Tell me why the rear is static positive camber

[JLS Crossle 42]

Why is the set up in the rear with positive Static camber?

This is the only car I have ever seen set up this way.

I can only conjecture that the negative goes away with aero load, squatting under throttle and large amount of camber gain in bump and very little chassis roll.

Or some combination of all of the above. Has anyone run the suspension geometry?

[brownslane]

I have and it's awful!

Car pitches and dives, squats and rolls. Front RC higher than the rear; camber curves that make you want to laugh.

The car is designed to handle like an under-sprung Crossle 32 with 500 HP!

With that said, everyone has the same bag of bolts; he who can drive it he best will run at the front.

To say that the geometry is "modern" is more than stretching the truth. But as Colin Chapman said "suspension works best when it doesn't"

T

[Trey Range]

I've wondered this too. But my inside rears wear more than outside, even with positive camber. Coming from BMW racecars that ran -3.5+ front and -2.0+ rear, I can't grasp how positive camber allows inside wear.

[Rick Ross]

FM's are very "soft" by formula car standards -- they roll a lot in the turns. The rear suspension geometry is such that the outside rear tire camber becomes much more negative when cornering. So even with a static setup of positive rear camber, when the chassis rolls towards the outside of a turn, the outsider rear tire camber becomes less positive (or even negative).

The large negative camber angles on a BMW mentioned in the previous post were probably for radial tires. In general, bias ply tires such as those used on the FM do not like large negative camber angles.

[JLS Crossle 42]

FM's are very "soft" by formula car standards -- they roll a lot in the turns. The rear suspension geometry is such that the outside rear tire camber becomes much more negative when cornering. So even with a static setup of positive rear camber, when the chassis rolls towards the outside of a turn, the outside rear tire camber becomes less positive (or even negative)
.

Since Roll will always increase camber, I surmise that there is a great deal of camber gain in bump. And with the short upper link that makes sense.

I know someone here has messed around with the suspension design in unlimited classes.

What changes did you make?

[brownslane]

Since Roll will always increase camber, I surmise that there is a great deal of camber gain in bump. And with the short upper link that makes sense.

I know someone here has messed around with the suspension design in unlimited classes.

What changes did you make?

WRONG!!! Roll will not always increase camber.

Positive camber change only occurs when the arcs transcribed by the upper and lower arms happen in a way that the upright "tilts" in the correct direction! In FM this is NOT the case. That is why the rear of these cars are so weird.

Lowering the inboard pickups of the upper arm, raising the upper pickup point on the upright, narrowing the inboard pickup point for the upper arm....all will change the camber curve. Similar (but opposite) changes on the lower arm will have a similar effect. I modeled the changes, built some bits and pieces, and had affected the changes.

For me, I have designed a complete new suspension package for FM. Changed the car to pushrod all round.

[Dwayne Anderson]

The FM car was built from A 1982 Hayashi FF . Marc Banher and I in his shop (Anaheim CA 1982) cut the back half of the FF and put the Mazda motor it it. When Marc built the Rear radias bar. The camber went to negitive at full bump. The cure was to run positive camber at ride height. The FF had rear rockers but they didnt want to use them. So there you have it. Dwayne Anderson

[JLS Crossle 42]

WRONG!!! Roll will not always increase camber.

.

I assume you mean Positive Camber,

So how in the absence of bump can roll not cause an increase in Positive Camber?

Do you have any pics of your new rear end set up?

[Dwayne Anderson]

The FM goes to to much neg camber at bump So we run positive camber at ride height

There is no new rear suspension that we run. We run a Stock FM. The rockers i talked about were on the 1982l Hayashi FF Dwayne

[JLS Crossle 42]

So what does this funky rear suspension mean to the driver or driving style which works well.