Alignment/Suspension Experts Wanted

Have you run out of camber adjustment and still need more? Are you using this thing competitively? Does it understeer? Do you have some desire for more self-centering? Do you think the steering is too light or do you want it heavier?
You can see where I stand on it for those reasons....

 

Yup, "beneficial" is a relative term. Increasing caster does a lot of things, including increasing weight jacking. It all depends on what you are looking to achieve. Doing one thing in isolation is rarely going to get you the results you want. That said, you only change one variable at a time. but you have to have a goal for the changes.

 

I know better than to claim to be an expert at anything. It only invites pissing contests. I can tell you what I know. Increasing caster increases the force needed to turn the steering because of the weight "jacking". In other words, caster has the effect of raising the front tires when turning. Ergo, more caster = greater lift. Greater lift = more force required to turn the wheel. This is not a bad thing at speed. The rule of thumb for a starting point is maximum caster and minimum camber for road racing. Caster and camber are also effected by roll center. If you are talking about camber change in corners, then roll center and control arm geometry will have a greater effect than caster on total camber change in a corner. The bottom line is that the car will respond best to what you feel comfortable with, the tire selection and the track conditions on a given day. It's rare that you will get a safe chance to push the car hard enough on the street to feel a big difference. BTW, early P 911's specs called for +7* to +9* caster). You just have to try different adjustments and find what is right for you.

 

I track pretty often. We can always use another ferrari tracker at the track. PM me your email address so I can keep you on my list if you are interested in more track days.

Caster has the great effect of return to center of the steering. In my early spin off the track days I found it easier to not correct but allow the car to correct it self as more caster naturally caused the wheel to want to right itself. Then when the steering was pretty much where I wanted it I would stop its motion and keep on going. This was way quicker than hand over hand recovery attempts which usually mad things worse. Also, more caster makes for better straight line tracking at high speed 100+ in my case which make early tracking feel safer. Now I don't spin so much so I can reduce the caster which increases the steering quickness. The car is not quite as stable at higher speeds 120+ but now with more experience it is plenty managable and a speed that is very comfortable due to repetition. So I say with all suspension settings try to hit somewhere in the middle/start factory and then tune in/out charactorisitcs as you develop. Finally, make one change at a time.

 

Every time you change a suspension setting there is a change in the compromises of the system. I agree with everything above, increased caster will increase the steering effort, and also make the self centering effect greater.

Caster is not generally a solution for understeer however. Try to adjust the tire pressures first, sometimes simple changes can make a big difference. Raise the front tire pressures a bit, or drop the rears a bit. Play with it and see what happens.

mechanically, the only possibility of a downside I see with increasing the caster of a 308 is that you may change the relationship of the tie rod in travel, (the car is lowered currently, which puts the tie rod location into its bump travel if you have not adjusted it) and you could introduce bump steer or possibly have toe out in droop which is also de-stabilizing. You will have to see how it feels if you dont have measuring equipment available. the steering arm of the 308 is fixed and non adjustable, so changes for bump steer must be made at the rack or tie rod end.

Hope it helps

Eric

 

Henry
FWIW, and this may give you a starting point, on my 308 - 16" with Hoosiers - I use
Max caster - 6deg (same as a 328)
2 Deg camber
Zero toe

Works for me

JM