and therefore should be quite capable of high speed stability.

The first place to start is the tires. Are they appropriate sizes and compound for the car? Are they new enough that they haven't hardened due to age? Are the inflation pressures correct?

The next place to look is alignment, but before you do that you need to first ensure that the wear items in the suspension are in good shape (covered in other posts in this thread). Next you should ensure that the ride height and rake is in the correct range. 348s are happiest when they are low, so get the car down as much as you can without it bottoming out frequently. Maintain the factory rake, or drop the front slightly more in relation to the rear.

As to alignment, more toe-in makes the car more stable. Too much toe-in makes the steering feel numb and increases tire wear. For more stability set the toe toward the big end of the range. More negative camber helps handling under high side loads, but it makes the car feel more nervous in a straight line. For straight line stability, adjust the camber to the small end of the range (less negative camber). Overall cornering grip will decrease but straight line stability and tire wear will improve. Finally, caster affects steering feel quite a bit as well. The more caster, the more the steering wheel wants to return to center, which improves straight line stability. The down side is that more caster increases steering effort, so you have to strike a balance that you can live with. IIRC, the stock 348 alignment settings don't call for a whole bunch of caster, presumably to help reduce steering effort. If you're okay with heavier steering effort, increasing caster is worth looking into. For an example of steering effort versus caster, drive a Porsche 911 SC-- those cars had no power steering and a good bit of caster. Heavy steering effort at slow speeds, but great stability at high speeds.

Even early 348s are capable of good high speed handling and stability as long as they are in good shape, have good tires fitted, and are correctly aligned for the intended purpose. Assuming your car is in decent shape and no components have been swapped for incorrect versions, getting the front end stable at high speed should be fairly simple, although it may require some trial and error. But due to its "race-car-like" suspension/steering setup, it'll still require more attention and involvement to drive at speed than less capable automobiles.

HTH.

 

The whole issue with high speed stability is suspension setup and alignment.

1) Have the front to rear chassis rake set properly
2) Get the car corner weighed
3) Have a proper wheel alignment done

There are other things that can affect handling like, worn bushings, worn shocks, worn wheel bearings. So while you are having the suspension set up have those inspected.

A few years back I got tired of burning through rear tires about every 5,000-ish miles, so I pulled out as much rear wheel negative camber as I could. I then got the front wheels aligned so that the car would drive straight. I'm not racing this thing on the track every weekend. SO I what with an alignment that would improve tire longevity. As a result my car handles just fine at higher speeds. You can see what I did in this thread. http://www.ferrarichat.com/forum/technical-q-sponsored-algar-ferrari/356344-348-rear-camber-adjustment.html

 

I ain't a 348 guy, but isn't there something about early vs. late cars & this issue?

 

Yep, the factory made a few changes to the 348 suspension through its production run, but this car should have had them all as it left the factory. Even the early cars can handle and drive excellently if the suspension is set up properly. It's just that mid engine sports cars are very, very sensitive to suspension setup. Ride height, rake, and alignment are all much more critical than they are on the typical transportation appliance.

 

The upper rear A-Arm had its inner (chassis) side pick up point moved downward by 20-25mm (forgot). This raised the real Roll axis and cause greater weight transfer to the outside front tire inducing understeer under cornering forces. This change was performed at the time of the Specialé and continued on 348s manufactured thereafter.

Surprisingly, the ride heights, and suspension alignments did not change.

But (as Ernie states) the ride height controls the handling, as little as 2 mm at the front is noticeable, and 3mm at the rear (where it is more sensitive) can change a car from oversteer to understeer. Once the car is in the "ballpark" minute adjustments at the rear are used to set the oversteer/understeer relationship. (A higher rear has more understeer).

 

My early '89 had some high speed stability issues that were corrected with alignment, wider Challenge wheels and the Serie Speciale front splitter.

 

Thanks for the update. Glad to hear it's handling properly now.

And MAN, bent a-arms?!?! Yeah that'll screw up the handling.

 

Tony and Anthony at Scuderia Performante are top notch guys - the absolute best in the business. 30 years of factory experience, these guys do the job right. They don't over sell or over service. They use common sense. Fair rates, work done right and best of all, just great guys all around! I was there a few weeks ago and picked up my Maserati GT which never drove better since they worked on it. Had dinner and drinks with the guys on Friday night and Anthony took me for the ride of my like on Saturday - man can he drive!!

 

I was going to suggest the 355 wheels. Outstanding job! I had an all stock 348 Spider and it was flawless up to my "chicken out" speed - 140 mph.

 

DO NOT LOOK AT THE SPEEDOMETER !!!!!

 

Then how's he gonna know when to chicken out???

Hellooooooo

LOL

 

So nice to get these issues resolved ..... F chat rocks.

 

You chicken out based on forward vision or by the feeling in the seat of your pants.
Speedometer not necessary.

 

you mean the dampness feeling?

 

Or the malodor... Modern tire compounds do wonders too. These cars see low miles and some are on 10 year old rubber. There is a new crop of high perf. 200 treadwear rated tires that wear fast, but are long lasting on low mile ferraris.

 

I was able to ride shotgun at a track event years ago in an F40. A sticker covered the speedometer: EYES UP

 

This is most true.
When I raced bikes there was no speedo

All eyes on the road