Dynamic Camber

[exFSAE]

Just curious.. not asking for setup specifics but mid-corner do you find your outside tires typically dead vertical, some negative camber still, or positive camber?

[exFSAE]

Just curious.. not asking for setup specifics but mid-corner do you find your outside tires typically dead vertical, some negative camber still, or positive camber?

[Dave K]

NOT positive.

[screwdriver]

We've had anything so far, depending on the setup. You know yourself what works best http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Dave K]

You know, i was kinda thinking, what about slight positive camber on the inside front wheel (due to castor and/or kinematics)? Is it safe to assume that the camber thrust from a positively cambered inside front wheel would aid in cornering?

[VFR750R]

I like how the title is Dynamic Camber and not designed camber, because a LOT of the pictures i see of fSAE cars in cornering have what appears to be positive camber on the outside tires.

Has anyone tried to accurately measure this with lasers or vertical sticks in corners with a camera?

[exFSAE]

Dave - depends. Check tire data. These tiny bias slicks do not behave like radials. There is one in particular whose cornering stiffness drops off like you wouldn't believe when you put any camber into it (at least according to some data).. with not much gain in peak grip.

That being the case I'd think running lots of caster to get that camber-into-the-turn effect would make the car understeer like a pig.

VFR - Don't know of anyone directly measuring it.. but with OptimumK you can get in the ballpark if you have logged Fx/Fy and your kinematics input.

And, at the last FSAE event I definitely saw at least one fairly quick team that was shredding up their outside shoulders.. must have been really riding on that with some positive camber mid corner.

[BillCobb]

I recommend using the Mx tire channel to optimize dynamic camber. In order to make use of caster, you have to know how to get some significant steer into the car to make it contribute to sideforce. Some will setups will require more steer than others and the understeer issue is a detail to be preassigned. That's why you need some tire data, a vehicle model, a track curvature to design for, a suspension point map to dial in the deflection, roll camber and ackerman, a power curve and a plan to execute the optimization. That's all there is to do. Go do it. You might consider a spreadsheet linked to Matlab for starters. Guide the optimizer with manual controls (sliders), then cut it loose. In most cases I've run into, body roll effects are overstatd and deflection camber effects are understated. Make up a sidepull rig, yank it at the dynamic cg location, and measure the wheel camber. Watch how much the contribution from wheel bearings and spindles is (are??).

[murpia]

If you're trying to get a good starting point on cambers at the track, tyre temperature spread is usually a good indicator.

Measure it properly: use a decent needle probe and measure each shoulder and the centre. Measure as soon as the car stops, make sure your driver is pushing all the way into the pitlane. If you see outside shoulders > inside then add camber. If you see inside shoulder > outside by more than 10% reduce camber. If you see centre > (average of shoulders) reduce pressure. If you see centre < (average of shoulders add pressure. Iterate as many times as you need to.

I'm not saying that will get you the optimum settings, but you'll have a decent place to start from.

Regards, Ian

[FATMOUSE]

Never really tested what the camber of the car actually was with the 2008 racer (Columbia U) but according to our kinematics software the camber should have stayed around -1 degree throughout the corner (for up to some 4 degrees of body roll). (For both inside and outside tyres, front and back)

That's what I felt would be safest guess in the absence of tyre data. This year will be different pending investigation of said tyre data.

-Arjun Roy
Columbia University FSAE (suspension)

[Austin B]

I'm sure our Keizer's didn't help with the whole camber situation either.

[Fil]

You should be mindful that alot of the camber compliance comes from wheel centres, rims, uprights, wishbones and the like flexing.

We had massive problems with too much positive camber mid corner, but it wasnt to do with the set up, it was traced back to flex in the wheel centre. We designed to set stiffness targets rather than strength. As a consequence our wheel centre design went from 600g to 1050g, but we have not had a centre failure in over 3 years and the car behaves alot better. there have been some interesting wheel designs lately, but they dont look to stiff.

Even have a look at the lateral deflections you get from fea in all your parts and see how much that effects your camber.