Wheel size discussion

[MCoach]

AG, MCoach,

Look at what yaw inertia will do for a given step or ramp steer on Lateral Acceleration Response Time (LART), Yaw Velocity Damping (YVD), Lateral Acceleration, Cg slip angle, and Yaw velocity Overshoot, Lateral Acceleration, Cg slip angle, and Yaw velocity settling time and look at a Bode Diagram with amplitude and phase shift for different yaw inertia (and by the way different tire - 10 and 13 " relaxation lengths) and you will tell me if yaw inertia is important or not.

If you are non convinced by the simulation and/or as a useful addition to your simulation, put a ballast at the CG (let's say 10 to 12 kgs), probably close to the driver's butt to keep the same a and b (same weight distribution - that is very important because 0.25 % weight distribution variation makes a significant handling difference - the ratio yaw moment derivative vs the yaw velocity derivative is a^2 and b^2 sensitive - if you don't you will change too many parameters at the time) and the same CG height.
Ask your driver to make a few laps and/or, even better, a simple slalom with 6 to 10 cones.

Then split your ballast in the same proportion as your weight distribution in 2 parts as far away as possible, keeping the same weight distribution and CG height (a part your ballast somewhere in the nose, the other part near the differential)
Ask your driver to drive the same course and ask him if he feels the difference. Look at your gyro signal and the derivative of your gyro signal vs your steering input.
Compare the change of yaw inertia due to your centered or split ballast with the yaw inertia of let's say 10 kg and 12 kg of non suspended mass per corner.

I have. Differentials such as near locked diffs and spools seem more important. Sideforce from hella big end plates and elements seem more important.

UNC Charlotte ballast tested about 15-20lbs of ballast added to the very nose of the car and then removed. Some of the drivers at least felt a difference, nearly identical lap times.

[Claude Rouelle]

MCoach,

I agree with you about the importance of diff, effect of shape, position and sizes of side pods and wing end plates on aero Fy and Mz but I am very skeptical about the conclusions you made based on another team test.

Changing the weight distribution AND the yaw inertia is not changing the yaw inertia only (that is the beginning of this thread); not a fair comparison: you change too many things at a time.

I am very skeptical about UNC test conclusions as it goes against what I see in simulation, I see in data, I got from experience and what other FS teams (who did specific and well organized tests) have told me and I have read in several decent design reports.

"...15-20lbs of ballast added to the very nose of the car and then removed. Some of the drivers at least felt a difference, nearly identical lap times" Hmmmm...

A few years ago a car did not pass technical inspection before the qualify cession (it was 2 kg under the weight limit) and the mechanics added 3 kgs on the front and front only without telling the engineers.
It was an LMP2 car that is about 1 ton with driver an fuel and major aero downforce.
We saw serious lap time difference and (pissed off) driver's comments. Data and simulation of balance control and stability also showed significant differences.
So no effect of an about 8 KG ballast on a 200 to 250 kg car + driver? Very skeptical... Try again with a professional driver if you can.

Maybe a UNC Charlotte guy can give here his own comments?

[JulianH]

"...15-20lbs of ballast added to the very nose of the car and then removed. Some of the drivers at least felt a difference, nearly identical lap times" Hmmmm...

A few years ago a car did not pass technical inspection before the qualify cession (it was 2 kg under the weight limit) and the mechanics added 3 kgs on the front and front only without telling the engineers.
It was an LMP2 car that is about 1 ton with driver an fuel and major aero downforce.
We saw serious lap time difference and (pissed off) driver's comments. Data and simulation of balance control and stability also showed significant differences.
So no effect of an about 8 KG ballast on a 200 to 250 kg car + driver? Very skeptical... Try again with a professional driver if you can.

Maybe a UNC Charlotte guy can give here his own comments?

Absolutely agree on "testing conditions".
Back in 2011 we did also some tests about weight sensitivity and CoG height, Inertias, etc.. So we used the 2011 car and put weight every corner that we could find in the car once a time and compared lap times. The driver just went faster and faster each lap. I think in the end he had like 40kg in the car and still ran the same laptimes.
But it was an amazing laptime drop after we removed all the weights and let him run as a reference in the last stint...

So if you test "wrong", you can prove that basically nothing is important

Btw on the topic:
We switched from 13 to 10 inch back in 2012 because of weight but mostly because of heat-up. We had a 180-ish kg non-aero car with 13" Hoosier and we simply were not able to heat them up significantly. With 10inch LC0 this was not an issue.
The 2012 car directly won the FSG AutoX (against GFR Combustion, probably first time an E-Car was faster than all combustion cars in AutoX).

Last year we switched back to 13inch because we started tyre development with Conti - they are not able to produce 10inch tires but the OD is roughly the same as for the 10inch Hoosiers.
As I am way too old, I cannot comment on how good they work. Zurich had the fastest FSG AutoX time again, so probably not too bad. Karlsruhe with Hoosier was not much slower (and won due to the cone) though...

[MCoach]

We switched from 13 to 10 inch back in 2012 because of weight but mostly because of heat-up. We had a 180-ish kg non-aero car with 13" Hoosier and we simply were not able to heat them up significantly. With 10inch LC0 this was not an issue.
The 2012 car directly won the FSG AutoX (against GFR Combustion, probably first time an E-Car was faster than all combustion cars in AutoX).

That's mostly was I getting at with the tire construction that benefits 10" tires.
Soft, squishy, and less thermal mass.

[P^squared]

Even after being discussed so many times, this is one debate that never gets old !!

@AG_ also refer: http://www.fsae.com/forums/showthrea...r-team-run-10s Post no. 5. @MCoach love the dyno queen analogy !

Waiting for the LC0 fans And someone from Delft to chime in . . .

[Claude Rouelle]

Absolutely agree on "testing conditions".
Back in 2011 we did also some tests about weight sensitivity and CoG height, Inertias, etc.. So we used the 2011 car and put weight every corner that we could find in the car once a time and compared lap times. The driver just went faster and faster each lap. I think in the end he had like 40kg in the car and still ran the same laptimes.
But it was an amazing laptime drop after we removed all the weights and let him run as a reference in the last stint...

So if you test "wrong", you can prove that basically nothing is important

Btw on the topic:
We switched from 13 to 10 inch back in 2012 because of weight but mostly because of heat-up. We had a 180-ish kg non-aero car with 13" Hoosier and we simply were not able to heat them up significantly. With 10inch LC0 this was not an issue.
The 2012 car directly won the FSG AutoX (against GFR Combustion, probably first time an E-Car was faster than all combustion cars in AutoX).

Last year we switched back to 13inch because we started tyre development with Conti - they are not able to produce 10inch tires but the OD is roughly the same as for the 10inch Hoosiers.
As I am way too old, I cannot comment on how good they work. Zurich had the fastest FSG AutoX time again, so probably not too bad. Karlsruhe with Hoosier was not much slower (and won due to the cone) though...

Felt in that trap too. Many years ago, I was testing in Formula One with Gabriele Tarquini (who I consider to be one of the best "Ass Sensor" driver in the field - He was able to 1) feel 2) remember 3) express the car behavior - Very useful for an engineer: I had a blast working with him). At that time we did not have simulation and data analysis as good (or as complicated...) as the ones we use today so the driver opinion had an even bigger importance.

Along the day the setup evolved, with decision mainly based on driver indications. Lap times were going down, driver was happy. At 3 PM (in the worse conditions, not 5 or 6 PM "happy hour" when track is still hot but air is cooler) I proposed to go back to the morning basic setup. The driver did not think it was a good idea but I insisted and he agreed.
With the original morning setup we went quicker. Gabriele told he was happy I enforced a back to back test; he was sure we were only making progresses.
With the different setup changes we mostly went in the wrong direction but most probably we went quicker because the track was "rubbered" in and the driver confidence and track "acclimation" went up.

Always worth to make test and counter test. And that was with an F1 driver. Do you imagine with most non professional FS drivers...

Tire and track temperature variation, tire pressure variation, ambient conditions variations as well as driver getting hot and increasing driver's confidence can fool any so called "objective" tests.
There are reasons why the passenger car industry (and recently some professional race teams) uses steering, brake and throttle robots for track testing and parametric in lab testing (tire flat track, 7 post rig, damper dyno) ...

Before you make car data analysis make a few KPI (Key Performance Indicators) about driver use of Throttle, Brake and Steering application, consistency, speed, integral etc...
If the human (driver) or ambient inputs are not consistent how can you declare that the car setup change are the only reasons for outputs variation.

Beware to look at lap times only. Lap time consistency, and lap time average and standard deviations are at least as important.

[Claude Rouelle]

That's mostly was I getting at with the tire construction that benefits 10" tires.
Soft, squishy, and less thermal mass.

Contrarily to what most people think more rubber = more temperature.

A race tire with 4 mm of compound will get more temperature and therefore maybe more grip if you are closer to the ideal temperature than a race tire with 3 mm of compound.

But more temperature..... doesn't mean more temperature quicker...