348 - high speed instability

I would say again that without any shadow of a doubt, mine is rock solid stable at high speed. I've taken it no faster than about 150mph though.

However, you appear to be confusing two separate things. The problem you are describing is tramlining i.e. where the front of the car wants to follow indents in the road.

My 348 did suffer from this, but surprisingly, I found one side effect of using (much) wider wheels and tyres than standard was that the tramlining effect was eliminated.

 

I have just fitted a set of Avon tires to a customer car....
it drives like a different vehicle, much more stable at the front. It's totally stock and had the usual instability issue before.

FWIW, Brian

 

I have found on mine that 25mm rear spacers make a huge difference in high speed stability. Adding the 15mm in the front is terrific for cosmetic reasons, but has the net effect of pulling 10mm of benefit out of the equation.

Other than track use, I think 25/15 is a great setup. On the track, stick to 25/0. Just my 2-cents opinion.

 

Absolutely agree.

Mine is now 25 rear, 0 front. But also got 20mm wider front tyres and 30mm wider rear tyres.

Specs are:

Front: 235/40zr18, 9.5J x 18 wheel

Rear: 285/35r/18, 11.5J x 18 wheel

See http://www.ferrarichat.com/forum/showthread.php?t=111741

 

Sy,

It just occurred to me that lowering 348 suspension requires loosening the tension in the springs. Someone please say so if I'm wrong about this, as I've never actually done it myself!

Therefore, given you car is lowered, it is also softened. A bad combination! Lowering should be accompanied by stiffening, not softening.

With softer suspension, combined with your use of odd front/rear height, plus your front spacers, and your worn bushes, I'm hardly surprised the handling is adversely affected.

At least you know that if you deal with these simple things, the car should be fine afterwards

Jas

 

There are spanner ring nuts on the lower part of the coil-over. It should not change the spring rate with lowering. If you lower too much though you may want stiffer springs to keep from bottoming out.

Lowering will NOT change sring rate.

Edit: I have not noticed any high speed instability atleast in straight line up to 140 mph. I do have the challenge set up with no spacers.

 

I started with the stock (1989) setup. Then added the Hill 15/25 mm setup. Based on Henkie's advise I removed the 15mm on the fronts recently and have a much more stable car now. I haven't checked the air pressures, but I will do that this weekend.
BT