| Author | Message | ||
| Philip Airey (Pma1010)
Member Username: Pma1010 Post Number: 312 Registered: 7-2002 |
Rob I had great fun today and, as you noted, the car is starting to feel really dialed in. This is in no small measure due to your excellent advice and perspectives. Thanks. ARB next. All - and a shameless plug from me as I know he won't overly promote himself - Rob has provided me with excellent advice for some time on chassis set up, tire pressures, ARB setting and more, both through this forum and by email. Really great stuff. He knows his chassis set ups (and more). He also made a special trip out to Gingerman today to assist me. Philip | ||
| Rob Schermerhorn (Rexrcr)
Member Username: Rexrcr Post Number: 735 Registered: 11-2002 |
Tim, you're right, the 355 Challenge ARB's are higher rate, and are also installed with adjustable drop links with proper spherical rod ends to zero the bar. Do a search, I've posted the specs for these pieces before. Ps, Philip, thanks for the drive today! | ||
| Tim N (Timn88)
Advanced Member Username: Timn88 Post Number: 3253 Registered: 6-2001 |
Maybe you could put on a set of challenge car sway bars. I'm sure the challenge peices are not the same as the street sways. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 874 Registered: 4-2002 |
The original suspension part is from my scanner in *.bmp format. I paste this into a CorelDraw page, and add the circles and arrows. Then I export the drawing into 640*480 to meat FerrariChat size constraints. "Is it essential to have the roll center of a vehicle below the CG of said vehicle for stability? Do we know where the CG in a 355 or 348 resides?" No, it is possible to have the roll centers above the CG and have a car that rolls inward in turns. However, the camber of the wheels will not give useful traction in situtaitons like this. The weight transfer still happens, but as the roll center is raised, more and more of the resistance to roll comes from the suspension bushings and less comes from the springs and shocks. | ||
| Ben Cannon (Artherd)
Member Username: Artherd Post Number: 546 Registered: 6-2002 |
Mitch, are these your own drawings (AutoCAD?) or do you have a software suite that does this kind of calculation? Is it essential to have the roll center of a vehicle below the CG of said vehicle for stability? Do we know where the CG in a 355 or 348 resides? Wish I was half the expert you are  Best! Ben. | ||
| Philip Airey (Pma1010)
Member Username: Pma1010 Post Number: 311 Registered: 7-2002 |
Rob, Bill FYI, the custom adjustable ARB on my 308 was $250. Unlike a fully adjustable bar, given the 308 space constraints, we settled on a two position bar. Shop that did it (will get the name if you are interested) advertises in GRM. I'd use them again but make sure they have the specs on the stock bar. And, what they send you looks anodised (sp?), but rusts. Paint or clear coat the bar. End links needed a little work to fit on the a-arm studs. HTH Rob, I'll have the car at Gingerman on Tuesday and will try the 36F, 32R tire pressure set up. Plan to tighten up the ARB for FCA meet on 9, 10 August. Look forward to seeing you there. Philip | ||
| Rob Schermerhorn (Rexrcr)
Member Username: Rexrcr Post Number: 728 Registered: 11-2002 |
Mitch, great drawings! What I found in performing the upper control arm (lowered by 20mm, 0.787") on 348 Challenge is it improved the driver's feedback of chassis dynamics. The theory from Ferrari was this improved communication through compliance. As we all know, in general, the average driver adapts well to a 'soft' suspension, relatively speaking. For racing, we ran 2.5 deg negative camber in front, and 3.2 deg negative rear. Ride heights dropped to 95mm front and 70mm rear, measured from the bottom of the chassis, not the center of the lower control arm inboard bushing. And, for 355 Challenge, spring rates were radically increased compared to 348. This does validate your conclusions In reality, as always in engineering, it's a compromise, the geometry is not ideal, and the greater gain is lowering CG and increasing the spring rates to limit roll center movement, control camber gain, etc. | ||
| Paul Brennan (Turboqv)
New member Username: Turboqv Post Number: 49 Registered: 3-2003 |
Mitch, Very informative post, thank you. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 856 Registered: 4-2002 |
And now back to our regularly scheduled program: The following figure shows an unlowered 355 rear suspension system, and what happens to the geometry when the chassis is lowered 1.0".  The suspension control arms articulate around point '1' causing a roll center of 4.83" at point '2'. When the chassis is lowered at points '3' the suspension arms now articulate around point '4' and cause roll center of 3.40" at point 5. You might also notice that this eats up 60% of the shock travel at point '6'. We lowered the chassis 1.0" and find out that the roll center goes down 1.43". This means that we need to increase the springs to account for the lower ground clearance, but we need to stiffen them again because the moment arm causing chassis roll is larger after we lower the car! We also find that the upper control arm pulls the hub in by 0.15" from lowering the chassis. Therefore to pull the lower hub pivot point in and regain static camber settings, we loose 0.30" of track. Therefore, a wheel with larger offset would be advised to retain track. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 855 Registered: 4-2002 |
I could not find the exact right thread to insert this information, but this thread was close enough to be connected with the underlying topic. The following figure shows the Rear suspension of an F355, and also represents the rear suspension of the 348 speciale and onward.  It has been porported that the rear suspension was changed by lowering the upper control arm chassis pivot point 0.6", and that this lowered the roll center at the rear. The original 355 suspension attachment points converge at point '1' giving an instant center around which the hub moves and this in turn gives a roll center height above ground of 4.83" at point '2'. When the inner pivot point at the chassis is raised 0.6" like in the pre speciale 348s (at point '3') the suspension links converge at a more distant instant center indicated by '4' and this creates a roll center of 3.20" at point '5'. So, if the upper inner pivot point was moved downwards 0.6" on the 348 speciale and onwards, this actually moved the roll center upwards (to 4.83") not downwards (from 3.20"). Raising the roll center reduces the lever arm and causes the springs to carry less of the roll rate of the chassis in turns, and more of the forces are transmitted through the suspension links, bushings, and arms. If the figure of 0.6" is inaccurate, I would be happy to rerun the numbers with the correct data. | ||
| Rob Schermerhorn (Rexrcr)
Member Username: Rexrcr Post Number: 727 Registered: 11-2002 |
Neal, Chassis roll is dynamic weight (force) transfer from one side of the car to the other while cornering, lateral acceleration. The amount is determined by center of gravity (CG) location and track width. The actual motion (as opposed to force) and the magnitude and rate at which it occurs can be influenced by spring, anti-roll bar and damping rates, and suspension geometry. Of course, the friction available at the tire is also a function, but for friction to be an influence on roll angle reduction, friction must be reduced. This is contrary to what racers and enthusiasts usually want, so I don't mention that one could mount less sticky tires to reduce body roll motion. Increasing tire size, with the assumption you desire to increase tire grip, will cause increased chassis roll motion (opposite of the goal). So, the factors that Mitch pointed out are pretty much all one can do to decrease roll motion while experiencing lateral acceleration (with the exception of installing active or semi-active damper system, and programming to reduce roll). | ||
| "The Don" (The_don)
Senior Member Username: The_don Post Number: 5856 Registered: 8-2002 |
Bill, what does "MY355" mean? do you mean "my 355"? or "My" has in model year. | ||
| neal (95spiderneal)
Junior Member Username: 95spiderneal Post Number: 200 Registered: 3-2002 |
how about just increasing tire/wheel sizes/pressures? | ||
| arthur chambers (Art355)
Intermediate Member Username: Art355 Post Number: 2050 Registered: 6-2001 |
Don't lower the chassis. You'll regret it. I did it on my, with shorter springs. Grounded everywhere. Made noise, couldn't go up drive ways, you name it a problem Art | ||
| Rob Schermerhorn (Rexrcr)
Member Username: Rexrcr Post Number: 724 Registered: 11-2002 |
Great advice Mitch. Here's mine, based off Mitch's: a) Easy and affordable, best ROI. b) I don't know anyone building larger ARB's, you'd be the first. Not as easy as (a), but for a production run, affordable. Ask Philip Airey how much his custom ARB was for the 308. Also, don't just guess at the size and spring rate of the new ARB, you want to improve the handling, not upset the ballance. c) Not recommended. Ferrari actually lowered the rear instant roll center in 1993 (discussed, search ) d) Always good, accomplished in (a), or just lower the OEM spring collars, Lowering Your Ferrari 348, 355, 550 IMO, drawbacks to (a) depends on your personal comfort and how your 'use' your car. If you track the car more than drive on the street, significant gains can be made here. For street, I can still 'tighten' up the chassis response and improve balance without losing too much 'boulevard ride' comfort. If you like the highway / Interstate ride characteristics now, just lower the chassis. | ||
| Mitch Alsup (Mitch_alsup)
Member Username: Mitch_alsup Post Number: 848 Registered: 4-2002 |
What do you expect to get from less body roll? I hardly notice any at all in my F355, except at the track when transitioning from max left cornering to max right cornering. But things you could do: a) increase spring and shock rate at each end b) increase anti-roll bar at each end c) raise roll center at each end d) decrease the center of gravity All but d) come with plenty of drawbacks | ||
| BILL CHIUSANO (My355)
Junior Member Username: My355 Post Number: 153 Registered: 3-2003 |
I would possibly be interested in less body roll in MY355. TIA |