348 Handling Problems

Thanks for the image of the shim John. I just found this interesting alignment thread you may want to check out.
http://www.ferrarichat.com/forum/showthread.php?t=14588&highlight=camber+shim

 

Philip, I don't think you can apply any theory accross the board, your point about the power steering is correct, take for example the non - powered steering of the Daytona which has a castor angle of 1° 30' compared to the power assisted 365GTC4 which has a castor angle of 3°

Regarding your second point, obviously you need to get a balance between cornering response and stability. The 348's have generally been a bit problematic when it comes to handling, especially the early cars, which is why Ferrari made changes to the later models which included moving the battery from the rear to the front, adding a lower lip-spoiler trim to front bumper, the position of the rear suspension "pick-up points" was lowered and different shockabsorbers and road springs were fitted - all to improve the handling / stability.

Tyres were also very crucial, when the rear tyres wore out first (as they do) just replacing the rears would upset the handling and it would not be restored until the part-worn fronts were replaced. It even states in the workshop manual that "due to the characteristics of the tyre, it is advisable to replace all four tyres at the same time"

Choice of tyre also could make a difference, personaly when I was road testing the 348's in the 1990's there was a choice in the UK between Bridgestone and Pirelli and Pirelli came out far better at giving staight line stability over the Bridgestone.

 

Some recent driving got me thinking about 348 handling too. I recently replaced my S03's with Kumhos, and found the twitchiness has gotten worse at high speed. Somewhere just north of 90mph, the car begins to feel extremely light and unstable. My correction (thus far) has been to immediately back off and simply drive slower.

That's fine (for now), but I'd like to have confidence in the stability of the car. Leaving the cost of these mods out of the picture, where should I start?

1. Verify toe-in/camber
2. Put 15mm (or so) spacers on
3. Look into a front lip/spoiler similar to the 348ss
4. Lower the car (and drive more carefully!) a smidge

Thanks in advance,
Daniel

 

When I was test driving those two 348s at Sport Auto this summer, the '93 (an SS) had incredible twitchy-ness at high speed (and some slop in the steering rack). It had new tires on it, but I don't remember what kind.

On the other hand, the '92, which I think had it's original tires, was solid as a rock, as was the '94 I drove in New Jersey later on.

Strange.

 

I put 4 new tires on the car and had a complete wheel alignment not too long ago. Stock wheels and tire sizes.

My car dances all over the freeway as well. It's a concentrated effort to stay in lane.

My car is a Speciale which means that it has the widened rear track.

What specific adjustments can I make to make the car more stable on the highway? I've read about futzing around with the "castor angle" and such. But wasn't all that stuff done during the alignment? Or was it perhaps not?

What have you guys done to address this "dancing" problem besides switching tire sizes? I haven't seen any definite answers.

 

The 348 was twitchy at high speeds leaving the factory. Go back and read any of the reviews of the day and chances are you'll find one of them talking about it. Getting new tires on the rear should be fine unless, as said above, your fronts are old as rocks and probably as hard. Then yes change all four.

Poor tires are not the issue here. They are just compounding the problem. Aerodynamics and mechanical set up are. Caster increase will help the situation. That would be my first adjustment. Second would be larger front sway bar. I'd check to see what the 348 Challenge guys are running and what set up they like. Adjustable front and rear would be perfect. Also if you wanted to get a more aggressive chin-spoiler/airdam. Or lower the front end an 1/2 inch to an inch to get more positive rake and jack some more weight onto the front tires.

Just my .02

 

Interestingly, I'd say that my new tires made the twitchy handling -worse- than on the old rock-hard S03's. Then again, it might just be my imagination.

I'm tempted to play with the adjustable suspension a little bit and see what happens. Other than a smashed up spoiler, it's a *free* modification for the sake of discovery.

The chin spoiler from Valence USA looks nice, but I wonder if it would provide any functional improvement? http://www.valenceusa.com/3_3_lip.html

 

When I had the severe problem with the new Bridgestones on my 348, I had a very interesting conversation on this subject with chatter David Feinberg. He told me that the same tires were used on Audi A4's, and that the only way to properly check and balance these tires was on a special machine that loaded the tread while they were being spun. I'm afraid I don't remember the exact details, except that some of the Bridgestones had construction flaws and the belts were shifting under load at high speeds. The balancing machine at the Audi dealership was supposed to be capable of detecting the problem.

As I've said many times before, my 348 was UNDRIVEABLE at freeway speed with the first set of replacement Bridgestones (rears only), and it has seemed fine (up to 100mph) on the second set (all four).

 

WOW that's expensive for that lip! We MR2 Turbo owners have the same problem as the 348 with high speed stability so that's one reason I'm a little conversant on the subject. We have these guys, MADPSI make a chin spoiler for us that they sell for about half the one you link to. And it's CF as well. They'd probably hook you up with something for your 348 at the same price if they can find a market for it! Worth looking into. It does make a slight difference to our the cars at higher speeds. Then again it's a much more aggressive change than the one on the 348. Call them and tell them what you're looking for. They do good work.

 

Does the freeway surface have grooves in it? Get an alignment.

 

348's have always had this problem, try disconnecting the rear sway bar. All the 348 challenge cars had some type of rear sway bar that was either cut under the bushing or annealed in order to render it useless.

 

I've never driven the model in question, but I'm in agrement with the above posts indicating that this behavior is more or less normal. When you put low-profile tires on a supple suspension, the car will tend to dart and weave slightly in response to road surfaces. It is one sure sign of a honed performance car. The old tires were probably too hard to really claw into the freeway grooves like the ultra-sticky S03s. As long as you aren't getting vibration I wouldn't think the problem is with a force imbalance in the belts.

If you find out that your car is within alignment spec, my suggestion is to try to get used to the feeling. The car is telling you what's happening at each contact patch, and it will make you a faster driver. Either that or get a bimmer.

 

Problems with 348 handling are IMO due to TOO MANY COOKS IN THE KITCHEN. These are are old now even the 94's are getting to be 11 yer old. Most I have seen have old original rubber bushings and leaking shocks, the owners have changes wheel tire combos or tires on OEM wheels, spacer, ride heights etc.. Some cares have srash damge and never aligned properly. I race my car and have helpped to fix others and here are my opinions. The 348 is very sensitive to chassis rake. It is more go kart-like than the 355 and perhaps those things may be tuned out of the 355 with things like power steering and adjustable electronic shocks. There in lay some of the better rookie driveability issues. That said if you want your 348 to handle you need to put good suspension bushing in, make sure shocks are in good shape, restore the factory chassis rake relative to your wheel tire set-up and then align the car. My last race alignment and corner weigting took 4 hours while I sat in the car! So those types of attention to detail make a huge difference in the cars handling. That said I have one problem and that is the abrupt terminal oversteer when driving 10/10ths on the race track but I think those are more this dumb driver than the car. By the way alignment is NOT toe/in and toe out. All setting must be adjusted and checked relative to the vehicle centerline (camber, toe,caster etc.) and your average random alignment guys says he can do it but he has NO clue! He is punching a timeclock and your Ferrari takes too long. Please go to a guy who set-up race cars and pay to get a decent job. Your car with finally drive right. 348's can handle awesome...

 

Your bushings are rubber and it's not the number of miles on the car but the number of years that have accumulated to dry out the rubber. Don't forget if each of your bushings is giving 1mm add that up. If you have four pick up points on each side that are moving around that much you're talking about 4mm worth of play within the suspension system. Factor in all four corners and we're now talking about 16mm worth of play. That's a little over half an inch (.63in) that's affecting the car. Under normal driving conditions you wouldn't even notice what effect this would have on the handling. But, under hard driving the effects to your alignment will become more apparent. If they're really worn out it then the car will kind of float between different alignments until the car loads up the bushings and takes a seat.

There are a number of urethane bushing makers out there. Energy Suspension is a heavy hitter and they are sold threw many board sponsors. You'll love the response a urethane bushing gives your car.

An easy way to test shocks is to push down on the corner of your car. It will bounce back up under the rebound of the spring. If the shock is working it will quickly settle. If not it will bounce a little. The shock is actually a damper. It doesn't absorb the "shock" the spring does that. It controls the bump and rebound the suspension goes through. It controls the time it takes to go from one to the other. This is what an adjustable shock gives you. The ability to control the resistance there by controlling the time it takes to move through bump and rebound or to have separate controls for either of the two.

The best way to test a shock is to remove it from the car all together and push down on it. If it's good it'll rebound back. If it's not it'll just sit there like the expensive paper weight it's now become.

 

I have always heard that rake is a problem, but no one ever suggests what that value is or should be.

What is it supposed to be? F->R -ve or +ve value. ie, is the rear supposed to be lower than the front or the other way around.

 

Yes your car needs new bushings it has low miles but sits and sits which can be worse than high miles. Get oem bushings or do what I did custom make them. As to shocks you ahve to take them off the car and have them on the shock dyno. No other reliable way. You may be surprised at the results of the 10 year old shocks. And when I say 10/10ths terminal oversteer I mean 10/10th's . You are not getting that unless you are on the track IMO or you are a very agressive risk taking street driver.

 

Then I think you have a problem. I definately would start by making sure that mechanically everything was right. Sometimes stupid things happen. Once at the end of a race I notices a bit of front end wobble from the sterring wheel. It was the end so I drove though it. I got home and put the car on the lift to do my routine post race service and my steering wheel hex bolts came loose! I have never even heard of that happening before. Silly things can happen that can make you crash. Then I would definately take my car to someone who can do a race alignment and tell that person you are having problems. He needs to have the stock chassis rake measurements etc... Once you have everything stock as a referrence point only then can you modify for driver preference. Make the sure the race shop starts from determining chassis centerline (most do this as a matter of course).

 

I too had a 1990 348ts.Had Brigestone S-01 all the way around.235/40-ZR17 on the front and 255/40-ZR17 rear.No handling issues as you described.Check front rid height,which can adversely affect over/understeer.Four wheel aliginment,good shocks,renew bushings,will do wonders for the 348.Sounds like your biggest problem is the different tires front and rear causing unblanced traction problems.

 

Whoa there. Gotta stop this one quick before this becomes ‘the truth’. There’s no ‘jacking weight’ going on with this change. ‘Weight jacking’ occurs only diagonally across the chassis to facilitate turning in one direction at the cost of the other direction. AKA ‘wedge’ as they’d say at Daytona.

First, reducing front ride height on a Ferrari 348 will have an immeasurable effect on front axle load in a static setting. Dynamically, I’d have to look at the data but the load transfer under braking total will remain the same but the split between how much force is transferred to the road via the control arms and how much via the spring/damper will change.

Second, on the 348, lowering the front respective to the rear, especially if the rear ride height remains stock, will have a detrimental effect on cornering stability, though will help slightly with the aero.

Not wanting to pick on you, just setting the engineering straight

Best regards,

Rob

 

Certainly a possibility.

This is an easy test, but doesn’t tell much unless the shocks are really wiped out.

The best way to test a shock is to remove it from the car and test on a damper dynamometer. That said, every 348 shock I’ve pulled apart required a rebuild, even on low mileage cars.

Best regards,

Rob

 

Not all. Actually most ran legal.

Though this points out an important point. 348's respond very well to shifting the roll couple distribution forward, and disconnecting the rear ARB is one way to do it, though not nearly the best. It was the easiest way to cheat in Challenge and probably not get caught.

Best regards,

Rob

 

Worth searching for a shop with this equipment. The ones I've seen are made by Hunter and go for over $10,000. Places a roller against the face of the tire and measures the way the carcass responds to a known input force. Will point out internal imbalances that can be compensated with using the balance weight.

Best regards,

Rob