why should rear roll centre higher than the front?

[Warpspeed]

Z,
Can you name even one modern well developed production vehicle that has the rear roll centre lower than the front?

Not asking for a dozen examples, just one.

[Charlie]

I have worked on a variety of motorsport formulas and I cannot recall encountering a rear roll center that was lower than the front yet. There are a variety of reasons for that I think, and I would not say it has to be so. But I would disagree that 'it is not' good for performance, or that the idea is dead.

[Trevor]

Originally posted by Z:
Don't bother with adjustable kinematics, or ARBs.

Z

Z, what is your reasoning for skipping anti roll bars? If you can package them in the design phase, they are a much more convenient way to adjust balance than springs which will usually require resetting corner weights or at a minimum getting the car off the ground.

[BillCobb]

Originally posted by Warpspeed:
Z,
Can you name even one modern well developed production vehicle that has the rear roll centre lower than the front?

Not asking for a dozen examples, just one.

I can. And, its from routine measurements made on a commercial MTS K&C machine. Not a one of a kind CAR either. Lots of them were made. Also, in case you are still in disbelief, there are lots of different ones on various models built by the Bite My Wallet Groupen, too. (Just in case the Groupies feel there is some kind of 'philosophy' behind a manufacturer's panache.

You ladies are all hung up on the notion that the roll centers are set and the car designed around them. It bees the other way around, chillens. Roll centers are established by a synthesis process that solves in closed form sets of equations involving TLLTD, D(ynamic)TLLTD, ride balance, and the powertrain inertial axis. Putting it another way, cross products are not good for that ever so popular 'safe and secure' feeling.

[Warpspeed]

I know of only one well known mass produced example, the Hillman Imp. That had an engine well behind the rear axle centreline and the weight distribution that implies.

No doubt plenty of back yard specials and freaks of nature have existed in the past, but can you find something from any of the big well known Multinational Corporations that do serious research into vehicle dynamics and employ real engineers to build world cars ?

Putting the odd ball freaks to one side, the vast majority of vehicles do have a lower front roll centre and higher front roll stiffness.

While testing and experimentation may prove otherwise, starting out with something fairly conventional that has a long history of working may not be a bad staring point for a totally fresh design.

[Claude Rouelle]

there are many cars with "lower-rear-RCs" that perform very well.

Z... you have an example?

Claude

[Z]

Originally posted by Warpspeed:
Can you name even one modern well developed production vehicle that has the rear roll centre lower than the front?

Tony (and Charlie and Claude),

Well... how about... just about every production car using pure trailing-arm rear suspension?

Trailing-arms have nominally ground level RCs. Strictly speaking, we should say they have "lateral n-lines that are always horizontal wrt car body". Combine this with the usual wishbone or McP-strut front suspensions that typically have RC roughly 5-10cm above ground, and... "lower rear RC"!

Historical note: Trailing-arms are cheap, simple, robust, package extremely well, have excellent rough road capability, and, despite the fact that their "RCs" zoom off past Pluto with the slightest body roll, they give very predictable and benign handling. Yet they were the last suspension type to appear on cars! Or, for that matter, on motorbikes (almost universal on bikes nowadays)!

French cars of the 1950s+ were the most common with wishbone front and trailing-arm rear. All the ones I have owned had great handling, in a French sort of way.
~~~o0o~~~

Originally posted by Trevor:
Z, what is your reasoning for skipping anti roll bars?

Trevor,

They are a newbie team.

I have seen cars win FSAE with no suspension movement whatsoever. Yep, win outright! They only needed the "suspension" to get through scrutineering. They would have been faster with some damped suspension movement, but apparently they had "issues" trying to figure out how to do that so it worked.

If the OP tries to design a car with adjustable everything, then chances are they will never finish it in time, and they will perform poorly. So I reckon design a very simple car, get it built early, do lots of testing, and if it doesn't handle 100% perfectly, then that doesn't really matter.

There are still lots of adjustments they have to learn. Tyre types, sizes, and pressures, and then toe and camber angles. That gets you most of the way (still with no suspension). Then spring rates, and maybe damping rates. And then how to drive fast...

Z

[DougMilliken]

Originally posted by Z:
Well... how about... just about every production car using pure trailing-arm rear suspension?

The original Mini (UK):
http://en.wikipedia.org/wiki/Mini
40+ years in production.

[NR-Cruelty]

Thanks all of you.
We are a new team but I had study about adjusting, racing and designing for years.
I can understand most of what you are taking about, and I learnt from your replies.

[Warpspeed]

Ah yes the Mini !
Isn't automotive engineering history a rich and fascinating topic.

Originally posted by Z:

Well... how about... just about every production car using pure trailing-arm rear suspension?...

Z

Nobody uses pure trailing arms anymore at either end, and we all know the reasons why.

I am sure the judges would be really impressed if you presented a pure rear trailing arm FSAE car.