Track width of FSAE cars

[MCoach]

It struck my curiosity of what drives teams reasoning for their selection of track width front and rear. Think of this as more of a poll of what you think is important. They vary around quite a bit from ETS with a very narrow track width to teams such as Uni Stuttgart that has a relatively large track width. After scanning through some old data and programs I've also noticed the trend of cars getting much smaller in overall dimensions even with the more strict implementations of the template rules.

Typically, what drives the selection on our car is dependent on the virtual swing arm for camber control, roll over considerations (no lift), roll stiffness targets, load distribution, and the little details that play into it, such as manufacturing tolerances for picking easy numbers to hit.

I'd just like to throw out the fact that in 2001 our car had a 57" front trackwidth.

What do you think is important in FSAE?

EDIT: brainfart, changed 2001 "wheelbase" to "trackwidth" :P

[mdavis]

At Cincinnati, we have a pretty hard maximum track width constraint given where our shop is. The track can be no wider than a standard double door. Our 2006 car pushes this dimension to where the car actually has to go out rear end first, then be rotated to where the wheel almost hits the wall on the opposite side of the hallway, crank the steering wheel to full lock and drag the car through the door.

As for the decision process this year, we tried to minimize car width while still passing tilt. There were some other factors that determine front to rear split and that kind of thing, but those are team secrets.

To me, minimizing track widths provides (inexperienced) drivers with more choices for driving line through tight courses, which is a plus. Limiting an inexperienced driver to a single line in testing/driver training may be a plus, but when it comes to the competition, I feel like they should have their choice of line (although where they are in the run order may dictate line choice more than they would like, but that is the teams fault for not picking the right time to run) as much as possible.

In terms of the other 2 dimensions, lowering height lowers CG, minimizing weight transfer and allowing for smaller track widths to still meet your lateral G targets. Minimizing vehicle length reduced PMOI which helps with getting the car to respond faster through the transition heavy courses that we've seen at Michigan. It will be interesting to see what type of course we see this year at MIS. 2011 was fairly slow, 2012 was fast as all get out. Only time will tell...

[BillCobb]

I'm guessing that most replies will state dimensional considerations: Tierod length, driveshaft length, slalom fit, swing arm length, driver comfort, etc. I'd add the additional burden of mass and inertial factors (radius of gyration and c.g. location). Actually, there can be 'optimal' value parameters based on these factors for a fixed mass that can make for high value dissertations. A surface plot showing the optimal potential well of max lateral capability vs. track and c.g. location is an excellant project with high value. A simulation to produce this needs to be able to perform adjustments of a number of other parameters which float with the the main ones, but you get the idea.

At least you don't have to make it thru a car wash or fit on shipping truck tracks like the very first competition. The GM PG car wash tore up quite a few cars in the WayBack era because of odd track(s) values. (That may be before some of you were born [or hatched]).

Whatever...

[Buckingham]

A=V^2/R (lat g, velocity, radius). The goal of racing isnt to maximize A, its to maximize V. Yes you need to look at how track width affects A, but it is EQUALLY important too look at how track width affects R. FSAE uses a constrained course, so how does overall vehicle width change R in a slalom, or in a 180 hairpin, or in a single lane change?

[Francis Gagné]

Originally posted by Buckingham:
A=V^2/R (lat g, velocity, radius). The goal of racing isnt to maximize A, its to maximize V. Yes you need to look at how track width affects A, but it is EQUALLY important too look at how track width affects R. FSAE uses a constrained course, so how does overall vehicle width change R in a slalom, or in a 180 hairpin, or in a single lane change?

In fact, in this case it's to minimze time t (=V/Length), since the length of the slalom depends on it's radius. We do something similar, we have a "lapsim" that account weight transfer, tire load sensitivity and adjust the radius of turns. Results varies with the track type, but it seems, for our tire, to indicate a narrow track. More sensitive tires may end up being "more optimal" with a wider track.

On the soft side, it is probably easier for the drivers too.

[MCoach]

Maximizing acceleration (A) just get's the car darting around the track. Maximizing velocity(V), minimizes time(t).To maximize V several factors play into that including tire forces (and moments), load sensitivity, and balance of the car. (How's that Izz looking?) But focusing on minimizing t through several events such as steady state cornering (skid pad), low speed transience (slalom) and acceleration gives a good idea of how the car will perform overall. If the car has enough grip to accelerate well, then it should brake well. Assume using max mu *0.9 (no ones perfect) during braking events and we're well on our way there...

Back to the focus...

Passing tilt is definitely a bottom line for track width. If you aren't going to pass tilt, then there is barely a chance to be competitive and some design choices should be re-evaluated.
Tilt test only simulates 1.7Gs and these cars have proved to be capable of more than that.

On polar moment of inertia, there is something to be said about chassis and tire set ups. I don't need to open my big mouth too much, so I'll just leave this here...
Most teams build near the bottom line of wheelbase (60 in; 1524mm) so something could be said for making a more "balanced" car, but it's just so enticing to keep it a bit short.

A low CG is great for keeping load transfer under control however, the current common list of tires seems to not care whether you have a CG of 13" (330mm) or 9" (229mm)...but your chassis and your suspension does. Which can lead to lower track widths...or wider, depending if you end up shiny side down or not. Considering a slalom, track width affects R by the amount the car needs to input as a step steer to navigate the event. A lower track width value gives a lower R value.

I'm curious just how far the limits on these things can be pushed. Tires and cars are nowhere near as finicky as planes, if something fails they come to a screeching (or sound or grinding carbon) halt. They don't fall out of the sky.

[Will C]

To throw some numbers out there, we have been running a track width of 1m (average) and a wheelbase a fraction over 1524mm since 2009. I’d be really interested to see who else is around this number.

It was found that having a narrower car could notably reduce lap times on the tight Australian tracks, by giving the driver a “straighter” line around the track.

Just throwing it out there, we’ve always had more trouble passing noise than tilt. All you need is some clever packaging

[Z]

Originally posted by Will C:
... we have been running a track width of 1m (average)
... All you need is some clever packaging

Will,

That would be at the narrowest end of the FSAE range.

Without giving any secrets away regarding your "clever packaging", could you tell us roughly how high your CG is?

Z

[Will C]

Being an engine guy I honestly wouldn’t be able to tell you where our CG is at.

What I can tell you, is that our car was designed to be able to handle a 2G corner and that during our 3 months of testing last year I never saw the car on two wheels (when it had a proper set up).

[MCoach]

Doing some quick math on based on track width and your roll value, that gives me a good guess at an upper limit.

The maximum it could be is about 9.75in (248mm)but my guess is that it is somewhere from 9.0 - 9.5in (228 - 241mm)

The Auckland car is the narrowest that I am aware of.