Ferrari 355F1 Berlinetta (Track Day)

1800/900

Helps the car turn at T1, T11, T12, T13, T15 and T20...

That's where ALL the time is...

 

You have both Shell and Agip sponsoring you? How did you work that out ?

 

I forgot about this great thread.

Rob,

Can you explain how this works? I have a hard time wrapping my head around this. 2200lbs front springs and I think "understeer"! There was a comparable front over rear split on my 348 racer. I never understood it. I just drove it and it worked!

 

That's what aero does for you.

 

I don't think it is aero. These are big streetcars going relatively slowly and I don't think they generate as much aero as one thinks. Horsepower is huge and useable how you get on power and off power and brakes and gearbox. A manual box shifts maybe 1/2 second and challenge box 40ms? All that stuff including aero add up. Then there is 20 years of chassis development. Look how a 911 has changed over the years. The guts there are much more similar than 355 to 458. Then look at funny chassis dynamics like the 355 flexes like a noodle. How much of the 2200lb heavy springs are really transferring energy into the chassis to act as an unpredicatable chassis torsion bar? The increase in stiffness beginning with the 360 really started to allow the springs to be springs.

 

^^^ this

 

Briefly: choice in approach / philosophy...

One way is big springs, other method is larger ARBs, "softer" springs.

Chassis stiffness is the #1 factor, and virtually no one pays much attention to this... So many roll cage designs are wasted opportunities for chassis improvement; the key is triangulation...

Best,
Rob

 

Well said. My 2 cents is, choose the set up that will make car feel most confident on the power from the center of the corner to the exit first and then work on reducing entry understeer. Many of the common complaints I hear about Ferrari's handling "Issues" are driver induced. For example, braking too late and charging too fast into the turn and then complaining about understeer. Then, deciding to make a set up change to help it turn in by stiffening up the rear, only to wind up complaining about exit "power on" oversteer. The comments are correct about the chassis softness of the 355 vs the later cars, so you need to consider that going too stiff on spring simply moves the loads to the chassis which then becomes the spring and is not well dampened or easily tune-able! Rob's point is a very important consideration, springing softer and controlling roll and balance with bars is the way to go if your chassis is a noodle.

 

Is that spring rate or wheel rate? Don't get the 2 confused. If you're talking about spring rate, then unless the 355 and Cayman have identical motion ratios in the suspension (extremely unlikely), they're not comparable.

Make sure if you do the comparison that you use data (mid-corner speeds and G-forces) and not feel. Often, a stiffer sprung car will 'feel' better but actually be slower. You get quicker responses from a stiffer suspension which 'feels' better, but it may end up not gripping as well and ultimately end up going slower. I experimented with this by switching suspension modes on my 355 during a practice autox. Sport mode invariably felt better but in a lot of turns the car was actually slower, so was not necessarily faster overall. In instances where there are multiple quick transitions it was faster in sport as the car could change direction quicker (slaloms especially), but in longer sweeping turns it was slower, especially if there were any bumps. I have stiffer than stock springs so that may be why the softer damping worked a little better. If you go too soft, the car will hit the bump stops and will be a nightmare.

I should add that when I did the experimentation I was on street tires (direzzas) and softer damping worked better. With R6's, sport mode works better as the tires have more grip. In short, you have to try and find out.

 

I'm telling you, you can't compare spring rates unless the motion ratio is the same. Doesn't matter if everything else about the cars is identical, if the motion ratio is different the wheel rate is different with the same springs. Motion ratio is not suspension movement, it's the ratio of spring movement to wheel movement and has to do with how far out on the control arm the spring is mounted compared to the pivot point of the control arm. Unless the springs are mounted identically and the control arms are identical length on both cars, they won't have the same wheel rate even if they have the same spring rate and can be drastically different.

 

I just looked at the Cayman R (2012) suspension setup, it's strut based so 1:1 motion on the spring meaning an 800lb/in spring gives 800lb/in wheel rate. On a 355, the motion ratio is something like 2:1 in front, meaning for every inch the wheel moves, the spring moves .5". That means to get an equivalent wheel rate on a 355, you'd need around 1600lb/in spring.

 

^^^ This!

Interesting, kudos for trying this.

What confuses the test though is that the dampers are adjusting whilst driving, so you're switching between two different programs, like two different ECU maps of spark/ injector timing. At max lateral acceleration (and other parameters) the two programs get close to the same damping settings.... Nevertheless, this is important data to pay attention to.

Bottom line is, I'm constantly suggesting to racers who've "lost their way" to go back to soft settings (sometimes both in spring and damping), and slowly increase forces (either spring or damping, sometimes both).

The key to bump rubbers is striking them with intention or trying to avoid them altogether.

If hitting the bump rubbers intentionally, use suspension packers.

Best,
Rob

 

Motion ratio for F355:
Front 0.70
Rear 0.85

Equation:
Wheel Rate = (Motion Ratio)^2 * Spring Rate

 

Stanislaus, I commend you in your relentless pursuit of the optimum F355 suspension set up. I recall having an interesting phone conversation with you a few years ago...

You're discovering the iterative process of sorting a chassis and optimizing for both the track, the tire, and the most important factor: the driver.

What Ferrari SpA did with F355C is polish up a wonderful road car as best they could in the amount of time given and budget allotted. As you see, the F355 responds well biasing the wheel rates significantly toward the front, performing the additional duty of major roll control, in addition to tire compliance, ride comfort (or lack of), etc.

To sort a given car, amateur racers have limited resources, so typically it's trial/ test/ change/ repeat until a trend is established.

You're on the right track, ultimately you must install a certain specification of spring(s), set dampers to something (with or without suspension computer control), and then drive, taking as much data as possible...

I'm happy to discuss strategy with you; a phone call would likely work best. Best time for an extended call is between 9:30am - 2:00pm Eastern (earlier and later is crazy around here).

Best,
Rob

 

Unless rules maxed define spring rates and you wanted to do something funny why would anyone except nascar want to run on bump rubbers? How many performance street cars if any are designed to use the rubbers for anything other than protecting from over travel? It seems to me that using rubbers means you lack travel and that is a bad thing but I hear about people tuning with rubbers and packers like it should be part of everyone's tuning armamentarium. I need a lesson on rubbers and packers.

 

There you go, to get an equivalent 800lb/in wheel rate that the Cayman has, you need 1600lb/in front springs, which is what the challenge has. You're going to have to find your 10 seconds somewhere else. I'd start with tires and work from there. It always starts with the tires.

If you get within 2 seconds, you can probably start to fine tune to get that last little bit, but honestly 10 seconds is an eternity. Do you have video of the caymans to see where the 355 is a lot slower? If it's in the turns, I'd be surprised unless they run a different tire.

I'll repeat, do not underestimate the difference tires make. If the Caymans run a different slick (brand or model) than the 355ch cars, it's very difficult to compare them.

 

I have data for numerous Caymans doing 2:24-2:29. Send me your best and I'll tell you exactly where it is...

 

Send me that data!