| Author | Message | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 730 Registered: 5-2002 |
Phil, just to be sure we are talking about the same thing, motion ratio is the distance the wheel moves/ the distance the shock/spring moves. The motion ratio is really not a constant, I usually use the number as the average in the +/- 1� of normal ride height. And you're right, the movement of the wheel isn't really anything like a perfect vertical, but is even less like an arc. It's an instant center problem with an apparent arc that varies dramatically in length and origin through the wheel travel. The vertical assumption using the lower ball joint gets you very close, but it is not perfect. You�re right, the effect of wheel spacers on suspension stiffness is something, but I really think it's negligible here, I guess that was my point. | ||
| Mitch Alsup (Mitch_alsup)
Intermediate Member Username: Mitch_alsup Post Number: 1110 Registered: 4-2002 |
The following drawing shows a 355 suspension setup, the 348 speciale and later 348s are the same except for wheels and tires. In the drawing the center of the contact patch is indicated with a Green arrow, and the center of the wheel bearing by a red arrow:  In the front, there is around 0.33" where the contact patch can be moved outward lowering the load on the bearings. In the rear, 0.90" of outward travel will result in lower bearing loads. CAVEAT: this is a static analysis, toe and camber enter into the actual dynamic loads (even while traving in a straight line.) But his shows that small spacers won't radically increase the bearing loads, and may even reduce them! | ||
| Phil Hughes (Ferrarifixer)
Junior Member Username: Ferrarifixer Post Number: 180 Registered: 7-2003 |
By the way, motion ratio is measured at the shock absorber/spring mountings, which on the later cars is getting further than ever away from the lower ball joint....take a look at the rear of a 360... | ||
| Phil Hughes (Ferrarifixer)
Junior Member Username: Ferrarifixer Post Number: 179 Registered: 7-2003 |
Sorry Mark, but no Ferrari has been built with perfect vertical wheel movement, and never will be. Camber gain and bump steer are built in as a pre-requisite, and therefore the wheel does prescribe an arc and does vary the motion ratio with wheel offset. Not by much though, but not nothing either. | ||
| Mark Eberhardt (Me_k)
Member Username: Me_k Post Number: 728 Registered: 5-2002 |
Yeah, what phil said...except the suspension will not get softer because in a double a-arm design, the wheel does not move in an arc really, it basically moves straight up and down. The motion ratio is measured at the lower ball joint and you're not changing that. You will be applying a little more load to the ball joints, but not much. The general rule is that if the wheels will fit in the fenders and not rub on anything, they're fine, enjoy them. If you have to start relocating things like shocks or fender lips to get them on (I had to move the rear shock mounts on my 308 to mount 550 wheels), you might an engineer to look at it, but it's still probably fine. The car will probably behave differently at the limits, but normally that can be corrected with tire pressure and alignment. Also, more + offset will move the wheel in not out because offest is the distance the mounting flange is from the centerline of the wheel. | ||
| Phil Hughes (Ferrarifixer)
Junior Member Username: Ferrarifixer Post Number: 177 Registered: 7-2003 |
Although there will be adverse effects, the severity is arguable. Yes, the wheel brgs will be under more load....so what? Who cares whether they last 150,000+km or 95,000+??? The gyroscopic steering forces will be increased, giving more kick back and bump steer. Also, the motion ratio will be increased making the springs and shocks effectively softer.....but not by much, and how close to the limit do you drive anyway??? Basic answer is that any change to Ferrari's design will see changes that the car builder did not intend....it's up to you to decide if you know better than Ferrari or not. If show is more important than personality.....go the airhead blonde for fun or if show is not the priority, go the smart brunette for a relationship!! Just my opinion.....!! | ||
| Omar (Auraraptor)
Intermediate Member Username: Auraraptor Post Number: 1017 Registered: 9-2002 |
I started a long thread on this a while back...search for the negetive side-effects of spacers. | ||
| Dave White (Dwhite)
Junior Member Username: Dwhite Post Number: 130 Registered: 5-2003 |
Yes I believe it will be a problem. The bearings will be under more load as the wheel will not be centered over the bearings properly. I belive there was a thread on this in the last month, might want to check the archives. | ||
| Doug Teague (1notred)
New member Username: 1notred Post Number: 1 Registered: 9-2003 |
While looking for wheels to make my 456M look more agressive, I ran across a set with more offfset: +.85" front, +.56" rear. These look great on the car, but move the wheels outboard. Will this be a problem? |