Suspension kinematics...

[mep]

Everytime I see the McLaren front suspension I wonder about the strange angle the wishbones have.
Of course it is a feature of the no-keel suspension layout but I think this has never been analysed here according to the location of instantaneous center(IC) and the roll center (RC).

I expected them to have a really high roll center with a high IC on the oposite side of the car.
I checked this with CAD on a picture and figured out that they have the IC below ground and on the side of the tyre.
According to the picture the roll center high for the MP4 24 should be around 67mm and for the RB 95mm.
They both run 5° of chamber at the front.
Also interesting is, that the IC of the Redbull is really far away of the car.





What do you think about it?

[qw56q]

I was wondering if you thought the mclaren's setup make it less susceptible to bump?

[Jersey Tom]

Hard to pick out accurate kinematics from photos.

And yea. They're different. Tough to say how critical the camber curves are given how little travel there is. IC differences are kinda interesting.

In any event it comes down to how the whole racecar package is supposed to work, and how they interpret the tire and chassis data.

Not sure from our standpoint which conclusions can be made.

[riff_raff]

mep,

F1 composite A-arms are attached without pivot joints (they use "flexures"), and thus are designed to be flexible suspension elements. They are not like conventional steel tube A-arms with spherical joints at the inboard/outboard attach points, and thus would not be subject to the same kinematic motions under bump and droop.

Other comments:

- 5 degrees of negative camber is normally a lot of camber. But based on the wear patterns those front tire treads show, it doesn't appear to be a problem.

- the parallel geometry of those upper and lower front A-arms would result in very little camber gain under bump, which would normally affect braking stability. But with 5 degrees (or whatever?) of static camber, maybe it's not an issue.

- It's my understanding that most suspension travel on an F1 chassis is due to the tire sidewall flexing. Care to try working out the relative chassis motions due to this tire sidewall flexing?

Regards,
Terry

[fastback33]

I seem to recall during one of the pre-race shows on speed, Matchett was talking about how modern F1 cars' RC's go way off into infinite. I forget the race though....

[bazanaius]

I agree with JT that deriving suspension kinematics from photos is probably not that useful, given the accuracy you can expect to get. For example, in the macca photo, he could be doing 200kph, with almost a ton of DF on the sprung mass. This would imply that the camber measurement you've taken isn't at static - 5 deg static camber seems alot (maybe 2 deg max?).
At the same time, any angle, pitch or other difference between the photos taken will affect your values, making it hard to compare.

[Belatti]

Also dont forget that the photos may be with the cars at some roll, too.
Alignment and geometries are measured in a static position with the car leveled.

[RacingManiac]

the whole flexture vs balljoint deal is interesting, I should ask one of my friend who's done a thesis on that....

[Jersey Tom]

The whole tire deflection thing really isn't too difficult..

[Krispy]

the whole flexture vs balljoint deal is interesting, I should ask one of my friend who's done a thesis on that....

Surely it has some point that it bends about. The only 'complications' I think would be the addition of extra "springs" in the wheel rate calculation. The good news is there is no "stiction".


About the note that the car when pictured could have taken some amount of roll. Arent the suspension setup so stiff in roll that the total roll gradient would be very small? I am guessing .1 deg/g? So the kinematic suspension change in roll would also be very small.

I know most of the suspenion movement in these newer F1 cars is in the tire deflection, and aren't there many comprimises made for aero reasons over mechanical grip by way of decent camber gain curves etc?

[RacingManiac]

well the added spring rate aren't that unusual in the production car sense, since road car uses rubber bushing that actually winds-up in deflection...

[mep]

Ok, first of all let’s talk about the quality of the results.

About the note that the car when pictured could have taken some amount of roll. Arent the suspension setup so stiff in roll that the total roll gradient would be very small? I am guessing .1 deg/g? So the kinematic suspension change in roll would also be very small.

Exactly
The same goes for bump because F1 suspensions are quite hard otherwise it would not be possible to run as close to the ground as we have seen it in Singapore for example.
Of course the results are not 100% accurate but I expect the tolerances to be quite small.
The roll center and the instantaneous center are moving anyways a bit.
They should not move too far for a well designed car as far as I know.
I guess the tolerances will be similar to the RC, IC movement so it is not so important what driving condition we have.
We just imagine a failure based circle around our result and we will know in which area the point is lying.
The real problem lies in the photos. They might be taken at some angle. The better pictures we have the better our results will be.
Ah by the way, dont get disturbet by the rest of the car on the pic. Especially not by the nose. We cut the picture in a layer lying on the suspension.

[LFR1Legend]

Jersey Tom, I've looked at your FSAE 1000 website and was wondering if I could see you MATLAB code for the gui tire analysis?? I've had the same idea in mind but here at school no professor is much help in the MATLAB field. Nice work thus far!!

[Jersey Tom]

Nah can't just give it away. Sorry. I can only go over how it works at a top level.

There's not ONE professor at your university that knows Matlab?

[LFR1Legend]

No not really, I mean we do have an engineering data analysis class that really doesn't go into much detail...other than that everyone really uses MATLAB as a calculator. I've got coefficients for my tire of study and understand the process of analysis but now I would like to include that into a simulation of sorts and determine things like how much im using the tire laterally (saturation), steering sensitivity, ect ect--from a steady-state standpoint of course. It's just a pain trying to put it all together!! It gets overwhelming and I start to question it all.