96DXCivic
96DXCivic Reader
10/6/09 9:59 p.m.

Ok so I am designing a suspension system but I am a bit confused on an ideal swingarm length. For maximum grip under acceleration and braking 0 degrees of camber is desired but for cornering 1.5 degrees of camber is best. I guess what I am asking is how quickly do you want to gain camber in vertical deflection?

Salanis
Salanis SuperDork
10/6/09 10:06 p.m.

How do you figure 1.5 degrees of camber? The ideal will depend on how hard you turn in what car.

1.5 is definitely low, though. On the Miata, I'd like to get 2.5 - 3.0 degrees of neg camber when static. And Miatas gain plenty of camber with deflection.

96DXCivic
96DXCivic Reader
10/6/09 10:39 p.m.

That is based on some tire test data I read for FSAE cars. This is a FSAE car I am working on. So I am looking for 2 inches of travel.

mad_machine
mad_machine SuperDork
10/6/09 10:43 p.m.

well, I am no engineer.. nor did I spend any time in a holiday inn express... but isn't roll usually a linier event? If it is, then I would think keeping the arc from 0 degrees to -1.5 smooth

RedS13Coupe
RedS13Coupe Reader
10/7/09 2:37 a.m.

If you want 0 degrees straight line, and 1.5 deg negative in a corner I would say find the compression of the outside suspension under cornering and gain camber as fast as needed to get what you want when you want it?

Ian F
Ian F HalfDork
10/7/09 7:42 a.m.

Not for nothing, but when I design a suspension system (something I do want to do eventually), I plan to buy one or more of the many well written books on the subject. You'll get much more/better info than anyone will have the time or inclination to post here.

Lastly... if you're designing an FSAE car, isn't there a team and instructor involved? For some reason I don't think the answer, "some guy on the web told me..." is what you want to tell you instructor when he asks questions about the design... at least not if you're hoping for a good grade.

alfadriver
alfadriver HalfDork
10/7/09 7:45 a.m.
Ian F wrote: Lastly... if you're designing an FSAE car, isn't there a team and instructor involved? For some reason I don't think the answer, "some guy on the web told me..." is what you want to tell you instructor when he asks questions about the design... at least not if you're hoping for a good grade.

Let alone the presentation.

E-

ClemSparks
ClemSparks SuperDork
10/7/09 8:19 a.m.

Just as a technical point, there was never a grade (or any credit) associated with my involvement in the FSAE program while I was in school. Quite the opposite, I think my grades suffered for it ;).

on second thought...that's not totally true. We did have a senior design project that was designing an intake...but that was our choice (we could have chosen any other project).

Clem

kb58
kb58 New Reader
10/7/09 9:03 a.m.

How much camber gain you need depends on a bunch of things: track width, CG height, wheel rate, tire width, tire type, etc, etc. It also depends what the car will be used for, as for where you want your instant centers. It's all a compromise.

ReverendDexter
ReverendDexter HalfDork
10/7/09 9:09 a.m.
iceracer
iceracer HalfDork
10/7/09 10:30 a.m.

Camber gain is generally related to roll.
The less roll, the less gain is needed. Also depression, as in braking, camber gain is not good.

iceracer
iceracer HalfDork
10/7/09 10:32 a.m.

Forgot this. One way to gain camber in a corner is to add caster. Then that will depend on KPI somewhat. Now it is getting confusing.

96DXCivic
96DXCivic Reader
10/7/09 10:48 a.m.

I have Milliken's Race Car Vehicle Dynamics, Carroll Smith's Tune to Win and Herb Adam's Chassis Engineering. That is my problem I am not sure which compromises to make in order to gain to get the right amount of camber gain in order to make up for the positive gain in roll. I was hoping for some practical advice on the static front view swing arm length.

iceracer
iceracer HalfDork
10/7/09 11:01 a.m.

Generally, the longer the arm, the less camber change.

96DXCivic
96DXCivic Reader
10/7/09 11:13 a.m.

Yup but is there any way to figure how much camber gain is needed.

marktmv
marktmv New Reader
10/7/09 1:53 p.m.

Well, since it doesn't sound like you're in danger of making it to the design finals at any FSAE event (because you are asking questions like this) I can give you the camber gain that I designed for my school's '08 car - 1.0 deg/in front and 0.7 deg/in rear. Don't ask me for the reasoning, I don't feel like going over all of my design process. You wanted a ballpark number - that's all you get.

Your best bet though is to get a hold of a copy of "Racecar Vehicle Dynamics" and some reliable tire data...

kb58
kb58 New Reader
10/7/09 2:36 p.m.

Until you answer the question: "How much will my car lean in a turn?" , you can't know how much camber gain to design in.

tuna55
tuna55 Reader
10/7/09 3:21 p.m.

kb58 is exactly right. From what I understand, from a pure cornering standpoint, is pick spring rates and sway bars (estimates), draw up the roll center, roll the car about the roll center (about its NEW role center) however much the spring rates and sway bars specify for a hard turn (use 1g or whatever). Now figure out how much camber you need to get the tire where you want it (sounds like you said -1.5 at this point. Calculate this WITH RESPECT TO THE GROUND). Now figure out what that is relative to the chassis, divide the roll in degrees, and you have your camber degree/roll degree.

If that made any sense.

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